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1

Water-gas shift reaction: finding the mechanistic boundary  

Microsoft Academic Search

The mechanism of the water-gas shift reaction is discussed for both copper\\/zinc oxide\\/alumina and iron oxide\\/chromium oxide catalysts. The associative and regenerative mechanisms are presented and the evidence concerning each mechanism is critically reviewed. It is concluded that for the low temperature shift reaction over copper\\/zinc oxide\\/alumina catalysts considerable evidence exists to support both mechanisms and it is possible that

C. Rhodes; G. J. Hutchings; A. M. Ward

1995-01-01

2

A microkinetic analysis of the reverse water gas shift reaction  

Microsoft Academic Search

The previously published model of the forward and reverse water gas shift reaction on copper (1) has been made more realistic by the incorporation of an energy barrier for the adsorption of hydrogen on to the copper. An activation energy barrier for the adsorption of hydrogen of 12 k cal mol?1 reduces the steady state hydrogen atom coverage of the

E. Tserpe; K. C. Waugh

1997-01-01

3

The water–gas-shift reaction at short contact times  

Microsoft Academic Search

We have examined the water–gas-shift reaction over noble metals and metals with ceria for catalyst contact times between 0.008 and 0.05 s for temperatures from 300 to 1000°C. With reactants of CO, H2, and H2O at a 1\\/2\\/4 composition, the reaction approached equilibrium at these contact times for temperatures as low as 380°C, which corresponds to a 50\\/1 H2\\/CO ratio. All

C Wheeler; A Jhalani; E. J Klein; S Tummala; L. D Schmidt

2004-01-01

4

Homogeneous catalysis of the water gas shift reaction by dodecacarbonyltriruthenium  

Microsoft Academic Search

Solutions prepared from Ruâ(CO)ââ in basic aqueous methanol, aqueous diglyme, aqueous THF, and aqueous methanol-heptane with cetyltrimethylammonium bromide (CTAB) have been shown to be catalysts for the water gas shift reaction under reasonably mild conditions (400 psi, 140°C). However, use of aqueous methanol as a solvent leads to higher reaction rates than aqueous diglyme or aqueous THF. Addition of heptane

Ohene-Aniapam

1984-01-01

5

Zeolite catalysts for the water gas shift reaction  

Microsoft Academic Search

Cu- and Cu,Zn-ZSM-5 zeolite catalysts were prepared using different cation exchange procedures. The samples were characterized by TPR; CO-FTIR; O2-TPD, XRD; BET and XPS. These catalysts showed appreciable activity and selectivity for the water gas shift reaction at 300–400°C and vapor\\/gas ratio=3. The Cu,Zn-ZSM-5 catalysts deactivated after a long exposure to steam, at high temperature. The catalytic activity of co-exchanged

Tânia Regina Oliveira de Souza; Suzana Modesto de Oliveira Brito; Heloysa Martins Carvalho Andrade

1999-01-01

6

Catalyst system for catalyzing the water gas shift reaction  

Microsoft Academic Search

The improved catalyst system developed by the University of Rochester for the water-gas shift reaction is very active at relatively low temperatures and is efficient in its utilization of the components forming the catalyst system. The homogeneous catalyst system contains rhodium carbonyl iodide in a water\\/acetic acid solvent. The system can be formed from (Rh(CO)âCl)â, aqueous HI, and glacial acetic

R. Eisenberg; C. H. Cheng

1978-01-01

7

Evaluation of Sorption-Enhanced Water Gas Shift Reaction  

SciTech Connect

Water-gas shift reaction, reacting water with CO is used to change the CO/H2 ratio for chemical production and for producing pure hydrogen. Water-gas shift (WGS) reaction in combination with CO2 absorption will have many applications in fuel cell and coal/biomass processing systems and will play a significant role in reducing CO2 from fossil fuel power generating systems such as IGCC by increasing system efficiencies and reducing fuel consumption. The exothermic and reversible WGS reaction, CO(g) + H2O(g) <=> CO2 (g) + H2 (g) ?H298 = - 41 kJ/mol (1), is not thermodynamically favorable at higher temperatures and for obtaining a higher conversion excess steam plus several reactors are used. Addition of excess steam and the required number of reactors to drive the reaction is expensive and it increases the cost of operation. Therefore, it is essential to develop new and novel materials that are robust, active, selective, and tolerant (less susceptible to poisoning and fouling) to contaminants in coal and in biomass.

Shamsi, Abolghasem

2008-10-01

8

Gold-based catalysts for the water–gas shift reaction: Active sites and reaction mechanism  

Microsoft Academic Search

The water–gas shift (WGS, CO+H2O?H2+CO2) reaction was studied on a series of gold\\/oxide catalysts. The results of in situ measurements with X-ray absorption spectroscopy indicate that the active phase of Au-ceria and Au-titania catalysts under the reaction conditions of the water–gas shift consists of metallic nanoparticles of gold on a partially reduced oxide support. In spite of the lack of

José A. Rodriguez

2011-01-01

9

Water-gas-shift reaction on metal nanoparticles and surfaces  

NASA Astrophysics Data System (ADS)

Density functional theory was employed to investigate the water-gas-shift reaction (WGS, CO+H2O-->H2+CO2) on Au29 and Cu29 nanoparticles seen with scanning tunneling microscopy in model Au/CeO2(111) and Cu/CeO2(111) catalysts. Au(100) and Cu(100) surfaces were also included for comparison. According to the calculations of the authors, the WGS on these systems operate via either redox or associative carboxyl mechanism, while the rate-limiting step is the same, water dissociation. The WGS activity decreases in a sequence: Cu29>Cu(100)>Au29>Au(100), which agrees well with the experimental observations. Both nanoparticles are more active than their parent bulk surfaces. The nanoscale promotion on the WGS activity is associated with the low-coordinated corner and the edge sites as well as the fluxionality of the particles, which makes the nanoparticles more active than the flat surfaces for breaking the O-H bond. In addition, the role of the oxide support during the WGS was addressed by comparing the activity seen in the calculations of the authors for the Au29 and Cu29 nanoparticles and activity reported for X/CeO2(111) and X/ZnO(000?)(X=Cu or Au) surfaces.

Liu, Ping; Rodriguez, José A.

2007-04-01

10

Low-temperature, sulfur-tolerant homogeneous catalysts for the water-gas shift reaction  

Microsoft Academic Search

Coal gasification in conjunction with the water-gas shift reaction represents a significant resource for the production of hydrogen, a gas of considerable industrial value. Current industrial water-gas shift reaction (WGSR) processes are operated in two stages: a high temperature shift (HTS) stage operating at about 350°C over sulfur-tolerant catalysts, followed by a low temperature shift (LTS) stage operating at about

R. B. Jr. Wilson; M. F. Asaro; E. J. Crawford; B. J. Wood; R. M. Laine; R. H. Schwaar

1989-01-01

11

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction  

Microsoft Academic Search

The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI's recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature.

R. M. Laine; B. J. Wood; G. N. Krishnan

1986-01-01

12

Density functional theory study on water–gas-shift reaction over molybdenum disulfide  

Microsoft Academic Search

Density functional theory calculations have been carried out to investigate the adsorption of reaction intermediates appearing during water–gas-shift reaction at the sulfur covered MoS2 (100) surfaces, Mo-termination with 37.5% S coverage and S-termination with 50% S coverage using periodic slabs. The pathway for water–gas-shift reaction on both terminations has been carefully studied where the most favorable reaction path precedes the

Xue-Rong Shi; Sheng-Guang Wang; Jia Hu; Hui Wang; Yan-Yan Chen; Zhangfeng Qin; Jianguo Wang

2009-01-01

13

Mechanism for the water–gas shift reaction on monofunctional platinum and cause of catalyst deactivation  

Microsoft Academic Search

The behavior of monofunctional platinum, Pt(111), for the water–gas shift reaction has been investigated using experimental and theoretical methods. Kinetic and isotopic measurements performed from 525 to 675K are consistent with an associative mechanism for the water–gas shift reaction in which carbon monoxide is oxidized by a hydroxyl group. The kinetically-relevant step consists of the unimolecular decomposition of an adsorbed

David W. Flaherty; Wen-Yueh Yu; Zachary D. Pozun; Graeme Henkelman; C. Buddie Mullins

2011-01-01

14

Mechanistic studies of the homogeneous catalysis of the water gas shift reaction by rhodium carbonyl iodide  

Microsoft Academic Search

The water gas shift reaction, HâO + CO = Hâ + COâ, is effectively catalyzed at low temperatures and pressures by a catalyst system based on rhodium carbonyl iodide. The results of semiquantitative kinetic studies and of quenching experiments are reported. In the temperature range 80 to 100°C the catalytic reaction shows first-order dependence on the partial pressure of CO

Edgar C. Baker; Dan E. Hendriksen; Richard Eisenberg

1980-01-01

15

PdZnAl catalysts for the reactions of water-gas-shift, methanol steam reforming, and reverse-water-gas-shift  

Microsoft Academic Search

Pd\\/ZnO\\/Al2O3 catalysts were studied for water-gas-shift (WGS), methanol steam reforming, and reverse-water-gas-shift (RWGS) reactions. WGS activity was found to be dependent on the Pd:Zn ratio with a maximum activity obtained at approximately 0.50, which was comparable to that of a commercial Pt-based catalyst. The catalyst stability was demonstrated for 100h time-on-stream at a temperature of 360°C without evidence of metal

Robert A. Dagle; Alexandru Platon; D. R. Palo; A. K. Datye; J. M. Vohs; Y. Wang

2008-01-01

16

Kinetics of the water–gas shift reaction over nanostructured copper–ceria catalysts  

Microsoft Academic Search

Water–gas shift reaction was studied over two nanostructured CuxCe1?xO2?y catalysts: a Cu0.1Ce0.9O2?y catalyst prepared by a sol–gel method and a Cu0.2Ce0.8O2?y catalyst prepared by co-precipitation method. A commercial low temperature water–gas shift CuO–ZnO–Al2O3 catalyst was used as reference. The kinetics was studied in a plug flow micro reactor at an atmospheric pressure in the temperature interval between 298 and 673K

Henrik Kušar; Stanko Ho?evar; Janez Levec

2006-01-01

17

Homogeneous catalysis of the water gas shift reaction using rhodium carbonyl iodide. [<95°C  

Microsoft Academic Search

A more active homogeneous catalyst system for the water gas shift reaction which functions at low temperatures (<95°C), and which, based on known rhodium complex chemistry, allows a reasonable proposal for the mechanism of the observed catalysis is reported.

Chien-Hong Cheng; Dan E. Hendriksen; Richard Eisenberg

1977-01-01

18

Ceria catalysts for water gas shift reaction: Influence of preparation method on their activity  

Microsoft Academic Search

The influence of the ceria catalysts preparation method on their structure and activity in water gas shift reaction has been studied. Ceria supports were prepared by the precipitation method from aqueous and organic solutions (e.g. alcohols) and the impregnation method used for active metal loading. Ceria catalysts were also prepared, by the coprecipitation method for total concentration of nitrate salts

C. Zerva; C. J. Philippopoulos

2006-01-01

19

Homogeneous catalysis of the water gas shift reaction by mixed-metal (iron\\/ruthenium) catalysts  

Microsoft Academic Search

For the water gas shift reaction HâO + CO ..-->.. COâ + Hâ, homogeneous catalysts may be prepared from ruthenium carbonyl. Mixed Ru\\/Fe carbonyl catalysts are more active in basic solutions than either one of these carbonyls alone. Activities of those and other carbonyl catalysts are tabulated. The mechanism of the catalytic effect is discussed. (DLC)

Peter C. Ford; Robert G. Rinker; Charles Ungermann; Richard M. Laine; Vincent Landis; Sergio A. Moya

1978-01-01

20

Homogeneous catalysis by ruthenium carbonyl in alkaline solution: the water gas shift reaction  

Microsoft Academic Search

The possible catalysis of the water gas shift reaction by metal carbonyl complexes is explored and conditions are described where a homogeneous solution prepared from triruthenium dodecacarbonyl (Ruâ(CO)ââ) is an active catalyst under relatively mild conditions. It is additionally noteworthy that the catalyst is very active toward decomposition of formate to Hâ and COâ under conditions active for the water

Richard M. Laine; Robert G. Rinker; Peter C. Ford

1977-01-01

21

Enhancement of water-gas shift reaction efficiency: catalysts and the catalyst bed arrangement  

NASA Astrophysics Data System (ADS)

The results of studies devoted to the search for catalysts of water-gas shift (WGS) reaction that are highly active in a wide temperature interval are generalized. New compositions based on traditional and alternative, as regards the chemical composition, catalysts of high- and low-temperature WGS reaction are considered in detail. The single-stage arrangement of WGS reaction ensuring small temperature gradients in the radial direction of the catalyst bed are discussed.

Baronskaya, Natal'ya A.; Minyukova, Tat'yana P.; Khassin, Aleksandr A.; Yurieva, Tamara M.; Parmon, Valentin N.

2010-12-01

22

A Microkinetic Analysis of the Water–Gas Shift Reaction under Industrial Conditions  

Microsoft Academic Search

To form the basis for a microkinetic understanding of the low-temperature water–gas shift reaction over Cu-based catalysts as operated industrially, the kinetics have been measured under a wide range of reaction conditions. To elucidate possible support effects the reaction was studied over catalysts of Cu supported on Al2O3, SiO2, or mixed ZnO\\/Al2O3. The proposed microkinetic model is based on a

C. V. Ovesen; B. S. Clausen; B. S. Hammershøi; G. Steffensen; T. Askgaard; I. Chorkendorff; J. K. Nørskov; P. B. Rasmussen; P. Stoltze; P. Taylor

1996-01-01

23

Water gas shift reaction of reformed fuel over supported Ru catalysts  

Microsoft Academic Search

Precious metal catalysts (Ir, Pd, Pt, Rh and Ru) supported on Al2O3 and Ru catalysts on CeO2, La2O3, MgO, Nb2O5, Ta2O5, TiO2, V2O5 and ZrO2 were investigated for water gas shift reaction of reformed gas. Ru\\/V2O3 catalyst reduced at 400°C in H2 demonstrated the highest activity for the shift reaction without producing methane. The activities for the shift reaction over

Toshimasa Utaka; Takeou Okanishi; Tatsuya Takeguchi; Ryuji Kikuchi; Koichi Eguchi

2003-01-01

24

Effects of H sub 2 S on Molten Carbonate Fuel Cells. Literature Survey of Water-Gas Shift Reaction.  

National Technical Information Service (NTIS)

A vast difference of opinion currently exists with regard to the effect of H sub 2 S-containing fuel gases on the rate of the water gas shift reaction in state-of-the-art molten carbonate fuel cell anodes. One position is that the water gas shift reaction...

R. J. Remick G. L. Anderson

1985-01-01

25

Homogeneous catalysis of the water gas shift reaction using a platinum chloride: tin chloride system  

Microsoft Academic Search

An efficient homogeneous catalyst consisting of KâPtClâ, SnClâ, HâO, and HCl dissolved in glacial acetic acid was developed for the water gas shift reaction, HâO + CO reversible Hâ + COâ. Requirements and features of the catalyst are: (1) no reaction takes place in the absence of the platinum chloride salt; (2) the omission of tin chlorides greatly diminishes catalytic

C. H. Chen; Richard Eisenberg

1978-01-01

26

Alkali-promoted alumina catalysts. II. Water-gas shift reaction  

Microsoft Academic Search

The water-gas shift reaction was investigated on alkali-promoted alumina catalysts prepared by mixing alumina with various alkali metal salts. Results showed that the activity for the CO + HâO reaction increased with the concentration of promoter until the surface was almost saturated by the alkali metal ions. At the same concentration of metal ions, the efficiency of promotion was in

Y. Amenomiya; G. Pleizier

1982-01-01

27

Photoacoustic measurements of water–gas shift reaction on ferric oxide catalyst  

Microsoft Academic Search

A photoacoustic spectroscopic (PAS) technique was applied to the kinetic study of the water–gas shift reaction in the presence of ?-Fe2O3 catalyst. The catalytic reaction was performed in the temperature range from 523 to 673K at various partial pressures of carbon monoxide and water–vapor in a closed-circulation reactor system using a differential photoacoustic cell. The variation of CO2 photoacoustic signal

Su-Jin Kim; In-Sik Byun; Ho-Youn Han; Hong-Lyoul Ju; Sung Han Lee; Joong-Gill Choi

2002-01-01

28

Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase.  

PubMed

We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH. PMID:18754658

Rozanska, Xavier; Vuilleumier, Rodolphe

2008-10-01

29

Maximizing H 2 production by combined partial oxidation of CH 4 and water gas shift reaction  

Microsoft Academic Search

A dense ceramic membrane reactor has been constructed to exclusively transport oxygen for the partial oxidation of methane (CH4) to syngas (a mixture of CO and H2) at temperatures of 850–900°C. H2 production is enhanced in a second catalytic reactor through the water gas shift reaction, in which the CO reacts with steam that is injected into the reactor at

P. S. Maiya; T. J. Anderson; R. L. Mieville; J. T. Dusek; J. J. Picciolo; U. Balachandran

2000-01-01

30

Cu\\/Zn-based catalysts improved by adding magnesium for water–gas shift reaction  

Microsoft Academic Search

Ternary Cu\\/MeO\\/ZnO (Me: alkaline-earth metal, Mg, Ca, Sr and Ba) catalysts were prepared by homogeneous precipitation (hp) using urea hydrolysis. The structure and the activity for the water–gas shift reaction of these catalysts were studied compared with those of the catalysts prepared by coprecipitation (cp). The highest activity was obtained over hp-Cu\\/MgO\\/ZnO among the catalysts tested. The catalyst precursors after

Tetsuya Shishido; Manabu Yamamoto; Ikuo Atake; Dalin Li; Yan Tian; Hiroyuki Morioka; Masahide Honda; Tsuneji Sano; Katsuomi Takehira

2006-01-01

31

Homogeneous catalysis of the water gas shift reaction using iron pentacarbonyl  

Microsoft Academic Search

Measurements have been carried out to determine the rate of hydrogen production by the water gas shift reaction (CO + HâO ..-->.. COâ + Hâ) operating at temperatures less than 200°C with iron pentacarbonyl serving as a catalyst precursor in a basic methanol-water solution. Turnover numbers of 2000 mol Hâ\\/mol Fe(CO)â per day are achieved at 180°C with this system.

Allen D. King; R. B. King; D. B. Yang

1980-01-01

32

Low-temperature water-gas shift reaction over Au\\/CeO 2 catalysts  

Microsoft Academic Search

A high and stable activity for gold\\/ceria catalyts has been established for the water-gas shift reaction. The relationship between gold loading and catalytic activity was studied over a wide temperature range. The influence of space velocity and H2O\\/CO ratio at different temperatures on the catalytic activity and stability was also investigated. The reduction\\/oxidation processes of ceria in the presence of

D Andreeva; V Idakiev; T Tabakova; L Ilieva; P Falaras; A Bourlinos; A Travlos

2002-01-01

33

Vanadium-promoted Pt\\/CeO 2 catalyst for water–gas shift reaction  

Microsoft Academic Search

Water–gas shift reaction has found new purpose and challenges due to its application in clean power generation systems based on fuel cells. It has been shown that the catalysts performance is dependent on both the metal phase and the nature of the support. In this contribution the modification of Pt\\/CeO2 catalyst with vanadium was exploited. Spectroscopic techniques revealed that distinct

Andréa M. Duarte de Farias; Pascal Bargiela; Maria da Graça C. Rocha; Marco A. Fraga

2008-01-01

34

Methanol synthesis and water-gas shift reactions on Raney copper catalysts  

Microsoft Academic Search

The use of Raney copper to catalyse the synthesis of methanol and the water-gas shift reaction is reviewed. The preparation of Raney copper and Raney copper-zinc alloys together with their leaching to form active catalysts is first considered. The production of methanol is promoted by copper and the major—but not the only—role of zinc oxide involves the production of higher

M. S. Wainwright; D. L. Trimm

1995-01-01

35

Synthesis and activity measurement of some water-gas shift reaction catalysts  

Microsoft Academic Search

The effect of calcination temperature on the activity and some properties of low temperature water gas shift reaction catalysts\\u000a has been investigated. The activities of catalysts have been determined using a fixed bed catalytic reactor. The following\\u000a results may be deduced from the present study. 1. The catalysts' total surface area decreased with increasing calcination\\u000a temperature, presumably due to the

Morteza Sohrabi; Akbar Irandoukht

2003-01-01

36

Copper-based catalysts for water gas shift reaction: Influence of support on their catalytic activity  

Microsoft Academic Search

Three copper containing catalysts supported on ceria and mixed oxides of ceria with zirconia and titania were prepared by co-precipitation method and their catalytic activity was tested for water gas shift (WGS) reaction. High surface area (>100m2\\/g) mixed oxides were obtained following the present method of preparation. The catalysts were characterized by XRD, H2-temperature programmed reduction (TPR), UV–vis and XPS.

S. Pradhan; A. Satyanarayana Reddy; R. N. Devi; Satyanarayana Chilukuri

2009-01-01

37

Deactivation Mechanisms for Pd\\/Ceria during the Water–Gas-Shift Reaction  

Microsoft Academic Search

The mechanism responsible for the irreversible deactivation of ceria-supported precious metals for the water–gas-shift reaction has been investigated through accelerated aging tests. It is shown that deactivation of Pd\\/ceria occurs more rapidly at 673 than 523 K when operating with an integral reactor in 25 Torr each of CO and H2O. By heating a fresh catalyst in H2, H2O, CO,

X. Wang; Raymond J Gorte; J. P. Wagner

2002-01-01

38

Kinetics of the reverse water-gas shift reaction over Cu(110)  

Microsoft Academic Search

The reverse water-gas shift reaction (COâ + Hâ â HâO + CO) has been studied over a clean Cu(110) single-crystal model catalyst at temperatures between 573 and 723 K. The steady-state kinetic measurements were carried out at medium pressures (10-2,000 Torr) in a microreactor after cleaning and characterization of the sample under UHV conditions. The Hâ\\/COâ-pressure ratios varied from 1,000:1

K. H. Ernst; C. T. Campbell; G. Moretti

1992-01-01

39

Reaction steps for the water-gas shift reaction and NOx storage\\/reduction catalysts studied by FTIR methods  

Microsoft Academic Search

Proton exchange membrane (PEM) fuel cells are an environmentally friendly source of energy since they are roughly twice as fuel efficient as internal combustion engines. The source of H2 is generally from hydrocarbons through the catalytic reforming and water-gas shift (WGS) reactions. The challenge on the WGS reaction is to find a catalyst that is more stable but has the

Joshua Lynn Ratts

2008-01-01

40

Microemulsion Prepared Pt in Ceria: Catalytically Active for Water Gas Shift Reaction but Totally Inert for Methanation  

Microsoft Academic Search

A core–shell Pt in ceria type of catalyst prepared by a microemulsion technique shows high activity for both water gas shift\\u000a and reverse water gas shift reactions but it does not catalyze methanation from carbon oxides and hydrogen feeds at all, whereas\\u000a Pt-ceria catalysts prepared by traditional methods are effective for all these reactions under comparable reaction conditions.\\u000a This clearly

Connie Mei Yu Yeung; Shik Chi Tsang

2009-01-01

41

A comparative study of water-gas-shift reaction over ceria supported metallic catalysts  

Microsoft Academic Search

Water-gas-shift (WGS) reaction rates have been measured on Pd\\/ceria, Ni\\/ceria, Fe\\/ceria, Co\\/ceria, ceria, and Pd\\/silica. Pd\\/ceria exhibited much higher activities than either ceria alone or Pd\\/silica, demonstrating a cooperative effect between Pd and ceria. Pd\\/ceria and Ni\\/ceria showed essentially the same activities and were much more active than either Co\\/ceria or Fe\\/ceria. Reaction orders on Pd\\/ceria were approximately zeroth-order in

S Hilaire; X Wang; T Luo; R. J Gorte; J Wagner

2001-01-01

42

Copper-supported catalysts in methanol synthesis and water gas shift reaction  

Microsoft Academic Search

The comparative studies of physicochemical properties of Cu-support catalysts (support = ZnO, Al2O3, Cr2O3, ZnAl2O4, FeAlO3, or CrAl3O6) and their catalytic activity in methanol synthesis and water gas shift reaction were the main goal of this work. The promotion\\u000a effect of copper addition in both reaction was proved. The formation of spinel type structure CuCr2O4, ZnAl2O4 and binary oxide CrAl3O6,

T. P. Maniecki; P. Mierczy?ski; W. K. Jó?wiak

2010-01-01

43

Water-gas shift reaction over supported Pt-CeO x catalysts  

Microsoft Academic Search

We conducted a comparative study for the water-gas shift (WGS) reaction over ceria-promoted Pt catalysts supported on various supports such as ?-Al2O3, SiO2, TiO2 (P-25), CeO2, SiO2-Al2O3, yttria-stabilized zirconia (YSZ) and ZrO2 in a rather severe reaction condition such as 6.7vol.% CO, 6.7vol.% CO2, and 33.2vol.% H2O in H2. Among them, Pt-Ce\\/TiO2 showed the highest WGS activity especially at low

Yong Tae Kim; Eun Duck Park; Hyun Chul Lee; Doohwan Lee; Kang Hee Lee

2009-01-01

44

PdZnAl Catalysts for the Reactions of Water-Gas-Shift, Methanol Steam Reforming, and Reverse-Water-Gas-Shift  

SciTech Connect

Pd/ZnO/Al2O3 catalysts were studied for water-gas-shift (WGS), methanol steam reforming, and reverse-water-gas-shift (RWGS) reactions. WGS activity was found to be dependent on the Pd:Zn ratio with a maximum activity obtained at approximately 0.50, which was comparable to that of a commercial Pt-based catalyst. The catalyst stability was demonstrated for 100 hours time-on-stream at a temperature of 3600C without evidence of metal sintering. WGS reaction rates were approximately 1st order with respect to CO concentration, and kinetic parameters were determined to be Ea = 58.3 kJ mol-1 and k0 = 6.1x107 min-1. During methanol steam reforming, the CO selectivities were observed to be lower than the calculated equilibrium values over a range of temperatures and steam/carbon ratios studied while the reaction rate constants were approximately of the same magnitude for both WGS and methanol steam reforming. These results indicate that although Pd/ZnO/Al2O3 are active WGS catalysts, WGS is not involved in methanol steam reforming. RWGS rate constants are on the order of about 20 times lower than that of methanol steam reforming, suggesting that RWGS reaction could be one of the sources for small amount of CO formation in methanol steam reforming.

Dagle, Robert A.; Platon, Alexandru; Datye, Abhaya K.; Vohs, John M.; Wang, Yong; Palo, Daniel R.

2008-03-07

45

Homogeneous catalysis of the water gas shift reaction by (polypyridine)rhodium complexes  

Microsoft Academic Search

Homogeneous catalysis of the water gas shift reaction under mild conditions (< 100°C (1 atm CO)) has been achieved with several (polypyridine)rhodium(I) complexes as catalyst precursors (polypyridine = 2,2'-bipyridine (bpy), 1,10-phenanthroline, pyrazine, 4,4'-dimethyl-2,2'-bipyridine), in alcohol-water mixtures. The complex Rh(bpy)â\\/sup +\\/ was found to be the most active catalyst precursor (approx. 3 turnovers\\/h at 90°C). In buffered water-ethanol (22:3) mixtures, the

Devinder Mahajan; Carol Creutz; Norman Sutin

1985-01-01

46

Kinetic studies of the water gas shift reaction on a sulfided cobalt/molybdena/alumina catalyst  

SciTech Connect

In this study, the applicability of low temperature oxygen chemisorption (LTOC) to measure the specific surface area of several rare-earth oxides (La, Ce, Pr, Nd, Tb) and the kinetics of the water-gas shift reaction over a sulfided cobalt-molybdena-alumina (AMOCAT 1A) catalyst are investigated. The LTOC results indicate that oxygen is possibly adsorbed in the molecular form, O/sub 2//sup -/, as observed by others after heat treatment of these oxides in vacuum. Lanthana and ceria were found to have ratios of total surface area to LTOC similar to those of chromia and molybdena respectively, after a comparable pretreatment. Furthermore, ceria is deduced to exist as a monolayer on the alumina support at loadings below 12%. An additional hour of reduction after the 6 hours of reduction shows a significant increase in LTOC on lanthana, neodymia and terbia which may be due to phase changes exhibited by these polymorphic oxides. The kinetics of the water-gas shift reaction has been extensively studied on iron oxide (high temperature shift) and copper oxide (low temperature shift) based catalysts. This investigation establishes the kinetics over a sulfided cobalt-molybdena-alumina (AMOCAT 1A) catalyst in the medium temperature shift range, 250-300/sup 0/C. The catalyst was sulfided in-situ in a high pressure integrated Berty reactor system. Reaction rates were measured for different CO/H/sub 2/O feed ratios in the range 0.3-3.0, with and without CO/sub 2/ in the feed. The reaction was carried out at several pressures in the range 5-27 atm. and GHSV's in the range 4800-2400 hr/sup 1/.

Srivatsa, N.R.

1987-01-01

47

Minimization of steam requirements and enhancement of water-gas shift reaction with warm gas temperature CO2 removal  

SciTech Connect

The disclosure utilizes a hydroxide sorbent for humidification and CO.sub.2 removal from a gaseous stream comprised of CO and CO.sub.2 prior to entry into a water-gas-shift reactor, in order to decrease CO.sub.2 concentration and increase H.sub.2O concentration and shift the water-gas shift reaction toward the forward reaction products CO.sub.2 and H.sub.2. The hydroxide sorbent may be utilized for absorbtion of CO.sub.2 exiting the water-gas shift reactor, producing an enriched H.sub.2 stream. The disclosure further provides for regeneration of the hydroxide sorbent at temperature approximating water-gas shift conditions, and for utilizing H.sub.2O product liberated as a result of the CO.sub.2 absorption.

Siriwardane, Ranjani V; Fisher, II, James C

2013-12-31

48

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction  

SciTech Connect

The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI's recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature. Based on this review, SRI will choose ten candidate systems to be evaluated as to their abilities to catalyze the WGSR using syngas derived from gasified coal. (2) Develop a test plan designed to effectively evaluate both the catalysts and, to some extent, reactor configuration for WGSR catalysis. (3) Perform a series of experiments to identify the most effective and economical of the ten candidate catalysts and then further evaluate the reaction kinetics of at least one selected catalyst system to develop sufficient data to provide the basis for the work in Task 4. (4) Develop a mathematical model of the final candidate system that uses rate expressions to describe the catalytic process. (5) Perform a techno-economical evaluation of the catalyst in terms of a proposed plant design based on the reaction model, current costs, and standard chemical engineering practice and compare the proposed design with a conventional hydrogen plant.

Laine, R.M.; Wood, B.J.; Krishnan, G.N.

1986-04-01

49

Carbon capture by sorption-enhanced water-gas shift reaction process using hydrotalcite-based material  

Microsoft Academic Search

A novel route for precombustion decarbonization is the sorption-enhanced water-gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water-gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic

E. R. van Selow; P. D. Cobden; P. A. Verbraeken; J. R. Hufton; R. W. van den Brink

2009-01-01

50

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction. Task 2, Test plan  

Microsoft Academic Search

The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI`s recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature.

R. M. Laine; B. J. Wood; G. N. Krishnan

1986-01-01

51

Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions  

SciTech Connect

We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}) used for producing H{sub 2}. The alkali ion-associated surface OH groups are activated by CO at low temperatures ({approx}100 C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O{sub x}(OH){sub y} species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

Zhai, Y.; Pierre, D; Si, R; Deng, W; Ferrin, P; Nilekar, A; Peng, G; Herron, J; Bell, D; et. al.

2010-01-01

52

Hydrodesulphurization of Light Gas Oil using hydrogen from the Water Gas Shift Reaction  

NASA Astrophysics Data System (ADS)

The production of clean fuel faces the challenges of high production cost and complying with stricter environmental regulations. In this research, the ability of using a novel technology of upgrading heavy oil to treat Light Gas Oil (LGO) will be investigated. The target of this project is to produce cleaner transportation fuel with much lower cost of production. Recently, a novel process for upgrading of heavy oil has been developed at University of Waterloo. It is combining the two essential processes in bitumen upgrading; emulsion breaking and hydroprocessing into one process. The water in the emulsion is used to generate in situ hydrogen from the Water Gas Shift Reaction (WGSR). This hydrogen can be used for the hydrogenation and hydrotreating reaction which includes sulfur removal instead of the expensive molecular hydrogen. This process can be carried out for the upgrading of the bitumen emulsion which would improve its quality. In this study, the hydrodesulphurization (HDS) of LGO was conducted using in situ hydrogen produced via the Water Gas Shift Reaction (WGSR). The main objective of this experimental study is to evaluate the possibility of producing clean LGO over dispersed molybdenum sulphide catalyst and to evaluate the effect of different promoters and syn-gas on the activity of the dispersed Mo catalyst. Experiments were carried out in a 300 ml Autoclave batch reactor under 600 psi (initially) at 391°C for 1 to 3 hours and different amounts of water. After the hydrotreating reaction, the gas samples were collected and the conversion of carbon monoxide to hydrogen via WGSR was determined using a refinery gas analyzer. The sulphur content in liquid sample was analyzed via X-Ray Fluorescence. Experimental results showed that using more water will enhance WGSR but at the same time inhibits the HDS reaction. It was also shown that the amount of sulfur removed depends on the reaction time. The plan is to investigate the effect of synthesis gas (syngas) molar ratio by varying CO to H2 ratio. It is also planned to use different catalysts promoters and compare them with the un-promoted Mo based catalysts to achieve the optimum reaction conditions for treating LGO. The results of this study showed that Ni and Co have a promoting effect over unpromoted Mo catalysts for both HDS and WGSR. Ni was found to be the best promoter for both reactions. Fe showed no significant effect for both WGSR and HDS. V and K have a good promoting effect in WGSR but they inhibited the HDS reaction. Potassium was found to be the strongest inhibitor for the HDS reaction since no sulfur was removed during the reaction. Keywords. LGO, HDS, in situ H2, WGSR, oil upgrading, syn-gas.

Alghamdi, Abdulaziz

53

Effect of Loading Potassium and Palladium over Iron-Based Catalyst for Low Temperature Water–Gas Shift Reaction  

Microsoft Academic Search

\\u000a Abstract  We investigated the effect of loading potassium over iron-based catalysts for water–gas shift (WGS) reaction at 573 K. The\\u000a iron-based water–gas shift catalyst has been known as a redox-mechanism catalyst. Therefore, to promote the redox reaction\\u000a over iron oxide, we impregnated a small amount of Pd on various iron oxides. Results revealed that coexisting potassium and\\u000a palladium accelerated the WGS reaction

Yasushi Sekine; Takahiro Chihara; Ryo Watanabe; Yuji Sakamoto; Masahiko Matsukata; Eiichi Kikuchi

2010-01-01

54

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction  

SciTech Connect

The purpose of this report is to update and reorganize our recent review on homogeneous catalysis of the water-gas shift reaction (WGSR) based on recent literature publications and patents. This updated version will serve as a means of selecting 10 candidate catalyst systems for use in developing effective, sulfur-tolerant, low temperature WGSR catalysts. This report discusses the variations possible in the basic chemistry associated with WGSR catalytic cycles, including basic, acidic, and neutral conditions. Then individual mechanism for specific WGSR catalyst systems are discussed. Finally, on the basis of the literature reports, a list is presented of candidate catalysts and basic systems we have chosen for study in Task 3.

Laine, R.M.

1986-01-20

55

Oxidation of Carbon Monoxide by Metal Ions and Homogeneous Catalysis of the Water Gas Shift Reaction and Related Processes  

Microsoft Academic Search

A variety of metal ions and complexes oxidize CO in aqueous solution through mechanisms that differ in detail but have in common the involvement of an intermediate hydroxycarbonyl complex (MCOOH). Such oxidation reactions can also be incorporated into various catalytic cycles including the homogeneously catalyzed water gas shift reaction.

Jack Halpern

1981-01-01

56

Modelling and Control of Metallurgical Processes. Part 2: A Generalized Shrinking Core Model Including the Water Gas Shift Reaction.  

National Technical Information Service (NTIS)

An outline of a mathematical model describing the simultaneous reduction of hematite by hydrogen and carbon monoxide is given. The model also includes the water gas shift reaction occurring both in the bulk gas and on the reaction interfaces inside the pe...

L. Kolbeinsen T. Onshus

1986-01-01

57

Water gas shift reaction kinetics and reactor modeling for fuel cell grade hydrogen  

NASA Astrophysics Data System (ADS)

The kinetics of the water gas shift reaction was studied to evaluate existing reaction mechanisms, test various rate expressions and simulate the performance in a methanol fuel processor for fuel cell applications. The reaction was carried out in a micro reactor testing unit using a commercial Sud-Chemie Cu/ZnO/Al 2O 3 catalyst between 120 and 250 °C with a range of feed rates and compositions. Using non-linear least squares optimization, the parameters in five rate expressions were fit to the experimental data. Based on a review of published work on the WGS reaction mechanism, our study found that a rate expression derived from a regenerative mechanism and another rate expression derived from adsorptive mechanism fit the experimental data equally well. Numerical integration of a one-dimensional PFR model was used for this parameter fitting. An empirical rate expression, rCO= kPCOPH 2O (1- ?) with activation energy of 47.4 kJ/mol was also obtained from the experimental data. Reactor performance was simulated to determine catalyst loadings required to achieve specific CO conversions as a function of temperature and water feed rate. These results are useful in studying the design trade offs available to reformer systems.

Choi, Yongtaek; Stenger, Harvey G.

58

Effects of Pretreatments of Cu\\/ZnO-Based Catalysts on Their Activities for the Water–Gas Shift Reaction  

Microsoft Academic Search

The effects of the pretreatments of Cu\\/ZnO-based catalysts prepared by a coprecipitation method on their activities for the water–gas shift reaction at 523K were investigated. The activity of a Cu\\/ZnO\\/ZrO2\\/Al2O3 catalyst for the water–gas shift reaction was less affected by calcination at temperatures ranging from 673-973K and by H2 treatment at 573 or 723K than that of a Cu\\/ZnO\\/Al2O3 catalyst.

Masahiro Saito; Kazumi Tomoda; Isao Takahara; Kazuhisa Murata; Megumu Inaba

2003-01-01

59

Study on the supported Cu-based catalysts for the low-temperature water–gas shift reaction  

Microsoft Academic Search

This paper presents a study on the influence of support (Al2O3, MgO, SiO2-Al2O3, SiO2-MgO, ?-zeolite, and CeO2) of Cu-ZnO catalysts for the low-temperature water–gas shift reaction. Supported Cu-ZnO catalysts were prepared by the conventional impregnation method, followed by the H2 reduction. The activity of Cu-ZnO catalysts for the water–gas shift (WGS) reaction was largely influenced by the kind of support;

Hidenori Yahiro; Keisuke Murawaki; Kazuhiko Saiki; Tetsuya Yamamoto; Hiroyuki Yamaura

2007-01-01

60

Mechanisms of Water-Gas Shift Catalysis.  

National Technical Information Service (NTIS)

Catalysis of the water-gas shift reaction in aqueous base solution was studied. Evaluation of the literature indicates that the catalytic cycle most likely involves formate synthesis and formate decomposition pathways. Below 350 deg. C, formate synthesis ...

M. A. Lilga D. M. Camaioni D. C. Elliott R. T. Hallen R. J. Robertus

1987-01-01

61

Density Functional Theory and Reaction Kinetics Studies of the Water–Gas Shift Reaction on Pt–Re Catalysts  

SciTech Connect

Periodic, self-consistent density functional theory calculations (DFT-GGA-PW91) on Pt(111) and Pt3Re(111) surfaces, reaction kinetics measurements, and microkinetic modeling are employed to study the mechanism of the water–gas shift (WGS) reaction over Pt and Pt–Re catalysts. The values of the reaction rates and reaction orders predicted by the model are in agreement with the ones experimentally determined; the calculated apparent activation energies are matched to within 6% of the experimental values. The primary reaction pathway is predicted to take place through adsorbed carboxyl (COOH) species, whereas formate (HCOO) is predicted to be a spectator species. We conclude that the clean Pt(111) is a good representation of the active site for the WGS reaction on Pt catalysts, whereas the active sites on the Pt–Re alloy catalyst likely contain partially oxidized metal ensembles.

Carrasquillo-Flores, Ronald; Gallo, Jean Marcel R.; Hahn, Konstanze; Dumesic, James A.; Mavrikakis, Manos

2013-12-01

62

Water gas shift reaction and selective oxidation of CO in microreactors  

Microsoft Academic Search

The following paper shows the successful application of some selective oxidation (selox) and water gas shift (WGS) catalysts to microreactors, which allow to reduce the CO content in a model gas mixture that contains the major product components of a reformer or of partial oxidizer used for hydrogen production for fuel cells. At small average residence times of less than

O. Goerke; P. Pfeifer; K. Schubert

2004-01-01

63

One-Dimensional Ceria as Catalyst for the Low-Temperature Water-Gas Shift Reaction  

SciTech Connect

Synchrotron-based in situ time-resolved X-ray diffraction and X-ray absorption spectroscopy were used to study pure ceria and Pd-loaded ceria nanotubes and nanorods (1D-ceria) as catalysts for the water-gas shift (WGS) reaction. While bulk ceria is very poor as WGS catalysts, pure 1D-ceria displayed catalytic activity at a temperature as low as 300 C. The reduction of the pure 1D-ceria in pure hydrogen started at 150 C, which is a much lower temperature than those previously reported for the reduction of 3D ceria nanoparticles. This low reduction temperature reflects the novel morphology of the oxide systems and may be responsible for the low-temperature WGS catalytic activity seen for the 1D-ceria. Pd-loaded 1D ceria displayed significant WGS activity starting at 200 C. During pretreatment in H{sub 2}, the ceria lattice parameter increased significantly around 60 C, which indicates that Pd-oxygen interactions may facilitate the reduction of Pd-loaded 1D-ceria. Pd and ceria both participate in the formation of the active sites for the catalytic reactions. The low-temperature hydrogen pretreatment results in higher WGS activity for Pd-loaded 1D-ceria.

Han, W.; Wen, W; Hanson, J; Teng, X; Marinkovic, N; Rodriguez, J

2009-01-01

64

Vehicle exhaust catalysis: I. The relative importance of catalytic oxidation, steam reforming and water-gas shift reactions  

Microsoft Academic Search

The activity of a monolithic three-way catalyst has been compared with the performance of the individual metals (Pt, Pd, Rh) for oxidation, steam reforming and water-gas shift. The presence of ceria was found to accelerate the last two reactions. The orders of activity were found to be: oxidation — presence or absence of ceria, Pt > Pd > three-way >

B. I. Whittington; C. J. Jiang; D. L. Trimm

1995-01-01

65

An analysis of the performance of membrane reactors for the water–gas shift reaction using gas feed mixtures  

Microsoft Academic Search

The water–gas shift (WGS) reaction in membrane reactors has been widely studied by several authors. From these works, the increase of the CO conversion above the equilibrium values appears to be possible when hydrogen is removed through the membrane.However, to date, this feasibility has been verified mostly when feeding pure reagents to the reactor, although in an industrial context the

A Criscuoli; A Basile; E Drioli

2000-01-01

66

Homogeneous catalysis of the water gas shift reaction by (polypyridine)rhodium complexes  

SciTech Connect

Homogeneous catalysis of the water gas shift reaction under mild conditions (< 100/sup 0/C (1 atm CO)) has been achieved with several (polypyridine)rhodium(I) complexes as catalyst precursors (polypyridine = 2,2'-bipyridine (bpy), 1,10-phenanthroline, pyrazine, 4,4'-dimethyl-2,2'-bipyridine), in alcohol-water mixtures. The complex Rh(bpy)/sub 2//sup +/ was found to be the most active catalyst precursor (approx. 3 turnovers/h at 90/sup 0/C). In buffered water-ethanol (22:3) mixtures, the rates of H/sub 2/ and CO/sub 2/ production were highest at Ph approx. 3. The pH dependence of the rates and solution UV spectra in the latter medium implicate Rh(bpy)/sub 2/(CO)H/sup 2 +/ as the catalyst; this species predominates below pH 3 and exhibits hydroxide-promoted activity suggestive of a metallocarboxylic acid mechanism. At pH > 3, the rhodium(I) species present exhibit little catalytic activity.

Mahajan, D.; Creutz, C.; Sutin, N.

1985-06-19

67

Role of the Water-Gas Shift Reaction in CO2 Capture from Gasification Syngas Using Limestones  

NASA Astrophysics Data System (ADS)

The work in this paper aims at determining the effect of gasification syngas on the carbonation reaction and conversion for several naturally occurring calcium-based sorbents. Experiments were performed via the use of a thermogravimetric analyzer (TGA) and it was observed that the presence of CO and H2 caused an increase in initial rate of approximately 70.6%. The increase in reaction rate was attributed to the CaO surface sites catalyzing the water-gas shift reaction; as well, the shift reaction was assumed to be responsible for the increase in activation energy for limestone based on the formation of intermediate complexes.

Lu, D. Y.; Symonds, R. T.; Hughes, R. W.; Anthony, E. J.

68

SiC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION  

SciTech Connect

This technical report summarizes our activities conducted in Yr II. In Yr I we successfully demonstrated the feasibility of preparing the hydrogen selective SiC membrane with a chemical vapor deposition (CVD) technique. In addition, a SiC macroporous membrane was fabricated as a substrate candidate for the proposed SiC membrane. In Yr II we have focused on the development of a microporous SiC membrane as an intermediate layer between the substrate and the final membrane layer prepared from CVD. Powders and supported thin silicon carbide films (membranes) were prepared by a sol-gel technique using silica sol precursors as the source of silicon, and phenolic resin as the source of carbon. The powders and films were prepared by the carbothermal reduction reaction between the silica and the carbon source. The XRD analysis indicates that the powders and films consist of SiC, while the surface area measurement indicates that they contain micropores. SEM and AFM studies of the same films also validate this observation. The powders and membranes were also stable under different corrosive and harsh environments. The effects of these different treatments on the internal surface area, pore size distribution, and transport properties, were studied for both the powders and the membranes using the aforementioned techniques and XPS. Finally the SiC membrane materials are shown to have satisfactory hydrothermal stability for the proposed application. In Yr III, we will focus on the demonstration of the potential benefit using the SiC membrane developed from Yr I and II for the water-gas-shift (WGS) reaction.

Paul K.T. Liu

2001-10-16

69

The low-temperature water–gas shift reaction catalyzed by sodium-carbonate-activated ruthenium mono(bipyridine)\\/SiO2 complexes  

Microsoft Academic Search

The effect of a new catalyst activation method on the catalytic activities of several chlorine-containing ruthenium mono(bipyridine) carbonyl complexes in the water–gas shift reaction (WGSR) was studied. The chemical activation of the silica-supported complexes by a sodium carbonate\\/methanol solution under CO atmosphere produced highly active low-temperature water–gas shift reaction catalysts.

Saija Luukkanen; Matti Haukka; Mirja Kallinen; Tapani A. Pakkanen

2000-01-01

70

Structure sensitivity of the low-temperature water-gas shift reaction on Cu–CeO 2 catalysts  

Microsoft Academic Search

We have investigated the structure sensitivity of the water-gas shift (WGS) reaction on Cu–CeO2 catalysts prepared at the nanoscale by different techniques. On the surface of ceria, different CuOx structures exist. We show here that only the strongly bound Cu–[Ox]–Ce species, probably associated with the surface oxygen vacancies of ceria, are active for catalyzing the low-temperature WGS reaction. Weakly bound

Rui Si; Joan Raitano; Nan Yi; Lihua Zhang; Siu-Wai Chan; Maria Flytzani-Stephanopoulos

2012-01-01

71

Homogeneous catalysis of the water gas shift reaction by ruthenium and other metal carbonyls: studies in alkaline solutions  

Microsoft Academic Search

Homogeneous catalysis of the water gas shift reaction (HâO + CO reversible Hâ + COâ) has been demonstrated for a number of metal carbonyl complexes under alkaline conditions. Characterization of the catalysts based on ruthenium carbonyl in alkaline, aqueous ethoxyethanol solution demonstrates that the principal species present under the reaction conditions are the carbonyl hydride anions HâRuâ(CO)ââ⁻ and HRuâCO)âââ». (The

Charles Ungermann; Vincent Landis; Sergio A. Moya; Haim Cohen; Howard Walker; Ralph G. Pearson; Robert G. Rinker; Peter C. Ford

1979-01-01

72

Kinetic modeling and first principles study of the water-gas shift and methanation reaction on group VIII metal catalysts  

Microsoft Academic Search

In this research kinetic modeling and first principles study of the water-gas shift (WGS) and methanation reactions on group VIII metal catalysts were carried out in an effort to develop fundamental mechanistic understanding. These tools were combined with experimental studies for quantitative modeling of WGS over Pt\\/Al2O3 catalysts. Self-consistent, periodic slab density functional theory DFT-GGA calculations were used to investigate

Abhijit A Phatak

2006-01-01

73

Development of chromium-free iron-based catalysts for high-temperature water-gas shift reaction  

Microsoft Academic Search

Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe\\/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can

Sittichai Natesakhawat; Xueqin Wang; Lingzhi Zhang; Umit S. Ozkan

2006-01-01

74

Homogeneous catalysis of the water-gas shift reaction by copper complexes in aqueous substituted pyridine solutions  

Microsoft Academic Search

Homogeneous catalysis of the water-gas shift reaction has been accomplished by the use of solutions of CuCl2 · 2H2O in aqueous pyridine and other substituted pyridine (methyl pyridines or dimethylpyridine) solutions. This system is stable, low active catalyst displaying turnover frequencies for hydrogen production (TF(H2)) of about 6 moles H2 per mole Cu per day for [Cu] = 20 mM,

Marta Mediavilla; Doris Pineda; Francisco Lopez; Delfin Moronta; Clementina Longo; Sergio A. Moya; Pablo J. Baricelli; Alvaro J. Pardey

1998-01-01

75

Catalyst size matters: Tuning the molecular mechanism of the water–gas shift reaction on titanium carbide based compounds  

Microsoft Academic Search

The molecular mechanism of the water–gas shift reaction catalyzed by titanium carbide compounds was studied using a density functional approach. Three different catalyst models have been considered: the extended TiC(001) surface, the Ti8C12 MetCar, and a Ti14C13 nanoparticle. Adsorption of reactants, intermediates, and products occurs on different sites, demonstrating the chemical versatility of the TiC substrates. Thus, adsorption energies depend

Francesc Viñes; Jose A. Rodriguez; Ping Liu; Francesc Illas

2008-01-01

76

Kinetic study of the water–gas shift reaction and its role in the conversion of methane to syngas over a Pt\\/MgO catalyst  

Microsoft Academic Search

Transient as well as steady-state kinetic experiments were applied for the derivation of the reaction mechanism and kinetic constants of the water–gas shift reaction over a Pt\\/MgO catalyst. Separate investigations on Pt-black and MgO were performed to elucidate the interaction of the metal and support component in the catalytic process. The rate of equilibration of the water–gas shift reaction was

D. Wolf; M. Barré-Chassonnery; M. Höhenberger; A. van Veen; M. Baerns

1998-01-01

77

Development of high performance Cu\\/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction  

Microsoft Academic Search

Our group’s studies on Cu\\/ZnO-based catalysts for methanol synthesis via hydrogenation of CO2 and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al2O3, ZrO2 or SiO2 improved its specific activity for methanol synthesis and the reverse

Masahiro Saito; Kazuhisa Murata

2004-01-01

78

Reaction-Relevant Gold Structures in the Low Temperature Water-Gas Shift Reaction on Au-CeO2  

SciTech Connect

Combined in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies have been conducted to follow gold structural changes of low-content (<1%Au) gold-ceria catalysts in water-gas shift (WGS) reaction tests at 100 and 200 C; and after heating the used catalysts in oxygen gas at 150 C. Gold in the fresh (400 C-calcined) material was atomically dispersed in cerium oxide. Under WGS reaction conditions, reduction of the oxidized gold species was observed, accompanied by gradual gold aggregation. The Au-Au coordination number is zero for the fresh material, but increases with the reaction temperature, to 6.5 {+-} 2.4 (after use at 100 C) and to 8.7 {+-} 1.5 (after 200 C) in a gas mixture containing 5% CO- 3% H2O in helium. The second important parameter is the reaction gas composition which determines the extent of Au-O reduction. The lower the reduction potential of the reaction gas mixture, the more oxidized the gold is in the used catalyst, and the higher its activity. The maximum activity of Au-CeO2 was that of the fully dispersed Au-O-Ce fresh material. Loss of surface oxygen took place during reaction, as measured by H2-TPR of the used samples, and it was commensurate with the activity loss. Attempts to reoxidize and redisperse the gold by heating in oxygen gas at 150 C were not effective. However, we report here that complete recovery of the surface oxygen amount and redispersion of gold in ceria was possible after a 400 C- oxygen treatment of both the 100 C- and 200 C- used catalyst samples, with concomitant recovery of the initial catalyst activity. These tests were conducted by consecutive H2-TPR/steady-state catalyst activity measurements in the same microreactor.

Deng,W.; Frenkel, A.; Si, R.; Flytzani-Stephanopoulos, M.

2008-01-01

79

Development of ZnO\\/Al 2O 3 catalyst for reverse-water-gas-shift reaction of CAMERE (carbon dioxide hydrogenation to form methanol via a reverse-water-gas-shift reaction) process  

Microsoft Academic Search

ZnO and ZnO\\/Al2O3 catalysts were studied for a reverse-water-gas-shift reaction (RWReaction). The catalytic activities depended on the compositions of Zn and Al at the temperature range of 673–973K and GHSV of 15,000. The activities were close to the equilibrium conversion at temperatures above 873K. The catalysts were characterized by using BET, TPR, XRD, SEM, and TEM. The ZnO\\/Al2O3 catalysts were

Sang-Woo Park; Oh-Shim Joo; Kwang-Deog Jung; Hyo Kim; Sung-Hwan Han

2001-01-01

80

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique  

Microsoft Academic Search

The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite

Keita Watanabe; Toshihiro Miyao; Kazutoshi Higashiyama; Hisao Yamashita; Masahiro Watanabe

2009-01-01

81

H 2 production through the water-gas shift reaction: An in situ time-resolved X-ray diffraction investigation of manganese OMS-2 catalyst  

Microsoft Academic Search

Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer–Emmett–Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction

Shanthakumar Sithambaram; Wen Wen; Eric Njagi; Xiong-Fei Shen; Jonathan C. Hanson; Steven L. Suib

2010-01-01

82

Influence of iron oxide support preparation method on the properties of Ru\\/Fe 2 O 3 catalysts for water-gas shift reaction  

Microsoft Academic Search

Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type ?-, ?-, ?- and ?-FeOOH,\\u000a and used as a support of ruthenium catalysts Ru\\/Fe2O3, employed in the water-gas shift reaction. In asprepared pure supports and ruthenium catalysts the main phase was ?-Fe2O3. After use in the water-gas shift reaction, the support showed the presence of

A. Basifiska; A. Nowacki; F. Domka

1999-01-01

83

Influence of the monoclinic and tetragonal zirconia phases on the water gas shift reaction. A theoretical study.  

PubMed

We present a theoretical study of the water gas shift reaction taking place on zirconia surfaces modeled by monoclinic and tetragonal clusters. In order to understand the charge transfer between the active species, in this work we analyze the influence of the geometry of monoclinic and tetragonal zirconia using reactivity descriptors such as electronic chemical potential (?), charge transfer (?N) and molecular hardness (?). We have found that the most preferred surface is tetragonal zirconia (tZrO2) indicating also that low charge transfer systems will generate less stable intermediates, that will allow to facilitate desorption process. PMID:23377895

Cerón, María Luisa; Herrera, Barbara; Araya, Paulo; Gracia, Francisco; Toro-Labbé, Alejandro

2013-07-01

84

Low-temperature water-gas shift reaction over Mn-promoted Cu\\/Al 2 O 3 catalysts  

Microsoft Academic Search

Water-gas-shift reaction was carried our over a series of Mn-promoted Cu\\/Al2O3 catalysts in the temperature range of 448–533 K. The catalysts were characterized suitably by various techniques. The catalyst\\u000a containing 8.55 wt% Mn was found to be the most active one among five catalysts tested. A maximum CO conversion of 90% was\\u000a obtained over this catalyst at 513 K with a CO space-time

Dinesh C. Yeragi; Narayan C. Pradhan; Ajay K. Dalai

2006-01-01

85

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction. Task 2, Test plan  

SciTech Connect

The objective of this project is to identify, prepare, test, characterize, and evaluate a practical, homogeneous catalyst for a water-gas shift process. The project effort is divided into the following five tasks: (1) Update SRI`s recent review of the literature on the catalysis of the water-gas shift reaction (WGSR) to include references after 1982 and those in the patent literature. Based on this review, SRI will choose ten candidate systems to be evaluated as to their abilities to catalyze the WGSR using syngas derived from gasified coal. (2) Develop a test plan designed to effectively evaluate both the catalysts and, to some extent, reactor configuration for WGSR catalysis. (3) Perform a series of experiments to identify the most effective and economical of the ten candidate catalysts and then further evaluate the reaction kinetics of at least one selected catalyst system to develop sufficient data to provide the basis for the work in Task 4. (4) Develop a mathematical model of the final candidate system that uses rate expressions to describe the catalytic process. (5) Perform a techno-economical evaluation of the catalyst in terms of a proposed plant design based on the reaction model, current costs, and standard chemical engineering practice and compare the proposed design with a conventional hydrogen plant.

Laine, R.M.; Wood, B.J.; Krishnan, G.N.

1986-04-01

86

The effect of reaction conditions on the stability of Au\\/CeZrO 4 catalysts in the low-temperature water–gas shift reaction  

Microsoft Academic Search

Au\\/CeZrO4 catalysts are highly active for the water–gas shift reaction but tend to be unstable and deactivate with time on stream. In this study, in situ DRIFTS-GC was used to investigate the nature of the Au under a range of reaction conditions as the deactivation rate is observed to vary with feed conditions (water concentration, presence of CO2) and reaction

H. Daly; A. Goguet; C. Hardacre; F. C. Meunier; R. Pilasombat; D. Thompsett

2010-01-01

87

Performance of Au/M(x)O(y)/TiO(2) Catalysts in Water-Gas Shift Reaction  

SciTech Connect

Our group recently developed a series of Au/M{sub x}O{sub y}/TiO{sub 2} catalysts for CO oxidation, and demonstrated that some of these catalysts are still active after high-temperature treatment whereas Au/TiO{sub 2} deactivates significantly due to the sintering of gold nanoparticles at elevated temperatures (Ma Z, Overbury SH, Dai S (2007) J Mol Catal A 273:97). In the current work, the performance of Au/M{sub x}O{sub y}/TiO{sub 2} (M = Al, Ca, Fe, Zn, Ga, Y, Zr, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) catalysts in water-gas shift (WGS) reaction was evaluated. The influences of different metal oxide (M{sub x}O{sub y}) additives and pretreatment temperatures were investigated, and the catalyst stability as a function of reaction time on stream was tested. Some of these novel gold catalysts, with high activity and stability in water-gas shift, furnish new possibilities for further fundamental research and industrial development.

Ma, Zhen [ORNL; Dai, Sheng [ORNL; Yin, Hongfeng [ORNL

2010-01-01

88

Heat Integration of the Water-Gas Shift Reaction System for Carbon Sequestration Ready IGCC Process with Chemical Looping  

SciTech Connect

Integrated gasification combined cycle (IGCC) technology has been considered as an important alternative for efficient power systems that can reduce fuel consumption and CO2 emissions. One of the technological schemes combines water-gas shift reaction and chemical-looping combustion as post gasification techniques in order to produce sequestration-ready CO2 and potentially reduce the size of the gas turbine. However, these schemes have not been energetically integrated and process synthesis techniques can be applied to obtain an optimal flowsheet. This work studies the heat exchange network synthesis (HENS) for the water-gas shift reaction train employing a set of alternative designs provided by Aspen energy analyzer (AEA) and combined in a process superstructure that was simulated in Aspen Plus (AP). This approach allows a rigorous evaluation of the alternative designs and their combinations avoiding all the AEA simplifications (linearized models of heat exchangers). A CAPE-OPEN compliant capability which makes use of a MINLP algorithm for sequential modular simulators was employed to obtain a heat exchange network that provided a cost of energy that was 27% lower than the base case. Highly influential parameters for the pos gasification technologies (i.e. CO/steam ratio, gasifier temperature and pressure) were calculated to obtain the minimum cost of energy while chemical looping parameters (oxidation and reduction temperature) were ensured to be satisfied.

Juan M. Salazara; Stephen E. Zitney; Urmila M. Diwekara

2010-01-01

89

Low-temperature activity of Au\\/CeO 2 for water gas shift reaction, and characterization by ADF-STEM, temperature-programmed reaction, and pulse reaction  

Microsoft Academic Search

In Au\\/CeO2 catalysts prepared by the deposition–precipitation method, many Au particles smaller than 3nm in diameter were clearly observed by annular dark field scanning transmission electron microscopy (ADF-STEM). The water gas shift activity of Au\\/CeO2 was compared with that of Pt\\/CeO2, Au\\/TiO2, and Cu\\/ZnO\\/Al2O3 by using temperature-programmed reaction (TPRe) measurement in a stream of a reaction gas mixture composed of

H. Sakurai; T. Akita; S. Tsubota; M. Kiuchi; M. Haruta

2005-01-01

90

Structure Sensitivity of the Low-temperature Water-gas Shift Reaction on Cu–CeO2 catalysts  

SciTech Connect

We have investigated the structure sensitivity of the water-gas shift (WGS) reaction on Cu-CeO{sub 2} catalysts prepared at the nanoscale by different techniques. On the surface of ceria, different CuO{sub x} structures exist. We show here that only the strongly bound Cu-[O{sub x}]-Ce species, probably associated with the surface oxygen vacancies of ceria, are active for catalyzing the low-temperature WGS reaction. Weakly bound CuO{sub x} clusters and CuO nanoparticles are spectator species in the reaction. Isolated Cu{sup 2+} ions doping the ceria surface are not active themselves, but they are important in that they create oxygen vacancies and can be used as a reservoir of copper to replenish surface Cu removed by leaching or sintering. Accordingly, synthesis techniques such as coprecipitation that allow for extensive solubility of Cu in ceria should be preferred over impregnation, deposition-precipitation, ion exchange or another two-step method whereby the copper precursor is added to already made ceria nanocrystals. For the synthesis of different structures, we have used two methods: a homogeneous coprecipitation (CP), involving hexamethylenetetramine as the precipitating agent and the pH buffer; and a deposition-precipitation (DP) technique. In the latter case, the ceria supports were first synthesized at the nanoscale with different shapes (rods, cubes) to investigate any potential shape effect on the reaction. Cu-CeO{sub 2} catalysts with different copper contents up to ca. 20 at.% were prepared. An indirect shape effect of CeO{sub 2}, manifested by the propensity to form oxygen vacancies and strongly bind copper in the active form, was established; i.e. the water-gas shift reaction is not structure-sensitive. The apparent activation energy of the reaction on all samples was similar, 50 {+-} 10 kJ/mol, in a product-free (2% CO-10% H{sub 2}O) gas mixture.

Si, R.; Zhang, L.; Raitano, J.; Yi, N.; Chan, S.-W.; Flytzani-Stephanopoulos, M.

2012-01-17

91

Carbon capture by sorption-enhanced water-gas shift reaction process using hydrotalcite-based material  

SciTech Connect

A novel route for precombustion decarbonization is the sorption-enhanced water-gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water-gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tablets of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400{sup o}C, the material shows a breakthrough capacity of 1.4 mmol/g. In subsequent experiments the material was mixed with tablets of promoted iron-chromium shift catalyst and exposed to a mixture of carbon dioxide, carbon monoxide, steam, hydrogen, and nitrogen. It is demonstrated that carbon monoxide conversion can be enhanced to 100% in the presence of a carbon dioxide sorbent. At breakthrough, carbon monoxide and carbon dioxide simultaneously appear at the end of the bed. During more than 300 cycles of adsorption/reaction and desorption, the capture rate, and carbon monoxide conversion are confirmed to be stable. Two different cycle types are investigated: one cycle with a CO{sub 2} rinse step and one cycle with a steam rinse step. The performance of both SEWGS cycles are discussed.

van Selow, E.R.; Cobden, P.D.; Verbraeken, P.A.; Hufton, J.R.; van den Brink, R.W. [Energy research Center of the Netherlands, Petten (Netherlands)

2009-05-15

92

Atomically dispersed Au-(OH)x species bound on titania catalyze the low-temperature water-gas shift reaction.  

PubMed

We report a new method for stabilizing appreciable loadings (~1 wt %) of isolated gold atoms on titania and show that these catalyze the low-temperature water-gas shift reaction. The method combines a typical gold deposition/precipitation method with UV irradiation of the titania support suspended in ethanol. Dissociation of H2O on the thus-created Au-O-TiO(x) sites is facile. At higher gold loadings, nanoparticles are formed, but they were shown to add no further activity to the atomically bound gold on titania. Removal of this "excess" gold by sodium cyanide leaching leaves the activity intact and the atomically dispersed gold still bound on titania. The new materials may catalyze a number of other reactions that require oxidized active metal sites. PMID:23437858

Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria

2013-03-13

93

Water-gas shift reaction on oxide/Cu(111): Rational catalyst screening from density functional theory  

NASA Astrophysics Data System (ADS)

Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO2/Cu(111), ZrO2/Cu(111) < MoO3/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

Liu, Ping

2010-11-01

94

Water-gas Shift Reaction on oxide/Cu(111): Rational Catalyst Screening from Density Functional Theory  

SciTech Connect

Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO{sub 2}/Cu(111), ZrO{sub 2}/Cu(111) < MoO{sub 3}/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

Liu, P.

2010-11-28

95

Mechanisms of the water-gas shift reaction catalyzed by ruthenium pentacarbonyl: a density functional theory study.  

PubMed

The mechanism of the water-gas shift reaction catalyzed by Ru(CO)5 is analyzed using density functional methods in solution within the conductor-like screening model. Four different mechanistic pathways have been considered. It turned out that the incorporation of solvent effects is very important for a reasonable comparison among the mechanistic alternatives. The explicit inclusion of a water solvent molecule significantly changes the barriers of those steps which involve proton transfer in the transition state. The corresponding barriers are either lowered or increased, depending on the structure of the corresponding cyclic transition states. The results show that protolysis steps become competitive due to solution effects. The formation of formic acid as an intermediate in another, alternative pathway is also found to be competitive. PMID:23600366

Schulz, Hannes; Görling, Andreas; Hieringer, Wolfgang

2013-05-01

96

Low temperature, sulfur tolerant homogeneous catalysts for the water-gas shift reaction. Task 1, Topical report No. 1  

SciTech Connect

The purpose of this report is to update and reorganize our recent review on homogeneous catalysis of the water-gas shift reaction (WGSR) based on recent literature publications and patents. This updated version will serve as a means of selecting 10 candidate catalyst systems for use in developing effective, sulfur-tolerant, low temperature WGSR catalysts. This report discusses the variations possible in the basic chemistry associated with WGSR catalytic cycles, including basic, acidic, and neutral conditions. Then individual mechanism for specific WGSR catalyst systems are discussed. Finally, on the basis of the literature reports, a list is presented of candidate catalysts and basic systems we have chosen for study in Task 3.

Laine, R.M.

1986-01-20

97

SIC-BASED HYDROGEN SELECTIVE MEMBRANES FOR WATER-GAS-SHIFT REACTION  

SciTech Connect

A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. SiC macro-porous membranes have been successfully fabricated via extrusion of commercially available SiC powder. Also, an SiC hydrogen selective thin film was prepared via our CVD/I technique. This composite membrane demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers and sol-gel techniques. Building upon the positive progress made in the membrane development study, we conducted an optimization study to develop an H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment. In addition, mathematical simulation has been performed to compare the performance of the membrane reactor (MR) vs conventional packed bed reactor for WGS reaction. Our result demonstrates that >99.999% conversion can be accomplished via WGS-MR using the hydrogen selective membrane developed by us. Further, water/CO ratio can be reduced, and >97% hydrogen recovery and <200 ppm CO can be accomplished according to the mathematical simulation. Thus, we believe that the operating economics of WGS can be improved significantly based upon the proposed MR concept. In parallel, gas separations and hydrothermal and long-term-storage stability of the hydrogen selected membrane have been experimentally demonstrated using a pilot-scale tubular membrane under a simulated WGS environment.

Paul K.T. Liu

2003-12-01

98

Studies of hydrogen production by the water gas shift reaction and related chemistry. Final technical report 1 September 1980-31 March 1983  

Microsoft Academic Search

Many systems have been investigated for the catalysis of the water gas shift reaction and for electrocatalytic oxidation of CO. These systems have involved precious metal complexes composed of Pt, Rh, and Ir, and reaction conditions for these systems have been especially mild: atmospheric pressures and low temperatures. In addition aqueous acidic conditions for these systems have been pursued with

Eisenberg

1983-01-01

99

The role of metals and influence of oxygen on ceria supported copper-palladium bimetallic catalysts for the oxygen-assisted water-gas shift reaction  

NASA Astrophysics Data System (ADS)

This study was focused to investigate the roles of Cu and Pd in CuPd/CeO 2 bimetallic catalysts containing 30 wt% Cu and 1 wt% Pd used in the oxygen-assisted water-gas shift (OWGS) reaction employing combined bulk and surface characterization techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), CO chemisorption, and in-situ X-ray photoelectron spectroscopy (XPS). The role of oxygen in aiding the water-gas shift reaction was also studied to determine an overall mechanism for the water-gas shift reaction. The catalytic activity for CO conversion and the stability of catalyst during on-stream operation increased upon adding Pd to Cu/CeO2 monometallic catalysts, especially when the OWLS reaction was performed under low temperatures. In-situ XPS studies of reduced catalysts showed the existence of Cu and Pd in their metallic states. The spectra also showed a shift in Cu 2p peaks toward lower binding energy with concommitant shift in the Pd 3d peaks toward higher BE. Addition of Pd decreased the surface Cu concentration while the concentration of Pd remained unaltered. The improved catalytic activity and stability of CuPd/CeO2 bimetallic catalyst was attributed to the Cu-Pd interaction. When the catalyst series was reduced in-situ under UHV conditions in the XPS chamber in order to better understand the metal-support interactions, it was found that the addition of 1%Pd to the Cu/CeO2 catalyst would greatly improve the reduction properties of the Cu and Ce under UHV conditions. When compared with results from the oxygen-assisted water-gas-shift reaction, it was found that the increased reduction from the addition of Pd aided in the reaction. When reaction kinetics of the water-gas shift and the oxygen-assisted water-gas shift reaction were examined, it was found that the addition of a small amount of air improved the overall reaction kinetics. In general, the activation energies decreased for the catalyst series when air was added to the feed stream. Based on kinetics, it is believed that the adsorbed oxygen acts as a promoter for the reaction, aiding in the dissociation of water on the catalyst surface. This evidence, in particular, helps support the redox mechanism for the water-gas shift reaction.

Fox, Elise Bickford

100

Water-gas shift: steady state isotope switching study of the water-gas shift reaction over Pt\\/ceria using in-situ DRIFTS  

Microsoft Academic Search

The stability of surface formates generated by reaction of bridging OH groups with CO is an important first criterion supporting the idea that the rate limiting step of WGS involves formate decomposition. The second important factor is that, in the presence of water, shown directly by the measurements obtained during this steady state isotope switching study, the forward decomposition of

Gary Jacobs; Adam C. Crawford; Burtron H. Davis

2005-01-01

101

Steam demand reduction of water–gas shift reaction in IGCC power plants with pre-combustion CO 2 capture  

Microsoft Academic Search

This paper presents the results of system assessments that were conducted to compare conventional and advanced water–gas shift reactor sections. The latter are specifically tailored for Integrated Gasification Combined Cycles (IGCC) power plants with pre-combustion CO2 capture. The advanced shift reactor section comprises four staged reactors with distributed feeds of synthesis gas and quench water in between the reactors. Conventional

M. C. Carbo; J. Boon; D. Jansen; H. A. J. van Dijk; J. W. Dijkstra; R. W. van den Brink; A. H. M. Verkooijen

2009-01-01

102

Hydrogen production through the water-gas shift reaction: thermodynamic equilibrium versus experimental results over supported Ni catalysts  

SciTech Connect

This paper discusses the experimental results of the water-gas shift reaction over supported nickel catalysts in comparison to thermodynamic equilibrium composition at the same reaction conditions. The effects of different supports on the performance of H{sub 2} production over nickel-supported catalysts are also evaluated at both low and high temperatures. Ceria-promoted nickel catalyst supported on powder alumina (Ni/CeO{sub 2}-Al{sub 2}O{sub 3}) demonstrated excellent performance. The catalyst was not stable at low temperature (250{sup o}C) but showed good stability at high temperature (450{sup o}C). At 450{sup o}C, with a catalyst loading of 0.05 g, CO/S (S = steam) ratio of 1:3, and gas hourly space velocity (GHSV) - 200 L h{sup -1} g{sub cat}{sup -1}, the activity of Ni/CeO{sub 2}-Al{sub 2}O{sub 3} was 95% with a H{sub 2} yield of 52% and a H{sub 2} selectivity of 73%.

Agus Haryanto; Sandun D. Fernando; S.D. Filip To; Philip H. Steele; Lester Pordesimo; Sushil Adhikari [Mississippi State University, MS (United States). Agricultural and Biological Engineering Department

2009-05-15

103

Chemistry and catalysis of the water gas shift reaction. 1. The kinetics over supported metal catalysts  

Microsoft Academic Search

The kinetics of the WGS reaction as catalyzed by alumina-supported Group VIIB, VIII, and IB metals are examined. For several metals a strong effect of support on metal activity is observed. For example, the turnover number (rate per surface metal atom) of Pt supported on AlâOâ is an order of magnitude higher than the turnover number of Pt on SiOâ.

D. C. Grenoble; M. M. Estadt; D. F. Ollis

1981-01-01

104

H2 production Through the Water-gas Shift Reaction: An in Situ Time-resolved X-ray Diffraction Investigation of Manganese OMS-2 Catalyst  

SciTech Connect

Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer-Emmett-Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction to generate hydrogen under laboratory conditions. An in situ study was conducted to monitor the structural changes in the catalyst during the water-gas shift reaction using synchrotron radiation-based time-resolved X-ray diffraction (TR-XRD). During the water-gas shift reaction, the mixed valent OMS-2 catalyst undergoes a structural transformation to form Mn{sub 2}O{sub 3} and finally to form MnO. The study showed that OMS-2 catalysts can be used as inexpensive catalysts for hydrogen generation.

Sithambaram, S.; Wen, W; Njagi, E; Shen, X; Hanson, J; Suib, S

2010-01-01

105

H2 Production Through the Water-gas Shift Reaction: An In situ Time-resolved X-ray Diffraction Investigation of Manganese OMS-2 Catalyst  

SciTech Connect

Manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by the reflux method was investigated for hydrogen generation via the water-gas shift reaction. Catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), The Brunauer-Emmett-Teller (BET) surface area and determination of average oxidation state (AOS). The OMS-2 catalyst showed very good catalytic activity for the water-gas shift reaction to generate hydrogen under laboratory conditions. An in situ study was conducted to monitor the structural changes in the catalyst during the water-gas shift reaction using synchrotron radiation-based time-resolved X-ray diffraction (TR-XRD). During the water-gas shift reaction, the mixed valent OMS-2 catalyst undergoes a structural transformation to form Mn{sub 2}O{sub 3} and finally to form MnO. The study showed that OMS-2 catalysts can be used as inexpensive catalysts for hydrogen generation.

Hanson, J.C.; Sithambaram, S.; Wen, W.; Njagi, E.; Shen, X.-F.; Suib, S.L.

2010-10-01

106

Studies related to the homogeneous catalysis of the water gas shift reaction. Final technical report, August 1, 1977November 30, 1984  

Microsoft Academic Search

The research carried out under the sponsorship of this contract was concerned with the development and the fundamental mechanistic evaluation of homogeneous catalysts for the water gas shift reaction (HâO + CO=Hâ + COâ). The scope of these studies included the screening and optimization of new catalysts and quantitative studies of key steps of proposed catalytic cycles. Such investigations provide

Ford

1984-01-01

107

Studies related to the homogeneous catalysis of the water gas shift reaction. Technical progress report, December 1, 1983November 30, 1984  

Microsoft Academic Search

Proposed are investigations related to the catalytic activation of carbon monoxide. These studies will be concerned with the design of catalysts for the water gas shift reaction and related processes such as the hydroformylation of olefins by homogeneous solution phase systems as well as by selected metal catalysts heterogenized by complexation to functional polymers. Also under investigation will be quantitative

Ford

1984-01-01

108

The activation of gold and the water-gas shift reaction: insights from studies with model catalysts.  

PubMed

The activation of gold in catalytic reactions has been the subject of intensive research that has led to the transformation of one of the least chemically reactive elements to a catalyst with excellent activity and selectivity. Scientists have performed numerous systematic experimental and theoretical studies using model systems, which have explained the role of Au in chemical reactions with progressively increasing degrees of structural and chemical complexity. We present an overview of recent studies of model Au(111), CeOx/Au(111), and Au/CeOx/TiO2(110) surfaces that use Au in different structural configurations specifically for the water-gas shift reaction (WGS, CO + H2O ? CO2 + H2), an important industrial process for the purification of CO. We demonstrate the significance of key structural components of the Au-based supported catalysts such as the metal-oxide interface (Au-Ox) toward the WGS catalytic activity, a "structure-activity" relationship. In the WGS reaction, Au(111) or Au nanoparticles have poor catalytic performance due to their inability to activate one of the most important steps of the reaction, the breaking of O-H bonds in the dissociation of water (H2O ? OH + H). The relatively large energetic barrier can be overcome by using O on Au(111) to facilitate the formation of OH at low temperatures, with eventual CO2 and H2 production upon reaction between CO and the adsorbed OH. However, the inability to replace the reacted O prevents a sustainable catalytic process from occurring on Au(111). The addition of a small concentration of CeOx nanoparticles on top of the Au(111) surface facilitates this rate-determining step and easily continues the catalytic cycle in the production of H2. We have discovered that CeOx nanoparticles in contact with Au(111) are rich in Ce(3+). They also have a distinct metal-oxide interface, which sustains excellent activity for the WGS reaction via the formation of a unique carboxylate intermediate, making CeOx/Au(111) more active than Cu/ZnO(0001?), Cu(100), and Cu(111) which are the typical catalysts for this reaction. Taking this knowledge one step further, bringing these components (oxide and metal nanoparticles) together over a second oxide in Au/CeOx/TiO2 produces a system with unique morphological and electronic properties. The result is a superior catalyst for the WGS reaction, both as a model system (Au/CeOx/TiO2(110)) and as powder material (Au/CeOx/TiO2(anatase)) optimized directly in a series of systematic investigations. PMID:24191672

Rodriguez, José A; Senanayake, Sanjaya D; Stacchiola, Dario; Liu, Ping; Hrbek, Jan

2014-03-18

109

Remarkable performance of Ir1/FeO(x) single-atom catalyst in water gas shift reaction.  

PubMed

High specific activity and cost effectiveness of single-atom catalysts hold practical value for water gas shift (WGS) reaction toward hydrogen energy. We reported the preparation and characterization of Ir single atoms supported on FeO(x) (Ir1/FeO(x)) catalysts, the activity of which is 1 order of magnitude higher than its cluster or nanoparticle counterparts and is even higher than those of the most active Au- or Pt-based catalysts. Extensive studies reveal that the single atoms accounted for ?70% of the total activity of catalysts containing single atoms, subnano clusters, and nanoparticles, thus serving as the most important active sites. The Ir single atoms seem to greatly enhance the reducibility of the FeO(x) support and generation of oxygen vacancies, leading to the excellent performance of the Ir1/FeO(x) single-atom catalyst. The results have broad implications on designing supported metal catalysts with better performance and lower cost. PMID:24090210

Lin, Jian; Wang, Aiqin; Qiao, Botao; Liu, Xiaoyan; Yang, Xiaofeng; Wang, Xiaodong; Liang, Jinxia; Li, Jun; Liu, Jingyue; Zhang, Tao

2013-10-16

110

Water-Gas --Shift Reaction on Gold Nanoparticles Supported on Iron Oxide Surfaces: A Scanning Tunneling Microscopy/Spectroscopy Study  

NASA Astrophysics Data System (ADS)

We present a Scanning Tunneling Microscopy (STM)/Scanning Tunneling Spectroscopy (STS) study of the Water-Gas-Shift reaction on a model catalyst system consisting of supported gold nanoparticles on a reduced Fe3O4(111) surface in ultrahigh vacuum. Gold forms two electrically distinct nanoparticles on an iron oxide surface upon annealing multilayer Au/Fe3O4(111) at 500 ^oC for 15 minutes. STS measurements show that large gold nanoparticles (˜ 8 nm) exhibit a metallic electronic structure while single gold adatoms bonded to the oxygen sites of the Fe3O4(111) surface are likely positively charged. This Au/Fe3O4(111) system is dosed with CO and H2O at various temperatures. The site specific adsorption and the interaction of CO with the Au nanoparticles will be presented and discussed along with the observation of the site specific dissociative adsorption of H2O to elucidate the catalytic properties of Au nanoparticles on a reducible iron oxide surface.

Taeg Rim, Kwang; Eom, Daejin; Liu, Li; Raitano, Joan; Chan, Siu-Wai; Flytzani-Stepanopoulous, Maria; Flynn, George

2010-03-01

111

Low-temperature water-gas shift reaction over Cu and Ni-loaded cerium oxide catalysts  

Microsoft Academic Search

In this paper we report on the activity of Cu- and Ni-containing cerium oxide catalysts for low-temperature water-gas shift (WGS). Bulk catalysts were prepared in nanocrystalline form by the urea co-precipitation–gelation method. Lanthanum dopant (10at.%) was used as a structural stabilizer of ceria, while the content of Cu or Ni was in the range of 5–15at.% (2–8wt.%). At low metal

Yue Li; Qi Fu; Maria Flytzani-Stephanopoulos

2000-01-01

112

A Steady-State Kinetic Model for Methanol Synthesis and the Water Gas Shift Reaction on a Commercial Cu\\/ZnO\\/Al 2O 3Catalyst  

Microsoft Academic Search

A detailed reaction network, derived from literature data and our own experimental work, is used as a basis for the development of a steady-state kinetic model for methanol synthesis and the water gas shift reaction on a commercial Cu\\/ZnO\\/Al2O3catalyst. Experimental data, obtained in a bench scale setup, operating between 180 and 280°C and at pressures up to 51 bar, are

K. M. Vanden Bussche; G. F. Froment

1996-01-01

113

FTIR Study of the Low-Temperature Water–Gas Shift Reaction on Au\\/Fe 2O 3 and Au\\/TiO 2 Catalysts  

Microsoft Academic Search

An FTIR and quadrupole mass spectroscopic study of the water–gas shift (WGS), the reverse WGS reactions, and the adsorption of the individual molecules involved has been carried out on Au\\/Fe2O3 and Au\\/TiO2 catalysts. The chemisorptions and the reactions on the two catalysts have been compared with the aim of gaining a better understanding of the role played by the two

F. Boccuzzi; A. Chiorino; M. Manzoli; D. Andreeva; T. Tabakova

1999-01-01

114

Water-Gas Shift and CO Methanation Reactions over Ni-CeO2(111) Catalysts  

SciTech Connect

X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO{sub 2}(111) surfaces. Upon adsorption on CeO{sub 2}(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500-800 K) leads to partial reduction of the ceria substrate with the formation of Ni{sup 2+} species that exists as NiO and/or Ce{sub 1-x}Ni{sub x}O{sub 2-y}. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO{sub 2}(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce{sup +3} cations, CO dissociates on the surface at 300 K forming NiC{sub x} compounds that may be involved in the formation of CH{sub 4} at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO{sub 2}(111) surfaces are able to catalyze the production of methane from CO and H{sub 2}, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO{sub 2}(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water-gas shift reaction.

S Senanayake; J Evans; S Agnoli; L Barrio; T Chen; J Hrbek; J Rodriguez

2011-12-31

115

Water-Gas Shift and CO Methanation Reactions over Ni-CeO2(111) Catalysts  

SciTech Connect

X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO2(111) surfaces. Upon adsorption on CeO2(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500 800 K) leads to partial reduction of the ceria substrate with the formation of Ni2? species that exists as NiO and/or Ce1-xNixO2-y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO2(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce?3 cations, CO dissociates on the surface at 300 K forming NiCx compounds that may be involved in the formation of CH4 at higher temperatures. At medium and large Ni coverages ([0.3 ML), the Ni/CeO2(111) surfaces are able to catalyze the production of methane from CO and H2, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (\\0.3 ML), the Ni/CeO2(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water gas shift reaction.

Senanayake, Sanjaya D [ORNL; Evans, Jaime [Universidad Central de Venezuela; Agnoli, Stefano [Brookhaven National Laboratory (BNL); Barrio, Laura [Brookhaven National Laboratory (BNL); Chen, Tsung-Liang [ORNL; Hrbek, Jan [Brookhaven National Laboratory (BNL); Radriguez, Jose [Brookhaven National Laboratory (BNL)

2011-01-01

116

Reverse water-gas shift reaction: steady state isotope switching study of the reverse water-gas shift reaction using in situ DRIFTS and a Pt\\/ceria catalyst  

Microsoft Academic Search

A previous investigation using steady state isotope switching in combination with DRIFTS demonstrated that surface formates exchange rapidly in a low temperature shift feed for the forward reaction. Transient decomposition of the pseudo-stable formate indicated that water autocatalyzes the forward shift reaction. In the present study, and including water in the RWGS feed (H2 and CO2), surface formates were found

Gary Jacobs; Burtron H. Davis

2005-01-01

117

A rationally designed CuFe2O4-mesoporous Al2O3 composite towards stable performance of high temperature water-gas shift reaction.  

PubMed

High temperature water-gas shift reaction was demonstrated for the first time on a CuFe2O4-mesoporous alumina nanocomposite between 350 and 550 °C with 70-80% CO-conversion using simulated waste derived syngas under realistic conditions. Despite high Al-content, the catalyst exhibited stable activity, which was attributed to the nano-architectured robust porous nature of alumina integrated with surrounding CuFe2O4. PMID:23928578

Subramanian, Vijayanand; Gnanakumar, Edwin S; Jeong, Dae-Woon; Han, Won-Bi; Gopinath, Chinnakonda S; Roh, Hyun-Seog

2013-12-14

118

Mechanistic aspects of the water–gas shift reaction on alumina-supported noble metal catalysts: In situ DRIFTS and SSITKA-mass spectrometry studies  

Microsoft Academic Search

Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with mass spectrometry were performed for the first time to study essential mechanistic aspects of the water–gas shift (WGS) reaction over alumina-supported Pt, Pd, and Rh catalysts. In particular, the concentrations (?molg?1) of active intermediate species found in the carbon-path from CO to the CO2 product gas (use of 13CO), and in

George G. Olympiou; Christos M. Kalamaras; Constantinos D. Zeinalipour-Yazdi; Angelos M. Efstathiou

2007-01-01

119

Active sites on Cu\\/SiO 2 prepared using the atomic layer epitaxy technique for a low-temperature water–gas shift reaction  

Microsoft Academic Search

The atomic layer epitaxy (ALE) technique has been used to prepare uniform copper nanoparticles dispersed on a silica support (ALE-Cu\\/SiO2 with 2.85±0.32 nm), which are highly active in the water–gas shift reaction. Infrared spectra of CO adsorption are employed to study the active sites on ALE-Cu\\/SiO2 surface, suggesting that two major active sites are found on the copper surface, namely

Ching-Shiun Chen; Jarrn-Horng Lin; Tzu-Wen Lai; Bao-Hui Li

2009-01-01

120

Studies of the water-gas-shift reaction on ceria-supported Pt, Pd, and Rh: Implications for oxygen-storage properties  

Microsoft Academic Search

Steady-state, water-gas-shift kinetics were measured on model, ceria-supported, Pd, Pt, and Rh catalysts and compared to rates obtained on alumina-supported catalysts. When ceria was calcined at low temperatures prior to addition of the precious metal, the specific rates were found to be identical for each of the metals, with an activation energy of 11 ± 1 kcal\\/mol and reaction orders

T. Bunluesin; R. J. Gorte; G. W. Graham

1998-01-01

121

Catalysis of the water gas shift reaction by cis -[Rh(CO) 2 (AMINE) 2 ](PF 6 ) complexes in an aqueous tetrabutylammonium hydrogensulfate solution  

Microsoft Academic Search

Rhodium(I) complexes, cis-[Rh(CO)2(amine)2](PF6) (amine = 4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) dissolved in an aqueous solution of\\u000a tetrabutylammonium hydrogensulfate (N(C4H9)4HSO4), catalyze the water-gas shift reaction (WGSR). The role of the coordinated amine on the catalytic activity was examined.

Germán Gascón; Marisol C. Ortega; José D. Suárez; Alvaro J. Pardey; Clementina Longo

2008-01-01

122

Influence of zirconia crystal phase on the catalytic performance of Au\\/ZrO 2 catalysts for low-temperature water gas shift reaction  

Microsoft Academic Search

The influence of crystal phase of zirconia on the performance of Au\\/ZrO2 catalysts for low temperature water gas shift reaction was investigated. Au\\/ZrO2 catalysts with pure tetragonal and monoclinic phases of ZrO2 were prepared by the deposition-precipitation method with similar gold loading and dispersion. It was found that the Au\\/m-ZrO2 catalyst showed much higher activity than that of the Au\\/t-ZrO2

Juan Li; Junli Chen; Wei Song; Junlong Liu; Wenjie Shen

2008-01-01

123

Determination of kinetic parameters for the water–gas shift reaction on copper catalysts under realistic conditions for fuel cell applications  

Microsoft Academic Search

The kinetic parameters for water–gas shift reaction on Cu-based catalysts were measured under fuel reformer conditions for fuel cell applications (7% CO, 8.5% CO2, 22% H2O, 37% H2, and 25% Ar) at 1 atm total pressure and temperature in the range of 200°C. The rate per unit of Cu surface area at the stated concentrations was 0.8×10?6 molm?2s?1 at 200°C.

N. A. Koryabkina; A. A. Phatak; W. F. Ruettinger; R. J. Farrauto; F. H. Ribeiro

2003-01-01

124

Hydrogen production by water–gas shift reaction over bimetallic Cu–Ni catalysts supported on La-doped mesoporous ceria  

Microsoft Academic Search

Water–gas shift reaction was investigated over a series of Ni, Cu and Cu–Ni bimetallic catalysts supported on La-doped mesoporous ceria. The catalysts were characterized by powder X-ray diffraction (XRD), high-temperature XRD (HTXRD), transmission electron microscopy (TEM), N2 adsorption analysis, and H2 temperature-programmed reduction (TPR). Combined results of powder XRD, HTXRD and TPR studies provided evidence of the formation of CuNi

Jiann-Horng Lin; Prakash Biswas; Vadim V. Guliants; Scott Misture

2010-01-01

125

Water-gas shift reaction over Cu\\/ZnO and Cu\\/ZnO\\/Al 2O 3 catalysts prepared by homogeneous precipitation  

Microsoft Academic Search

Both binary Cu\\/ZnO and ternary Cu\\/ZnO\\/Al2O3 catalysts were prepared by homogeneous precipitation (hp) using urea hydrolysis. The structure and the activity for the water-gas shift reaction of these catalysts were studied compared with those prepared by coprecipitation (cp). The binary precursors contained hydroxycarbonates such as malachite and aurichalcite phases, whereas the ternary precursors were composed of hydrotalcite, malachite and aurichalcite

Tetsuya Shishido; Manabu Yamamoto; Dalin Li; Yan Tian; Hiroyuki Morioka; Masahide Honda; Tsuneji Sano; Katsuomi Takehira

2006-01-01

126

Supported Copper, Nickel and Copper-Nickel Nanoparticle Catalysts for Low Temperature Water-Gas-Shift Reaction  

NASA Astrophysics Data System (ADS)

Hydrogen is being considered worldwide as a future replacement for gasoline, diesel fuel, natural gas in both the transportation and non-transportation sectors. Hydrogen is a versatile energy carrier that can be produced from a variety of widely available primary energy sources, including coal, natural gas, biomass, solar, wind, and nuclear power. Coal, the most abundant fossil fuel on the planet, is being looked at as the possible future major source of H2, due to the development of the integrated gasification combined cycle (IGCC) and integrated gasification fuel cell technologies (IGFC). The gasification of coal produces syngas consisting of predominately carbon monoxide and hydrogen with some remaining hydrocarbons, carbon dioxide and water. Then, the water-gas shift reaction is used to convert CO to CO2 and additional hydrogen. The present work describes the synthesis of model Cu, Ni and Cu-Ni catalysts prepared from metal colloids, and compares their behavior in the WGS reaction to that of traditional impregnation catalysts. Initially, we systematically explored the performance of traditional Cu, Ni and Cu-Ni WGS catalysts made by impregnation methods. Various bimetallic Cu-Ni catalysts were prepared by supported impregnation and compared to monometallic Cu and Ni catalysts. The presence of Cu in bimetallic catalysts suppressed undesirable methanation side reaction, while the Ni component was important for high WGS activity. Colloidal Cu, Ni and Cu-Ni alloy nanoparticles obtained by chemical reduction were deposited onto alumina to prepare supported catalysts. The resulting Cu and Ni nanoparticle catalysts were found to be 2.5 times more active in the WGS reaction per unit mass of active metal as compared to catalysts prepared by the conventional impregnation technique. The powder XRD and HAADF-STEM provided evidence supporting the formation of Cu-Ni particles containing the Cu core and Cu-Ni alloy shell. The XPS data indicated surface segregation of Cu in the bimetallic Cu-Ni catalysts after reduction. The colloidal Cu5Ni5 alloy catalyst exhibited the WGS reaction rate that was higher than that observed over colloidal Cu and Ni catalysts indicating for the very first time a favorable bimetallic effect for the Cu-Ni system. The presence of Cu in these bimetallic catalysts induced favorable structural and electronic effects not only for enhancing the WGS activity, but also for suppressing methane yield. Bimetallic Cu-Ni catalysts possessing a core-shell structure were synthesized that provided important insights into their structure-activity relationships in the WGS reaction. We employed a successive reduction route to synthesize Cu Ni and Ni Cu core-shell nanoparticles and deposited them onto alumina support to obtain supported bimetallic catalysts. The powder XRD patterns, CO chemisorption data, and UV-vis spectra indicated the formation of core-shell structures in the bimetallic Cu-Ni nanoparticles. Cu Ni catalysts showed similar WGS activities to supported Ni catalysts but lower methanation activity. Suppressed methanation activity observed for Cu Ni nanoparticles may be due to Cu segregation to the surface. Supported Ni Cu catalysts displayed WGS activity comparable to supported Cu catalysts. Therefore, these findings strongly suggested that supported Cu, Ni and Cu-Ni alloy nanoparticle catalysts prepared from metal colloids are very promising as highly active WGS catalysts.

Lin, Jiann-Horng

127

In Situ Time-Resolved Characterization of Novel Cu-MoO2 Catalysts During the Water-Gas Shift Reaction  

SciTech Connect

A novel and active Cu-MoO{sub 2} catalyst was synthesized by partial reduction of a precursor CuMoO{sub 4} mixed-metal oxide with CO or H{sub 2} at 200-250 C. The phase transformations of Cu-MoO{sub 2} during H{sub 2} reduction and the water-gas shift reaction could be followed by In situ time resolved XRD techniques. During the reduction process the diffraction pattern of the CuMoO{sub 4} collapsed and the copper metal lines were observed on an amorphous material background that was assigned to molybdenum oxides. During the first pass of water-gas shift (WGS) reaction, diffraction lines for Cu{sub 6}Mo{sub 5}O{sub 18} and MoO{sub 2} appeared around 350 C and Cu{sub 6}Mo{sub 5}O{sub 18} was further transformed to Cu/MoO{sub 2} at higher temperature. During subsequent passes, significant WGS catalytic activity was observed with relatively stable plateaus in product formation around 350, 400 and 500 C. The interfacial interactions between Cu clusters and MoO{sub 2} increased the water-gas shift catalytic activities at 350 and 400 C.

Wen ,W.; Liu, J.; White, M.; Marinkovic, N.; Hanson, J.; Rodriguez, J.

2007-01-01

128

MgO–Al 2 O 3 Mixed Oxides-Supported Co–Mo-Based Catalysts for High-Temperature Water–Gas Shift Reaction  

Microsoft Academic Search

MgO–Al2O3 mixed oxides were prepared and used as the support of Co–Mo-based water–gas shift reaction (WGSR) catalysts. X-ray diffraction\\u000a (XRD) characterization showed that the MgO–Al2O3 mixed oxides support is composed of MgO, ?-Al2O3, and magnesia–alumina spinel. The MgO–Al2O3 mixed oxides-supported Co–Mo-based catalysts exhibited high shift activity at high temperature (360–450 °C) and high stability.\\u000a The addition of potassium enhanced the activities

Huifang Wang; Yixin Lian; Qing Zhang; Qiaoling Li; Weiping Fang; Yiquan Yang

2008-01-01

129

Untangling the Water Gas Shift from Fischer-Tropsch: A Gordian Knot.  

National Technical Information Service (NTIS)

The water gas shift reaction is an integral part of the Fischer-Tropsch synthesis. Although it may appear convenient to consider the water gas shift a separate reaction, in some cases, a detailed examination of the mechanism indicates theat the water gas ...

C. K. Rofer-Depoorter

1983-01-01

130

The role of copper in catalytic performance of a Fe-Cu-Al-O catalyst for water gas shift reaction.  

PubMed

A Fe-Cu-Al-O water gas shift catalyst with a Fe : Cu atomic ratio of 4 : 1 upon pretreatment at 350 °C in H2 exhibits a conversion higher than a physical mixture of Fe-Al-O and Cu-Al-O by ~40% over a temperature range of 300 °C-450 °C. In situ ambient pressure X-ray photoelectron spectroscopy studies suggest that the surface region of Fe-Cu-Al-O was restructured into a double-layer structure consisting of a surface layer of Fe3O4 and a metallic Cu layer below it upon pretreatment at 350 °C. The strong metal (Cu)-oxide (Fe3O4) interface effect of this double layer structure enhances the catalytic activity of Fe3O4 in WGS. PMID:23323268

Ye, Yingchun; Wang, Lei; Zhang, Shiran; Zhu, Yuan; Shan, Junjun; Tao, Franklin Feng

2013-05-14

131

Water-Gas Shift with Integrated Hydrogen Separation.  

National Technical Information Service (NTIS)

Optimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membra...

M. Flytzani-Stephanopoulos J. Meldon X. Qi

2001-01-01

132

The synthesis of methanol and the reverse water-gas shift reaction over Zn-deposited Cu(100) and Cu(110) surfaces: comparison with Zn/Cu(111)  

NASA Astrophysics Data System (ADS)

The catalytic activity of Zn vapor-deposited Cu(100) and Cu(110) surfaces for methanol synthesis by the hydrogenation of CO 2 and the reverse water-gas shift reaction were studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). At a reaction temperature of 523 K, no promotional effect of Zn was observed for the methanol synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111), on which a significant promotion of methanol synthesis activity appeared to be due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the catalytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twice that measured before heating, which was close to the methanol synthesis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift reaction on Zn/Cu(110), indicating that the active site for methanol synthesis was not identical to that for the reverse water-gas shift reaction. In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110), whose coverage increased with increasing Zn coverage at 0< ?Zn<0.2. No correlation between the formate coverage and the methanol synthesis activity was obtained, which was in contrast to the results for Zn/Cu(111). Thus, the structure sensitivity observed in the catalytic activity of methanol synthesis over Zn-deposited Cu surfaces is ascribed to the significant difference in the reactivity of the formate intermediate.

Nakamura, I.; Fujitani, T.; Uchijima, T.; Nakamura, J.

1998-03-01

133

Theoretical study of gas-phase reactions of Fe(CO){sub 5} with OH{sup {minus}} and their relevance for the water gas shift reaction  

SciTech Connect

Revision of the homogeneously Fe(CO){sub 5}-catalyzed water gas shift reaction in the gas phase has been performed by means of quantum chemical calculations using gradient-corrected density functional theory (B3LYP) and ab initio methods at the CCSD(T) level. The classically assumed reaction path has been scrutinized step by step, and enlarged with novel mechanistic proposals. The calculations lend additional credit to some of the previously accepted steps in the catalytic cycle, such as the initial attack of OH{sup {minus}} to Fe(CO){sub 5} and also to the recently accepted decarboxylation of (CO){sub 4}FeCOOH{sup {minus}} (via a concerted mechanism involving a four-centered transition state), as well as to the acidification of the metal hydride (CO){sub 4}Fe{sub 4}H{sub {minus}} with water to yield the dihydride (CO){sub 4}FeH{sub 2}. The present investigation also examines in terms of energies and activation barriers the existence/participation of new intermediates (in particular, a metalloformate species, a water-hydride adduct, and a dihydrogen complex), not mentioned in prior studies. Finally, a transition-metal-containing S{sub N}2-type reaction is explored for the last stages of this chemical process as a mechanistic alternative to regenerate the starting catalyst.

Torrent, M.; Sola, M. [Univ. de Girona (Spain). Institut de Quimica Computacional] [Univ. de Girona (Spain). Institut de Quimica Computacional; Frenking, G. [Philipps-Universitaet Marburg (Germany)] [Philipps-Universitaet Marburg (Germany)

1999-07-19

134

Advanced Water-Gas Shift Membrane Reactor  

SciTech Connect

The overall objectives for this project were: (1) to identify a suitable PdCu tri-metallic alloy membrane with high stability and commercially relevant hydrogen permeation in the presence of trace amounts of carbon monoxide and sulfur; and (2) to identify and synthesize a water gas shift catalyst with a high operating life that is sulfur and chlorine tolerant at low concentrations of these impurities. This work successfully achieved the first project objective to identify a suitable PdCu tri-metallic alloy membrane composition, Pd{sub 0.47}Cu{sub 0.52}G5{sub 0.01}, that was selected based on atomistic and thermodynamic modeling alone. The second objective was partially successful in that catalysts were identified and evaluated that can withstand sulfur in high concentrations and at high pressures, but a long operating life was not achieved at the end of the project. From the limited durability testing it appears that the best catalyst, Pt-Re/Ce{sub 0.333}Zr{sub 0.333}E4{sub 0.333}O{sub 2}, is unable to maintain a long operating life at space velocities of 200,000 h{sup -1}. The reasons for the low durability do not appear to be related to the high concentrations of H{sub 2}S, but rather due to the high operating pressure and the influence the pressure has on the WGS reaction at this space velocity.

Sean Emerson; Thomas Vanderspurt; Susanne Opalka; Rakesh Radhakrishnan; Rhonda Willigan

2009-01-07

135

Nano-structured CeO 2 supported Cu-Pd bimetallic catalysts for the oxygen-assisted water–gas-shift reaction  

Microsoft Academic Search

The present work focuses on the development of novel Cu-Pd bimetallic catalysts supported on nano-sized high-surface-area CeO2 for the oxygen-assisted water–gas-shift (OWGS) reaction. High-surface-area CeO2 was synthesized by urea gelation (UG) and template-assisted (TA) methods. The UG method offered CeO2 with a BET surface area of about 215m2\\/g, significantly higher than that of commercially available CeO2. Cu and Pd were

Elise S. Bickford; Subramani Velu; Chunshan Song

2005-01-01

136

Preparation of a mesoporous ceria–zirconia supported Ni–Fe catalyst for the high temperature water–gas shift reaction  

Microsoft Academic Search

A Ni–Fe\\/ceria–zirconia catalyst with ordered mesostructure was prepared by the hard-template method employing mesoporous silica (KIT-6) as a template to impart its highly ordered structure to the ceria–zirconia mixed oxide support. Catalytic activities of the Ni–Fe\\/CeO2–ZrO2 catalyst for the water–gas shift reaction were superior to those of a commercial Fe–Cr-based catalyst. The ordered structure of Ni–Fe\\/CeO2–ZrO2 catalyst became more stable

Keita Watanabe; Toshihiro Miyao; Kazutoshi Higashiyama; Hisao Yamashita; Masahiro Watanabe

2011-01-01

137

Homogeneous Catalysis of the Water Gas Shift Reaction by Bridged Dinuclear Pyrazolate Rhodium Complexes. FT-IR, 1H and 13C NMR In Situ Studies  

Microsoft Academic Search

Homogeneous catalysts for the water gas shift reaction prepared from Rh2(µ-Pz)2(COD)2 (Pz = pyrazolate ion and COD = 1,5-cyclooctadiene) in aqueous organic solvent media (pyridine, 4-picoline or 2-ethoxyethanol) and Rh2(µ-Pz)2(CO)2(TPPMS)2 (TPPMS = meta-sulfonatophenyl-diphenyldiphosphine) in acidic aqueous media under mild conditions are described. In situ FT-IR, 1H and 13C NMR spectroscopic studies of the Rh2(µ-Pz)2(COD)2 catalytic system reveal the presence of

A. J. Pardey; M. Fernández; M. A. Moreno; J. Alvarez; A. B. Rivas; M. C. Ortega; B. Mendez; P. J. Baricelli; C. Longo

2000-01-01

138

In situ time-resolved characterization of novel Cu–MoO 2 catalysts during the water–gas shift reaction  

Microsoft Academic Search

A novel and active Cu–MoO2 catalyst was synthesized by partial reduction of a precursor CuMoO4 mixed-metal oxide with CO or H2 at 200–250 °C. The phase transformations of Cu–MoO2 during H2 reduction and the water–gas shift reaction could be followed by in situ time resolved XRD techniques. During the reduction process the diffraction pattern of the CuMoO4 collapsed and the copper metal

Wen Wen; Liu Jing; Michael G. White; Nebojsa Marinkovic; Jonathan C. Hanson; José A. Rodriguez

2007-01-01

139

Catalysis of the water–gas shift reaction by [Rh(COD)(4-picoline) 2]PF 6 immobilized on poly(4-vinylpyridine)  

Microsoft Academic Search

The effect of temperature on the water–gas shift reaction, catalyzed by poly(4-vinylpyridine) immobilized [Rh(COD)(4-picoline)2]PF6 (COD=1,5-cyclooctadiene), has been studied under continuous-flow conditions at 100–180°C. The morphology of the immobilized catalyst was studied using a scanning electron microscope. The immobilized catalyst was also characterized by DTA–TGA analysis, FT-IR, UV–VIS reflectance, electron paramagnetic spectroscopy (EPR) and X-ray photoelectron spectroscopy (XPS), and surface area

Alvaro J Pardey; Mar??a Fernández; Juan Alvarez; Caribay Urbina; Delfin Moronta; Vladimir Leon; Matti Haukka; Tapani A Pakkanen

2000-01-01

140

Studies relevant to the catalytic activation of carbon monoxide: the water gas shift reaction and related processes. Technical progress report, December 1, 1983-November 30, 1984  

SciTech Connect

Proposed are investigations related to the catalytic activation of carbon monoxide. These studies will be concerned with the design of catalysts for the water gas shift reaction and related processes such as the hydroformylation of olefins by homogeneous solution phase systems as well as by selected metal catalysts heterogenized by complexation to functionalized polymers. Also under investigation will be quantitative mechanistic aspects of reactions considered key to probable catalyst cycles. These are principally concerned with the fundamental chemistry of metal carbonyl and metal carbonyl hydride complexes including acid/base properties, reductive elimination, substitution and cluster fragmentation reactions and the nucleophilic activation of metal coordinated carbonyls toward reaction with water or dihydrogen. The goal of these studies is to provide chemical guidelines for the molecular design of new and more efficient catalysts for the utilization of carbonaceous materials such as coal for the production of fuels and other organic chemicals. 70 references.

Ford, P.C.

1984-01-01

141

Wall-catalyzed Water-Gas Shift Reaction in Multi-tubular, Pd and 80wt%Pd-20wt%Cu Membrane Reactors at 1173K  

SciTech Connect

The high-temperature, water-gas shift reaction was conducted in 100 wt%Pd and 80 wt%Pd–20 wt%Cu (Pd80 wt%Cu) shell-and-tube membrane reactors at 1173 K with a 241 kPa (35 psig) trans-membrane pressure differential in the absence of heterogeneous catalyst particles. The tube bundle consisted of four parallel 15.25 cm long, 3.175 mm OD Pd-based tubes with a wall thickness of 125 ?m. The modest catalytic activity of the Pd-based membrane surface for the forward WGSR, the high rate of hydrogen extraction through the Pd-based membranes, and the long residence times (1–5 s) resulted in a dramatic shift in carbon monoxide conversions of 93% at 1173 K and a 1.5:1 steam-to-carbon monoxide feed ratio—a value well above the equilibrium value of 54% associated with a conventional (non-membrane) reactor. Carbon monoxide conversions decreased from 93% to 66% and hydrogen recovery from 90% to 85% at a residence time of 5 s when the Pd was replaced with Pd80 wt%Cu, due to the lower permeance of the Pd80 wt%Cu alloy. SEM-EDS analysis of the membrane tubes suggested that the water-gas shift environment caused pinhole formation in the retentate surfaces of the Pd and Pd80 wt%Cu after approximately 8 days of operation.

Osemwengie, I.; Enick, R.M.; Killmeyer, R.P.

2007-07-20

142

Activity of CeOx and TiOx Nanoparticles Grown on Au(111) in the Water-Gas Shift Reaction  

SciTech Connect

The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO2-x/Au(111) and CeO2-x/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide.

Rodriguez,J.; Ma, S.; Liu, P.; Hrbek, J.; Evans, J.; Perez, M.

2007-01-01

143

Activity of CeOx and TiOx nanoparticles grown on Au(111) in the water-gas shift reaction.  

PubMed

The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO-->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO(2-x)/Au(111) and CeO(2-x)/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide. PMID:18079397

Rodriguez, J A; Ma, S; Liu, P; Hrbek, J; Evans, J; Pérez, M

2007-12-14

144

In Situ Time-Resolved Characterization of Au-CeO2 Catalysts During Water Gas Shift Reactions: presence of Au and O Vacancies in the Active Phase  

SciTech Connect

Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {l_brace}Au+AuO{sub x}{r_brace}-CeO{sub 2} catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 C, a complete AuO{sub x}{yields}Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO{sub 2}(111) single crystal corroborate that cationic Au{sup {delta}} species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with the active sites involving small gold clusters (<2 nm) and O vacancies.

Wang,X.; Rodriguez, J.; Hanson, J.; Perez, M.; Evans, J.

2005-01-01

145

Characterization of CeO2-Supported Cu-Pd Bimetallic Catalyst for the Oxygen-Assisted Water-Gas Shift Reaction  

SciTech Connect

This study was focused to investigate the roles of Cu and Pd in CuPd/CeO2 bimetallic catalysts containing 20-30 wt% Cu and 0.5-1 wt% Pd used in the oxygen-assisted water-gas shift (OWGS) reaction employing a combined bulk and surface characterization techniques such as XRD, TPR, CO chemisorption, and in-situ XPS. The catalytic activity for CO conversion and the stability of catalyst during on-stream operation increased by the addition of Cu to Pd/CeO2 or Pd to Cu/CeO2 monometallic catalysts, especially when the OWGS reaction was performed under low temperatures, below 200oC. The bimetallic catalyst after leaching with nitric acid retained about 60% of its original activity. The TPR of monometallic Cu/CeO2 showed reduction of CuO supported on CeO2 in two distinct regions, around 150 and 250oC. The high temperature peak disappeared and reduction occurred in a single step around 150oC upon Pd addition. The Pd dispersion decreased from 38.5% for Pd/CeO2 to below 1% for CuPd/CeO2 bimetallic catalyst. In-situ XPS studies showed a shift in Cu 2p peaks toward lower binding energy (BE) with concommitant shift in the Pd 3d peaks toward higher BE. Addition of Pd decreased the surface Cu concentration while the concentration of Pd remained unaltered. All these observations indicated the formation of Cu-Pd surface alloy. The valence band XP spectra collected below 10 eV corroborated the core level XP spectra and indicated that Cu is mainly involved in the catalytic reaction. The improved catalytic activity and stability of CuPd/CeO2 bimetallic catalyst was attributed to the alloy formation.

Fox, Elise; Velu, Subramani; Engelhard, Mark H.; Chin, Ya-Huei; Miller, Jeffrey T.; Kropf, Jeremy; Song, Chunshan

2008-12-10

146

Photocatalytic water decomposition and water-gas shift reactions over NaOH-coated, platinized TiOâ  

Microsoft Academic Search

The photocatalytic decomposition of gaseous water takes place over platinized TiOâ coated with NaOH (more than 7 wt %). The quantum efficiency of Hâ and Oâ production reaches about 7% (20 ..mu..mole Hâ\\/h) at the beginning of the reaction but declines with accumulation of the products due to the thermal back reaction over Pt. The effect of the back reaction

S. Sato; J. M. White

1981-01-01

147

Novel Au/La2O3 and Au/La2O2SO4 catalysts for the water-gas shift reaction prepared via an anion adsorption method.  

PubMed

An anion-adsorption technique in which [Au(OH)(4)](-) is preferentially adsorbed onto La(2)O(3) and La(2)O(2)SO(4) surfaces is used to prepare two catalysts active for the low-temperature water-gas shift reaction. PMID:22498919

Lessard, Joseph D; Valsamakis, Ioannis; Flytzani-Stephanopoulos, Maria

2012-05-18

148

Homogeneous catalysis of the water gas shift reaction with the use of groupd 6 transition metal carbonyls: Cr(CO)â, Mo(CO)â, and W(CO)â  

Microsoft Academic Search

Measurements have been carried out to determine the rate of hydrogen production by the water gas shift reaction (CO + HâO ..-->.. COâ + Hâ) operating at temperatures of 200°C and lower with hexacarbonyls of chromium, molybdenum, and tungsten serving as catalyst precursors in basic methanol-water solutions. The catalytic behavior of each of these systems is similar and turnover numbers

A. D. Jr. Kind; R. B. King; D. B. Yang

1981-01-01

149

Interaction of CO with OH on Au(111): HCOO, CO3, and HOCO as Key Intermediates in the Water-Gas Shift Reaction  

SciTech Connect

We have investigated the role of formate (HCOO), carbonate (CO{sub 3}), and carboxyl (HOCO) species as possible intermediates in the OH{sub ads} + CO{sub gas} {yields} CO{sub 2,gas} + 0.5H{sub 2,gas} reaction on Au(111) using synchrotron-based core level photoemission, near-edge X-ray absorption fine structure (NEXAFS), and infrared absorption spectroscopy (IR). Adsorbed HCOO, CO{sub 3}, and OH species were prepared by adsorbing formic acid, carbon dioxide, and water on a Au(111) surface precovered with 0.2 ML of atomic oxygen, respectively. HCOOH interacts weakly with Au(111), but on O/Au(111) it dissociates its acidic H to yield adsorbed formate. The results of NEXAFS, IR, and density-functional calculations indicate that the formate adopts a bidentate configuration on Au(111). Since the HCOO groups are stable on Au(111) up to temperatures near 350 K, it is not likely that formate is a key intermediate for the OH{sub ads} + CO{sub gas} {yields} CO{sub 2,gas} + 0.5H{sub 2,gas} reaction at low temperatures. In fact, the formation of this species could lead eventually to surface poisoning. When compared to a formate species, a carbonate species formed by the reaction of CO{sub 2} with O/Au(111) has low stability, decomposing at temperatures between 100 and 125 K, and should not poison the gold surface. Neither HCOO nor CO{sub 3} was detected during the reaction of CO with OH on Au(111) at 90-120 K. The results of photoemission and IR spectroscopy point to HO {leftrightarrow} CO interactions, consistent with the formation of an unstable HOCO intermediate which has a very short lifetime on the gold surface. The possible mechanism for the low-temperature water-gas shift on gold catalysts is discussed in light of these results.

Senanayake, S.; Stacchiola, D; Liu, P; Mullins, C; Hrbek, J; Rodriguez, J

2009-01-01

150

New insight into mechanisms in water-gas-shift reaction on Au/CeO2(111): a density functional theory and kinetic study.  

PubMed

Using density functional theory (DFT) and kinetic analyses, a new carboxyl mechanism for the water-gas-shift reaction (WGSR) on Au/CeO2(111) is proposed. Many elementary steps in the WGSR are studied using an Au cluster supported on CeO2(111). It is found that (i) water can readily dissociate at the interface between Au and CeO2; (ii) CO2 can be produced via two steps: adsorbed CO on the Au cluster reacts with active OH on ceria to form the carboxyl (COOH) species and then COOH reacts with OH to release CO2; and (iii) two adsorbed H atoms recombine to form molecular H2 on the Au cluster. Our kinetic analyses show that the turnover frequency of the carboxyl mechanism is consistent with the experimental one while the rates of redox and formate mechanisms are much slower than that of carboxyl mechanism. It is suggested that the carboxyl pathway is likely to be responsible for WGSR on Au/CeO2. PMID:22455041

Chen, Ying; Wang, Haifeng; Burch, Robbie; Hardacre, Christopher; Hu, P

2011-01-01

151

Seeking a mechanistic analogue of the water-gas shift reaction: carboxamido ligand formation and isocyanate elimination from complexes containing the Tp'PtMe fragment.  

PubMed

A series of stable, isolable Tp'Pt(IV) carboxamido complexes of the type Tp'PtMe(2)(C(O)NHR) (R = Et, (n)Pr, (i)Pr, (t)Bu, Bn, Ph) has been synthesized by addition of amide nucleophiles to the carbonyl ligand in Tp'Pt(Me)(CO) followed by trapping of the Pt(II) intermediate with methyl iodide as the methylating reagent. These compounds mimic elusive intermediates resulting from hydroxide addition to platinum-bound CO in the Water-Gas Shift Reaction (WGSR). Seeking parallels to WGSR chemistry, we find that deprotonation of the carboxamido NH initiates elimination and the isocyanate-derived products form; the resulting platinum fragment can be protonated to reoxidize the metal center and generate Tp'PtMe(2)H, the synthetic precursor to Tp'Pt(Me)(CO). Mechanistic studies on the formation of and elimination from Tp'PtMe(2)(C(O)NHR) suggest a stepwise process with deprotonation from a Pt(IV) species as the key step prompting elimination. PMID:22563841

Frauhiger, Bryan E; Ondisco, Matthew T; White, Peter S; Templeton, Joseph L

2012-05-30

152

On the Importance of Metal–Oxide Interface Sites for the Water–Gas Shift Reaction Over Pt/CeO2 Catalysts  

SciTech Connect

The mechanism of water–gas shift reaction at the three-phase boundary of Pt/CeO2 catalysts has been investigated using density functional theory and microkinetic modeling to better understand the importance of metal–oxide interface sites in heterogeneous catalysis. Analysis of a microkinetic model based on parameters obtained from first principles suggests that both the “Redox pathway” and the “Associative carboxyl pathway with redox regeneration” could operate on Pt/CeO2 catalysts. Although (1) only few interfacial Pt atoms are found to be catalytically active at low temperatures due to strong adsorption of CO and (2) interfacial O–H bond breakage is difficult due to the high reducibility of ceria, interface sites are 2–3 orders of magnitude more active than Pt (1 1 1) and stepped Pt surface sites and therefore effectively determine the overall activity of Pt/CeO2. The high activity of Pt/CeO2 interface sites originates from a significantly enhanced water activation and dissociation at interfacial oxygen vacancies.

Aranifard, Sara; Ammal, Salai Cheettu; Heyden, Andreas

2014-01-01

153

Catalytic links among the water–gas shift, water-assisted formic acid decomposition, and methanol steam reforming reactions over Pt-promoted thoria  

Microsoft Academic Search

Implied in the proposed water–gas shift (WGS) mechanisms for Pt\\/ceria and Pt\\/thoria catalysts is the presumption that reduced defect centers are formed on the surface. This X-ray absorption near-edge spectroscopy study provides direct results indicating that Pt facilitates reduction in the surface shell of thoria. Mechanistic arguments from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) are provided suggesting

Gary Jacobs; Patricia M. Patterson; Uschi M. Graham; Adam C. Crawford; Alan Dozier; Burtron H. Davis

2005-01-01

154

Ceria-based Catalysts for the Production of H2 Through the Water-gas-shift Reaction: Time-Resolved XRD and XAFS Studies  

SciTech Connect

Hydrogen is a potential alternate energy source for satisfying many of our energy needs. In this work, we studied H2 production from the water-gas-shift (WGS) reaction over Ce1-x Cu x O2 catalysts, prepared with a novel microemulsion method, using two synchrotron-based techniques: time-resolved X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). The results are compared with those reported for conventional CuO x /CeO2 and AuO x /CeO2 catalysts obtained through impregnation of ceria. For the fresh Ce1-x Cu x O2 catalysts, the results of XAFS measurements at the Cu K-edge indicate that Cu is in an oxidation state higher than in CuO. Nevertheless, under WGS reaction conditions the Ce1-x Cu x O2 catalysts undergo reduction and the active phase contains very small particles of metallic Cu and CeO2-x . Time-resolved XRD and XAFS results also indicate that Cud+ and Aud+ species present in fresh CuO x /CeO2 and AuO x /CeO2 catalysts do not survive above 200 C under the WGS conditions. In all these systems, the ceria lattice displayed a significant increase after exposure to CO and a decrease in H2O, indicating that CO reduced ceria while H2O oxidized it. Our data suggest that H2O dissociation occurred on the Ovacancy sites or the Cu-Ovacancy and Au-Ovacancy interfaces. The rate of H2 generation by a Ce0.95Cu0.05O2 catalyst was comparable to that of a 5 wt% CuO x /CeO2 catalyst and much bigger than those of pure ceria or CuO.

Wang,X.; Rodriguez, J.; Hanson, J.; Gamarra, D.; Marinez-Arias, A.; Fernandez-Garcia, M.

2008-01-01

155

Flame Synthesis of Nanosized Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O Catalysts for the Water-Gas Shift (WGS) Reaction  

SciTech Connect

A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m{sup 2}/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe{sub 2}O{sub 3}) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe{sub 2}O{sub 3}, NiO) within the host matrix (CeO{sub 2}). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO{sub 2}, easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO{sub 2} with a feed mixture having a hydrogen to carbon monoxide (H{sub 2}/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions.

Pati, R.; Lee, I; Hou, S; Akhuemonkhan, O; Gaskell, K; Wang, Q; Frenkel, A; Chu, D; Salamanca-Riba, L; Ehrman, S

2009-01-01

156

WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION  

SciTech Connect

Optimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperature to improve reaction kinetics. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. In the first year of the project, we prepared a series of nanostructured Cu- and Fe-containing ceria catalysts by a special gelation/precipitation technique followed by air calcination at 650 C. Each sample was characterized by ICP for elemental composition analysis, BET-N2 desorption for surface area measurement, and by temperature-programmed reduction in H{sub 2} to evaluate catalyst reducibility. Screening WGS tests with catalyst powders were conducted in a flow microreactor at temperatures in the range of 200-550 C. On the basis of both activity and stability of catalysts in simulated coal gas, and in CO{sub 2}-rich gases, a Cu-CeO{sub 2} catalyst formulation was selected for further study in this project. Details from the catalyst development and testing work are given in this report. Also in this report, we present H{sub 2} permeation data collected with unsupported flat membranes of pure Pd and Pd-alloys over a wide temperature window.

Maria Flytzani-Stephanopoulos; Jerry Meldon; Xiaomei Qi

2001-12-01

157

Effects of the partial replacement of La by M (M=Ce, Ca and Sr) in La 2- x M x CuO 4 perovskites on catalysis of the water-gas shift reaction  

Microsoft Academic Search

The performance of La2-xMxCuO4 perovskites (where M = Ce, Ca or Sr) as catalysts for the water-gas shift reaction was investigated at 290 °C and 360 °C. The catalysts were characterized by EDS, XRD, N2 adsorption-desorption, XPS and XANES. The XRD results showed that all the perovskites exhibited a single phase (the presence of perovskite structure), suggesting the incorporation of

S. S. Maluf; E. M. Assaf

2010-01-01

158

Comparison of the activity of Au\\/CeO 2 and Au\\/Fe 2 O 3 catalysts for the CO oxidation and the water-gas shift reactions  

Microsoft Academic Search

We compare the activity and relevant gold species of nanostructured gold–cerium oxide and gold–iron oxide catalysts for the\\u000a CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO\\u000a oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze\\u000a the water-gas shift

Weiling Deng; Colin Carpenter; Nan Yi; Maria Flytzani-Stephanopoulos

2007-01-01

159

Unique properties of ceria nanoparticles supported on metals: novel inverse ceria/copper catalysts for CO oxidation and the water-gas shift reaction.  

PubMed

Oxides play a central role in important industrial processes, including applications such as the production of renewable energy, remediation of environmental pollutants, and the synthesis of fine chemicals. They were originally used as catalyst supports and were thought to be chemically inert, but now they are used to build catalysts tailored toward improved selectivity and activity in chemical reactions. Many studies have compared the morphological, electronic, and chemical properties of oxide materials with those of unoxidized metals. Researchers know much less about the properties of oxides at the nanoscale, which display distinct behavior from their bulk counterparts. More is known about metal nanoparticles. Inverse-model catalysts, composed of oxide nanoparticles supported on metal or oxide substrates instead of the reverse (oxides supporting metal nanoparticles), are excellent tools for systematically testing the properties of novel catalytic oxide materials. Inverse models are prepared in situ and can be studied with a variety of surface science tools (e.g. scanning tunneling microscopy, X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron microscopy) and theoretical tools (e.g. density functional theory). Meanwhile, their catalytic activity can be tested simultaneously in a reactor. This approach makes it possible to identify specific functions or structures that affect catalyst performance or reaction selectivity. Insights gained from these tests help to tailor powder systems, with the primary objective of rational design (experimental and theoretical) of catalysts for specific chemical reactions. This Account describes the properties of inverse catalysts composed of CeOx nanoparticles supported on Cu(111) or CuOx/Cu(111) as determined through the methods described above. Ceria is an important material for redox chemistry because of its interchangeable oxidation states (Ce?? and Ce³?). Cu(111), meanwhile, is a standard catalyst for reactions such as CO oxidation and the water-gas shift (WGS). This metal serves as an ideal replacement for other noble metals that are neither abundant nor cost effective. To prepare the inverse system we deposited nanoparticles (2-20 nm) of cerium oxide onto the Cu(111) surface. During this process, the Cu(111) surface grows an oxide layer that is characteristic of Cu?O (Cu¹?). This oxide can influence the growth of ceria nanoparticles. Evidence suggests triangular-shaped CeO?(111) grows on Cu?O(111) surfaces while rectangular CeO?(100) grows on Cu?O?(111) surfaces. We used the CeOx/Cu?O/Cu(111) inverse system to study two catalytic processes: the WGS (CO + H?O ? CO? + H?) and CO oxidation (2CO + O? ? 2CO?). We discovered that the addition of small amounts of ceria nanoparticles can activate the Cu(111) surface and achieve remarkable enhancement of catalytic activity in the investigated reactions. In the case of the WGS, the CeOx nanoparticle facilitated this process by acting at the interface with Cu to dissociate water. In the CO oxidation case, an enhancement in the dissociation of O? by the nanoparticles was a key factor. The strong interaction between CeOx nanoparticles and Cu(111) when preoxidized and reduced in CO resulted in a massive surface reconstruction of the copper substrate with the introduction of microterraces that covered 25-35% of the surface. This constitutes a new mechanism for surface reconstruction not observed before. These microterraces helped to facilitate a further enhancement of activity towards the WGS by opening an additional channel for the dissociation of water. In summary, inverse catalysts of CeOx/Cu(111) and CeO?/Cu?O/Cu(111) demonstrate the versatility of a model system to obtain insightful knowledge of catalytic processes. These systems will continue to offer a unique opportunity to probe key catalytic components and elucidate the relationship between structure and reactivity of novel materials and reactions in the future. PMID:23286528

Senanayake, Sanjaya D; Stacchiola, Dario; Rodriguez, Jose A

2013-08-20

160

WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION PROCESS  

SciTech Connect

This project involved fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2} -separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams were examined in the project. Cu-cerium oxide was identified as the most promising high-temperature water-gas shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. The high-temperature shift catalyst composition was optimized by proper selection of dopant type and amount in ceria. The formulation 10at%Cu-Ce(30at%La)O{sub x} showed the best performance, and was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The apparent activation energy, measured over aged catalysts, was equal to 70.2 kJ/mol. Reaction orders in CO, H{sub 2}O, CO{sub 2} and H{sub 2} were found to be 0.8, 0.2, -0.3, and -0.3, respectively. This shows that H{sub 2}O has very little effect on the reaction rate, and that both CO{sub 2} and H{sub 2} weakly inhibit the reaction. Good stability of catalyst performance was found in 40-hr long tests. A flat (38 cm{sup 2}) Pd-Cu alloy membrane reactor was used with the catalyst washcoated on oxidized aluminum screens close coupled with the membrane. To achieve higher loadings, catalyst granules were layered on the membrane itself to test the combined HTS activity/ H{sub 2} -separation efficiency of the composite. Simulated coal gas mixtures were used and the effect of membrane on the conversion of CO over the catalyst was evidenced at high space velocities. Equilibrium CO conversion at 400 C was measured at a space velocity of 30,000 h{sup -1} with the 10{micro}m- thick Pd{sub 60}Cu{sub 40} membrane operating under a pressure differential of 100 psi. No carbon deposition took place during operation. The performance of the coupled Cu-ceria catalyst/membrane system at 400 C was stable in {approx} 30 h of continuous operation. The overall conclusion from this project is that Cu-doped ceria catalysts are suitable for use in high-temperature water-gas shift membrane reactors. CO{sub 2}-rich operation does not affect the catalyst activity or stability; neither does it affect hydrogen permeation through the Pd-Cu membrane. Operation in the temperature range of 400-430 C is recommended.

Maria Flytzani-Stephanopoulos; Xiaomei Qi; Scott Kronewitter

2004-02-01

161

WATER-GAS SHIFT WITH INTEGRATED HYDROGEN SEPARATION PROCESS  

SciTech Connect

Optimization of the water-gas shift (WGS) reaction system for hydrogen production for fuel cells is of particular interest to the energy industry. To this end, it is desirable to couple the WGS reaction to hydrogen separation using a semi-permeable membrane, with both processes carried out at high temperatures to improve reaction kinetics and permeation. Reduced equilibrium conversion of the WGS reaction at high temperatures is overcome by product H{sub 2} removal via the membrane. This project involves fundamental research and development of novel cerium oxide-based catalysts for the water-gas-shift reaction and the integration of these catalysts with Pd-alloy H{sub 2}-separation membranes supplying high purity hydrogen for fuel cell use. Conditions matching the requirements of coal gasifier-exit gas streams will be examined in the project. The first-year screening studies of WGS catalysts identified Cu-ceria as the most promising high-temperature shift catalyst for integration with H{sub 2}-selective membranes. Formulations containing iron oxide were found to deactivate in the presence of CO{sub 2}, and were thus eliminated from further consideration. Cu-containing ceria catalysts, on the other hand, showed high stability in CO{sub 2}-rich gases. This type gas will be present over much of the catalyst, as the membrane removes the hydrogen produced from the shift reaction. Several catalyst formulations were prepared, characterized and tested in the first year of study. Details from the catalyst development and testing work were given in our first annual technical report. Hydrogen permeation through Pd and Pd-alloy foils was investigated in a small membrane reactor constructed during the first year of the project. The effect of temperature on the hydrogen flux through pure Pd, Pd{sub 60}Cu{sub 40} and Pd{sub 75}Ag{sub 25} alloy membranes, each 25 {micro}m thick, was evaluated in the temperature range from 250 C to 500 C at upstream pressure of 4.4 atm and permeate hydrogen pressure of 1 atm. Flux decay was observed for the Pd-Cu membrane above 500 C. From 350-450 C, an average hydrogen flux value of 0.2 mol H{sub 2}/m{sup 2}/s was measured over this Pd-alloy membrane. These results are in good agreement with literature data. In this year's report, we discuss reaction rate measurements, optimization of catalyst kinetics by proper choice of dopant oxide (lanthana) in ceria, long-term stability studies, and H{sub 2} permeation data collected with unsupported flat, 10 {micro}m-thick Pd-Cu membranes over a wide temperature window and in various gas mixtures. The high-temperature shift catalyst composition was further improved, by proper selection of dopant type and amount. The formulation 10 at%Cu-Ce(30 at%La)Ox was the best; this was selected for further kinetic studies. WGS reaction rates were measured in a simulated coal-gas mixture. The stability of catalyst performance was examined in 40-hr long tests. A series of hydrogen permeation tests were conducted in a small flat-membrane reactor using the 10 m{micro}-thick Pd-Cu membranes. Small inhibitory effects of CO and CO{sub 2} were found at temperatures above 350 C, while H{sub 2}O vapor had no effect on hydrogen permeation. No carbon deposition took place during many hours of membrane operation. The reaction extent on the blank (catalyst-free) membrane was also negligible. A larger flat-membrane reactor will be used next year with the catalyst wash coated on screens close coupled with the Pd-Cu membrane.

Maria Flytzani-Stephanopoulos, PI; Jerry Meldon, Co-PI; Xiaomei Qi

2002-12-01

162

Comparison of the Activity of Au/CeO2 and Au/Fe2O3 Catalysts for the CO Oxidation and the Water-gas Shift Reactions  

SciTech Connect

We compare the activity and relevant gold species of nanostructured gold-cerium oxide and gold-iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH {>=}12. Both parent and leached catalysts were investigated. The activity of the leached gold-iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H{sub 2} up to 400 C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold-ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV-Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.

Deng,W.; Carpenter, C.; Yi, N.; Flytzani-Stephanopoulos, M.

2007-01-01

163

Development of an Advanced Water-Gas Shift Conversion System. Quarterly Progress Report, May-July 1984.  

National Technical Information Service (NTIS)

The objective of current work is to conduct research and development to investigate the use of an aqueous catalyst system for conducting the water-gas shift reaction. This objective will be accomplished by performing continuous laboratory scale experiment...

L. J. Sealock, D. C. Elliott, R. S. Butner

1984-01-01

164

Active Nonmetallic Au and Pt Species on Ceria-Based Water-Gas Shift Catalysts  

Microsoft Academic Search

Traditional analysis of reactions catalyzed by supported metals involves the structure of the metallic particles. However, we report here that for the class of nanostructured gold- or platinum-cerium oxide catalysts, which are active for the water-gas shift reaction, metal nanoparticles do not participate in the reaction. Nonmetallic gold or platinum species strongly associated with surface cerium-oxygen groups are responsible for

Qi Fu; Howard Saltsburg; Maria Flytzani-Stephanopoulos

2003-01-01

165

Nature of Ptn/TiO2(110) Interface under Water-Gas Shift Reaction Conditions: A Constrained ab Initio Thermodynamics Study  

SciTech Connect

The electronic structure of small Ptn (n = 1-8) clusters supported on the stoichiometric and partially reduced rutile TiO2(110) surface have been investigated using density functional theory. Pt atoms prefer to form a close-packed structure with (111) facet near an oxygen vacancy of the TiO2 support and a less dense structure with (100) facet away from oxygen vacant sites. Themain focus of this study is on identifying a realistic catalyst model for the Pt/TiO2 interface under watergas shift (WGS) reaction conditions. Constrained ab initio thermodynamic simulations on the stability of oxygen vacancies and formation of adsorbed gas phase molecules such as oxygen, CO, and hydrogen at the metal/oxide interface reveal that under WGS reaction conditions the formation of surface oxygen vacancies are thermodynamically favorable, platinum oxide species (PtOx) can easily be reduced and should not be present, CO adsorbs only weakly on interfacial Pt atoms, and CO poisoning of these sites should be less important. While hydrogen generally interacts weakly with interfacial Pt atoms, it forms very stable hydride species on Pt atoms neighboring an oxygen vacancy of the TiO2(110) support, possibly negatively affecting the WGS reaction rate.

Ammal, Salai Cheettu; Heyden, Andreas

2011-10-06

166

In situ time-resolved characterization of Au-CeO2 and AuOx-CeO2 catalysts during the water-gas shift reaction: Presence of Au and O vacancies in the active phase  

NASA Astrophysics Data System (ADS)

Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {Au+AuOx}-CeO2 catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 °C, a complete AuOx-->Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO2(111) single crystal corroborate that cationic Au?+ species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with the active sites involving small gold clusters (<2 nm) and O vacancies.

Wang, X.; Rodriguez, J. A.; Hanson, J. C.; Pérez, M.; Evans, J.

2005-12-01

167

In situ time-resolved characterization of Au-CeO2 and AuOx-CeO2 catalysts during the water-gas shift reaction: presence of Au and O vacancies in the active phase.  

PubMed

Synchrotron-based in situ time-resolved x-ray diffraction and x-ray absorption spectroscopies were used to study the behavior of nanostructured {Au+AuO(x)}-CeO(2) catalysts under the water-gas shift (WGS) reaction. At temperatures above 250 degrees C, a complete AuO(x)-->Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO(2)(111) single crystal corroborate that cationic Au(delta+) species cannot be the key sites responsible for the WGS activity at high temperatures. The rate determining steps for the WGS seem to occur at the gold-ceria interface, with the active sites involving small gold clusters (<2 nm) and O vacancies. PMID:16375458

Wang, X; Rodriguez, J A; Hanson, J C; Pérez, M; Evans, J

2005-12-01

168

WATER-GAS SHIFT KINETICS OVER IRON OXIDE CATALYSTS AT MEMBRANE REACTOR CONDITIONS  

SciTech Connect

This report covers the second year of a project investigating water-gas shift catalysts for use in membrane reactors. It has been established that a simple iron high temperature shift catalyst becomes ineffective in a membrane reactor because the reaction rate is severely inhibited by the build-up of the product CO{sub 2}. During the past year, an improved microkinetic model for water-gas shift over iron oxide was developed. Its principal advantage over prior models is that it displays the correct asymptotic behavior at all temperatures and pressures as the composition approaches equilibrium. This model has been used to explore whether it might be possible to improve the performance of iron high temperature shift catalysts under conditions of high CO{sub 2} partial pressure. The model predicts that weakening the surface oxygen bond strength by less than 5% should lead to higher catalytic activity as well as resistance to rate inhibition at higher CO{sub 2} partial pressures. Two promoted iron high temperature shift catalysts were studied. Ceria and copper were each studied as promoters since there were indications in the literature that they might weaken the surface oxygen bond strength. Ceria was found to be ineffective as a promoter, but preliminary results with copper promoted FeCr high temperature shift catalyst show it to be much more resistant to rate inhibition by high levels of CO{sub 2}. Finally, the performance of sulfided CoMo/Al{sub 2}O{sub 3} catalysts under conditions of high CO{sub 2} partial pressure was simulated using an available microkinetic model for water-gas shift over this catalyst. The model suggests that this catalyst might be quite effective in a medium temperature water-gas shift membrane reactor, provided that the membrane was resistant to the H{sub 2}S that is required in the feed.

Carl R.F. Lund

2001-08-10

169

Catalytic, nucleophilic allylation of aldehydes with 2-substituted allylic acetates: carbon-carbon bond formation driven by the water-gas shift reaction.  

PubMed

The ruthenium-catalyzed allylation of aldehydes with allylic acetates has been expanded to incorporate substituents at the 2-position of the allylic components. Allylic acetates bearing a variety of substituents (CO2-t-Bu, COMe, Ph, CH(OEt)2, and Me) undergo high-yielding additions with aromatic, ?,?-unsaturated, and aliphatic aldehydes. The conditions of the reaction were found to be mild (75 °C, 24-48 h) and only required the use of 2-3 mol % of the triruthenium dodecacarbonyl catalyst under 40-80 psi of CO. The stoichiometries of water and allylic acetate employed were found to be critical to reaction efficiency. PMID:24927196

Denmark, Scott E; Matesich, Zachery D

2014-07-01

170

Flame Synthesis of Nanosized Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O Catalysts for the Water-Gas Shift (WGS) Reaction.  

National Technical Information Service (NTIS)

A flame synthesis method has been used to prepare nanosized, high- surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction an...

I. C. Lee K. J. Gaskell O. Akhuemonkhan R. K. Pati S. Hou

2009-01-01

171

Theoretical analysis of the effect of catalyst mass distribution and operation parameters on the performance of a Pd-based membrane reactor for water–gas shift reaction  

Microsoft Academic Search

In the development of environmental friendly and highly efficient energy processes, membrane reactors hold an important role for their ability to carry out, simultaneously and in the same unit, the separation and reaction steps. Taking advantage of the synergies deriving from this coupling, they achieve comparable results to the conventional reactors at less severe conditions. A sensitivity analysis has been

Giovanni Chiappetta; Gabriele Clarizia; Enrico Drioli

2008-01-01

172

Statistical optimization by response surface methodology for water-gas shift reaction in a H 2-rich stream over Cu–Zn–Fe composite-oxide catalysts  

Microsoft Academic Search

The catalytic performance of Cu–Zn–Fe composite-oxide catalysts prepared by the urea–nitrate combustion (UNC) method for the WGS reaction was investigated in this study. The catalysts were characterized by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), and the Brunauer–Emmet–Teller (BET) method. In order to reduce the total number of experiments to achieve the optimal condition of CO conversion in the

Nutthavich Thouchprasitchai; Apanee Luengnaruemitchai; Sangobtip Pongstabodee

2011-01-01

173

Controlled deposition from the gas phase of surface species on amorphous supports: Preparation of ruthenium-bipyridine catalysts for 1-hexane hydroformylation and water-gas shift reaction  

Microsoft Academic Search

Controlled stepwise surface reactions were studied to prepare supported ruthenium-bipyridine catalysts. Ru[sub 3](CO)[sub 12] and 2,2[prime]-bipyridine were introduced onto the support from the gas phase in a fluidized bed reactor. With this method the introduction of the precursors can be carried out independently by successive pulses. The possibilities to control metal content, properties of the surface species, and dispersion were

P. Hirva; T. Venaelaeinen; T. A. Pakkanen

1994-01-01

174

Kinetics of ¹³CO exchange with ¹²CO in (HMâ(¹²CO)ââ)⁻ and (DMâ(¹²CO)ââ)⁻ (M = Ru or Os): relationship between exchange pathway and catalytic activity in the catalysis of the water gas shift reaction  

Microsoft Academic Search

The roles of the anions (HRuâ(CO)ââ)⁻ and (HOsâ(CO)ââ)⁻ in the catalysis of the water gas shift reaction are investigated. The kinetics of ¹³CO exchange with ¹²CO provides confirmation of the greater activity of the ruthenium based anion.

M. W. Payne; D. L. Leussing; S. G. Shore

1987-01-01

175

Hydroformylation of 1Hexene Catalyzed by [Rh(COD)(2Picoline) 2 ]PF 6 Immobilized on Poly(4-Vinylpyridine) Under Water Gas Shift Reaction Conditions  

Microsoft Academic Search

Reported here is the influence of the reaction conditions variation (1-hexene\\/rhodium content (S\\/C) = 16 - 105, temperature (T) = 70 - 110 C and carbon monoxide pressure (P(CO)) = 0.6 - 1.8 atm) on the catalytic hydroformylation of 1-hexene to aldehydes (heptanal and 2-methyl-hexanal) by the rhodium(I)\\u000a complex, [Rh(COD)(2-picoline)2]PF6 (COD = 1,5-cyclooctadiene)immobilized on poly(4-vinylpyridine) in contact with 10 mL

Alvaro J. Pardey; José Brito; María Fernández; Angel B. Rivas; Marisol C. Ortega; Clementina Longo; Pablo J. Baricelli; Eduardo Lujano; Sergio A. Moya

2001-01-01

176

In situ pulse diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) mass spectrometry study of the water-gas shift reaction on nickel(II) oxide-zinc(II) oxide catalysts.  

PubMed

The water-gas shift (WGS) reaction has been studied by pulsing carbon monoxide (CO) into a steady-state water (H2O)-Ar flow over nickel(II) oxide-zinc oxide (NiO-ZnO) catalysts using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) coupled with a mass spectrometer method using the pulse technique (in situ pulse DRIFTS-MS) for different flow rates (gas hourly space velocity [GHSV] of 24,000-72,000 h(-1)) and reaction temperatures (250-350 °C). The results obtained from the in situ pulse DRIFTS-MS revealed that there are two types of water adsorption bands on the surface of the catalyst: (i) molecular adsorption (infrared [IR] bands in the 2500-3600 cm(-1) range and at 1640 cm(-1)), and (ii) dissociative adsorption at 3700 cm(-1), where carboxyl bands are formed at 1461 and 1368 cm(-1) and the gas-phase CO is adsorbed at 2187 and 2111 cm(-1) on the surface of the catalyst. After using a GHSV = 24,000 h(-1) H2O/Ar flow, we probed the existence of two active intermediates via the formation of two hydrogen production peaks. The products of hydrogen gas (H2) and carbon dioxide (CO2) had two pathways: the redox process and the associative process via the intermediate of the carboxyl group. In situ pulse DRIFTS-MS proves to be an effective approach for studying the nature of adsorbed species on the catalyst surface and the nature of the reaction product. PMID:24480281

Tang, Chih-Wei; Chuang, Steven S C

2014-02-01

177

Reactivity of iron carbonyl complexes in a hydrated sodium-Y zeolite matrix and catalysis of the resulting hydride anion HFe/sub 3/(CO)/sub 11//sup -/ for water-gas-shift reaction  

SciTech Connect

Iron carbonyls Fe(CO)/sub 5/, Fe/sub 2/(CO)/sub 9/, and Fe/sub 3/(CO)/sub 12/ have been introduced into a hydrated Na-Y zeolite. Fe(CO)/sub 5/ was only weakly adsorbed on the zeolite. Fe/sub 2/(CO)/sub 9/ and Fe/sub 3/(CO)/sub 12/ were reactive in the hydrated zeolite cages to yield a hydride anion species HFe/sub 3/(CO)/sub 11//sup -/ which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 cm/sup -1/, UV-vis spectrum at 540 nm, and gas-phase analyses. The red shift of absorption band of the bridging carbonyl indicated ionic interaction of a bridging carbonyl with an Al/sup 3 +/ ion in the zeolite matrix. The formation of the anion species was not observed in a dehydrated Na-Y zeolite, indicating the importance of water or a surface hydroxyl group n the reaction. The reaction course from di- or trinuclear iron carbonyl to the hydride anion has been studied by an ESR technique. Fe/sub 2/(CO)/sub 8//sup -/, Fe(CO)/sub 4//sup -/, and Fe/sub 3/(CO)/sub 11//sup -/ species were detected as intermediates, and reaction schemes have been proposed. The resulting HFe/sub 3/(CO)/sub 11//sup -/ was stable at or below 413 K both in a vacuum or in a CO atmosphere. Above this temperature it was gradually decomposed. Catalytic activity of the HFe/sub 3/(CO)/sub 11//sup -/ species was examined for water-gas-shift reaction at 333-453 K and atmospheric pressure. The activity was very high and comparable to that reported in the homogeneous phase at high pressure. Kinetics and spectroscopic studies indicated that the reaction between HFe/sub 3/(CO)/sub 11//sup -/ and H/sub 2/O would be rate-determining.

Iwamoto, M.; Nakamura, S.; Kusano, H.; Kagawa, S.

1986-10-09

178

Origin and Activity of Oxidized Gold in Water-Gas-Shift Catalysis  

NASA Astrophysics Data System (ADS)

As a promising route for large-scale H2 production, the water-gas-shift reaction (WGS, CO+H2O?CO2+H2) on ceria-supported Au catalysts is of enormous potential in efforts to move towards a hydrogen economy. Recent research suggests that this reaction is in fact catalyzed by Au cations instead of the conventionally regarded metallic Au particles. Here density functional theory calculations demonstrate that the presence of empty localized nonbonding f states in CeO2 permits the oxidation of Au, enabling subsequent CO adsorption. A feasible reaction pathway leading to H2 production is identified, and it is concluded that four to six atom Au clusters at the O-vacancy sites of ceria catalyze the WGS reaction.

Liu, Zhi-Pan; Jenkins, Stephen J.; King, David A.

2005-05-01

179

Development of Novel Water-Gas Shift Membrane Reactor  

SciTech Connect

This report summarizes the objectives, technical barrier, approach, and accomplishments for the development of a novel water-gas-shift (WGS) membrane reactor for hydrogen enhancement and CO reduction. We have synthesized novel CO{sub 2}-selective membranes with high CO{sub 2} permeabilities and high CO{sub 2}/H{sub 2} and CO{sub 2}/CO selectivities by incorporating amino groups in polymer networks. We have also developed a one-dimensional non-isothermal model for the countercurrent WGS membrane reactor. The modeling results have shown that H{sub 2} enhancement (>99.6% H{sub 2} for the steam reforming of methane and >54% H{sub 2} for the autothermal reforming of gasoline with air on a dry basis) via CO{sub 2} removal and CO reduction to 10 ppm or lower are achievable for synthesis gases. With this model, we have elucidated the effects of system parameters, including CO{sub 2}/H{sub 2} selectivity, CO{sub 2} permeability, sweep/feed flow rate ratio, feed temperature, sweep temperature, feed pressure, catalyst activity, and feed CO concentration, on the membrane reactor performance. Based on the modeling study using the membrane data obtained, we showed the feasibility of achieving H{sub 2} enhancement via CO{sub 2} removal, CO reduction to {le} 10 ppm, and high H{sub 2} recovery. Using the membrane synthesized, we have obtained <10 ppm CO in the H{sub 2} product in WGS membrane reactor experiments. From the experiments, we verified the model developed. In addition, we removed CO{sub 2} from a syngas containing 17% CO{sub 2} to about 30 ppm. The CO{sub 2} removal data agreed well with the model developed. The syngas with about 0.1% CO{sub 2} and 1% CO was processed to convert the carbon oxides to methane via methanation to obtain <5 ppm CO in the H{sub 2} product.

Ho, W. S. Winston

2004-12-29

180

Water-gas shift on gold catalysts: catalyst systems and fundamental studies.  

PubMed

Since the pioneering finding by Haruta et al. that small gold nanoparticles on reducible supports can be highly active for low-temperature CO oxidation, the synthesis, characterization, and application of supported gold catalysts have attracted much attention. The water-gas shift reaction (WGSR: CO + H2O = CO2 + H2) is important for removing CO and upgrading the purity of H2 for fuel cell applications, ammonia synthesis, and selective hydrogenation processes. In recent years, much attention has been paid to exploration the possibility of using supported gold nanocatalysts for WGSR and understanding the fundamental aspects related to catalyst deactivation mechanisms, nature of active sites, and reaction mechanisms. Here we summarize recent advances in the development of supported gold catalysts for this reaction and fundamental insights that can be gained, and furnish our assessment on the status of research progress. PMID:23928722

Tao, Franklin Feng; Ma, Zhen

2013-10-01

181

Integration of a Structural Water Gas Shift Catalyst with a Vanadium Alloy Hydrogen Transport Device.  

National Technical Information Service (NTIS)

This project is in response to a requirement for a system that combines water gas shift technology with separation technology for coal derived synthesis gas. The justification of such a system would be improved efficiency for the overall hydrogen producti...

M. Argyle T. Barton T. Popa

2009-01-01

182

The Integration of a Structural Water Gas Shift Catalyst with a Vanadium Alloy Hydrogen Transport Device  

SciTech Connect

This project is in response to a requirement for a system that combines water gas shift technology with separation technology for coal derived synthesis gas. The justification of such a system would be improved efficiency for the overall hydrogen production. By removing hydrogen from the synthesis gas stream, the water gas shift equilibrium would force more carbon monoxide to carbon dioxide and maximize the total hydrogen produced. Additional benefit would derive from the reduction in capital cost of plant by the removal of one step in the process by integrating water gas shift with the membrane separation device. The answer turns out to be that the integration of hydrogen separation and water gas shift catalysis is possible and desirable. There are no significant roadblocks to that combination of technologies. The problem becomes one of design and selection of materials to optimize, or at least maximize performance of the two integrated steps. A goal of the project was to investigate the effects of alloying elements on the performance of vanadium membranes with respect to hydrogen flux and fabricability. Vanadium was chosen as a compromise between performance and cost. It is clear that the vanadium alloys for this application can be produced, but the approach is not simple and the results inconsistent. For any future contracts, large single batches of alloy would be obtained and rolled with larger facilities to produce the most consistent thin foils possible. Brazing was identified as a very likely choice for sealing the membranes to structural components. As alloying was beneficial to hydrogen transport, it became important to identify where those alloying elements might be detrimental to brazing. Cataloging positive and negative alloying effects was a significant portion of the initial project work on vanadium alloying. A water gas shift catalyst with ceramic like structural characteristics was the second large goal of the project. Alumina was added as a component of conventional high temperature water gas shift iron oxide based catalysts. The catalysts contained Fe-Al-Cr-Cu-O and were synthesized by co-precipitation. A series of catalysts were prepared with 5 to 50 wt% Al{sub 2}O{sub 3}, with 8 wt% Cr{sub 2}O{sub 3}, 4 wt% CuO, and the balance Fe{sub 2}O{sub 3}. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeO{sub x}, 8 wt% Cr{sub 2}O{sub 3}, and 4 wt% CuO) with no alumina. Alumina addition to conventional high temperature water gas shift catalysts at concentrations of approximately 15 wt% increased CO conversion rates and increase thermal stability. A series of high temperature water gas shift catalysts containing iron, chromia, and copper oxides were prepared with small amounts of added ceria in the system Fe-Cr-Cu-Ce-O. The catalysts were also tested kinetically under WGS conditions. 2-4 wt% ceria addition (at the expense of the iron oxide content) resulted in increased reaction rates (from 22-32% higher) compared to the reference catalyst. The project goal of a 10,000 liter per day WGS-membrane reactor was achieved by a device operating on coal derived syngas containing significant amounts of carbon monoxide and hydrogen sulfide. The membrane flux was equivalent to 52 scfh/ft{sup 2} based on a 600 psi syngas inlet pressure and corresponded to membranes costing $191 per square foot. Over 40 hours of exposure time to syngas has been achieved for a double membrane reactor. Two modules of the Chart reactor were tested under coal syngas for over 75 hours with a single module tested for 50 hours. The permeance values for the Chart membranes were similar to the REB reactor though total flux was reduced due to significantly thicker membranes. Overall testing of membrane reactors on coal derived syngas was over 115 hours for all reactors tested. Testing of the REB double membrane device exceeded 40 hours. Performance of the double membrane reactor has been similar to the results for the single reactor with good maintenance of flux even after these long exposures to hydrogen sulfide. Of special in

Thomas Barton; Tiberiu Popa

2009-06-30

183

Iron-ceria Aerogels Doped with Palladium as Water-gas Shift Catalysts for the Production of Hydrogen  

Microsoft Academic Search

Mixed 4.5% iron oxide-95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water-gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate

Sumit Bali; Frank E. Huggins; Richard D. Ernst; Ronald J. Pugmire; Gerald P. Huffman; Edward M. Eyring

2010-01-01

184

Probing the low-temperature water-gas shift activity of alkali-promoted platinum catalysts stabilized on carbon supports.  

PubMed

We report on the direct promotional effect of sodium on the water-gas shift activity of platinum supported on oxygen-free multiwalled carbon nanotubes. Whereas the Na-free Pt catalysts are shown to be completely inactive, the addition of sodium is found to improve the water-gas shift activity to levels comparable to those obtained with highly active Pt catalysts on metal oxide supports. The structure and morphology of the catalyst surface was followed using aberration-corrected HAADF-STEM, which showed that atomically dispersed platinum species are stabilized by the addition of sodium. In situ atmospheric-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments demonstrated that oxidized platinum Pt-OHx contributions in the Pt 4f signal are higher in the presence of sodium, providing evidence for a previously reported active-site structure of the form Pt-Nax-Oy-(OH)z. Pt remained oxidized in all redox experiments, even when a H2-rich gas mixture was used, but the extent of its oxidation followed the oxidation potential of the gas. These findings offer new insights into the nature of the active platinum-based site for the water-gas shift reaction. A strong inhibitory effect of hydrogen was observed on the reaction kinetics, effectively raising the apparent activation energy from 70 ± 5 kJ/mol (in product-free gas) to 105 ± 7 kJ/mol (in full reformate gas). Increased hydrogen uptake was observed on these materials when both Pt and Na were present on the catalyst, suggesting that hydrogen desorption might limit the water-gas shift reaction rate under such conditions. PMID:24502260

Zugic, Branko; Zhang, Shiran; Bell, David C; Tao, Franklin Feng; Flytzani-Stephanopoulos, Maria

2014-02-26

185

Operation, Modeling and Analysis of the Reverse Water Gas Shift Process  

NASA Technical Reports Server (NTRS)

The Reverse Water Gas Shift process is a candidate technology for water and oxygen production on Mars under the In-Situ Propellant Production project. This report focuses on the operation and analysis of the Reverse Water Gas Shift (RWGS) process, which has been constructed at Kennedy Space Center. A summary of results from the initial operation of the RWGS, process along with an analysis of these results is included in this report. In addition an evaluation of a material balance model developed from the work performed previously under the summer program is included along with recommendations for further experimental work.

Whitlow, Jonathan E.

2001-01-01

186

Au-mixed lanthanum/cerium oxide catalysts for water-gas-shift  

SciTech Connect

We report on the synthesis of highly homogeneous mixed La/Ce-oxides via a microemulsion-templated approach, and their evaluation as active supports for Au in the water gas shift (WGS) reaction. Both structure and reducibility of the oxides could be tailored by adjusting the La content across the entire range of La:Ce-ratios. The reducibility of the Au-free oxides shows an optimum at ?25% La content, which can be traced back to improved oxygen mobility due to formation of oxygen vacancies and to the formation of more strongly bound oxygen upon La addition. Deposition of Au onto these oxides gives rise to an additional, low-temperature reduction peak, presumably due to hydrogen spill-over from the noble metal onto the oxide support. The WGS activity of Au/La{sub x}Ce{sub 1?x}O{sub 2?0.5x} catalysts correlates closely with the reducibility of the oxide supports, and hence with La content, demonstrating that carefully controlled synthesis of nanostructured catalysts with uniform, tailored composition allows for fine control of reactive properties of these materials, and might ultimately open the way towards a more rational design of catalysts.

Wang, Yanan; Liang, Shuang; Cao, Anmin; Thompson, Robert L; Veser, Goetz

2010-08-01

187

Au-mixed lanthanum/cerium oxide catalysts for water gas shift  

SciTech Connect

We report on the synthesis of highly homogeneous mixed La/Ce-oxides via a microemulsion-templated approach, and their evaluation as active supports for Au in the water gas shift (WGS) reaction. Both structure and reducibility of the oxides could be tailored by adjusting the La content across the entire range of La:Ce-ratios. The reducibility of the Au-free oxides shows an optimum at ?25% La content, which can be traced back to improved oxygen mobility due to formation of oxygen vacancies and to the formation of more strongly bound oxygen upon La addition. Deposition of Au onto these oxides gives rise to an additional, low-temperature reduction peak, presumably due to hydrogen spill-over from the noble metal onto the oxide support. The WGS activity of Au/La{sub x}Ce{sub 1?x}O{sub 2?0.5x} catalysts correlates closely with the reducibility of the oxide supports, and hence with La content, demonstrating that carefully controlled synthesis of nanostructured catalysts with uniform, tailored composition allows for fine control of reactive properties of these materials, and might ultimately open the way towards a more rational design of catalysts.

Yanan Wanga; Shuang Lianga; Anmin Cao, Robert L. Thompson; Götz Veser

2010-06-11

188

Atomistic Thermodynamic Approach for Determining Cu Catalyst Morphologies Under Reactive Water-Gas-Shift Conditions  

NASA Astrophysics Data System (ADS)

The water gas shift reactions (WGS) are widely used in several industrial processes and are catalyzed by Cu catalysts. In coal derived syngas, there are sulfur (S) impurities which can adsorb on the Cu surfaces and block the active sites of the catalyst and can result in catalyst deactivation. The sulfur adsorption will compete with other possible adsorbates such as CO, O, H and CO2 making a quantitative estimate of the impact of sulfur on reactivity difficult. To determine the interactions between these possible adsorbates with Cu, the adsorption properties of these different adsorbates on low Miller index facets of Cu surfaces were studied in the limit where these surfaces are in thermodynamic equilibrium with the reactive environment. The effect of S adsorption on the surface electronic structure was significant and coverage dependent. In addition to a site-blocking deactivation mechanism, we found that sulfur modifies the surface electronic structure in a way that makes the Cu less reactive. Our results show that the adsorbates play a key role in defining the catalyst morphologies. We conclude that the presence of sulfur and other reactive adsorbates can impact the reactivity of the catalysts through several mechanisms including site-blocking, surface electronic structure modification and changes in the distribution and types of reactive sites through catalyst morphology changes.

Inoglu, Nilay; Kitchin, John

2009-03-01

189

Integrated Water Gas Shift Membrane Reactors Utilizing Novel, Non Precious Metal Mixed Matrix Membrane  

SciTech Connect

Nanoparticles of zeolitic imidazolate frameworks and other related hybrid materials were prepared by modifying published synthesis procedures by introducing bases, changing stoichiometric ratios, or adjusting reaction conditions. These materials were stable at temperatures >300 °C and were compatible with the polymer matrices used to prepare mixed- matrix membranes (MMMs). MMMs tested at 300 °C exhibited a >30 fold increase in permeability, compared to those measured at 35 °C, while maintaining H{sub 2}/CO{sub 2} selectivity. Measurements at high pressure (up to 30 atm) and high temperature (up to 300 °C) resulted in an increase in gas flux across the membrane with retention of selectivity. No variations in permeability were observed at high pressures at either 35 or 300 °C. CO{sub 2}-induced plasticization was not observed for Matrimid®, VTEC, and PBI polymers or their MMMs at 30 atm and 300 °C. Membrane surface modification by cross-linking with ethanol diamine resulted in an increase in H{sub 2}/CO{sub 2} selectivity at 35 °C. Spectrometric analysis showed that the cross-linking was effective to temperatures <150 °C. At higher temperatures, the cross-linked membranes exhibit a H{sub 2}/CO{sub 2} selectivity similar to the uncross-linked polymer. Performance of the polybenzimidazole (PBI) hollow fibers prepared at Santa Fe Science and Technology (SFST, Inc.) showed increased flux o to a flat PBI membrane. A water-gas shift reactor has been built and currently being optimized for testing under DOE conditions.

Ferraris, John

2013-09-30

190

Cu\\/ZnO\\/Al 2O 3 water–gas shift catalysts for practical fuel cell applications: the performance in shut-down\\/start-up operation  

Microsoft Academic Search

The Cu\\/ZnO\\/Al2O3 catalysts were prepared by the coprecipitation method, and were evaluated in the water–gas shift (WGS) reaction. The effects of the calcination temperature on the BET surface area and crystallite size were characterized. In WGS reaction, the Cu\\/ZnO\\/Al2O3 catalysts suffered from continuous deactivation in shut-down\\/start-up operation – the daily requirement for mobile and residential fuel cell systems. Among them,

Pingjun Guo; Liangfeng Chen; Qiuyun Yang; Minghua Qiao; Hui Li; Hexing Li; Hualong Xu; Kangnian Fan

2009-01-01

191

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst  

SciTech Connect

A cobalt Fischer-Tropsch catalyst (CO/MgO/silica) was reduced and slurried in combination with reduced Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst. Combined catalyst system was run at fixed process conditions for more than 400 hours. The system showed stable selectivity. The Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst remained reasonably active in the presence of the cobalt catalyst. Hydrocarbon selectivity of the cobalt and Cu/ZnO/Al[sub 2]0[sub 3] catalyst system compared favorably to selectivity of iron-based catalysts. Methane selectivity was slightly higher for the cobalt-based system, but C[sub 5][sup +] selectivity was essentially the same. The hydrocarbon product distribution appeared to exhibit a double-a behavior. a[sub 1] was near 0.80 which is higher than that of iron catalysts, while a[sub 2] was calculated to be 0.86 which is somewhat lower than would be typical for an iron-based catalyst.

Yates, I.C.; Satterfield, C.N.

1988-01-01

192

Iron-ceria Aerogels Doped with Palladium as Water-gas Shift Catalysts for the Production of Hydrogen  

SciTech Connect

Mixed 4.5% iron oxide-95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water-gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate and iron(III) chloride hexahydrate precursor. Palladium was doped onto some of these materials by gas-phase incorporation (GPI) using ({eta}{sup 3}-allyl)({eta}{sup 5}-cyclopentadienyl)palladium as the volatile Pd precursor. Water-gas shift catalytic activities were evaluated in a six-channel fixed-bed reactor at atmospheric pressure and reaction temperatures ranging from 150 to 350 C. Both 1% and 2% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels showed WGS activities that increased significantly from 150 to 350 C. The activities of 1% Pd-doped 4.5% iron oxide-95.5% cerium oxide aerogels were also compared with that of the 1% Pd-doped ceria aerogel without iron. The WGS activity of 1% Pd on 4.5% iron oxide-95.5% cerium oxide aerogels is substantially higher (5 times) than the activity of 1% Pd-doped ceria aerogel without iron. The gas-phase incorporation results in a better Pd dispersion. Ceria aerogel provides a nonrigid structure wherein iron is not significantly incorporated inside the matrix, thereby resulting in better contact between the Fe and Pd and thus enhancing the WGS activity. Further, neither Fe nor Pd is reduced during the ceria-aerogel-catalyzed WGS reaction. This behavior contrasts with that noted for other Fe-based WGS catalysts, in which the original ferric oxide is typically reduced to a nonstoichiometric magnetite form.

Bali, S.; Huggins, F; Ernst, R; Pugmire, R; Huffman, G; Eyring, E

2010-01-01

193

An Investigation of the Reverse Water Gas Shift Process and Operating Alternatives  

NASA Technical Reports Server (NTRS)

The Reverse Water Gas Shift (RWGS) process can produce water and ultimately oxygen through electrolysis. This technology is being investigated for possible use in the exploration of Mars as well as a potential process to aid in the regeneration of oxygen from carbon dioxide. The initial part of this report summarizes the results obtained from operation of the RWGS process at Kennedy Space Center during May and June of this year. It has been demonstrated that close to complete conversion can be achieved with the RWGS process under certain operating conditions. The report also presents results obtained through simulation for an alternative staged configuration for RWGS which eliminates the recycle compressor. This configuration looks promising and hence seems worthy of experimental investigation.

Whitlow, Jonathan E.

2002-01-01

194

X-ray structure and reactivity of (Ru(bpy)/sub 2/(CO)H)PF/sub 6/ x 1/2 C/sub 3/H/sub 6/O (bpy = 2,2'-bipyridyl), a possible intermediate in the water-gas shift reaction catalyzed by ruthenium polypyridyl complexes  

SciTech Connect

The structure of (Ru(C/sub 10/H/sub 8/N/sub 2/)/sub 2/(CO)H)PF/sub 6/ x 1/2 C/sub 3/H/sub 6/O is reported. The compound crystallizes in the monoclinic C2/c space group with unit cell parameters a = 26.680 (4) A, b = 7.005 (3) A, c = 25.936 (2) A, and ..beta.. = 93.96 (2)/sup 0/ (V = 4836.04 A/sup 3/, Z = 8). The cationic species has a cis geometry for CO and H. The ruthenium-hydride and ruthenium-carbon distances are 1.68 (4) and 1.804 (6) A, respectively. The average ruthenium-nitrogen distance is 2.109 A. In acidic solution the title compound acts as a hydride donor to produce dihydrogen gas in a pseudo-first-order reaction; the second-order rate constant for this reaction is 0.105 -/+ 0.01 dm/sup 3/ mol/sup -1/ s/sup -1/ at 303 K with an activation energy 56 -/+ 2 kJ mol/sup -1/. A value of -100 -/+ 8 J mol/sup -1/ deg/sup -1/ has been obtained for the entropy of activation. The consequences of these results for the possible reaction mechanism of the homogeneous water-gas shift reaction catalyzed by (Ru(bpy)/sub 2/(CO)Cl)/sup +/ are discussed. 15 references, 4 figures, 6 tables.

Haasnoot, J.G.; Hinrichs, W.; Weir, O.; Vos, J.G.

1986-11-05

195

In situ/operando studies for the production of hydrogen through the water-gas shift on metal oxide catalysts.  

PubMed

In this perspective article, we show how a series of in situ techniques {X-ray diffraction (XRD), pair-distribution-function analysis (PDF), X-ray absorption fine structure (XAFS), environmental transmission electron microscopy (ETEM), infrared spectroscopy (IR), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)} can be combined to perform detailed studies of the structural, electronic and chemical properties of metal oxide catalysts used for the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O ? H2 + CO2). Under reaction conditions most WGS catalysts undergo chemical transformations that drastically modify their composition with respect to that obtained during the synthesis process. Experiments of time-resolved in situ XRD, XAFS, and PDF indicate that the active phase of catalysts which combine Cu, Au or Pt with oxides such as ZnO, CeO2, TiO2, CeOx/TiO2 and Fe2O3 essentially involves nanoparticles of the reduced noble metals. The oxide support undergoes partial reduction and is not a simple spectator, facilitating the dissociation of water and in some cases modifying the chemical properties of the supported metal. Therefore, to optimize the performance of these catalysts one must take into consideration the properties of the metal and oxide phases. IR and AP-XPS have been used to study the reaction mechanism for the WGS on metal oxide catalysts. Data of IR spectroscopy indicate that formate species are not necessarily involved in the main reaction path for the water-gas shift on Cu-, Au- and Pt-based catalysts. Thus, a pure redox mechanism or associative mechanisms that involve either carbonate-like (CO3, HCO3) or carboxyl (HOCO) species should be considered. In the last two decades, there have been tremendous advances in our ability to study catalytic materials under reaction conditions and we are moving towards the major goal of fully understanding how the active sites for the production of hydrogen through the WGS actually work. PMID:23660768

Rodriguez, José A; Hanson, Jonathan C; Stacchiola, Dario; Senanayake, Sanjaya D

2013-08-01

196

Water gas shift membrane reactor for CO 2 control in IGCC systems: techno-economic feasibility study  

Microsoft Academic Search

A novel reactor concept, the water gas shift membrane reactor (WGS-MR) for CO2 removal in IGCC systems has been investigated. In order to establish full insight in the possibilities of the application of such a reactor, a multidisciplinary feasibility study has been carried out comprising system integration studies, catalyst research, membrane research, membrane reactor modelling and bench scale membrane reactor

M Bracht; P. T Alderliesten; R Kloster; R Pruschek; G Haupt; E Xue; J. R. H Ross; M. K Koukou; N Papayannakos

1997-01-01

197

LYAPUNOV-Based Sensor Failure Detection and Recovery for the Reverse Water Gas Shift Process  

NASA Technical Reports Server (NTRS)

Livingstone, a model-based AI software system, is planned for use in the autonomous fault diagnosis, reconfiguration, and control of the oxygen-producing reverse water gas shift (RWGS) process test-bed located in the Applied Chemistry Laboratory at KSC. In this report the RWGS process is first briefly described and an overview of Livingstone is given. Next, a Lyapunov-based approach for detecting and recovering from sensor failures, differing significantly from that used by Livingstone, is presented. In this new method, models used are in t e m of the defining differential equations of system components, thus differing from the qualitative, static models used by Livingstone. An easily computed scalar inequality constraint, expressed in terms of sensed system variables, is used to determine the existence of sensor failures. In the event of sensor failure, an observer/estimator is used for determining which sensors have failed. The theory underlying the new approach is developed. Finally, a recommendation is made to use the Lyapunov-based approach to complement the capability of Livingstone and to use this combination in the RWGS process.

Haralambous, Michael G.

2002-01-01

198

Lyapunov-Based Sensor Failure Detection And Recovery For The Reverse Water Gas Shift Process  

NASA Technical Reports Server (NTRS)

Livingstone, a model-based AI software system, is planned for use in the autonomous fault diagnosis, reconfiguration, and control of the oxygen-producing reverse water gas shift (RWGS) process test-bed located in the Applied Chemistry Laboratory at KSC. In this report the RWGS process is first briefly described and an overview of Livingstone is given. Next, a Lyapunov-based approach for detecting and recovering from sensor failures, differing significantly from that used by Livingstone, is presented. In this new method, models used are in terms of the defining differential equations of system components, thus differing from the qualitative, static models used by Livingstone. An easily computed scalar inequality constraint, expressed in terms of sensed system variables, is used to determine the existence of sensor failures. In the event of sensor failure, an observer/estimator is used for determining which sensors have failed. The theory underlying the new approach is developed. Finally, a recommendation is made to use the Lyapunov-based approach to complement the capability of Livingstone and to use this combination in the RWGS process.

Haralambous, Michael G.

2001-01-01

199

Exposed surfaces on shape-controlled ceria nanoparticles revealed through AC-TEM and water-gas shift reactivity.  

PubMed

Aberration-corrected transmission electron microscopy and high-angle annular dark field imaging was used to investigate the surface structures and internal defects of CeO2 nanoparticles (octahedra, rods, and cubes). Further, their catalytic reactivity in the water-gas shift (WGS) reaction and the exposed surface sites by using FTIR spectroscopy were tested. Rods and octahedra expose stable (111) surfaces whereas cubes have primarily (100) facets. Rods also had internal voids and surface steps. The exposed planes are consistent with observed reactivity patterns, and the normalized WGS reactivity of octahedra and rods were similar, but the cubes were more reactive. In situ FTIR spectroscopy showed that rods and octahedra exhibit similar spectra for -OH groups and that carbonates and formates formed upon exposure to CO whereas for cubes clear differences were observed. These results provide definitive information on the nature of the exposed surfaces in these CeO2 nanostructures and their influence on the WGS reactivity. PMID:24108516

Agarwal, Shilpa; Lefferts, Leon; Mojet, Barbara L; Ligthart, D A J Michel; Hensen, Emiel J M; Mitchell, David R G; Erasmus, Willem J; Anderson, Bruce G; Olivier, Ezra J; Neethling, Johannes H; Datye, Abhaya K

2013-10-01

200

Parametric Gasification of Oak and Pine Feedstocks Using the TCPDU and Slipstream Water-Gas Shift Catalysis  

SciTech Connect

With oak and pine feedstocks, the Gasification of Biomass to Hydrogen project maximizes hydrogen production using the Full Stream Reformer during water-gas shift fixed-bed reactor testing. Results indicate that higher steam-to-biomass ratio and higher thermal cracker temperature yield higher hydrogen concentration. NREL's techno-economic models and analyses indicate hydrogen production from biomass may be viable at an estimated cost of $1.77/kg (current) and $1.47/kg (advanced in 2015). To verify these estimates, NREL used the Thermochemical Process Development Unit (TCPDU), an integrated system of unit operations that investigates biomass thermochemical conversion to gaseous and liquid fuels and chemicals.

Hrdlicka, J.; Feik, C.; Carpenter, D.; Pomeroy, M.

2008-12-01

201

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Final technical progress report, September 12, 1991--December 11, 1994  

SciTech Connect

The objective of this research was to investigate sulfur-resistant catalysts for the conversion of synthesis gas having H{sub 2}/CO {le} 1 into C{sub 1}--C{sub 4} alcohols, especially ethanol, by a highly selective and efficient pathway, while also promoting the water gas shift reaction (WGSR). The catalysts chosen are bifunctional, base-hydrogenation, sulfur-tolerant transition metal sulfides with heavy alkali, e.g. Cs{sup +}, promoter dispersed on their surfaces. The modes of activation of H{sub 2} and CO on MoS{sub 2} and alkali-doped MoS{sub 2} were considered, and computational analyses of the thermodynamic stability of transition metal sulfides and of the electronic structure of these sulfide catalysts were carried out. In the preparation of the cesium-promoted MoS{sub 2} catalysts, a variety of preparation methods using CsOOCH were examined. In all cases, doping with CsOOCH led to a lost of surface area. The undoped molybdenum disulfide catalyst only produced hydrocarbons. Cs-doped MoS{sub 2} catalysts all produced linear alcohols, along with smaller amounts of hydrocarbons. With a 20 wt% CsOOCH/MoS{sub 2} catalyst, temperature, pressure, and flow rate dependences of the synthesis reactions were investigated in the presence and absence of H{sub 2}S in the H{sub 2}/CO = 1/1 synthesis gas during short term testing experiments. It was shown that with a carefully prepared 10 wt% CsOOCH/MoS{sub 2} catalyst, reproducible and high alcohol synthesis activity could be obtained. For example, at 295 C with H{sub 2}/CO = 1 synthesis gas at 8.3 MPa and with GHSV = 7,760 l/kg cat/hr, the total alcohol space time yield was ca 300 g/kg cat/hr (accompanied with a hydrocarbon space time yield of ca 60 g/kg cat/hr). Over a testing period of ca 130 hr, no net deactivation of the catalyst was observed. 90 refs., 82 figs., 14 tabs.

Klier, K.; Herman, R.G.; Deemer, M.; Richards-Babb, M.; Carr, T.

1995-07-01

202

Robust Low-Cost Water-Gas Shift Membrane Reactor for High-Purity Hydrogen Production form Coal-Derived Syngas  

SciTech Connect

This report details work performed in an effort to develop a low-cost, robust water gas shift membrane reactor to convert coal-derived syngas into high purity hydrogen. A sulfur- and halide-tolerant water gas shift catalyst and a sulfur-tolerant dense metallic hydrogen-permeable membrane were developed. The materials were integrated into a water gas shift membrane reactor in order to demonstrate the production of >99.97% pure hydrogen from a simulated coal-derived syngas stream containing 2000 ppm hydrogen sulfide. The objectives of the program were to (1) develop a contaminant-tolerant water gas shift catalyst that is able to achieve equilibrium carbon monoxide conversion at high space velocity and low steam to carbon monoxide ratio, (2) develop a contaminant-tolerant hydrogen-permeable membrane with a higher permeability than palladium, (3) demonstrate 1 L/h purified hydrogen production from coal-derived syngas in an integrated catalytic membrane reactor, and (4) conduct a cost analysis of the developed technology.

James Torkelson; Neng Ye; Zhijiang Li; Decio Coutinho; Mark Fokema

2008-05-31

203

Sorption-Enhanced Synthetic Natural Gas (SNG) Production from Syngas: A Novel Process Combining CO Methanation, Water-Gas Shift, and CO2 Capture  

SciTech Connect

Synthetic natural gas (SNG) production from syngas is under investigation again due to the desire for less dependency from imports and the opportunity for increasing coal utilization and reducing green house gas emission. CO methanation is highly exothermic and substantial heat is liberated which can lead to process thermal imbalance and deactivation of the catalyst. As a result, conversion per pass is limited and substantial syngas recycle is employed in conventional processes. Furthermore, the conversion of syngas to SNG is typically performed at moderate temperatures (275 to 325°C) to ensure high CH4 yields since this reaction is thermodynamically limited. In this study, the effectiveness of a novel integrated process for the SNG production from syngas at high temperature (i.e. 600?C) was investigated. This integrated process consists of combining a CO methanation nickel-based catalyst with a high temperature CO2 capture sorbent in a single reactor. Integration with CO2 separation eliminates the reverse-water-gas shift and the requirement for a separate water-gas shift (WGS) unit. Easing of thermodynamic constraint offers the opportunity of enhancing yield to CH4 at higher operating temperature (500-700ºC) which also favors methanation kinetics and improves the overall process efficiency due to exploitation of reaction heat at higher temperatures. Furthermore, simultaneous CO2 capture eliminates green house gas emission. In this work, sorption-enhanced CO methanation was demonstrated using a mixture of a 68% CaO/32% MgAl2O4 sorbent and a CO methanation catalyst (Ni/Al2O3, Ni/MgAl2O4, or Ni/SiC) utilizing a syngas ratio (H2/CO) of 1, gas-hour-space velocity (GHSV) of 22 000 hr-1, pressure of 1 bar and a temperature of 600oC. These conditions resulted in ~90% yield to methane, which was maintained until the sorbent became saturated with CO2. By contrast, without the use of sorbent, equilibrium yield to methane is only 22%. Cyclic stability of the methanation catalyst and durability of the sorbent were also studied in the multiple carbonation-decarbonation cycle studies proving the potential of this integrated process in a practical application.

Lebarbier, Vanessa MC; Dagle, Robert A.; Kovarik, Libor; Albrecht, Karl O.; Li, Xiaohong S.; Li, Liyu; Taylor, Charles E.; Bao, Xinhe; Wang, Yong

2014-01-01

204

Robust Low-Cost Water-Gas Shift Membrane Reactor For High-Purity Hydrogen Production from Coal-Derived Syngas (Rept. for June 1, 2005-May 31, 2008).  

National Technical Information Service (NTIS)

This report details work performed in an effort to develop a low-cost, robust water gas shift membrane reactor to convert coal-derived syngas into high purity hydrogen. A sulfur- and halide-tolerant water gas shift catalyst and a sulfur-tolerant dense met...

D. Coutinho J. Torkelson M. Fokema N. Ye Z. Li

2008-01-01

205

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts; Technical progress report, June 1992--August 1992  

SciTech Connect

During this quarter, high pressure (up to 100 atm = 10.3 MPa), high temperature (up to 350{degrees}C) catalyst testing was carried out with the 20 Wt% CS/MoS{sub 2} catalyst that was prepared. It was verified that this is an active catalyst for the synthesis of linear C{sub l}-C{sub 4} alcohols and that the yield increases with increasing temperature. However, the product selectivity is shifted toward enhanced hydrocarbon production, principally of methane. Temperature, pressure, and flow rate dependences of the synthesis reactions were also investigated in the presence and absence of H{sub 2}S in the H{sub 2}/CO = 1/1 Synthesis gas during short term testing experiments. The temperature seemed to produce the largest effect on alcohol yield and on the hydrocarbon selectivity, with both increasing with increasing temperature. The presence of 45.5 ppM H{sub 2}S in the synthesis gas did increase the C{sub 2}{sup +} alcohol/methanol molar ratio at 285{degrees}C, but this effect was not noticeable at higher temperatures under the reaction conditions that were employed. On the other hand, the presence of H{sub 2}S decreased the yield of methane at high temperatures (340--350{degrees}C), but this effect was not noticeable at the lower temperatures that were utilized. At high temperature and pressure (350{degrees}C and 10.3 MPa) with 45.5 ppM H{sub 2}S in the synthesis gas, it was shown that increasing the gas hourly space velocity of the synthesis gas reactant significantly decreased the yield of methane, while affecting the yield of alcohols to a much lesser extent.

Klier, K.; Herman, R.G.; Deemer, M.

1992-09-01

206

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. [Quarterly] report, October 1, 1988--December 31, 1988  

SciTech Connect

A cobalt Fischer-Tropsch catalyst (CO/MgO/silica) was reduced and slurried in combination with reduced Cu/ZnO/Al{sub 2}0{sub 3} water-gas-shift catalyst. Combined catalyst system was run at fixed process conditions for more than 400 hours. The system showed stable selectivity. The Cu/ZnO/Al{sub 2}0{sub 3} water-gas-shift catalyst remained reasonably active in the presence of the cobalt catalyst. Hydrocarbon selectivity of the cobalt and Cu/ZnO/Al{sub 2}0{sub 3} catalyst system compared favorably to selectivity of iron-based catalysts. Methane selectivity was slightly higher for the cobalt-based system, but C{sub 5}{sup +} selectivity was essentially the same. The hydrocarbon product distribution appeared to exhibit a double-a behavior. a{sub 1} was near 0.80 which is higher than that of iron catalysts, while a{sub 2} was calculated to be 0.86 which is somewhat lower than would be typical for an iron-based catalyst.

Yates, I.C.; Satterfield, C.N.

1988-12-31

207

Homogeneous transition metal catalysis: from the water gas shift reaction to nuclear waste vitrification  

Microsoft Academic Search

A US–Hungarian cooperative research project between Professor R. Bruce King at the University of Georgia and Professor László Markó at the University of Veszprém during the period 1977 to 1986 was a major stimulus in extending the scope of Professor King’s research at the University of Georgia from synthetic transition metal organometallic chemistry to homogeneous catalysis. Since that US–Hungarian cooperative

R. B. King

1999-01-01

208

Adsorption of water on polycrystalline copper: Relevance to the water gas shift reaction  

Microsoft Academic Search

This paper is concerned with the interaction of water with a polycrystalline copper surface. It shows that a small fraction (7-8%) of the copper surface will readily dissociatively chemisorb water, while the major portion of the surface adsorbs water in a molecular form (ÎH(ads) = 45 kJ\\/mol). The structure sensitivity of the adsorption of water on the polycrystalline surface is

E. Colbourn; R. A. Hadden; G. Webb; Waugh Vandervell

1991-01-01

209

Acid leached Raney copper catalysts for the water–gas shift reaction  

Microsoft Academic Search

Raney copper catalysts were prepared by leaching a ternary alloy of composition Cu(24.8) Zn(25.2) Al(48.3) in nitric and perchloric acid. The acid leaching process was examined as a function of acid strength and total leach time. Similarities in acid and caustic leaching were observed. For example, during the first hour of leaching in both media, aluminium was extracted at a

J. R. Mellor; N. J. Coville; S. H. Durbach; R. G. Copperthwaite

1998-01-01

210

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, September 1993--November 1993  

SciTech Connect

During calcination of the precipitated and dried MoS{sub 3} to form MOS{sub 2}, it was found that small sample sizes were needed to provide thermal control of the highly exothermic decomposition reaction in the 8 mm ID quartz tube used for this purpose. Characterization of MoS{sub 2} and Cs/MoS{sub 2} catalysts have been carried out by X-ray powder diffraction (XRD) after each synthesis step. In addition, the XRD analyses were conducted after prolonged air exposure of the Cs-doped MoS{sub 2} catalyst. It was shown that prolonged exposure to the ambient atmosphere led to segregation and crystallization of the cesium formate dopant. Thus, catalytic testing should be carried out with freshly prepared samples that are protected from the ambient atmosphere. Catalytic testing is underway to determine if there is an inverse correlation of catalytic activity and selectivity with prolonged air exposure of the catalyst.

Klier, K.; Herman, R.; Deemer, M.

1994-03-01

211

Impact of Contaminants Present in Coal-Biomass Derived Synthesis Gas on Water-gas Shift and Fischer-Tropsch Synthesis Catalysts  

SciTech Connect

Co-gasification of biomass and coal in large-scale, Integrated Gasification Combined Cycle (IGCC) plants increases the efficiency and reduces the environmental impact of making synthesis gas ("syngas") that can be used in Coal-Biomass-to-Liquids (CBTL) processes for producing transportation fuels. However, the water-gas shift (WGS) and Fischer-Tropsch synthesis (FTS) catalysts used in these processes may be poisoned by multiple contaminants found in coal-biomass derived syngas; sulfur species, trace toxic metals, halides, nitrogen species, the vapors of alkali metals and their salts (e.g., KCl and NaCl), ammonia, and phosphorous. Thus, it is essential to develop a fundamental understanding of poisoning/inhibition mechanisms before investing in the development of any costly mitigation technologies. We therefore investigated the impact of potential contaminants (H{sub 2}S, NH{sub 3}, HCN, AsH{sub 3}, PH{sub 3}, HCl, NaCl, KCl, AS{sub 3}, NH{sub 4}NO{sub 3}, NH{sub 4}OH, KNO{sub 3}, HBr, HF, and HNO{sub 3}) on the performance and lifetime of commercially available and generic (prepared in-house) WGS and FT catalysts; ferrochrome-based high-temperature WGS catalyst (HT-WGS, Shiftmax 120�, Süd-Chemie), low-temperature Cu/ZnO-based WGS catalyst (LT-WGS, Shiftmax 230�, Süd-Chemie), and iron- and cobalt-based Fischer-Trospch synthesis catalysts (Fe-FT & Co-FT, UK-CAER). In this project, TDA Research, Inc. collaborated with a team at the University of Kentucky Center for Applied Energy Research (UK-CAER) led by Dr. Burt Davis. We first conducted a detailed thermodynamic analysis. The three primary mechanisms whereby the contaminants may deactivate the catalyst are condensation, deposition, and reaction. AsH{sub 3}, PH{sub 3}, H{sub 2}S, HCl, NH{sub 3} and HCN were found to have a major impact on the Fe-FT catalyst by producing reaction products, while NaCl, KCl and PH{sub 3} produce trace amounts of deposition products. The impact of the contaminants on the activity, selectivity, and deactivation rates (lifetime) of the catalysts was determined in bench-scale tests. Most of the contaminants appeared to adsorb onto (or react with) the HT- and LT-WGS catalysts were they were co-fed with the syngas: � 4.5 ppmv AsH{sub 3} or 1 ppmv PH{sub 3} in the syngas impacted the selectivity and CO conversion of both catalysts; � H{sub 2}S slowly degraded both WGS catalysts; - A binary mixture of H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv) impacted the activity of the LT-WGS catalyst, but not the HT-WGS catalyst � Moderate levels of NH{sub 3} (100 ppmv) or HCN (10 ppmv) had no impact � NaCl or KCl had essentially no effect on the HT-WGS catalyst, but the activity of the LT-WGS catalyst decreased very slowly Long-term experiments on the Co-FT catalyst at 260 and 270 °C showed that all of the contaminants impacted it to some extent with the exception of NaCl and HF. Irrespective of its source (e.g., NH{sub 3}, KNO{sub 3}, or HNO{sub 3}), ammonia suppressed the activity of the Co-FT catalyst to a moderate degree. There was essentially no impact the Fe-FT catalyst when up to 100 ppmw halide compounds (NaCl and KCl), or up to 40 ppmw alkali bicarbonates (NaHCO{sub 3} and KHCO{sub 3}). After testing, BET analysis showed that the surface areas, and pore volumes and diameters of both WGS catalysts decreased during both single and binary H2S and NH3 tests, which was attributed to sintering and pore filling by the impurities. The HT-WGS catalyst was evaluated with XRD after testing in syngas that contained 1 ppmv PH{sub 3}, or 2 ppmv H{sub 2}S, or both H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv). The peaks became sharper during testing, which was indicative of crystal growth and sintering, but no new phases were detected. After LT-WGS tests (3-33 ppmv NH{sub 3} and/or 0-88 ppmv H{sub 2}S) there were a few new phases that appeared, including sulfides. The fresh Fe-FT catalyst was nanocrystalline and amorphous. ICP-AA spectroscopy and other methods (e.g., chromatography) were used to analyze for

Gokhan Alptekin

2012-09-30

212

Role of metal components in Pd?Cu bimetallic catalysts supported on CeO2 for the oxygen-enhanced water gas shift  

SciTech Connect

Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O{sub 2} is added to H{sub 2}-rich reformate gas to enhance CO shift. Among CeO{sub 2}-supported bimetallic catalysts, Pd-Cu and Pt-Cu combinations were found to show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H{sub 2} yield than WGS at low temperature around 250 C. Temperature programmed reduction (TPR) showed strong interaction between Pd and Cu in Pd-Cu/CeO{sub 2} by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO{sub 2}. Extended X-ray absorption fine structure (EXAFS) analysis revealed that such bimetallic Pd-Cu and Pt-Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. Oxygen storage capacity (OSC) measurements point to higher resistance of Pd-Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd-Cu was found to promote CO shift, rather than CO oxidation by increasing the number of active sites and by suppressing H{sub 2} activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H{sub 2} and the loss of H{sub 2} by oxidation in OWGS. Transient response technique revealed that Cu in Pd-Cu enhances desorption of strongly chemisorbed CO{sub 2} on catalyst surface in contrast to very slow CO{sub 2} desorption from surface of monometallic Pd. Thus, the excellent OWGS activity of Pd-Cu catalyst has been attributed to the complementary roles of the two metals for enhancing CO shift, which is realized by its alloy structure and the accompanying strong interaction between metal components.

Kugai, J.; Miller, J. T.; Guo, N.; Song, C. (Chemical Sciences and Engineering Division); ( PSC-USR); (Penn State Univ.)

2011-06-01

213

Cu–Al 2O 3–CuAl 2O 4 water–gas shift catalyst for hydrogen production in fuel cell applications: Mechanism of deactivation under start–stop operating conditions  

Microsoft Academic Search

This paper analyzes the mechanism of deactivation of a new Cu–Al2O3–CuAl2O4 water–gas shift (WGS) catalyst recently developed for small-scale hydrogen generation applications, such as fuel cell-based residential power generators and hydrogen fueling stations. The catalyst has good potential for use in small-scale fuel processors working under essentially steady-state conditions, such as on-site hydrogen generation systems for hydrogen filling stations. However,

Oleg Ilinich; Wolfgang Ruettinger; Xinsheng Liu; Robert Farrauto

2007-01-01

214

Nuclear field shift effect in chemical exchange reactions  

NASA Astrophysics Data System (ADS)

The classic theory of stable isotope fractionation in chemical exchange reactions has been established by Bigeleisen, Mayer, and Urey in 1947. The theory was based on the difference of molecular vibrational energies of isotopomers that are proportional to the respective masses, and hence, results in mass-dependent isotope effect only. In 1996, this conventional mass-dependent theory has been expanded by Bigeleisen to include a mass-independent term named the nuclear field shift effect. The nuclear field shift is an isotope shift in orbital electrons, which results from the isotopic difference in nuclear size and shape. The new equation defined by Bigeleisen (at a constant temperature) can be simply expressed as, ln ? = ? A + (? m/mm') B, where ? is the isotope separation factor, ? isotopic difference in mean-square nuclear charge radius, ?m difference between isotopic masses m and m'. A and B are scaling factors of the nuclear field shift effect and the conventional mass effect, respectively. Since this new theory was presented, the mass-independent isotope fractionation of various elements, e.g, Ti, Cr, Ni, Zn, Sr, Zr, Mo, Ru, Cd, Te, Ba, Nd, Sm, Gd, Yb, and U, found in chemical exchange systems has been successfully explained as the nuclear field shift effect. In our most recent studies, the nuclear field shift effect of Cr, Mo, Ru, Cd, and Te isotopes has been found in laboratory scale experiments. The isotopes of these elements were fractionated by using a liquid-liquid extraction system (a ligand exchange system) at room temperature. The isotopic analysis was performed by the multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with a typical precision of <100 ppm (at ENS Lyon or UC Davis). Isotope enrichment factors did not show mass-dependent trend, but possessed a similar variation of their nuclear charge radii. For Cr, we tested a different chemical exchange system (a redox system): at high temperature (723-1023 K), an eutectic melt was contacted with a liquid metal. In this system, the nuclear field shift effect of Cr was also found. All these experimental results suggest that the nuclear field shift effect may occur in every chemical exchange reaction at various temperatures to various degrees. Therefore, isotopic anomalies found in a natural system might be partly or largely affected by the nuclear field shift effect via chemical reactions occurred in the nature. In order to clarify the degree and significance of its contribution, we may need to pay more attention to the nuclear field shift effect created chemically.

Fujii, T.; Moynier, F.; Yin, Q.; Albarède, F.

2007-12-01

215

A simulation study on the enhancement of the shift reaction by water injection into a gasifier  

Microsoft Academic Search

Although coal gasification is a clean and efficient use of coal, a reduction of CO2 emissions is needed to mitigate global warming. The aim of this study was to improve the thermal efficiency of fuel production and electricity generation by dry coal feed gasification. The primary cause of thermal efficiency loss is steam use in a water-gas shift reactor. The

F. Kiso; M. Matsuo

2011-01-01

216

Water gas furnace  

SciTech Connect

A water gas furnace comprising an outer container to provide a housing in which coke is placed into its lower part. A water container is placed within the housing. The coke is ignited and heats the water in the container converting it into steam. The steam is ejected into the coke, which together with air, produces water gas. Preferably, pumice stones are placed above the coke. The water gas is accepted into the pores of the pumice stones, where the heated pumice stones ignite the water gas, producing heat. The heat is extracted by a heat exchanger provided about the housing.

Gallaro, C.

1985-12-03

217

CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS-SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2  

SciTech Connect

For the purpose of process simulation and economic analysis of the proposed CO{sub 2} selective membrane process, we began to generate the equilibrium and rate data at the operating condition interested to our applications. In the last quarter we presented the results obtained at 200 C. In this quarter, we have concentrated on the experiments at 250 C and CO{sub 2} pressure of 0 to 1 bar. In this report we present the equilibrium isotherm and the mathematical treatment using the commonly accepted Langmuir equation. The data fit the Langmuir isotherm well and will be used for future adsorber and membrane reactor modeling. In addition, unsupported hydrotalcite membranes have been successfully synthesized on the silicon wafer with micro-channels. The membrane developed in this quarter ranges 2 to 5 {micro}m in thickness. No visible cracks or defects were observed. Performance characterization of these membranes will begin in the next quarter. Since the interference from substrate in the characterization of the supported membrane is no longer existent, it is hoped that the hydrotalcite membrane thus formed can be optimized for its CO{sub 2} selectivity and performance with the aid of the morphological and performance characterization.

Paul K. T. Liu

2004-11-01

218

CO(2) Selective Ceramic Membrane for Water-Gas Shift Reaction with Concomitant Recovery of CO(2).  

National Technical Information Service (NTIS)

CO(sub 2) diffusivity through hydrotalcite materials at 200 to 250 C was determined based upon the weight pick-up vs time. D/r(sup 2) (diffusivity/radius(sup 2)) for CO(sub 2) ranges from 3 x 10(sup -4) to 1 x 10(sup -3) depending upon the temperature. Th...

P. K. T. Liu

2003-01-01

219

Investigation of the Reverse Water Gas Shift Reaction for Production of Oxygen From Mars Atmospheric Carbon Dioxide  

NASA Technical Reports Server (NTRS)

The first phase of the research includes a comprehensive analytical study examining the potential applications for engineering subsystems and mission strategies made possible by such RWGS based subsystems, and will include an actual experimental demonstration and performance characterization of a full-scale brassboard RWGS working unit. By the time of this presentation the laboratory demonstration unit will not yet be operational but we will present the results of our analytical studies to date and plans for the ongoing work.

Meyer, Tom; Zubrin, Robert

1997-01-01

220

CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT FOR THE RECOVERY OF CO2  

SciTech Connect

In this quarter we focus on the membrane synthesis via interphase impregnation and slip casting. The slip casting method shows very promising. A well-organized hydrotalcite layer has been deposited on the porous ceramic substrate. Under SEM examination, few defects were recognized. In addition, its particle size in the range of {approx}500{angstrom} is comparable to our existing Al{sub 2}O{sub 3} membrane with 100{angstrom} pore size. This membrane could be qualified for post-treatment with CVD/I to seal the opening to become a CO{sub 2}-affinity membrane. On the other hand, the hydrotalcite membrane prepared via impregnation requires further refinement. After 4th impregnation defects in the range of 0.2 micron were observed under SEM examination, likely due to the incomplete coverage. In the next quarter, we will improve the in-situ technique to overcome this problem.

Paul K.T. Liu

2002-11-15

221

CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2  

SciTech Connect

During Year I this project has been focused on these two topic areas: (i) understanding comprehensively the CO{sub 2} affinity vs temperature, reversibility of CO{sub 2} affinity, and the role of water in order to select an optimum hydrotalcite composition for membrane preparation, and (ii) developing a membrane synthesis protocol for depositing the hydrotalcite material into a commercially available ceramic membrane from us. This annual report documents the progress we have made in these areas. In summary, the Year I study has demonstrated the technical feasibility of preparing a hydrotalcite. The proposed membrane synthesis protocol will be refined and optimized in Year II. In addition, surface analysis techniques employing FTIR and DRIFTS have been developed. These techniques have been applied to a hydrotalcite model compound to demonstrate our ability to screen hydrotalcite materials in terms of its composition and % of cation substitution. These techniques will be utilized in Year II to formulate an optimized hydrotalcite candidate for preparing a membrane with maximized CO{sub 2} transport at the proposed process condition.

Paul K.T. Liu

2001-09-30

222

CO2 SELECTIVE CERAMIC MEMBRANE FOR WATER-GAS SHIFT REACTION WITH CONCOMITANT RECOVERY OF CO2  

SciTech Connect

This quarterly report focuses on the two specific topics: (1) Reversibility of CO{sub 2} affinity of hydrotalcite materials; and (2)In-situ crystallization of hydrotalcite on commercial tubular ceramic membrane as substrate. The former relates to the foundation of the use of the hydrotalcite material as a membrane. The later addresses the first step of the membrane synthesis we propose. Our study concludes that the CO{sub 2} affinity of the hydrotalcite material is reversible at 150 C and in the presence of water using TG/MS. Additional study at a high pressure and/or high temperature will be performed to scope the operating range of the membrane. On the other hand, the in-situ crystallization is proven to be an effective first step for the hydrotalcite membrane synthesis. Our result indicates that about hydrotalcite covers about 50% of the porosity of the substrate, ideal as a seed for the 2nd step involving in-situ crystal growth. Our next quarterly report will report the result from the study on the 2nd step.

Unknown

2001-10-03

223

Intrinsic kinetics of the gas–solid Fischer–Tropsch and water gas shift reactions over a precipitated iron catalyst  

Microsoft Academic Search

The kinetics of the gas–solid Fischer–Tropsch synthesis over a commercial Fe–Cu–K–SiO2 catalyst was studied in a continuous spinning basket reactor. Experimental conditions were varied as follows: reactor pressure of 0.8–4.0MPa, H2\\/CO feed ratio of 0.25–4.0, and space velocity of 0.5–2.0×10?3Nm3kgcat?1s?1 at a constant temperature of 523K. A number of Langmuir–Hinshelwood–Hougen–Watson type rate equations were derived on the basis of a

Gerard P. van der Laan; Antonie A. C. M. Beenackers

2000-01-01

224

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst. (Quarterly) report, April 1, 1990--June 30, 1990.  

National Technical Information Service (NTIS)

Experiments on cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas were performed. Data have been collected at 220C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcat(center dot)min) with H(sub 2)/CO of 1.45 ...

I. C. Yates C. N. Satterfield

1990-01-01

225

Low Temperature Water–gas Shift: Differences in Oxidation States Observed with Partially Reduced Pt/MnOX and Pt/CeOX Catalysts Yield Differences in OH Group Reactivity  

SciTech Connect

The Pt-ceria synergy may be described as the dehydrogenation of formate formed on the surface of the partially reducible oxide (PRO), ceria, by Pt across the interface, with H{sub 2}O participating in the transition state. However, due to the rising costs of rare earth oxides like ceria, replacement by a less expensive partially reducible oxide, like manganese oxide, is desirable. In this contribution, a comparison between Pt/ceria and Pt/manganese oxide catalysts possessing comparable Pt dispersions reveals that there are significant differences and certain similarities in the nature of the two Pt/PRO catalysts. With ceria, partial reduction involves reduction of the oxide surface shell, with Ce{sup 3+} at the surface and Ce{sup 4+} in the bulk. In the case of manganese oxide, partial reduction results in a mixture of Mn{sup 3+} and Mn{sup 2+}, with Mn{sup 2+} located at the surface. With Pt/CeO{sub X}, a high density of defect-associated bridging OH groups react with CO to yield a high density of the formate intermediate. With Pt/MnO{sub X}, the fraction of reactive OH groups is low and much lower formate band intensities result upon CO adsorption; moreover, there is a greater fraction of OH groups that are essentially unreactive. Thus, much lower CO conversion rates are observed with Pt/MnO{sub X} during low temperature water-gas shift. As with ceria, increasing the Pt loading facilitates partial reduction of MnO{sub X} to lower temperature, indicating metal-oxide interactions should be taken into account.

Ribeiro, M.; Jacobs, G; Graham, U; Azzam, K; Linganiso, L; Davis, B

2010-01-01

226

Acceptance on the move: public reaction to shifting vaccination realities.  

PubMed

This review examines four events related to vaccination that have occurred in recent years: (a) the ongoing recovery from the MMR/Autism scare in the UK, (b) the upgrading of the Varicella vaccine to a universal childhood vaccine, (c) the major effort of authorities to provide a vaccine for A/H1N1 influenza and its rejection by the public, and, d) the current attempts to change the HPV vaccine target from girls only to boys and girls. All of these changes have been met with shifts in the public acceptance of the relevant vaccine. These shifts are characterized not only by the number of people willing to be vaccinated, but also by the attitudes and the motives related to acceptance. Examination of the interrelationship between changes in vaccination realities, and changes in acceptance patterns suggests that today, the public has a better understanding of vaccination, is acting in a more reflexive way, and is capable of changing attitudes and behavior. All together, changes in vaccination enhance debates and dialogues about vaccines, and lead to higher awareness and more conscious acceptance. PMID:22108039

Velan, Baruch

2011-12-01

227

Novel parallel reaction between a [1,5] sigmatropic alkylthio shift and a [1,5] sigmatropic hydrogen shift observed in a 2H-azepine ring.  

PubMed

Although heating 2-methoxy-2H-azepine results in a [1,5] sigmatropic hydrogen shift, heating 2-propylthio-2H-azepine results in not only a [1,5] sigmatropic hydrogen shift but also a [1,5] sigmatropic propylthio shift. Kinetic measurements reveal that migratory aptitudes increase in the order of MeO < H, PrS. These [1,5] sigmatropic shifts are discussed on the basis of ab initio DFT calculations. [reaction: see text]. PMID:17107049

Kubota, Yasuhiro; Satake, Kyosuke; Okamoto, Hideki; Kimura, Masaru

2006-11-23

228

Chemical and Physical Properties of Copper-Based Catalysts for CO Shift Reaction and Methanol Synthesis  

Microsoft Academic Search

The modern low-pressure methanol synthesis catalysts are based on copper-containing systems such as Cu\\/ZnO\\/Al2O3 and Cu\\/ZnO\\/Cr2O3 with various compositions. These catalysts are also highly active for the low-temperature CO shift reaction. For both reactions the nature of the active sites is still an open question.

Giovanna Ghiotti; Flora Boccuzzi

1987-01-01

229

Wall-catalyzed Water-Gas Shift Reaction in Multi-tubular, Pd and 80wt%Pd-20wt%Cu Membrane Reactors at 1173K  

SciTech Connect

Ignition and unburned hydrogen escaping from hydrogen jet diffusion flames diluted with nitrogen up to 70% were experimentally studied. The successful ignition locations were about 2/3 of the flame length above the jet exit for undiluted flames and moved much closer to the exit for diluted flames. For higher levels of dilution or higher flow rates, there existed a region within which a diluted hydrogen diffusion flame can be ignited and burns with a stable liftoff height. This is contrary to previous findings that pure and diluted hydrogen jet diffusion cannot achieve a stable lifted flame configuration. With liftoff, the flame is noisy and short with significant amount of unburned hydrogen escaping into the product gases. If ignition is initiated below this region, the flame propagates upstream quickly and attaches to the burner rim. Results from measurements of unburned hydrogen in the combustion products showed that the amount of unburned hydrogen increased as the nitrogen dilution level was increased. Thus, hydrogen diffusion flame diluted with nitrogen cannot burn completely.

Tran, P.X.; Chen, R.-H. (University of Central Florida, Orlando, FL)

2007-08-01

230

Genesis and evolution of surface species during Pt atomic layer deposition on oxide supports characterized by in-situ XAFS analysis and water-gas shift reaction  

Microsoft Academic Search

Platinum atomic layer deposition (ALD) using MeCpPtMe was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area AlO, TiO, and SrTiO supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles

Worajit Setthapun; W. Damion Williams; Seung Min Kim; Hao Feng; Jeffrey W. Elam; Federico A. Rabuffetti; Kenneth R. Poeppelmeier; Peter C. Stair; Eric A. Stach; Fabio H. Ribeiro; Jeffrey T. Miller; Christopher L. Marshall

2010-01-01

231

Mesoporous and nanostructured CeO 2 as supports of nano-sized gold catalysts for low-temperature water-gas shift reaction  

Microsoft Academic Search

Mesoporous particles and 1D nanorods of cerium oxides have been prepared by modifying the hydrothermal route of a surfactant-assisted controllable synthesis. Mesoporous cerias were obtained in a sealed glass vessel under continuous stirring, while ceria nanorods were obtained in a Teflon-lined autoclave without stirring. The mesoporous cerias did not show long-range mesoscopic organization, exhibiting a broad mesopore size distribution in

Zhong-Yong Yuan; Vasko Idakiev; Aurélien Vantomme; Tatyana Tabakova; Tie-Zhen Ren; Bao-Lian Su

2008-01-01

232

Evaluation of C-14 as a natural tracer for injected fluids at theAidlin sector of The Geysers geothermal system through modeling ofmineral-water-gas Reactions  

SciTech Connect

A reactive-transport model for 14C was developed to test itsapplicability to the Aidlin geothermal system. Using TOUGHREACT, wedeveloped a 1-D grid to evaluate the effects of water injection andsubsequent water-rock-gas interaction on the compositions of the producedfluids. A dual-permeability model of the fracture-matrix system was usedto describe reaction-transport processes in which the permeability of thefractures is many orders of magnitude higher than that of the rockmatrix. The geochemical system included the principal minerals(K-feldspar, plagioclase, calcite, silica polymorphs) of themetagraywackes that comprise the geothermal reservoir rocks. Initialsimulation results predict that the gas-phase CO2 in the reservoir willbecome more enriched in 14C as air-equilibrated injectate water (with amodern carbon signature) is incorporated into the system, and that thesechanges will precede accompanying decreases in reservoir temperature. Theeffects of injection on 14C in the rock matrix will be lessened somewhatbecause of the dissolution of matrix calcite with "dead"carbon.

Dobson, Patrick; Sonnenthal, Eric; Lewicki, Jennifer; Kennedy, Mack

2006-06-01

233

The scaling and shift of morphogen gene expression boundary in a nonlinear reaction diffusion system.  

PubMed

The scaling and shift of the gene expression boundary in a developing embryo are two key problems with regard to morphogen gradient formation in developmental biology. In this study, a bigradient model was applied to a nonlinear reaction diffusion system (NRDS) to investigate the location of morphogen gene expression boundary. In contrast to the traditional synthesis-diffusion-degradation model, the introduction of NRDS in this study contributes to the precise gene expression boundary at arbitrary location along the anterior-posterior axis other than simply midembryo even when the linear characteristic lengths of two morphogens are equal. The scaling location depends on the ratio of two morphogen influxes ([Formula: see text]) and concentrations ([Formula: see text]) as well as the nonlinear reaction diffusion parameters ([Formula: see text]). We also formulate a direct relationship between the shift in the gene expression boundary and the influx of morphogen and find that enhancing the morphogen influx is helpful to build up a robust gene expression boundary. By analyzing the robustness of the morphogen gene expression boundary and comparing with the relevant results in linear reaction diffusion system, we determine the precise range of the ratio of the two morphogen influxes with a lower shift in the morphogen gene expression boundary and increased system robustness. PMID:24824850

Li, Wei-Shen; Shao, Yuan-Zhi

2014-06-01

234

Sensitivity of Fischer-Tropsch Synthesis and Water-Gas Shift Catalystes to Poisons form High-Temperature High-Pressure Entrained-Flow (EF) Oxygen-Blown Gasifier Gasification of Coal\\/Biomass Mixtures  

Microsoft Academic Search

There has been a recent shift in interest in converting not only natural gas and coal derived syngas to Fischer-Tropsch synthesis products, but also converting biomass-derived syngas, as well as syngas derived from coal and biomass mixtures. As such, conventional catalysts based on iron and cobalt may not be suitable without proper development. This is because, while ash, sulfur compounds,

Burton Davis; Gary Jacobs; Wenping Ma; Khalid Azzam; Janet ChakkamadathilMohandas; Wilson Shafer

2009-01-01

235

Shift in the speed of reaction-diffusion equation with a cut-off: Pushed and bistable fronts  

NASA Astrophysics Data System (ADS)

We study the change in the speed of pushed and bistable fronts of the reaction-diffusion equation in the presence of a small cut-off. We give explicit formulas for the shift in the speed for arbitrary reaction terms f(u). The dependence of the speed shift on the cut-off parameter is a function of the front speed and profile in the absence of the cut-off. In order to determine the speed shift we solve the leading order approximation to the front profile u(z) in the neighborhood of the leading edge and use a variational principle for the speed. We apply the general formula to the Nagumo equation and recover the results which have been obtained recently by geometric analysis. The formulas given are of general validity and we also apply them to a class of reaction terms which have not been considered elsewhere.

Benguria, R. D.; Depassier, M. C.

2014-07-01

236

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts  

SciTech Connect

During this quarter, the high pressure (up to 100 atm), high temperature (up to 350{degrees}C) catalyst testing system was rebuilt with clean tubing, etc. A new preparation of MoS{sub 2} catalyst was carried out, and this catalyst will be doped with alkali and tested during the next quarter of research.

Klier, K.; Herman, R.G.; Richards-Babb, M.

1992-06-01

237

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts  

SciTech Connect

The objective of the proposed research is to investigate and develop a novel catalytic process for the conversion of coal-derived synthesis gas into high octane C{sub 1}-C{sub 4} alcohols, especially ethanol, by a highly selective and efficient pathway. (VC)

Klier, K.; Herman, R.G.

1992-03-01

238

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts  

SciTech Connect

During this quarter, the surface areas of various catalysts were determined. The surface area of the catalyst tested last quarter was determined for the undoped catalyst, the doped catalyst before testing, and the doped catalyst after testing. These surface areas were then compared with ones reported earlier. After testing under high temperature and high pressure conditions for 551 hours, there was a loss of surface area. This might be due possibly to agglomeration of cesium formate on the surface. Higher surface area catalysts were also produced. Two samples of MoS[sub 2] were synthesized with surface areas of 96 m2/g and 91 m2/g. These were obtained by varying the heating rate of MoS[sub 3] and the calcination temperature.

Klier, K.; Herman, R.G.; Deemer, M.

1992-12-01

239

Catalysis by Single Atoms: Water Gas Shift and Ethylene Hydrogenation.  

National Technical Information Service (NTIS)

Oxides are used extensively in industry for catalytic oxidation, oxidative dehydrogenation and catalytic combustion. Our work explores the following idea: by creating -VO-M-O-N-O bonds at the surface of an N-xO-y oxide, we can activate the middle oxygen a...

H. Metiu

2009-01-01

240

[Ethacrynic acid does not disrupt homeostatic reactions of the kidneys to hemodynamic shifts].  

PubMed

Arterial pressure and diuresis were determined in anesthetized dogs against the background of single (15 mg/kg) and continuous (5 mg/kg/rhr) intravenous administration of uregit (etacrylic acid). Acute hemodynamic shifts produced by compression of common carotid arteries, vena cava anterior, intravenous administration of ephedrine (1 mg/kg) or of sodium nitrite (3 mg/kg) were attended by an increased renal excretion of sodium, potasium and water in hypertension and their passage - in hypertension. Mechaninisms governing the express regulation of the water and electrolytes homeostasis and their relation to the active transpor of sodium are considered. Arguments in favour of a conjecture as to the localization of the mechanism responsible for the express regulation of the electrolytes homeostasis in acute hemodynamic shifts are advanced. PMID:1227904

Brancheveski?, L L

1975-01-01

241

Determination of shift in electrodic reaction rates due to the presence of stress  

NASA Astrophysics Data System (ADS)

An extension of Butler-Volmer formulation is proposed to determine the stress-induced changes in electrodic reaction rates. Gibbs-Duhem equation is used to determine the stress-dependent chemical potential and the corresponding change in the reaction rate. The scope of possible amplification or reduction in the reaction rates due to tensile and compressive stress fields is explored numerically. Though quantitative experimental validation remains to be pursued, behavioral agreement of the extended Butler-Volmer model with some observations made in the field of corrosive dissolution is established. Our numerical results also indicate that in addition to altering the speed of a reaction, a stress field can modify the shape of an anodic dissolution front. The effect of stress-generated surface patterns is also considered. It is well-established that a stress field can create surface patterns due to surface wrinkling or surface diffusion. We determine the possible significance of such patterns on the reaction rate, and identify the factors that may enhance their contribution to electrodic reaction rates.

Sarkar, Swarnavo; Aquino, Wilkins

2013-03-01

242

Protein-chromophore interactions: spectral shifts report the consequences of mutations in the bacterial photosynthetic reaction center  

NASA Astrophysics Data System (ADS)

Features of the low temperature absorption spectra of reaction centers from a large family of Rhodobacter capsulatus strains carrying site-specific mutations at the M208Tyr and L181Phe positions are presented. Through systematic analysis of the observed electronic transitions (with accompanying vibronic bands), the primary effects of many of the mutations have been identified and explained in terms of the reaction center structure. Some of the observed shifts are comparable to those that have been seen in other systems as a result of formation of hydrogen bonds or hexacoordination of the central Mg atom in bacteriochlorophyll species. Shifts of the Q y and Q x bacteriochlorophyll bands are also seen as a result of distant mutations near the quinones that change the charge distribution of the reaction center. We include kinetic data which show that the spectral and kinetic characteristics of different cofactors can be modulated depending on the particular amino acid that is substituted at the M208 site.

DiMagno, T. J.; Laible, P. D.; Reddy, N. R.; Small, G. J.; Norris, J. R.; Schiffer, M.; Hanson, D. K.

1998-08-01

243

Computational comparison of the kinetic stabilities of diamino- and diamidocarbenes in the 1,2-H shift reaction.  

PubMed

In this study, we performed several DFT, MP2, and BD(T) calculations on the 1,2-H shift reactions of two diaminocarbenes (1, 2) and a diamidocarbene (3) using the Gaussian 09 program. In Gaussian 09, the BD(T) method keyword requests a Brueckner doubles calculation including a perturbative triples contribution. Although N-heterocyclic carbenes (NHC) are typically known for their exceptional ?-donor abilities, recent studies have indicated that ?-interactions also play a role in the bonding between NHCs and transition metals or BX3 (X = H, OH, NH2, CH3, CN, NC, F, Cl, and Br) (Nemcsok et al. Organomet 23:3640-3646, 2004, Esrafili. J Mol Model 18:2003-2011, 2012). In order to study the importance of ?-interactions between carbenes and transition metals, Hobbs and co-workers (Hobbs et al. New J Chem 34:1295-1308, 2010) focused on the synthesis of NHCs with reduced-energy lowest unoccupied molecular orbitals. By introducing an oxalamide moiety into the heterocyclic backbone, they found the resulting carbene possessed higher electrophilicity than usual NHCs. According to our results, the N,N'-diamidocarbene should be more stable than the diaminocarbenes with respect to the 1,2-H shift reaction. PMID:23559095

Lai, Chin-Hung

2013-08-01

244

Reactivity of iron carbonyl complexes in a hydrated sodium-Y zeolite matrix and catalysis of the resulting hydride anion HFeâ(CO)âââ» for water-gas-shift reaction  

Microsoft Academic Search

Iron carbonyls Fe(CO)â, Feâ(CO)â, and Feâ(CO)ââ have been introduced into a hydrated Na-Y zeolite. Fe(CO)â was only weakly adsorbed on the zeolite. Feâ(CO)â and Feâ(CO)ââ were reactive in the hydrated zeolite cages to yield a hydride anion species HFeâ(CO)âââ» which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 cm⁻¹, UV-vis spectrum at 540 nm, and gas-phase

Masakazu Iwamoto; Shinichiro Nakamura; Hideto Kusano; Shuichi Kagawa

1986-01-01

245

A Effective Range Determination of Phase Shifts for the Elastic Proton HELIUM3 Reaction Between the Energies of 0 and 12 Mev  

Microsoft Academic Search

New measurements have been made of the observables from the {^3vec He(vec p, p)^3}He reaction in the energy range of 0 to 12 MeV. The new data were used in a global phase shift fit that utilized an energy dependent expansion of the phase shift parameters. The observable measurements were made possible through the construction of a new polarized ^3He

Marcus Tedrow Alley

1992-01-01

246

Side reaction of S-to-N acetamidomethyl shift during disulfide bond formation by iodine oxidation of S-acetamidomethyl-cysteine in a glutamine-containing peptide.  

PubMed

During the time course of disulfide bond formation by iodine oxidation (in a methanolic and hydrochloric acid solution) of a cysteinyl(S-acetamidomethyl)-glutaminyl tridecapeptide, we observed by ESI, FAB mass spectrometry (pseudo-molecular ion and ion-fragments) and 1H-NMR a side reaction due to a shift of the Acm leaving group from cysteine to the carboxamide side chain of glutamine. This type of Acm-shift at low level was described previously by L.W. Mendelson et al. (Int. J. Pept. Protein Res. 35:249-257) for an aspariginyl-cysteinyl(S-acetamidomethyl) peptide in an anhydrous hydrochloric solution. We report here the efficiency of glutamine as a scavenger to suppress the S-->N shift of the acetamidomethyl group during S-acetamidomethyl cleavage and sulfhydryl oxidation with iodine, as the folded tridecapeptide was obtained with the expected molecular weight. PMID:8838414

Lamthanh, H; Virelizier, H; Frayssinhes, D

1995-01-01

247

Stereochemistry of the intramolecular shift of the C-C bond in the reactions of cyclopropene compounds with electrophilic reagents  

SciTech Connect

The characteristic direction in the reactions of cyclopropene compounds with electrophilic reagents leads to the formation of acyclic products, which can in principle have the E and Z configurations. Earlier it was shown that the E isomer is formed preferentially in the reaction of 1-methylcyclopropene with bromine and almost exclusively in the reaction with N-bromosuccinimide. In the present communication the authors give stereochemical data on the reaction of 1-methylcyclopropene with deuterium chloride in CH/sub 3/COOD.

Kartashov, V.R.; Afanas'ev, P.S.; Skorobogatova, E.V.; Chertkov, V.A.; Ermolaeva, V.N.; Sergeev, N.M.; Zefirov, N.S.

1986-09-20

248

Isocyanide-based multicomponent reactions: concise synthesis of spirocyclic oxindoles with molecular complexity by using a [1,5]-hydrogen shift as the key step.  

PubMed

A concise multicomponent reaction of isocyanide, ?-substituted allenoate, and methyleneindolinone has been disclosed. This protocol provides a fast and straightforward approach to synthesize unusual tricyclic oxindoles in an efficient and atom-economic manner. Mechanistically, the present cycloaddition may proceed through a cascade sequence involving double Michael addition, double cyclization, double [1,5]-hydrogen shift, and group migration. The introduction of a special alkyl group to the allenoate is believed to play a key role in the cascade reaction. This method also features a broad substrate scope, which is particularly useful for the delivery of a large number of compounds. PMID:24700458

Su, Shikuan; Li, Chunju; Jia, Xueshun; Li, Jian

2014-05-12

249

Doppler shift as a tool for studies of resonant (p,n) reactions with RIBs: Spectroscopy of 7He  

SciTech Connect

We report on a new methods for studies of neutron rich systems through resonant (p,n) reaction with radioactive ion beams. A specific example of the spectroscopy of 7He and future application of the proposed methods are discussed.

Boutachkov, P.; Aprahamian, A.; Kolata, J. J.; Lamm, L. O.; Quinn, M.; Skorodumov, B. B.; Woehr, A. [Physics Department, University of Notre Dame, Notre Dame, IN 46556 (United States); Rogachev, G. V. [Physics Department, Florida State University, Tallahassee, FL 32306 (United States); Goldberg, V. Z.; Chubarian, G. [Texas A and M University, College Station, TX 77843 (United States); Becchetti, F. D.; Chen, Y. [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States); Bychowski, J. P. [Physics Department, Hope College, Holland, MI 49422 (United States); Physics Department, University of Notre Dame, Notre Dame, IN 46556 (United States); DeYoung, P. A. [Physics Department, Hope College, Holland, MI 49422 (United States); Peaslee, G. F. [Chemistry Department, Hope College, Holland, MI 49422 (United States)

2006-03-13

250

Intermediate partitioning kinetic isotope effects for the NIH shift of 4-hydroxyphenylpyruvate dioxygenase and the hydroxylation reaction of hydroxymandelate synthase reveal mechanistic complexity.  

PubMed

4-Hydroxyphenylpyruvate dioxygenase (HPPD) and hydroxymandelate synthase (HMS) are similar enzymes that catalyze complex dioxygenation reactions using the substrates 4-hydroxyphenylpyruvate (HPP) and dioxygen. Both enzymes decarboxylate HPP and then hydroxylate the resulting hydroxyphenylacetate (HPA). The hydroxylation reaction catalyzed by HPPD displaces the aceto substituent of HPA in a 1,2-shift to form 2,5-dihydroxyphenylacetate (homogentisate, HG), whereas the hydroxylation reaction of HMS places a hydroxyl on the benzylic carbon forming 3'-hydroxyphenylacetate (S-hydroxymandelate, HMA) without ensuing chemistry. The wild-type form of HPPD and variants of both enzymes uncouple to form both native and non-native products. We have used intermediate partitioning to probe bifurcating steps that form these products by substituting deuteriums for protiums at the benzylic position of the HPP substrate. These substitutions result in altered ratios of products that can be used to calculate kinetic isotope effects (KIE) for the formation of a specific product. For HPPD, secondary normal KIEs indicate that cleavage of the bond in the displacement reaction prior to the shift occurs by a homolytic mechanism. NMR analysis of HG derived from HPPD reacting with enantiomerically pure R-3'-deutero-HPP indicates that no rotation about the bond to the radical occurs, suggesting that collapse of the biradical intermediate is rapid. The production of HMA was observed in HMS and HPPD variant reactions. HMS hydroxylates to form exclusively S-hydroxymandelate. When HMS is reacted with R-3'-deutero-HPP, the observed kinetic isotope effect represents geometry changes in the initial transition state for the nonabstracted proton. These data show evidence of sp(3) hybridization in a HPPD variant and sp(2) hybridization in HMS variants, suggesting that HMS stabilizes a more advanced transition state in order to catalyze H-atom abstraction. PMID:23941465

Shah, Dhara D; Conrad, John A; Moran, Graham R

2013-09-01

251

Free-Surface Turbulence and Air-Water Gas Exchange.  

National Technical Information Service (NTIS)

This thesis investigates the physical mechanisms of air-water gas transfer through direct measurements of turbulence at the air-water interface. To enable this study, a new approach to the particle image velocimetry (PIV) technique is developed in order t...

S. P. McKenna

2000-01-01

252

Characterization of reaction between ZnO and COS  

SciTech Connect

In order to understand the behavior of COS in a ZnO desulfurization reactor, the reaction between ZnO and COS was studied in the presence of gases which compose a coal-derived gas. The behavior of COS in the reaction zone of a ZnO packed bed can be predicted as follows: H{sub 2}S in coal-derived gas reacts more easily with ZnO than COS; most of COS is converted to H{sub 2}S by catalytic hydrolysis and then reacts with ZnO, although a part of COS may react directly with ZnO; H{sub 2} accelerates the conversion of COS to H{sub 2}S; the water-gas shift reaction accelerates the reaction between ZnO and COS; and CO{sub 2} does not affect the reaction.

Sasaoka, Eiji [Okayama Prefectural Univ., Soja, Okayama (Japan). Faculty of Health and Welfare Science] [Okayama Prefectural Univ., Soja, Okayama (Japan). Faculty of Health and Welfare Science; Taniguchi, Kazuo; Uddin, M.A.; Hirano, Shigeru; Kasaoka, Shigeaki; Sakata, Yusaku [Okayama Univ. (Japan). Faculty of Engineering] [Okayama Univ. (Japan). Faculty of Engineering

1996-07-01

253

High-pressure catalytic reactions over single-crystal metal surfaces  

NASA Astrophysics Data System (ADS)

Studies dealing with high-pressure catalytic reactions over single-crystal surfaces are reviewed. The coupling of an apparatus for the measurement of reaction kinetics at elevated pressures with an ultrahigh vacuum system for surface analysis allows detailed study of structure sensitivity, the effects of promoters and inhibitors on catalytic activity, and, in certain cases, identification of reaction intermediates by post-reaction surface analysis. Examples are provided which demonstrate the relevance of single-crystal studies for modeling the behaviour of high-surface-area supported catalysts. Studies of CO methanation and CO oxidation over single-crystal surfaces provide convincing evidence that these reactions are structure insensitive. For structure-sensitive reactions (ammonia synthesis, alkane hydrogenolysis, alkane isomerization, water-gas shift reaction, etc.) model single-crystal studies allow correlations to be established between surface structure and catalytic activity. The effects of both electronegative (S and P) and electropositive (alkali metals) impurities upon the catalytic activity of metal single crystals for ammonia synthesis, CO methanation, alkane hydrogenolysis, ethylene epoxidation and water-gas shift are discussed. The roles of "ensemble" and "ligand" effects in bimetallic catalysts are examined in light of data obtained using surfaces prepared by vapor-depositing one metal onto a crystal face of a dissimilar metal.

Rodriguez, JoséA.; Wayne Goodman, D.

1991-11-01

254

Computational Chemistry-Based Identification of Ultra-Low Temperature Water-Gas-Shift Catalysts  

SciTech Connect

The current work seeks to identify novel, catalytically-active, stable, poison-resistant LWGS catalysts that retain the superior activity typical of conventional Cu catalysts but can be operated at similar or lower temperatures. A database for the Binding Energies (BEs) of the LWGS relevant species, namely CO, O and OH on the most-stable, close-packed facets of a set of 17 catalytically relevant transition metals was established. This BE data and a database of previously established segregation energies was utilized to predict the stability of bimetallic NSAs that could be synthesized by combinations of the 17 parent transition metals. NSAs that were potentially stable both in vacuo and under the influence of strong-binding WGS intermediates were then selected for adsorption studies. A set of 40 NSAs were identified that satisfied all three screener criteria and the binding energies of CO, O and OH were calculated on a set of 66, 43 and 79 NSA candidates respectively. Several NSAs were found that bound intermediates weaker than the monometallic catalysts and were thus potentially poison-resistant. Finally, kinetic studies were performed and resulted in the discovery of a specific NSA-based bimetallic catalyst Cu/Pt that is potentially a promising LWGS catalyst. This stable Cu/Pt subsurface alloy is expected to provide facile H{sub 2}O activation and remain relatively resistant from the poisoning by CO, S and formate intermediates.

Manos Mavrikakis

2008-08-31

255

Measuring electronic coupling in the reaction center of purple photosynthetic bacteria by two-color, three-pulse photon echo peak shift spectroscopy.  

PubMed

One- and two-color, three-pulse photon echo peak shift spectroscopy (1C and 2C3PEPS) was used to estimate the electronic coupling between the accessory bacteriochlorophyll (B) and the bacteriopheophytin (H) in the reaction center of the purple photosynthetic bacterium Rhodobacter sphaeroides as approximately 170 +/- 30 cm-1. This is the first direct experimental determination of this parameter; it is within the range of values found in previously published calculations. The 1C3PEPS signal of the Qy band of the bacteriochlorophyll B shows that it is weakly coupled to nuclear motions of the bath, whereas the 1C3PEPS signal of the Qy band of the bacteriopheophytin, H, shows that it is more strongly coupled to the bath, but has minimal inhomogeneous broadening. Our simulations capture the major features of the data with the theoretical framework developed in our group to separately calculate the response functions and population dynamics. PMID:17530796

Parkinson, Dilworth Y; Lee, Hohjai; Fleming, Graham R

2007-06-28

256

Exploring 1,2-Hydrogen Shift in Silicon Nanoparticles: Reaction Kinetics from Quantum Chemical Calculations and Derivation of Transition State Group Additivity Database  

NASA Astrophysics Data System (ADS)

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, Ã, and the activation energy, Ea, were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict à and Ea. The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative à value and the Evans-Polanyi correlation to predict Ea. The structural factors that have the most pronounced effect on à and Ea were considered, and the presence of rings was shown to influence these values strongly.

Adamczyk, Andrew J.; Reyniers, Marie-Francoise; Marin, Guy B.; Broadbelt, Linda J.

2009-09-01

257

Exploring 1,2-hydrogen shift in silicon nanoparticles: reaction kinetics from quantum chemical calculations and derivation of transition state group additivity database.  

PubMed

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, A, and the activation energy, E(a), were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict A and E(a). The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative A value and the Evans-Polanyi correlation to predict E(a). The structural factors that have the most pronounced effect on A and E(a) were considered, and the presence of rings was shown to influence these values strongly. PMID:19764804

Adamczyk, Andrew J; Reyniers, Marie-Francoise; Marin, Guy B; Broadbelt, Linda J

2009-10-15

258

Effect of time pressure on attentional shift and anticipatory postural control during unilateral shoulder abduction reactions in an oddball-like paradigm  

PubMed Central

Background The effect of time pressure on attentional shift and anticipatory postural control was investigated during unilateral shoulder abduction reactions in an oddball-like paradigm. Methods A cue signal (S1) - imperative signal (S2) sequence was repeated with various S2-S1 intervals (1.0, 1.5, and 2.0 s). S2 comprised target and non-target stimuli presented at the position (9° to the left or the right) indicated by S1. Right shoulder abduction was performed only in response to target stimuli, which were presented with a 30% probability. The P1, N1, N2, and P3 components of event-related potentials were analyzed, and onset times of postural muscles (electromyographic activity of erector spinae and gluteus medius) were quantified with respect to middle deltoid activation. Results There was no significant effect of S2-S1 interval on the latency or amplitude of P1, N1, or N2. The percentage of subjects with bimodal P3 peaks was significantly smaller and the slope of the P3 waveform in the 100 ms after the first peak was significantly steeper with a 1.0-s S2-S1 interval than with a 1.5- or 2.0-s S2-S1 interval. The onset of postural muscle activity was significantly later in the shorter interval conditions. Conclusions These results suggest that with a shorter S2-S1 interval, that is, higher time pressure, attention was allocated to hasten the latter part of cognitive processing that may relate to attentional shift from S2 to next S1, which led to insufficient postural preparation associated with arm movement and anticipatory attention directed to S2.

2014-01-01

259

13C chemical shift map of the active cofactors in photosynthetic reaction centers of Rhodobacter sphaeroides revealed by photo-CIDNP MAS NMR.  

PubMed

13C photo-CIDNP MAS NMR studies have been performed on reaction centers (RCs) of Rhodobacter sphaeroides wild type (WT) that have been selectively labeled with an isotope using [5-13C]-delta-aminolevulinic acid.HCl in all the BChl and BPhe cofactors at positions C-4, C-5, C-9, C-10, C-14, C-15, C-16, and C-20. 13C CP/MAS NMR and 13C-13C dipolar correlation photo-CIDNP MAS NMR provide a chemical shift map of the cofactors involved in the electron transfer process in the RC at the atomic scale. The 13C-13C dipolar correlation photo-CIDNP spectra reveal three strong components, originating from two BChl cofactors, called P1 and P2 and assigned to the special pair, as well as one BPhe, PhiA. In addition, there is a weak component observed that arises from a third BChl cofactor, denoted P3, which appears to originate from the accessory BChl BA. An almost complete set of assignments of all the aromatic carbon atoms in the macrocycles of BChl and BPhe is achieved in combination with previous photo-CIDNP studies on site-directed BChl/BPhe-labeled RCs [Schulten, E. A. M., Matysik, J., Alia, Kiihne, S., Raap, J., Lugtenburg, J., Gast, P., Hoff, A. J., and de Groot, H. J. M. (2002) Biochemistry 41, 8708-8717], allowing a comprehensive map of the ground-state electronic structure of the photochemically active cofactors to be constructed for the first time. The reasons for the anomaly of P2 and the origin of the polarization on P3 are discussed. PMID:17630781

Prakash, Shipra; Alia, A; Gast, Peter; de Groot, Huub J M; Jeschke, Gunnar; Matysik, Jörg

2007-08-01

260

The Effect of Rain on Air-Water Gas Exchange  

NASA Technical Reports Server (NTRS)

The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

Ho, David T.; Bliven, Larry F.; Wanninkhof, Rik; Schlosser, Peter

1997-01-01

261

Shift Registers  

NSDL National Science Digital Library

All About Circuits is a website that âÂÂprovides a series of online textbooks covering electricity and electronics.â Written by Tony R. Kuphaldt, the textbooks available here are wonderful resources for students, teachers, and anyone who is interested in learning more about electronics. This specific section, Shift Registers, is the twelfth chapter in Volume IV âÂÂDigital. A few of the topics covered in this chapter include: Serial-in, serial-out shift register, Parallel-in, parallel-out shift register, and Ring counters. Diagrams and detailed descriptions of concepts are included throughout the chapter to provide users with a comprehensive lesson. Visitors to the site are also encouraged to discuss concepts and topics using the All About Circuits discussion forums (registration with the site is required to post materials).

Kuphaldt, Tony R.

2008-07-18

262

Generation of quaternary centers by reductive cross-coupling: shifting of regioselectivity in a subset of allylic alcohol-based coupling reactions  

Microsoft Academic Search

Regioselective titanium alkoxide-mediated reductive cross-coupling reactions of allylic alcohols with vinylsilanes and imines have previously been demonstrated to proceed with allylic transposition by formal metallo-[3,3]-rearrangement [thought to proceed by a sequence of: (1) directed carbometalation, and (2) syn-elimination]. While many examples have been described that support this reaction path, a collection of substrates have recently been identified that react by

Dexi Yang; Justin K. Belardi; Glenn C. Micalizio

2011-01-01

263

Fluid Shifts  

NASA Technical Reports Server (NTRS)

NASA is focusing on long-duration missions on the International Space Station (ISS) and future exploration-class missions beyond low Earth orbit. Visual acuity changes observed after short-duration missions were largely transient, but more than 30% of ISS astronauts experience more profound, chronic changes with objective structural and functional findings such as papilledema and choroidal folds. Globe flattening, optic nerve sheath dilation, and optic nerve tortuosity also are apparent. This pattern is referred to as the visual impairment and intracranial pressure (VIIP) syndrome. VIIP signs and symptoms, as well as postflight lumbar puncture data, suggest that elevated intracranial pressure (ICP) may be associated with the space flight-induced cephalad fluid shifts, but this hypothesis has not been tested. The purpose of this study is to characterize fluid distribution and compartmentalization associated with long-duration space flight, and to correlate these findings with vision changes and other elements of the VIIP syndrome. We also seek to determine whether the magnitude of fluid shifts during space flight, as well as the VIIP-related effects of those shifts, is predicted by the crewmember's pre-flight condition and responses to acute hemodynamic manipulations (such as head-down tilt). Lastly, we will evaluate the patterns of fluid distribution in ISS astronauts during acute reversal of fluid shifts through application of lower body negative pressure (LBNP) interventions to characterize and explain general and individual responses. We will examine a variety of physiologic variables in 10 long-duration ISS crewmembers using the test conditions and timeline presented in the Figure below. Measures include: (1) fluid compartmentalization (total body water by D2O, extracellular fluid by NaBr, intracellular fluid by calculation, plasma volume by CO rebreathe, interstitial fluid by calculation); (2) forehead/eyelids, tibia, calcaneus tissue thickness (by ultrasound); (3) vascular dimensions by ultrasound (jugular veins, cerebral and carotid arteries, vertebral arteries and veins, portal vein); (4) vascular dynamics by MRI (head/neck blood flow, cerebrospinal fluid pulsatility); (5) ocular measures (optical coherence tomography, intraocular pressure, 2-dimensional ultrasound including optic nerve sheath diameter, globe flattening, and retina-choroid thickness, Doppler ultrasound of ophthalmic and retinal arteries, and veins); (6) cardiac variables by ultrasound (inferior vena cava, tricuspid flow and tissue Doppler, pulmonic valve, stroke volume, right heart dimensions and function, four-chamber views); and (7) ICP measures (tympanic membrane displacement, distortion-product otoacoustic emissions, and ICP calculated by MRI). On the ground, acute head-down tilt will induce cephalad fluid shifts, whereas LBNP will oppose these shifts. Controlled Mueller maneuvers will manipulate cardiovascular variables. Through interventions applied before, during, and after flight, we intend to fully evaluate the relationship between fluid shifts and the VIIP syndrome. This study has been selected for flight implementation and is one of the candidate investigations being considered for the one year mission.

Stenger, Michael; Hargens, A.; Dulchavsky, S.; Ebert, D.; Lee, S.; Sargsyan, A.; Martin, D.; Lui, J.; Macias, B.; Arbeille, P.; Platts, S.

2014-01-01

264

Generation of quaternary centers by reductive cross-coupling: shifting of regioselectivity in a subset of allylic alcohol-based coupling reactions  

PubMed Central

Regioselective titanium alkoxide-mediated reductive cross-coupling reactions of allylic alcohols with vinylsilanes and imines have previously been demonstrated to proceed with allylic transposition by formal metallo-[3,3]-rearrangement [thought to proceed by a sequence of: 1) directed carbometalation, and 2) syn-elimination]. While many examples have been described that support this reaction path, a collection of substrates have recently been identified that react by way of an alternative pathway, delivering a concise convergent route to coupled products bearing a quaternary center.

Yang, Dexi; Belardi, Justin K.; Micalizio, Glenn C.

2011-01-01

265

Generation of quaternary centers by reductive cross-coupling: shifting of regioselectivity in a subset of allylic alcohol-based coupling reactions.  

PubMed

Regioselective titanium alkoxide-mediated reductive cross-coupling reactions of allylic alcohols with vinylsilanes and imines have previously been demonstrated to proceed with allylic transposition by formal metallo-[3,3]-rearrangement [thought to proceed by a sequence of: 1) directed carbometalation, and 2) syn-elimination]. While many examples have been described that support this reaction path, a collection of substrates have recently been identified that react by way of an alternative pathway, delivering a concise convergent route to coupled products bearing a quaternary center. PMID:21666832

Yang, Dexi; Belardi, Justin K; Micalizio, Glenn C

2011-04-27

266

KINETIC UNDERSTANDING OF THE SYNGAS-TO-DME REACTION SYSTEM AND ITS IMPLICATIONS TO PROCESS AND ECONOMICS  

SciTech Connect

In a single-step synthesis gas-to-dimethyl ether process, synthesis gas (or syngas, a mixture of H{sub 2} and CO) is converted into dimethyl ether (DME) in a single reactor. The three reactions involved in this process, methanol synthesis, methanol dehydration and water gas shift, form an interesting reaction network. The interplay among these three reactions results in excellent syngas conversion or reactor productivity. A fundamental understanding of this interplay helps to explain many experimental and simulation observations, to identify optimal reaction conditions, and to provide guidelines for process development. The higher syngas conversion or reactor productivity in the syngas-to-DME reaction system, compared to that in the syngas-to-methanol reaction system, is referred to as chemical synergy. This synergy exhibits a strong dependence on the composition of the reactor feed. To demonstrate the extent of this dependence, simulations with adjusted activity for each reaction were performed to reveal the relative rate of each reaction. The results show that the water gas shift reaction is the most rapid, being practically controlled by the equilibrium. Both methanol synthesis and methanol dehydration reactions are kinetically controlled. The kinetics of the dehydration reactions is greater than that of the methanol synthesis reaction in the CO-rich regime. However, the rates of these two reactions come closer as the H{sub 2} concentration in the reactor feed increases. The role of the dehydration reaction is to remove the equilibrium barrier for the methanol synthesis reaction. The role of the water gas shift reaction is more complex; it helps the kinetics of methanol dehydration by keeping the water concentration low, which in turn enhances methanol synthesis. It also readjusts the H{sub 2}:CO ratio in the reactor as the reactions proceed. In the CO-rich regime, the water gas shift reaction supplements the limiting reactant, H{sub 2}, by reacting water with CO. This enhances both the kinetics and thermodynamic driving force of the methanol synthesis reaction. In the H{sub 2}-rich regime, water gas shift consumes the limiting reactant, CO, which harms both the kinetics and thermodynamics of methanol synthesis. An understanding of these complex roles of the methanol dehydration and water gas shift reactions and of their dependence on the syngas composition explains why the synergy is high in the CO-rich regime, but decreases with increasing H{sub 2} or CO{sub 2} content in the reactor feed. The methanol equivalent productivity of the syngas-to-DME reactor is also a strong function of the reactor feed. A mathematical approach was developed to understand this dependence. The approach divides a power law type of rate equation into two terms, the kinetic term (the rate of the forward reaction) and the thermodynamics or driving force term (1- approach to equilibrium). The equations for the best feed composition for each term were derived. The approach was developed for the single reaction system, and then extended to the syngas-to-DME reaction system. The equations provide insights into why and how the methanol synthesis in the syngasto-DME system depends on the other two reactions. They can also be used to calculate the best feed composition for a given conversion. The analysis shows that for typical commercial syngas conversion, the optimal H{sub 2}:CO ratio for the LPDME{trademark} reactor is around 1-to-1, in good agreement with the results from the simulation. While the 1-to-1 feed provides a good foundation for some process configurations, it does not match the composition of natural gas-derived syngas, which typically has a H{sub 2}:CO ratio of 2:1 or greater. The process would also produce one CO{sub 2} molecule for every DME product, both a materials utilization and an environmental problem. However, recycling CO{sub 2} to the syngas generation unit can solve all of these problems. Integration schemes with different syngas generation technologies (dry reforming, steam methane reforming and partial oxidation) were

Xiang-Dong Peng

2002-12-01

267

Characteristic features of Raman band shifts of scheelite-type molybdate catalysts exchanged with the {sup 18}O tracer via redox reactions  

SciTech Connect

The oxide oxygen of scheelite-type {alpha}-MnMoO{sub 4}, {beta}-CoMoO{sub 4}, and {alpha}-Bi{sub 2}Mo{sub 3}O{sub 12} were exchanged with the {sup 18}O tracer using a reduction-oxidation method. The Raman band shifts in the spectra of these catalysts were examined. Normal coordination analysis and diatomic approximation reported in previous literature have shown that the Raman bands are correlated to the Mo-O stretchings of these molybdate catalysts. With {alpha}-MnMoO{sub 4}, the band at 945 cm{sup {minus}1} corresponding to the shortest Mo=O of a Mo tetrahedron was exchanged preferentially while with {beta}-CoMoO{sub 4} which is isotypic with {alpha}-MnMoO{sub 4}, all the oxygen of Mo tetrahedra were exchanged with an increase in the {sup 18}O exchange. With {alpha}-Bi{sub 2}Mo{sub 3}O{sub 12} which has two twin Mo tetrahedra, the bands at 865 and 845 cm{sup {minus}1} were shifted preferentially. Oxygen insertion seems to take place more selectively on the Mo tetrahedron sites where Bi ions are present. A comparative study and discussions on the preferential exchange in these molybdates and reoxidation sites have been reported here. 29 refs., 7 figs., 7 tabs.

Ono, Takehiko; Ogata, Nobuaki; Miyaryo, Yasuhiro [Univ. of Osaka Prefecture (Japan)] [Univ. of Osaka Prefecture (Japan)

1996-06-01

268

CHLORIDE POISONING OF WATER GAS SHIFT ACTIVITY ON NICKEL CATALYSTS DURING STEAM REFORMING. (R822721C633)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

269

CHLORIDE POISONING OF WATER GAS SHIFT ACTIVITY ON NICKEL CATALYSTS DURING STEAM REFORMING. (R826694C633)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

270

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, December 1991--February 1992  

SciTech Connect

The objective of the proposed research is to investigate and develop a novel catalytic process for the conversion of coal-derived synthesis gas into high octane C{sub 1}-C{sub 4} alcohols, especially ethanol, by a highly selective and efficient pathway. (VC)

Klier, K.; Herman, R.G.

1992-03-01

271

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, March 1994--May 1994  

SciTech Connect

During this quarter, the cesium formate-doped and the undoped molybdenum disulfide previously prepared were sent out to Galbraith Laboratories for elemental analysis for cesium, molybdenum, and sulfur. A new Na/MoS{sub 2} catalyst was prepared under an inert atmosphere by an intercalation technique using sodium metal dissolved in liquid ammonia. This sample will be fully characterized. An all-glass apparatus was constructed for carrying out systematic intercalation procedures with alkali metals dissolved in liquid ammonia. This apparatus will insure that the dispersed catalysts are prepared in an oxygen/moisture-free environment. The stainless steel continuous flow high pressure/high temperature catalyst testing system was rebuilt and the analytical end of the unit was upgraded.

Klier, K; Herman, R.G.; Deemer, M.

1994-06-01

272

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, September 1992--November 1992  

SciTech Connect

During this quarter, the surface areas of various catalysts were determined. The surface area of the catalyst tested last quarter was determined for the undoped catalyst, the doped catalyst before testing, and the doped catalyst after testing. These surface areas were then compared with ones reported earlier. After testing under high temperature and high pressure conditions for 551 hours, there was a loss of surface area. This might be due possibly to agglomeration of cesium formate on the surface. Higher surface area catalysts were also produced. Two samples of MoS{sub 2} were synthesized with surface areas of 96 m2/g and 91 m2/g. These were obtained by varying the heating rate of MoS{sub 3} and the calcination temperature.

Klier, K.; Herman, R.G.; Deemer, M.

1992-12-01

273

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, March--May 1992  

SciTech Connect

During this quarter, the high pressure (up to 100 atm), high temperature (up to 350{degrees}C) catalyst testing system was rebuilt with clean tubing, etc. A new preparation of MoS{sub 2} catalyst was carried out, and this catalyst will be doped with alkali and tested during the next quarter of research.

Klier, K.; Herman, R.G.; Richards-Babb, M.

1992-06-01

274

Advanced Water-Gas Shift Membrane Reactor. Final Technical Report, 1 July 2005 to 30 June 2007.  

National Technical Information Service (NTIS)

The overall objectives for this project were: (1) to identify a suitable PdCu tri-metallic alloy membrane with high stability and commercially relevant hydrogen permeation in the presence of trace amounts of carbon monoxide and sulfur; and (2) to identify...

R. Radhakrishnan R. Willigan S. Opalka S. C. Emerson T. H. Vanderspurt

2007-01-01

275

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, March 1993--May 1993.  

National Technical Information Service (NTIS)

Study of preparation of MoS(sub 3), decomposition to form MoS(sub 2), and the Cs-containing reagents and techniques to achieve surface doping of the MoS(sub 2) with Cs was begun. Goal is to achieve a high surface area catalyst containing lower quantities ...

K. Klier R. G. Herman M. Richards-Babb

1993-01-01

276

Ethanol synthesis and water gas shift over bifunctional sulfide catalysts. Technical progress report, March 1993--May 1993  

SciTech Connect

Study of preparation of MoS{sub 3}, decomposition to form MoS{sub 2}, and the Cs-containing reagents and techniques to achieve surface doping of the MoS{sub 2} with Cs was begun. Goal is to achieve a high surface area catalyst containing lower quantities of the Cs promoter in a highly dispersed state. Using high resolution electron spectroscopy for chemical analysis and solid state Extended Hueckel (EH) theory investigation and interpretation of electronic structure of MoS{sub 2} (hexagonal 2H form, 2 MoS{sub 2} molecules/unit cell) was carried out. The theoretical valence band of MoS{sub 2} was obtained by modification of density of states. Qualitative agreement theoretical and experimental MoS{sub 2} valence bands was obtained after parameterization of EH input ionization potentials H{sub ii} and Slater-type orbital (STO) double zeta coefficients c{sub i}. Theoretical energy dispersion curves 2-D and 3-D MoS{sub 2} also compared well with experimental energy dispersion curves. Highest occupied band of valence band is shown to consist of contributions not only from Mo 4d{sub z2} orbitals but also from Mo 4d{sub xy} and Mo 4d{sub x2-y2} orbitals. The theoretical systems 2-D MoS{sub 2} and 3-D MoS{sub 2}, containing zero for the former and an infinite number of Van der Waals gaps for the latter, exhibit direct and indirect gaps, respectively. Nature of 2H-MoS{sub 2} indirect gap is found to be directly linked to the interaction of crystal orbitals across Van der Waals gap between adjacent layers of MoS{sub 2} in the realistic 3-D model. Thus, the electronic properties and ability of adsorbing and activating hydrogen of very small and thin particles of MoS{sub 2} might be expected to be different from large bulk particles of MoS{sub 2}.

Klier, K.; Herman, R.G.; Richards-Babb, M.

1993-06-01

277

Thermochemical cyclic system for splitting water and/or carbon dioxide by means of cerium compounds and reactions useful therein  

DOEpatents

A thermochemical cyclic process for producing hydrogen from water comprises reacting ceric oxide with monobasic or dibasic alkali metal phosphate to yield a solid reaction product, oxygen and water. The solid reaction product, alkali metal carbonate or bicarbonate, and water, are reacted to yield hydrogen, ceric oxide, carbon dioxide and trialkali metal phosphate. Ceric oxide is recycled. Trialkali metal phosphate, carbon dioxide and water are reacted to yield monobasic or dibasic alkali metal phosphate and alkali metal bicarbonate, which are recycled. The cylic process can be modified for producing carbon monoxide from carbon dioxide by reacting the alkali metal cerous phosphate and alkali metal carbonate or bicarbonate in the absence of water to produce carbon monoxide, ceric oxide, carbon dioxide and trialkali metal phosphate. Carbon monoxide can be converted to hydrogen by the water gas shift reaction.

Bamberger, Carlos E. (Oak Ridge, TN); Robinson, Paul R. (Knoxville, TN)

1980-01-01

278

The reaction of European lobster larvae (Homarus gammarus) to different quality food: effects of ontogenetic shifts and pre-feeding history.  

PubMed

Young larval stages of many organisms represent bottlenecks in the life-history of many species. The high mortality commonly observed in, for example, decapod larvae has often been linked to poor nutrition, with most studies focussing on food quantity. Here, we focus instead on the effects of quality and have investigated its effects on the nutritional condition of lobster larvae. We established a tri-trophic food chain consisting of the cryptophyte Rhodomonas salina, the calanoid copepod Acartia tonsa and larvae of the European lobster Homarus gammarus. In a set of experiments, we manipulated the C:N:P stoichiometry of the primary producers, and accordingly those of the primary consumer. In a first experiment, R. salina was grown under N- and P-limitation and the nutrient content of the algae was manipulated by addition of the limiting nutrient to create a food quality gradient. In a second experiment, the effect on lobster larvae of long- and short-term exposure to food of varying quality during ontogenetic development was investigated. The condition of the lobster larvae was negatively affected even by subtle N- and P-nutrient limitations of the algae. Furthermore, younger lobster larvae were more vulnerable to nutrient limitation than older ones, suggesting an ontogenetic shift in the capacity of lobster larvae to cope with low quality food. The results presented here might have substantial consequences for the survival of lobster larvae in the field, as, in the light of future climate change and re-oligotrophication of the North Sea, lobster larvae might face marked changes in temperature and nutrient conditions, thus significantly altering their condition and growth. PMID:24072442

Schoo, Katherina L; Aberle, Nicole; Malzahn, Arne M; Schmalenbach, Isabel; Boersma, Maarten

2014-02-01

279

Turbulence and Wave Breaking Effects on Air-Water Gas Exchange  

Microsoft Academic Search

We present an experimental characterization of the effects of turbulence and breaking gravity waves on air-water gas exchange in standing waves. We identify two regimes that govern aeration rates: turbulent transport when no wave breaking occurs and bubble dominated transport when wave breaking occurs. In both regimes, we correlate the qualitative changes in the aeration rate with corresponding changes in

Evelyn J. Boettcher; Jay Fineberg; Daniel P. Lathrop

2000-01-01

280

Process of producing water gas and extracting oil from oil shale  

Microsoft Academic Search

A process is described of producing water gas and extracting oil from oil shale which consists in igniting a confined body of shale at its upper surface, admitting air for combustion above the confined ignited body, drawing the steam and combustion gases downwardly through the shale body to decompose the carbonaceous matter and kerogen contained within the shale by the

A. Schilling; R. Sachse; D. Liamin; T. Callaert

1929-01-01

281

On mechanisms of rain-induced air-water gas exchange  

NASA Astrophysics Data System (ADS)

Previous studies have shown that rain significantly enhances the rate of air-water gas exchange. However, even though an empirical correlation between the rain rate or kinetic energy flux (KEF) delivered to the water surface by rain and the gas transfer velocity has been established, the physical mechanisms underlying the gas exchange enhancement remain unexamined. During a series of experiments, the processes behind rain-induced air-water gas exchange were examined at NASA's Rain-Sea Interaction Facility (RSIF). Gas transfer velocities for helium (He), nitrous oxide (N2O), and sulfur hexafluoride (SF6) were determined for 22 rain rates (13.6 to 115.2 mm h-1) and three drop sizes (2.3, 2.8, 4.2 mm). Bubbles generated by the raindrops were characterized using a video-microscope technique, and surface waves were characterized by a capacitance probe. Additionally, rain-generated turbulence was inferred from friction velocities u*w calculated from KEF. Together, these data suggest that rain-induced air-water gas exchange is mainly caused by turbulence-driven exchange processes, with bubbles contributing anywhere from 0 to 20%, depending on rain rate, drop size, and the solubility of the gas tracer. Furthermore, the data confirm that the previously selected variable KEF is the best correlate for rain-induced air-water gas exchange.

Ho, David T.; Asher, William E.; Bliven, Larry F.; Schlosser, Peter; Gordan, Elizabeth L.

2000-10-01

282

Oxygen-regulated mRNAs for light-harvesting and reaction center complexes and for bacteriochlorophyll and carotenoid biosynthesis in Rhodobacter capsulatus during the shift from anaerobic to aerobic growth.  

PubMed Central

The stability and regulation by oxygen of mRNAs for the photosynthetic apparatus in Rhodobacter capsulatus have been studied by using proflavin to inhibit transcription and by shifting cells from anaerobic to aerobic conditions. The results from the inhibition experiments show that the mRNA for the light-harvesting LH-II polypeptides (beta, alpha) is more stable than that for the light-harvesting LH-I polypeptides (beta, alpha) during anaerobic growth, whereas the mRNAs for the reaction center polypeptides L (RC-L), M (RC-M), and H (RC-H) are less stable than both the LH-I and LH-II mRNAs. When photosynthetic cells are shifted from anaerobic to aerobic conditions, an immediate decrease in the levels of mRNA for the LH-I, LH-II, RC-L, RC-M, and RC-H proteins was observed. The level of mRNA for the LH-II proteins, however, is more sensitive to oxygen and is reduced faster than the level of mRNA for the LH-I proteins. These results suggest that oxygen represses the expression of genes coding for the light-harvesting antenna and reaction center complexes and may selectively accelerate the degradation of mRNA for the LH-II proteins. The mRNAs for several enzymes in the bacteriochlorophyll biosynthetic pathway are regulated by oxygen in a similar manner. The mRNAs for carotenoid biosynthetic enzymes, however, are regulated by oxygen in a different way. We have found that the amounts of mRNAs for carotenoid biosynthetic enzyme, relative to the amounts of mRNAs for LH and RC, increased during the shift from anaerobic to aerobic conditions. We have particularly shown that although the expression of most photosynthetic genes in R. capsulatus is repressed by oxygen, the crtA gene, located in the BamHI H fragment of the R' plasmid pRPS404 and responsible for the oxidation of spheroidene to spheroidenone, responds to oxygen in an opposite fashion. This exzymatic oxidation may protect the photosynthetic apparatus from photooxidative damage. Images

Zhu, Y S; Cook, D N; Leach, F; Armstrong, G A; Alberti, M; Hearst, J E

1986-01-01

283

Kinetics of coal gasification reactions at process conditions. Final technical report  

SciTech Connect

An entire fixed bed coal gasification reactor is suspended from a large analytical balance for thermogravimetric measurement of the reaction rate. This thermobalance has advantages over the hanging basket types in that sample size can be larger, thermocouples can be embedded directly in the reacting bed, and there is more control over extraparticle mass transfer resistance. Steam gasification of a North Dakota lignitic coal was studied at pressures from 20 to 33 atmospheres and temperatures from 720 to 900/sup 0/C. The observed reaction order was close to one. The gasification rates were essentially independent of the measured temperature. The suggested explanation for this behavior was that the particles act collectively, giving a large resistance to mass and heat transport. The reaction took place under a strong diffusional control. Gas chromatographic analysis of the products indicated that the carbon-steam reaction is the principal gasification mechanism. Steam was in excess, and the products underwent the water-gas shift reaction. Hydrogasification studies were complicated by the observation of an ignition phenomena in the coal bed when the exothermic heat of reaction could not be removed fast enough. An expression for the temperature dependence of the reaction rate was determined. 6 references, 28 figures, 9 tables.

Gardner, N.C.; Zheng, C.; Pehmoeller, D.; Gorecka, B.

1984-01-01

284

Isoindolones and related N-heterocycles via palladium nanoparticle-catalyzed 3-component cascade reactions.  

PubMed

Non-phosphine-containing cyclopalladated N-heterocycles possessing either sp2 C-Pd(II) or sp3 C-Pd(II) bonds and simple Pd(II) salts are precursors of Pd(0) nanoparticles whose initial morphology is dependent on the nature of the precursor. Addition of polyvinylpyrrolidone (pvp) dramatically increases catalyst lifetime. Nanoparticle generation can be achieved at ambient temperature in the presence of carbon monoxide by a process akin to the water-gas shift reaction. Allene also lowers the temperature required for nanoparticle generation. 3-Component catalytic cascades employing one or both of these substrates provide access to a variety of 5- and 6-membered N-heterocycles including isoindolones, N-aminoisoindolones, phthalazones, dihydroisoquinolines, and isoquinolones. PMID:17695711

Grigg, R; Sridharan, V

2006-01-01

285

Psychopathology of Shift Work.  

ERIC Educational Resources Information Center

Examined incidence and nature of general psychopathology among Nigerian shift workers (N=320). Found shift workers more significantly psychopathological than non-shift workers (p<0.001). Prominent disorders among shift workers were intellectual, sleep, mood, and general somatic disorders. No significant difference could be attributed to gender and…

Akinnawo, Ebenezer Olutope

1989-01-01

286

Improved Reduction of Carbon Monoxide by Highly Efficient Catalytic Shift for Fuel Cell Applications  

Microsoft Academic Search

The generation of high purity hydrogen from reformed hydrocarbon fuels, or syngas, is essential for efficient operation of the fuel cell (PEMFC, Polymer Electrolyte Membrane Fuel Cell). Usually, major components of reformed gas are H2, CO, CO2 and H2O. Especially a major component, CO poisons the electrode of fuel cells. The water gas shifter (WGS) that shifts CO to CO2

M. J. Youn; Y. N. Chun

2008-01-01

287

Combined cycle power plant with integrated coal gasification, CO shift and CO 2 washing  

Microsoft Academic Search

Studies on CO2 removal from coal-fired power stations indicate that net efficiencies of 40 % are feasible. About 88% of very clean CO2 can be bled off in the gaseous or liquid state of aggregation. This can be achieved with IGCC's employing water gas shift and physical absorption for CO2 separation or, potentially, H2\\/CO2 separation with membranes and the usual

R. Pruschek; G. Oeljeklaus; V. Brand; G. Haupt; G. Zimmermann; J. S. Ribberink

1995-01-01

288

Tandem pseudopericyclic reactions: [1,5]-X sigmatropic shift/6pi-electrocyclic ring closure converting N-(2-X-carbonyl)phenyl ketenimines into 2-X-quinolin-4(3H)-ones.  

PubMed

N-(2-X-Carbonyl)phenyl ketenimines undergo, under mild thermal conditions, [1,5]-migration of the X group from the carbonyl carbon to the electron-deficient central carbon atom of the ketenimine fragment, followed by a 6pi-electrocyclic ring closure of the resulting ketene to provide 2-X-substituted quinolin-4(3H)-ones in a sequential one-pot manner. The X groups tested are electron-donor groups, such as alkylthio, arylthio, arylseleno, aryloxy, and amino. When involving alkylthio, arylthio, and arylseleno groups, the complete transformation takes place in refluxing toluene, whereas for aryloxy and amino groups the starting ketenimines must be heated at 230 degrees C in a sealed tube in the absence of solvent. The mechanism for the conversion of these ketenimines into quinolin-4(3H)-ones has been studied by ab initio and DFT calculations, using as model compounds N-(2-X-carbonyl)vinyl ketenimines bearing different X groups (X = F, Cl, OH, SH, NH(2), and PH(2)) converting into 4(3H)-pyridones. This computational study afforded two general reaction pathways for the first step of the sequence, the [1,5]-X shift, depending on the nature of X. When X is F, Cl, OH, or SH, the migration occurs in a concerted mode, whereas when X is NH(2) or PH(2), it involves a two-step sequence. The order of migratory aptitudes of the X substituents at the acyl group is predicted to be PH(2) > Cl > SH > NH(2) > F> OH. The second step of the full transformation, the 6pi-electrocyclic ring closure, is calculated to be concerted and with low energy barriers in all the cases. We have included in the calculations an alternative mode of cyclization of the N-(2-X-carbonyl)vinyl ketenimines, the 6pi-electrocyclic ring closure leading to 1,3-oxazines that involves its 1-oxo-5-aza-1,3,5-hexatrienic system. Additionally, the pseudopericyclic topology of the transition states for some of the [1,5]-X migrations (X = F, Cl, OH, SH), for the 6pi-electrocyclization of the ketene intermediates to the 4(3H)-pyridones, and for the 6pi-electrocyclization of the starting ketenimines into 1,3-oxazines could be established on the basis of their geometries, natural bond orbital analyses, and magnetic properties. The calculations predict that the 4(3H)-pyridones are the thermodynamically controlled products and that the 1,3-oxazines should be the kinetically controlled ones. PMID:17025302

Alajarín, Mateo; Ortín, María-Mar; Sanchez-Andrada, Pilar; Vidal, Angel

2006-10-13

289

Biological Rhythms and Shift Work: Shift Work and Nursing.  

National Technical Information Service (NTIS)

Shift work within the nursing profession is examined. The authors first address the prevalence of shift work in nursing, its patterns, and the evidence for dissatisfaction with shift work. Next, the consequences of shift work are discussed, such as family...

C. S. Weisman

1989-01-01

290

NMR shift reagents  

SciTech Connect

This practical guide to current and potential users of lanthanide shift reagents (LSR) describes the selection of a LSR and the experimental techniques necessary to prepare and properly employ the various types of LSR. It gives a thorough review of previous literature reports in which lanthanide tris chelates and binuclear lanthanide-silver shift reagents were used in organic solvents to study achiral and chiral substrates, with particular focus on the sterochemical and conformational information obtained through use of LSR. It describes LSR suitable for use in aqueous solutions as well as computer fitting of lanthanide shift data through the dipolar shift equation. Other valuable information includes over 800 structures and 1500 references.

Wenzel, T.J.

1987-01-01

291

Molecular implementation of molecular shift register memories  

NASA Technical Reports Server (NTRS)

An electronic shift register memory (20) at the molecular level is described. The memory elements are based on a chain of electron transfer molecules (22) and the information is shifted by photoinduced (26) electron transfer reactions. Thus, multi-step sequences of charge transfer reactions are used to move charge with high efficiency down a molecular chain. The device integrates compositions of the invention onto a VLSI substrate (36), providing an example of a molecular electronic device which may be fabricated. Three energy level schemes, molecular implementation of these schemes, optical excitation strategies, charge amplification strategies, and error correction strategies are described.

Beratan, David N. (Inventor); Onuchic, Jose N. (Inventor)

1991-01-01

292

Making Shifts toward Proficiency  

ERIC Educational Resources Information Center

The Leading for Mathematical Proficiency (LMP) Framework (Bay-Williams et al.) has three components: (1) The Standards for Mathematical Practice; (2) Shifts in classroom practice; and (3) Teaching skills. This article briefly describes each component of the LMP framework and then focuses more in depth on the second component, the shifts in…

McGatha, Maggie B.; Bay-Williams, Jennifer M.

2013-01-01

293

Style Shift in Translation  

ERIC Educational Resources Information Center

The phenomenon of style shift in translated texts is ascribed mainly to textual incompatibility in terms of rhetorical asymmetry and divergence at the formality level. Mandatory shifts result from a systematic dissimilarity between the source language and the target language in terms of the underlying system of syntax, semantics and rhetorical…

Al-Qinai, Jamal

2009-01-01

294

Water-gas exchange of organochlorine pesticides at Lake Chaohu, a large Chinese lake.  

PubMed

Organochlorine pesticides (OCPs), a potential threat to ecosystems and human health, are still widely residual in the environment. The residual levels of OCPs in the water and gas phase were monitored in Lake Chaohu, a large Chinese lake, from March 2010 to February 2011. Nineteen types of OCPs were detected in the water with a total concentration of 7.27 ± 3.32 ng/l. Aldrin, DDTs and HCHs were the major OCPs in the water, accounting for 38.3%, 28.9% and 23.6% of the total, respectively. The highest mean concentration (12.32 ng/l) in the water was found in September, while the lowest (1.74 ng/l) was found in November. Twenty types of gaseous OCPs were detected in the atmosphere with a total concentration of 542.0 ± 636.5 pg/m(3). Endosulfan, DDTs and chlordane were the major gaseous OCPs in the atmosphere, accounting for 48.9%, 22.5% and 14.4% of the total, respectively. The mean concentration of gaseous OCPs was significantly higher in summer than in winter. o,p'-DDE was the main metabolite of DDT in both the water and gas phase. Of the HCHs, 52.3% existed as ?-HCH in the water, while ?-HCH (37.9%) and ?-HCH (30.9%) were dominant isomers in the gas phase. The average fluxes were -21.11, -3.30, -152.41, -35.50 and -1314.15 ng/(m(2) day) for ?-HCH, ?-HCH, HCB, DDT and DDE, respectively. The water-gas exchanges of the five types of OCPs indicate that water was the main potential source of gaseous OCPs in the atmosphere. A sensitivity analysis indicated that the water-gas flux of ?-HCH, ?-HCH and DDT is more vulnerable than that of HCB and DDE to the variation of the parameters. The possible source of the HCHs in the water was from the historical usage of lindane; however, that in the air was mainly from the recent usage of lindane. The technical DDT and dicofol might be the source of DDTs in the water and air. PMID:23238597

Ouyang, Hui-Ling; He, Wei; Qin, Ning; Kong, Xiang-Zhen; Liu, Wen-Xiu; He, Qi-Shuang; Yang, Chen; Jiang, Yu-Jiao; Wang, Qing-Mei; Yang, Bin; Xu, Fu-Liu

2013-04-01

295

Air-water gas exchange of organochlorine compounds in Lake Baikal, Russia  

SciTech Connect

Air and surface water samples were collected at Lake Baikal, Russia, during June 1991 to determine concentrations of organochlorine pesticides and polychlorinated biphenyl (PCB) congeners. These data were combined with Henry`s law constants to estimate the gas flux rate across the air-water interface of each compound class. Air samples were collected at Lake Baikal and from nearby Irkutsk. Water samples were collected from three mid-lake stations and at the mouth of two major tributaries. Average air concentrations of chlorinated bornanes (14 pg m{sup -3}), chlordanes (4.9 pg m{sup -3}), and hexachlorobenzene (HCB) (194 pg m{sup -3}) were similar to global backgound of Arctic levels. However, air concentrations of hexachlorocyclohexanes (HCHs), DDTs, and PCBs were closer to those observed in the Great Lakes region. Significantly higher levels of these three compound classes in air over Irkutsk suggests that regional atmospheric transport and deposition may be an important source of these persistent compounds to Lake Baikal. Air-water gas exchange calculations resulted in net depositional flux values for {alpha}-HCH, {gamma}-HCH, DDTs, and chlorinated bornanes at 112, 23, 3.6, and 2.4 ng m{sup -2} d{sup -1}, respectively. The total net flux of 22 PCB congeners, chlordanes, and HCB was from water to air (volatilization) at 47, 1.8, and 32 ng m{sup -2} d{sup -1}, respectively. 50 refs., 7 figs., 5 tabs.

McConnell, L.L. [USDA, Beltsville, MD (United States)] [USDA, Beltsville, MD (United States); Kucklick, J.R. [National Marine Fisheries Service, Charleston, SC (United States)] [National Marine Fisheries Service, Charleston, SC (United States); Bidleman, T.F. [Univ. of South Carolina, Columbia, SC (United States)] [Univ. of South Carolina, Columbia, SC (United States); Ivanov, G.P. [Limnological Inst., Irkutsk (Russian Federation)] [Limnological Inst., Irkutsk (Russian Federation); Chernyak, S.M. [Inst. of Fisheries, Moscow (Russian Federation)] [Inst. of Fisheries, Moscow (Russian Federation)

1996-10-01

296

Air water gas exchange of ?-hexachlorocyclohexane enantiomers in the South Atlantic Ocean and Antarctica  

NASA Astrophysics Data System (ADS)

Between November 1997 and February 1998, air and water samples were collected on the African side of the South Atlantic Ocean to Antarctica, on board the S.A. Agulhas, to determine the spatial distribution of ?-hexachlorocyclohexane ( ?-HCH) and the net direction of air/water gas exchange. The ?-HCH concentrations in air and surface water were much lower than in Arctic regions, consistent with the historically lower usage of technical HCH in the Southern Hemisphere. The water/air fugacity ratios of ?-HCH were ?1.0, indicating steady state or net deposition conditions. The ?-HCH in water was enantioselectively metabolized, with resulting enantiomer fractions (EFs) that differed from the racemic (0.500) value of the technical product. The EFs decreased from >0.500 at the lower latitudes to <0.500 farther south, indicating preferential loss of (-) ?-HCH or (+) ?-HCH in different ocean regions. EFs in the air boundary layer reflected those in surface water, showing the bidirectional nature of gas exchange.

Jantunen, Liisa M.; Kylin, Henrik; Bidleman, Terry F.

2004-11-01

297

Stabilization of water/gas oil emulsions by desulfurizing cells of Gordonia alkanivorans RIPI90A.  

PubMed

It has been previously reported that resting-cells, non-proliferating cells, of Gordonia alkanivorans RIPI90A can convert dibenzothiophene (DBT) to 2-hydroxybiphenyl (2-HBP) via the 4S pathway in a biphasic system. The main goal of the current work was to study the behaviour of resting-cells of this strain in biphasic organic media. Resting-cells showed strong affinity for sulfurous organic substrates and were able to stabilize water/gas oil emulsions by attaching to the interface without decreasing the surface tension of their environment. This was consistent with the behaviour of the whole cells but not the surfactants, suggesting that microbial cell-mediated emulsification occurs. It was found that the emulsion-stabilizing activity of the resting-cells was influenced by the growth stage, but was not directly influenced by the metabolic activity of the resting-cells. This activity may be related to cell-surface hydrophobicity, which results from the unique chemical structure of the cell surface. In some biphasic biodesulfurization (BDS) bioreactors, emulsions are created without addition of any surfactant. Cell surface-mediated stabilization helps prolong the emulsions and therefore overcomes mass-transfer limitations in bioreactors. The simultaneous occurrence of emulsion-stabilizing and desulfurization activities of resting-cells was observed for what is believed to be the first time. The results suggest that this strain may have potential for the BDS of diesel oils. PMID:17464072

Mohebali, Ghasemali; Ball, Andrew; Kaytash, Ashk; Rasekh, Behnam

2007-05-01

298

Chemical-Shift Concertina.  

National Technical Information Service (NTIS)

The phase-alternated experiment in liquids, a multiple-pulse NMR experiment capable of scaling chemical shifts, is examined theoretically and experimentally. The theory of the experiment is worked out using both the average-Hamiltonian and classical magne...

J. D. Ellett J. S. Waugh

1969-01-01

299

Climate science: Shifting storms  

NASA Astrophysics Data System (ADS)

An analysis of historical storm data reveals that the average latitude at which tropical cyclones attain their maximum intensity has undergone a pronounced shift towards the poles over the past three decades. See Letter p.349

Ramsay, Hamish

2014-05-01

300

Auditory Attention Shifting.  

National Technical Information Service (NTIS)

This research effort measured the spectral and temporal dynamics of human auditory attentional control, concentrating on the requirements for efficient shifting of auditory attention within the frequency spectrum of normal human hearing.

A. Reeves B. Scharf

2008-01-01

301

Our World: Fluid Shift  

NASA Video Gallery

Learn about the circulatory system and how gravity aids blood flow in our bodies here on Earth. Find out how NASA flight surgeons help the astronauts deal with the fluid shift that happens during s...

302

Molecular Electronic Shift Registers  

NASA Technical Reports Server (NTRS)

Molecular-scale shift registers eventually constructed as parts of high-density integrated memory circuits. In principle, variety of organic molecules makes possible large number of different configurations and modes of operation for such shift-register devices. Several classes of devices and implementations in some specific types of molecules proposed. All based on transfer of electrons or holes along chains of repeating molecular units.

Beratan, David N.; Onuchic, Jose N.

1990-01-01

303

Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis  

NASA Astrophysics Data System (ADS)

Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their “Pt-like” properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O2, H2O, CO and CO2) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts.

Stottlemyer, Alan L.; Kelly, Thomas G.; Meng, Qinghe; Chen, Jingguang G.

2012-09-01

304

Reactions of oxygen-containing molecules on transition metal carbides: Surface science insight into potential applications in catalysis and electrocatalysis  

NASA Astrophysics Data System (ADS)

Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their "Pt-like" properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O2, H2O, CO and CO2) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts.

Stottlemyer, Alan L.; Kelly, Thomas G.; Meng, Qinghe; Chen, Jingguang G.

2012-09-01

305

Determination of the Effect of Coal/Biomass-Derived Syngas Contaminants on the Performance of Fischer-Tropsch and Water-Gas-Shift Catalysts.  

National Technical Information Service (NTIS)

Today, nearly all liquid fuels and commodity chemicals are produced from non-renewable resources such as crude oil and natural gas. Because of increasing scrutiny of carbon dioxide (CO(sub 2)) emissions produced using traditional fossil-fuel resources, th...

B. S. Turk J. Farmer J. P. Trembly M. E. Cooper R. P. Gupta

2013-01-01

306

Computational Chemistry-Based Identification of Ultra-Low Temperature Water-Gas-Shift Catalysts. Final Technical Report from September 1, 2006 to June 30, 2008.  

National Technical Information Service (NTIS)

The current work seeks to identify novel, catalytically-active, stable, poisonresistant LWGS catalysts that retain the superior activity typical of conventional Cu catalysts but can be operated at similar or lower temperatures. A database for the Binding ...

M. Mavrikakis

2008-01-01

307

Low-temperature water–gas shift: impact of Pt promoter loading on the partial reduction of ceria and consequences for catalyst design  

Microsoft Academic Search

Partial reduction of ceria generates catalytically active bridging OH groups on the surface of ceria. Pt facilitates this surface reduction process, and in this work, the impact of the Pt promoter loading on catalyst structural-property relationships was explored. XANES spectra were recorded under H2 treatment for a series of Pt\\/ceria catalysts with increasing Pt loading at both the Pt and

Gary Jacobs; Uschi M. Graham; Emilie Chenu; Patricia M. Patterson; Alan Dozier; Burtron H. Davis

2005-01-01

308

Shifts that divide populations  

NASA Astrophysics Data System (ADS)

If fitness landscape is non-concave, And the shift is wide, Then there is a good chance That population would divide. How does a population of organisms in an ecosystem respond to shifts in the environment? Answers to this question are critical to our understanding of the ecosystem and thus ability to manage it toward more desirable outcomes. We have developed a model of adaptation, based on replicator dynamics, in which we derive a simple but insightful threshold condition that separates two important types of responses: 'cohesive transition' in which the whole population changes gradually together, and 'population-dividing transition' in which the population splits into two groups with one eventually dominating the other. The threshold depends on the magnitude of the shift and the shape of the fitness landscape. Division in populations can fundamentally alter the functioning of the system; knowing the condition that gives rise to such division is thus fundamentally important.

Muneepeerakul, R.; Qubbaj, M. R.; Aggarwal, R.; Anderies, J. M.; Janssen, M. A.

2013-12-01

309

Experimental Study of the Reaction pi exp - p Implies pi exp 0 pi exp 0 N at 2.01 GeV/C. Its Use in a Simultaneous Phase Shift Analysis of the pi pi Channels.  

National Technical Information Service (NTIS)

We report results on pi exp + pi exp - implies pi exp 0 pi exp 0 total and differential cross sections from threshold to 1.1 GeV pi pi mass. These results have been obtained from a high-statistics experiment studying the reaction pi exp - p implies pi exp...

M. David

1979-01-01

310

Phase shift behavior at degenerate continuum bound states  

Microsoft Academic Search

A special case of a nonlocal potential which has a degenerate continuum bound state is studied using the Bolsterli criterion for defining the phase shift, and is found to be consistent with Levinson's theorem and the Wigner inequality. NUCLEAR REACTIONS Phase shift behavior for nonlocal potentials, degenerate continuum bound states, Levinson's theorem.

L. L. Foldy

1982-01-01

311

Trophic shift, not collapse  

USGS Publications Warehouse

scientists who are closely monitoring Lake Huron’s food web, we believe that the ongoing changes are more accurately characterized as a trophic shift in which benthic pathways have become more prominent. While decreases in abundance have occurred for some species, others are experiencing improved reproduction resulting in the restoration of several important native species.

Madenjian, Charles P.; Rutherford, Edward S.; Stow, Craig A.; Roseman, Edward F.; He, Ji X.

2013-01-01

312

Proton Chemical Shifts  

NSDL National Science Digital Library

Created by Hans Reich, professor of organic chemistry at the Uiversity of Wisconsin-Madison, this site contains a compilation of proton chemical shifts and coupling constants. This is an excellent resource for providing students familiarity with Nuclear Magnetic Resonance (NMR) Spectroscopy Data.

Reich, Hans J.

2007-11-16

313

Thermochemical properties, DeltafH degrees (298), S degrees (298), and Cp degrees (T), for n-butyl and n-pentyl hydroperoxides and the alkyl and peroxy radicals, transition states, and kinetics for intramolecular hydrogen shift reactions of the peroxy radicals.  

PubMed

Alkyl radicals in atmospheric and combustion environments undergo a rapid association with molecular oxygen (3O2) to form an alkyl peroxy radical (ROO*). One important reaction of these peroxy radicals is the intramolecular H-shift (intramolecular abstraction) to form a hydroperoxide alkyl radical (R'*COOH), where the hydroperoxide alkyl radical may undergo chemical activation reaction with O2 and result in chain branching at moderate to low temperatures. The thermochemistry and trends in kinetic parameters for the hydrogen shift reactions from each carbon (4-8-member-ring TST's) in n-butyl and n-pentyl peroxy radicals (CCCCOO* and CCCCCOO*) are analyzed using density functional and ab initio calculation methods. Thermochemical properties, DeltafH degrees (298 K), C-H bond energies, S degrees (298 K), and Cp degrees (T) of saturated linear C4 and C5 aliphatic peroxides (ROOH), as well as the corresponding hydroperoxide alkyl radicals (R'*COOH), are determined. DeltafH degrees (298 K) are obtained from isodesmic reactions and the total energies of the CBS-QB3 and B3LYP computational methods. Contributions to the entropy and the heat capacity from translation, vibration, and external rotation are calculated using the rigid-rotor-harmonic-oscillator approximation based on the CBS-QB3 frequencies and structures. The results indicate that pre-exponential factors, A(T), decrease with the increase of the ring size (4-8-member-ring TS, H-atom included). The DeltaH for 4-, 5-, 6-, and 7-member rings in n-butyl (and n-pentyl) peroxy are 40.8 (40.8), 31.4 (31.5), 20.5 (20.0), 22.6-p (19.4) kcal mol(-1), respectively. The DeltaH for the 8-member ring in n-pentylperoxy is 23.8-p kcal mol(-1), All abstractions are from secondary (-CH2-) groups except those marked (-p), which are from primary sites. Enthalpy and barrier values from the B3LYP/6-311++G(2d,p) and BHandHLYP/6-311G(d,p) methods are compared with CBS-QB3 results. The B3LYP results show good agreement with the higher level CBS-QB3 calculation method; the BHandH barriers for the intramolecular peroxy H-shifts are not acceptable. PMID:17585739

Zhu, Li; Bozzelli, Joseph W; Kardos, Lisa M

2007-07-19

314

Nursing rotas. Shift up.  

PubMed

Trusts may wish to consider more flexible, staggered daytime shifts, which accommodate married nurses--for instance, 9.30 am-3.30 pm on weekdays with longer hours at weekends/on nights to ensure that contractual requirements are met. For larger trusts, creche/nursery facilities may solve the problem. After-school clubs on site on a voluntary basis may also mean that more married women and unmarried women with children could more easily accommodate standard shifts. The tribunal decision seems to condone the provision of somewhat ad hoc training and supervision, whereas in professional practice continuous supervision and participation in professional developments are essential elements in the provision of safe, high-quality clinical practice. PMID:10623151

Lloyd, R; Goulding, J

1999-10-14

315

Ambiguous red shifts  

NASA Astrophysics Data System (ADS)

A one-parameter conformal invariance of Maxwell's equations allows the wavelengths of electromagnetic waves to change as they propagate, and do so even in otherwise field-free space. This produces an ambiguity in interpretations of stellar red shifts. Experiments that will determine the value of the group parameter, and thereby remove the ambiguity, are proposed. They are based on an analysis of the anomalous frequency shifts uncovered in the Pioneer 10 and 11 spacecraft studies, and physical interpretation of an isomorphism discovered by E.L. Hill. If the group parameter is found to be non-zero, Hubble's relations will have to be reinterpreted and space-time metrics will have to be altered. The cosmological consequences of the transformations are even more extensive because, though they change frequencies they do not alter the energy and momentum conservation laws of classical and quantum-electrodynamical fields established by Cunningham and by Bia?ynicki-Birula.

Wulfman, Carl E.

2010-12-01

316

The shifting beverage landscape.  

PubMed

STOREY, M.L. The shifting beverage landscape. PHYSIOL BEHAV, 2010. - Simultaneous lifestyle changes have occurred in the last few decades, creating an imbalance in energy intake and energy expenditure that has led to overweight and obesity. Trends in the food supply show that total daily calories available per capita increased 28% since 1970. Total energy intake among men and women has also increased dramatically since that time. Some have suggested that intake of beverages has had a disproportional impact on obesity. Data collected by the Beverage Marketing Corporation between 1988-2008 demonstrate that, in reality, fewer calories per ounce are being produced by the beverage industry. Moreover, data from the National Cancer Institute show that soft drink intake represents 5.5% of daily calories. Data from NHANES 1999-2003 vs. 2003-06 may demonstrate a shift in beverage consumption for age/gender groups, ages 6 to>60years. The beverages provided in schools have significantly changed since 2006 when the beverage industry implemented School Beverage Guidelines. This voluntary action has removed full-calorie soft drinks from participating schools across the country. This shift to lower-calorie and smaller-portion beverages in school has led to a significant decrease in total beverage calories in schools. These data support the concept that to prevent and treat obesity, public health efforts should focus on energy balance and that a narrow focus on sweetened beverages is unlikely to have any meaningful impact on this complex problem. PMID:20188750

Storey, Maureen

2010-04-26

317

Hot compressed water—a suitable and sustainable solvent and reaction medium?  

NASA Astrophysics Data System (ADS)

Hot compressed water in the sub- and supercritical state exhibits exciting physical and chemical properties, which can be varied continuously from gas-like to liquid-like behaviour. Correspondingly, the solvent properties can change from non-polar behaviour as present, for example, in organic solvents to highly ionic characteristics like in salt melts. This opens up several promising opportunities for separation processes and chemical reactions. Under supercritical conditions, substantial amounts of gases and organic substances can homogeneously be mixed with water, which then can be separated by adjusting the subcritical conditions by forming additional phases. This can beneficially be combined with chemical reactions occurring in the homogeneous state leading to integrated processes, which are more effective and competitive. Three approaches to the technical application of hot compressed water are presented to show and discuss the technology, potential, technical hurdles and future research demand in this area of research and development. In supercritical water oxidation (SCWO) water is used as a medium in which organic pollutants are completely degraded under the addition of oxygen, which is completely miscible with water under the process conditions of up to 650 °C and pressures around 25 MPa. Thus, high space-time yields in compact reactor designs can be realized. Hydrogen is produced from biomass by hydrothermal gasification. Here, in an excess of water, the reaction at temperatures up to 700 °C and pressures around 30 MPa directly leads to valuable hydrogen instead of synthetic gas, as in conventional gasification processes, or methane at subcritical conditions in water. After reaction, pressurized hydrogen is obtained and can easily be enriched due to the different partition coefficients of hydrogen and carbon dioxide between the aqueous and gas phase. Even homogeneous catalysis is possible in supercritical water. This has been demonstrated with the cobalt-catalysed cyclotrimerization of acetylenes to form benzene derivatives or hydroformylation to produce aldehydes from olefins. There, only the addition of CO is necessary, the H2 required being formed by the equilibrium of the water-gas-shift reaction. After a homogeneous reaction in the supercritical state, the reaction mixture can be separated at subcritical conditions. In support of the chemical and technical developments and to principally understand the experimental findings fundamental aspects have to be investigated as well. Intensive studies have been devoted to chemical kinetics including the modelling with elementary reaction steps, e.g. to separate ionic and radical reaction pathways. Depending on the reaction conditions, ionic or radical reaction pathways can be favoured or suppressed, allowing for control selectivity. Furthermore, corrosion of relevant reactor materials has been investigated.

Dinjus, E.; Kruse, A.

2004-04-01

318

STEM Colorado: Doppler Shift  

NSDL National Science Digital Library

This applet demonstrates the Doppler shift. The user can control the frequency of the sound source and the sound speed. The chart recorder at the bottom displays the wave crests as detected by the receiver and their frequency. It also displays the instantaneous wavelength if the ear is at rest. The user can drag the source or the receiver to any location in the display and choose the velocity of each. This is part of a larger collection of applets by STEM Colorado focused mostly on topics in astronomy.

Mccray, Richard; Koelemay, Andrew

2008-08-30

319

Gasification of biomass in water\\/gas-stabilized plasma for syngas production  

Microsoft Academic Search

The experimental reactor PLASGAS for plasma pyrolysis and vitrification equipped with the hybrid gas-water stabilized torch\\u000a was used in the experiments. The plasma torch is characterized by low density, high temperature plasma with very low mass\\u000a flow rates and high enthalpy. High plasma enthalpy is advantageous for adjustment of higher reaction temperatures with high\\u000a energy efficiency. Gasification of biomass was

M. Hrabovsky; M. Konrad; V. Kopecky; M. Hlina; T. Kavka; G. van Oost; E. Beeckman; B. Defoort

2006-01-01

320

Simplified power shift transmission  

SciTech Connect

A multi-speed transmission is described for transferring power between a first shaft and a second shaft, the transmission comprising: a compound planetary assembly including a sun gear, a ring gear concentric with the sun gear, a reaction gear concentric with the ring gear, a planetary gear carrier rotatably supporting first and second sets of planet gears, the first planet gear set intermeshing with the ring gear. The sun gear and the second planet gear set intermesh with the first planet gear set and the reaction gear, means for selectively coupling the first shaft with the sun gear and the reaction gear, and means for selectively preventing rotation of the ring gear, and reaction gear and the planetary carrier; a simple planetary assembly comprising a sun gear component concentric with the sun gear of the compound planetary assembly, a ring gear component concentric with both of the sun gears, and a planetary gear carrier component rotatably supporting a set of planet gears, the planet gear set meshing with the sun gear and the ring gear of the simple planetary.

Michael, R.A.

1987-04-21

321

Phase-Shift Effect Magnetometer.  

National Technical Information Service (NTIS)

The primary objective of the research project was to determine the feasibility of using phase shift phenomenon as the transducing principal of a magnetometer. The findings show that, not only is a phase shift effect magnetometer possible, but high sensiti...

R. C. Dinsmore

1991-01-01

322

Even-shift orthogonal sequences  

Microsoft Academic Search

A class of binary sequences whose elements are either1or-1and whose autocorrelation function is0for all even shifts except the zero shift is discussed. These sequences will be calledEsequences. It is proved that everyEsequence is paired with anotherEsequence, its mate, so that the cross-correlation function between them is0for all even shifts including the zero shift. Using these sequences, new complete orthogonal function

Y. Taki; H. Miyakawa; M. Hatori; S. Namba

1969-01-01

323

Social interaction modifies neural response to gaze shifts.  

PubMed

Monitoring gaze shifts is important for social interactions. The direction of gaze can reveal intentions and help to predict future actions. Here we examined whether behavioural and neural responses to gaze shifts were modulated by the social context of the gaze shift in two linked experiments. Two faces were presented, one gazing directly at the subject (the 'social' face) and one with averted gaze (the 'unsocial' face). One face then made a gaze shift that was either towards a visible target ('correct') or towards another location in space ('incorrect'). Both behavioural and neural responses to gaze shifts were modulated by the social context and the goal directedness of the gaze shift. Reaction times were significantly faster in response to 'correct' and 'social' compared with 'incorrect' and 'unsocial' gaze shifts, respectively. Using functional magnetic resonance imaging, we found significantly greater activation in the parieto-frontal attentional network, and in some parts of the posterior superior temporal sulcus, in response to 'incorrect' and 'unsocial' compared with 'incorrect' and 'social' gaze shifts, respectively. Conversely, we found greater activation in the medial prefrontal cortex and precuneus in response to 'correct' and 'social' compared with 'incorrect' and 'unsocial' gaze shifts. This activity may reflect the experience of joint attention associated with these gaze shifts. PMID:18985119

Bristow, Davina; Rees, Geraint; Frith, Christopher D

2007-03-01

324

Phase shifting diffraction interferometer  

DOEpatents

An interferometer which has the capability of measuring optical elements and systems with an accuracy of {lambda}/1000 where {lambda} is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about {lambda}/50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms. 8 figs.

Sommargren, G.E.

1996-08-29

325

Phase shifting diffraction interferometer  

DOEpatents

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Sommargren, Gary E. (Santa Cruz, CA) [Santa Cruz, CA

1996-01-01

326

Phase shifting interferometer  

DOEpatents

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. Whereas current interferometers illuminate the optic to be tested with an aberrated wavefront which also limits the accuracy of the measurement, this interferometer uses an essentially perfect spherical measurement wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Sommargren, Gary E. (Santa Cruz, CA) [Santa Cruz, CA

1999-01-01

327

Hydraulically actuated well shifting tool  

SciTech Connect

This patent describes a hydraulically actuated shifting tool for actuating a sliding member in a well tool. It comprises: a housing having a hydraulic fluid bore therein; shifting dog means positioned on the housing for movement away and toward the housing; locking dog means positioned on the housing for movement away and toward the body; shifting dog hydraulic actuating means in fluid communication with the bore for causing engagement of the shifting dogs with the sliding member; locking dog hydraulic actuating means in communication with the bore for causing engagement of the locking dogs with the locking means; and hydraulic shifting means in communication with the bore for causing relative movement between the shifting dog means and the locking dog means for shifting the sliding sleeve.

Roth, B.A.

1992-10-20

328

Features of the behaviour of double-chained cationic surfactant monomer in a monolayer at the water-gas interface.  

PubMed

We studied the formation of a double-chained cationic monomer, N,N-diallyl-N-cetyl-N-dodecyloxycarbonyl methylammonium bromide, in a monolayer at the water-gas interface. An increase in surface pressure induced the transition from the liquid-expanded to liquid-condensed state with tail-packing and then head-packing of the monomer, which was accompanied by a decrease in the mobility of monomer molecules. An increase in the ionic strength of the subphase led to the compression of the layer, and addition of ethanol or detergents caused its dilution. Polyethylene glycol and polyacrylic acid induced the formation of a complex between the monomer and polymer. PMID:11368499

Egorov, V V; Suprun, N V; Klyamkin, A A; Zubov, V P

2000-01-01

329

Emission spectroscopy of a microhollow cathode discharge plasma in helium-water gas mixtures  

NASA Astrophysics Data System (ADS)

A dc microhollow cathode discharge (MHCD) plasma was generated inflowing helium gas containing water vapor. The cathode hole diameters were 0.3, 0.7, 1.0, and 2.0 mm, each with a length of 2.0 mm. Emission spectroscopy was carried out to investigate the discharge mode and to determine the plasma parameters. For the 0.3-mm cathode, stable MHCDs in an abnormal glow mode existed at pressures up to 100 kPa, whereas for larger diameters, a plasma was not generated at atmospheric pressure. An analysis of the lineshapes relevant to He at 667.8 nm and to H? at 656.3 nm implied an electron density and gas temperature of 2 × 1014 cm-3 and 1100 K, respectively, for a 100-kPa discharge in the negative glow region. The dependence of the OH band, and H? intensities on the discharge current exhibited different behaviors. Specifically, the OH spectrum had a maximum intensity at a certain current, while the H atom intensity kept increasing with the discharge current. This observation implies that a high concentration of OH radicals results in quenching, leading to the production of H atoms via the reaction OH + e- --> O + H + e-.

Namba, S.; Yamasaki, T.; Hane, Y.; Fukuhara, D.; Kozue, K.; Takiyama, K.

2011-10-01

330

Shift work and pathological conditions  

PubMed Central

Shift work exerts major influences on the physiological functions of the human body. These are primarily mediated by the disruption of circadian rhythms since most body functions are circadian rhythmic. Next to the disturbances caused by changes in the circadian system, shift work has also been suggested to be related to a number of other health disorders. The present study summarizes recently published data on the potential relationship between disorders and shift working.

van Mark, Anke; Spallek, Michael; Kessel, Richard; Brinkmann, Elke

2006-01-01

331

Phase-shift coherence holography.  

PubMed

We propose and experimentally demonstrate a new reconstruction scheme for coherence holography using computer-generated phase-shift coherence holograms. A 3D object encoded into the spatial coherence function is reconstructed directly from a set of incoherently illuminated computer-generated holograms with numerically introduced phase shifts. Although a rotating ground glass is used to introduce spatially incoherent illumination, the phase-shifting portion of the system is simple and free from mechanically moving components. PMID:20479864

Naik, Dinesh N; Ezawa, Takahiro; Miyamoto, Yoko; Takeda, Mitsuo

2010-05-15

332

On Isotope Shifts  

NASA Astrophysics Data System (ADS)

It was noted by Zamick (Ann.Phys66,784(1971) That the same formula used by Talmi and De Shalit for binding energies (Rev.Mod.Phys.34, 704 (1962)) could also be used for nuclear radii i.e. isotope shifts. The argument is simple-both the radius operator and nuclear interaction are scalars under rotation. The formula has the change of square radius relative to a reference as nC+ (n(n-1)/2)A +[n/2]B. There have been many experimental papers which discuss this work as well as associated work by Talmi(NPA 423,189 (1984).The formula was originally used for the Calcium isotopes but most recently for Argon isotopes (K.Blaum et.al. NPA 799,30(2008)).There was also work on the Bismus and Lead Isotopes by M.R. Pearson et.al. (J.Phys G.26,1829(2000)). The formula displays even-odd staggering for both binding energies and nuclear radii.Sheline et.al. discuss ``inverse staggering'' as possibly evidence of Octupole deformation for certain Barium and Cesium isotopes (PRC38,2952(1988)). Other work of note is due to H.D. Wohlfahrt PRC 23,533(1981). It is my feeling that the above and other experimental results are somewhat scattered and it would be useful to collect them all and have a unified discussion of the implications of these very interesting experiments not only with the above formula but with other theoretical formulations. )

Zamick, Larry

2010-02-01

333

Tune shifts and beta function shifts due to linear coupling  

SciTech Connect

Linear coupling effects due to skew quadrupole fields have become more important for proton synchrotrons. Large tune shifts can be generated by linear coupling. A higher order tune shift, roughly quadratic in the skew quadrupole field, may be present, which may require a more complex correction system. There may be large shifts in the beta functions, and some reduction in the dynamic aperture. Analytical results have been found for the higher order tune shift and the beta function shifts. Numerical results for these effects are given for RHIC, and a correction system is proposed for these effects. A correction system with about 4 or 5 families of skew quadrupole correctors appears able to correct the above effects.

Parzen, G.

1991-01-01

334

Tune shifts and beta function shifts due to linear coupling  

SciTech Connect

Linear coupling effects due to skew quadrupole fields have become more important for proton synchrotrons. Large tune shifts can be generated by linear coupling. A higher order tune shift, roughly quadratic in the skew quadrupole field, may be present, which may require a more complex correction system. There may be large shifts in the beta functions, and some reduction in the dynamic aperture. Analytical results have been found for the higher order tune shift and the beta function shifts. Numerical results for these effects are given for RHIC, and a correction system is proposed for these effects. A correction system with about 4 or 5 families of skew quadrupole correctors appears able to correct the above effects.

Parzen, G.

1991-12-31

335

Drug Reactions  

MedlinePLUS

... adverse drug reaction. One medicine might cause an adverse reaction if it’s taken with another medicine. One way ... reaction. Are prescription medicines the only cause of adverse reactions? No. Even medicines that you don't need ...

336

Flexible Schedules and Shift Work.  

ERIC Educational Resources Information Center

Flexible work hours have gained prominence, as more than 25 million workers (27.6% of all full-time workers) can now vary their schedules. However, there has been little change since the mid-1980s in the proportion who work a shift other than a regular daytime shift. (JOW)

Beers, Thomas M.

2000-01-01

337

Wind driven vertical transport in a vegetated, wetland water column with air-water gas exchange  

NASA Astrophysics Data System (ADS)

Flow around arrays of cylinders at low and intermediate Reynolds numbers has been studied numerically, analytically and experimentally. Early results demonstrated that at flow around randomly oriented cylinders exhibits reduced turbulent length scales and reduced diffusivity when compared to similarly forced, unimpeded flows (Nepf 1999). While horizontal dispersion in flows through cylinder arrays has received considerable research attention, the case of vertical dispersion of reactive constituents has not. This case is relevant to the vertical transfer of dissolved gases in wetlands with emergent vegetation. We present results showing that the presence of vegetation can significantly enhance vertical transport, including gas transfer across the air-water interface. Specifically, we study a wind-sheared air-water interface in which randomly arrayed cylinders represent emergent vegetation. Wind is one of several processes that may govern physical dispersion of dissolved gases in wetlands. Wind represents the dominant force for gas transfer across the air-water interface in the ocean. Empirical relationships between wind and the gas transfer coefficient, k, have been used to estimate spatial variability of CO2 exchange across the worlds’ oceans. Because wetlands with emergent vegetation are different from oceans, different model of wind effects is needed. We investigated the vertical transport of dissolved oxygen in a scaled wetland model built inside a laboratory tank equipped with an open-ended wind tunnel. Plastic tubing immersed in water to a depth of approximately 40 cm represented emergent vegetation of cylindrical form such as hard-stem bulrush (Schoenoplectus acutus). After partially removing the oxygen from the tank water via reaction with sodium sulfite, we used an optical probe to measure dissolved oxygen at mid-depth as the tank water re-equilibrated with the air above. We used dissolved oxygen time-series for a range of mean wind speeds to estimate the gas transfer coefficient, k, for both a vegetated condition and a control condition (no cylinders). The presence of cylinders in the tank substantially increased the rate of the gas transfer. For the highest wind speed, the gas transfer coefficient was several times higher when cylinders were present compared to when they were not. The gas transfer coefficient for the vegetated condition also proved sensitive to wind speed, increasing markedly with increasing mean wind speeds. Profiles of dissolved oxygen revealed well-mixed conditions in the bulk water column following prolonged air-flow above the water surface, suggesting application of the thin-film model is appropriate. The enhanced gas exchange observed might be explained by increased turbulent kinetic energy within the water column and the anisotropy of the cylinder array, which constrains horizontal motions more than vertical motions. Improved understanding of gas exchange in vegetated water columns may be of particularly use to investigations of carbon fluxes and soil accretion in wetlands. Reference: Nepf, H. (1999), Drag, turbulence, and diffusion in flow through emergent vegetation, Water Resour. Res., 35(2), 479-489.

Poindexter, C.; Variano, E. A.

2010-12-01

338

Design and analysis of multivariable predictive control applied to an oil-water-gas separator: A polynomial approach  

NASA Astrophysics Data System (ADS)

This dissertation uses a polynomial-operator technique to study stability and performance of unconstrained multivariable predictive control. A simple and direct way to determine stability of the closed-loop system is developed. It is shown that to guarantee stability of the closed-loop two transfer matrices must be stable. These are represented as fraction descriptions, a ratio of "numerator" and "denominator" polynomial matrices from which the poles can be determined. Because both transfer matrices possess the same denominator matrix the position of the roots of its determinant give sufficient conditions for stability of the closed-loop. Furthermore it is shown that if a coprime fraction description is done for the process transfer matrix then it is necessary and sufficient to check if the roots of the determinant of the denominator matrix lie inside the unit circle. This technique avoids the inversion of transfer matrices which is a numerically difficult task allowing the tuning of multivariable systems with many inputs and outputs. Performance is also studied and it is proven that the system has zero offset response to step changes in the reference, a property known to be valid for the single-input single-output case. For systems with an equal number of inputs and outputs the "inversion of the plant" is also proven. In this case the weights on the input are zero and the solution to the optimization problem results in a controller that inverts the plant and the output matches the reference. The use of a multivariable predictive control for an oil-water-gas separator is studied. The nonlinear model of the plant is linearized around a steady state and different predictive controllers are designed for it. The controller responds positively to changes in the parameters and performance objectives are pursued. Results show agreement with the simulations done for the linear model, it is concluded that predictive control is a successful control strategy for oil-water-gas separators. This method becomes an important tool for the analysis of predictive controllers, allowing the study of the effect of tuning parameters on the behavior of the system when the constraints are removed.

Nunes, Giovani Cavalcanti

339

Reaction of silicon ion (/sup 2/P) with silane (SiH/sub 4/, SiD/sub 4/). Heats of formation of SiH/sub n/, SiH/sub n//sup +/ (n = 1, 2, 3), and SiH/sub n//sup +/ (n = 0, 1, 2, 3). Remarkable isotope exchange reaction involving four hydrogen shifts  

SciTech Connect

The reaction of ground-state silicon ion with silane is investigated by using a guided ion beam tandem mass spectrometer. Reaction cross sections of all possible fragments, Si/sub m/H/sub n//sup +/ (m = 1, 2; n = 0, 1, 2, 3), as a function of relative kinetic energy are determined. All thermal energies, the major product is Si/sub 2/H/sub 2//sup +/. One remarkable reaction, the interchange of the projectile silicon ion with the target silicon atom, is observed at near zero kinetic energy. Labeling experiments employing /sup 30/Si/sup +/ for the beam or SiD/sub 4/ for the reactant indicate the intermediacy of the disilicon hydrides for the formation of the observed products. From the endothermicities of several reactions, the 298 K heats of formation for several ionic and neutral silicon hydrides are derived: ..delta..H/sub f//sup 0/(SiH) = 90.0 +/- 1.7, ..delta..H/sub f//sup 0/(SiH/sub 2/) = 69.0 +/- 2, ..delta..H/sub f//sup 0/(SiH/sub 3/) = 48.5 +/- 1.6, ..delta..H/sub f//sup 0/(SiH/sub 2//sup +/) = 276.1 +/- 1.7, ..delta..H/sub f//sup 0/(SiH/sub 3//sup +/) = 237.1 +/- 2, ..delta..H/sub f//sup 0/(Si/sub 2//sup +/) less than or equal to 328.0 +/- 2, ..delta..H/sub f//sup 0/(Si/sub 2/H/sup +/) less than or equal to 304.4 +/- 1.6, ..delta..H/sub f//sup 0/(Si/sub 2/H/sub 2/) less than or equal to 268.0 +/- 2.6, ..delta..H/sub f//sup 0/(Si/sub 2/H/sub 3//sup +/) = 266 +/- 2, all in kcal/mol. From an evaluation of these and other experiments, values of ..delta..H/sub f//sup 0/(SiH/sub 2//sup +/) and ..delta..H/sub f//sup 0/(SiH/sub 2/) of 278.0 +/- 1.4 and 68.5 +/- 1.5 kcal/mol, respectively, are recommended.

Boo, B.H.; Armentrout, P.B.

1987-06-10

340

Biological conversion of synthesis gas culture development  

SciTech Connect

Research continues on the conversion of synthesis by shift reactions involving bacteria. Topics discussed here include: biological water gas shift, sulfur gas utilization, experimental screening procedures, water gas shift studies, H{sub 2}S removal studies, COS degradation by selected CO-utilizing bacteria, and indirect COS utilization by Chlorobia. (VC)

Klasson, K.T.; Basu, R.; Johnson, E.R.; Clausen, E.C.; Gaddy, J.L.

1992-03-01

341

Cancellation of nonlinear Zeeman shifts with light shifts  

Microsoft Academic Search

Nonlinear Zeeman (NLZ) shifts arising from magnetic-field mixing of the two hyperfine ground states in alkali-metal atoms lead to splitting of magnetic-resonance lines. This is a major source of sensitivity degradation and the so-called ``heading errors'' of alkali-metal-vapor atomic magnetometers operating in the geophysical field range (B≈0.2-0.7G) . Here, it is shown theoretically and experimentally that NLZ shifts can be

K. Jensen; V. M. Acosta; J. M. Higbie; M. P. Ledbetter; S. M. Rochester; D. Budker

2009-01-01

342

Health Consequences of Shift Work.  

National Technical Information Service (NTIS)

This 30-month study, conducted by SRI and sponsored by the National Institute for Occupational Safety and Health, investigated the effect of working unconventional hours, i.e., afternoon, night, and rotating shifts, on the psychological and physiological ...

D. L. Tasto M. J. Colligan E. W. Skjei S. J. Polly

1978-01-01

343

Additivity of NMR isotope shifts  

SciTech Connect

One of the most interesting and useful aspects of the isotope effect on nuclear magnetic shielding is the proportionality of the shift to the number of substituted atoms in equivalent positions. In this paper we show the quantitative basis for the additivity of isotope shifts in NMR, using the CX/sub 4-n/Y/sub n/ (X,Y = H,D,T) system and the linear triatomic systems CO/sub 2/, NNO, and OCS as examples. We also predict small deviations from additivity and find that these deviations are consistent with those observed for /sup 14/N shifts in the NH/sub 4-n/D/sup +//sub n/ homologous series. Furthermore, we determine the mass dependence of the one-bond isotope shift.

Jameson, C.J.; Osten, H.

1984-11-15

344

[Shift work and breast cancer].  

PubMed

The International Agency on Research on Cancer (IARC) has recently classified "shiftwork that involves circadian disruption" as "probably carcinogenic to humans" (Group 2A) on the basis of "limited evidence in humans for the carcinogenicity of shift-work that involves nightwork", and "sufficient evidence in experimental animals for the carcinogenicity of light during the daily dark period (biological night)". The epidemiologic evidence of a relationship between shift and night work and breast cancer in women is based upon nine studies, six of which suggest a moderately increased risk to develop breast cancer after prolonged exposure to shift and night work. The aim of this paper is to summarize the possible physio-pathological mechanisms (internal disruption of biological circadian rhythms and clock genes, melatonin suppression through light by night, sleep deprivation) and the problems connected with a proper risk assessment of the risk for breast cancer risk in women shift workers. PMID:21086703

Costa, G

2010-01-01

345

Refining the shifted topological vertex  

SciTech Connect

We study aspects of the refining and shifting properties of the 3d MacMahon function C{sub 3}(q) used in topological string theory and BKP hierarchy. We derive the explicit expressions of the shifted topological vertex S{sub {lambda}}{sub {mu}}{sub {nu}}(q) and its refined version T{sub {lambda}}{sub {mu}}{sub {nu}}(q,t). These vertices complete results in literature.

Drissi, L. B.; Jehjouh, H.; Saidi, E. H. [Faculte des Sciences, Laboratory/UFR-Physique des Hautes Energies, Rabat, 1014 (Morocco); Groupement National de Physique des Hautes Energies (GNPHE), Siege focal:FS, Rabat, 1014 (Morocco)

2009-01-15

346

Determination of Gas and Water Volume Fraction in Oil Water Gas Pipe Flow Using Neural Networks Based on Dual Modality Densitometry  

Microsoft Academic Search

\\u000a The models of dual modality densitometry were developed. It can be used for measuring the gas volume fraction and water volume\\u000a fraction in oil water gas pipe flow. The models are complex. In order to solve models, it often uses simplified models. This\\u000a reduces measurement precision. The method of measuring gas and water volume fraction using neural networks was presented.

Chunguo Jing; Guangzhong Xing; Bin Liu; Qiuguo Bai

2006-01-01

347

Rapid quality checking of polyethylene water\\/gas-pipelines: a model based on pyrolysis-gas chromatography\\/mass spectrometry and discriminant analysis  

Microsoft Academic Search

Eighty-five samples taken from polyethylene (PE) water\\/gas-ducts were pyrolyzed (from triplicate to 9-fold analyses) at 700°C for 20 s in an N2 atmosphere using a platinum coil pyrolyzer and a tube cooled in liquid nitrogen. The pyrolyzed products were identified and quantified by gas chromatography\\/mass spectrometry (GC\\/MS), and subjected to discriminant analysis. The samples included intact materials and sections fractured

Guido C Galletti; Paola Bocchini; Francesca Pinelli; Romina Pozzi

2003-01-01

348

Estimation of Doppler Shift and Differential Doppler Shift.  

National Technical Information Service (NTIS)

This report is concerned with the measurement of frequency (Doppler shift) by a collection of sensors which may be grouped into two or more clusters (subarrays). The signal may be a sinusoid, or it may be a narrowband gaussian process whose center frequen...

P. M. Schultheiss

1977-01-01

349

Inositol phosphates induce DAPI fluorescence shift.  

PubMed

The polymer inorganic polyP (polyphosphate) and inositol phosphates, such as IP6 (inositol hexakisphosphate; also known as phytic acid), share many biophysical features. These similarities must be attributed to the phosphate groups present in these molecules. Given the ability of polyP to modify the excitation-emission spectra of DAPI we decided to investigate whether inositol phosphates possess the same property. We discovered that DAPI-IP6 complexes emit at approximately 550 nm when excited with light of wavelength 410-420 nm. IP5 (inositol pentakisphosphate) is also able to induce a similar shift in DAPI fluorescence. Conversely, IP3 (inositol trisphosphate) and IP4 (inositol tetrakisphosphate) are unable to shift DAPI fluorescence. We have employed this newly discovered feature of DAPI to study the enzymatic activity of the inositol polyphosphate multikinase and to monitor phytase phosphatase reactions. Finally, we used DAPI-IP6 fluorescence to determine the amount of IP6 in plant seeds. Using an IP6 standard curve this straight-forward analysis revealed that among the samples tested, borlotti beans possess the highest level of IP6 (9.4 mg/g of dry mass), whereas the Indian urad bean the lowest (3.2 mg/g of dry mass). The newly identified fluorescence properties of the DAPI-IP5 and DAPI-IP6 complexes allow the levels and enzymatic conversion of these two important messengers to be rapidly and reliably monitored. PMID:24670057

Kolozsvari, Bernadett; Parisi, Federica; Saiardi, Adolfo

2014-06-15

350

A molecular shift register based on electron transfer  

NASA Technical Reports Server (NTRS)

An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

1988-01-01

351

Doppler Shift in a Plasma.  

National Technical Information Service (NTIS)

It is first shown that the ideal electron plasma (presence of protons neglected) is unique among all dispersive media in that it does not distinguish any inertial frame of reference in terms of utility. The theory of the Doppler shift in an ideal plasma i...

B. Manz

1968-01-01

352

Illinois Shifting Gears Policy Evaluation  

ERIC Educational Resources Information Center

Illinois Shifting Gears is a multilevel initiative that has simultaneously created bridge programs in the field and altered state policy to facilitate the creation of more programs in the future. These efforts have informed each other, giving policymakers the opportunity to interact with practitioners, troubleshoot bridge programs, and make…

Weitzel, Peter C.

2009-01-01

353

Foundation Shifts Tack on Studies  

ERIC Educational Resources Information Center

Five years into an eight-year study of its high school improvement efforts, the Bill & Melinda Gates Foundation is shifting its strategy for evaluating the $1.3 billion grant program. The foundation's initiative, which is underwriting change efforts in more than 1,800 schools, is the nation's largest privately funded attempt to improve high…

Viadero, Debra

2006-01-01

354

Organizational change as shifting conversations  

Microsoft Academic Search

This article explores producing and managing change within conversationally constructed realities. Conversations are proposed as both the medium and product of reality construction within which change is a process of shifting conversations in the network of conversations that constitute organizations. In this context, change entails bringing new conversations into a sustained existence and the job of change managers is to

Jeffrey D. Ford

1999-01-01

355

Leadership Shifts in Changing Field  

ERIC Educational Resources Information Center

As groups representing local and state education players struggle to remain relevant in a policy conversation often dominated by foundations, think tanks, new advocacy groups, and political and business figures, a shift in leadership has been under way at major associations. Most of the changes have come as part of the natural churn; former…

Zubrzycki, Jaclyn

2013-01-01

356

Digital Phase-Shift Standard  

NASA Technical Reports Server (NTRS)

Digital phase-shift standard used in combination with oscillator to calibrate other phase standards and phase-angle voltmeters. Phase-shifter circuit provides two square-wave outputs, A and B, with phase difference between them selectable in 30 degrees increments. Circuit is used with input signals as low as 1 volt rms, in almost any waveform.

Cramp, J. A.

1983-01-01

357

Phase-Shifting Shearing Interferometer  

NASA Technical Reports Server (NTRS)

A single-element phase-shifting interferometer has been developed based on the lateral shearing interferometer. This new interferometer requires no precise alignment, and the phase is continuously varied by changes in the voltage across a commercially available liquid-crystal phase retarder.

Griffin, DeVon W.

2001-01-01

358

Flexible shift scheduling of physicians.  

PubMed

This research addresses a shift scheduling problem in which physicians at a German university hospital are assigned to demand periods over a planning horizon that can extend up to several weeks. When performing the scheduling it is necessary to take into account a variety of legal and institutional constraints that are imposed by a national labor agreement, which governs all physicians in German university hospitals. Currently, most medical departments develop their staff schedules manually at great cost and time. To solve the problem, a new modeling approach is developed that requires shifts to be generated implicitly. Rather than beginning with a predetermined number of shift types and start times, shifts are allowed to start at every pre-defined period in the planning horizon and extend up to 13 h with an hour-long break included. The objective is to find an assignment such that the total hours that have to be paid out as overtime are minimal under the restrictions given by the labor agreement. The problem is formulated as a mixed-integer program and solved with CPLEX. During the solution process individual lines-of-work are constructed for each physician. Using data from an anesthesia department, computational results indicate that high quality schedules can be obtained much more quickly than by current practice. PMID:19739361

Brunner, Jens O; Bard, Jonathan F; Kolisch, Rainer

2009-09-01

359

Doppler phase shifting using dual, switched phase shifting devices  

NASA Technical Reports Server (NTRS)

A system of inducing a phase shift using moving reflector elements. The moving reflectors can be moving mirrors or an acousto-optical filter. The moving reflectors oscillate i.e. the move first in a first direction and then in a second direction. Two different reflectors are used so that the light can be switched between the reflectors. During a first portion of the cycle the light is coupled to the first modulator which moves the reflector in the first direction. The second modulator is out of phase with the first modulator, and the light is switched to that second modulator during a second portion of the cycle. The second modulator is also moving in the first direction when the light is applied thereto. In this way, the light obtains a constant direction Doppler shift.

Gutierrez, Roman C. (Inventor)

2002-01-01

360

Epoxide Reactions  

NASA Astrophysics Data System (ADS)

This puzzle presents 16 numbered reactions of epoxides and 11 possible products designated by letters. The reactions are matched with the letters corresponding to the products to answer a playful question.

Bertolini, Thomas

2002-07-01

361

Reaction time  

Microsoft Academic Search

Reviews five studies of reaction time published during 1917-1918. The Studies pertain to (a) effect of continuous, intermittent, continuous-intermittent auditory distraction upon sensory reactions to auditory stimuli (b) processes involved in the fore-period, main period and after-period of the controlled associative reaction with special reference to the analysis of fore-period (c) use of reaction key suspended as a pendulum and

V. A. C. Henmon

1918-01-01

362

Special Reactions  

NSDL National Science Digital Library

The basics of chemical reactions were covered in the first chemistry book, including how to write and balance chemical equations that represent those reactions. There is also a quick review of chemical reactions in Chapter 1 of this book. We're going to d

Robertson, William C.

2010-03-01

363

Enzyme Reactions  

NSDL National Science Digital Library

This video shows an enzyme reaction lab. The teacher demonstrates how the enzyme, catalase, reacts with hydrogen peroxide (a substrate found in cells). The teacher first demonstrates a normal enzyme reaction. He or she then goes on to show how manipulating temperature and pH will affect the reaction of an enzyme.

School, Minerva D.

2011-10-03

364

Anthropometric changes and fluid shifts  

NASA Technical Reports Server (NTRS)

In an effort to obtain the most comprehensive and coherent picture of changes under weightlessness, a set of measurements on Skylab 2 was initiated and at every opportunity, additional studies were added. All pertinent information from ancillary sources were gleaned and collated. On Skylab 2, the initial anthropometric studies were scheduled in conjunction with muscle study. A single set of facial photographs was made in-flight. Additional measurements were made on Skylab 3, with photographs and truncal and limb girth measurements in-flight. Prior to Skylab 4, it was felt there was considerable evidence for large and rapid fluid shifts, so a series of in-flight volume and center of mass measurements and infrared photographs were scheduled to be conducted in the Skylab 4 mission. A number of changes were properly documented for the first time, most important of which were the fluid shifts. The following description of Skylab anthropometrics address work done on Skylab 4 primarily.

Thornton, W. E.; Hoffler, G. W.; Rummel, J. A.

1977-01-01

365

In situ Characterization of Pt Catalysts Supported on Ceria Modified TiO(2) for the WGS reaction: Influence of Ceria Loading  

SciTech Connect

This work analyzes the influence of cerium content (6-15 wt%) on a TiO{sub 2} support over the structure and water gas shift (WGS) activity of Pt catalysts. The structural properties of these Pt/Ce-TiO{sub 2} catalysts were characterized by XRD, TEM and XANES. Physicochemical characterization of the catalysts showed differences in the structure and dispersion of Ce entities on the support with Ce loading. For the samples with low ceria content (6 wt%), cerium is deposited on the support in the form of CeO{sub x} clusters in a highly dispersed state in close interaction with the Ti atoms. The formation of CeO{sub x} clusters at low Ce-loading on the support facilitates the dispersion of small particles of Pt and improves the reducibility of ceria component at low temperatures. The changes in platinum dispersion and support reducibility with Ce-loading on the TiO{sub 2} support lead to significant differences in the WGS activity. Pt supported on the sample with lower Ce content (6 wt%) shows better activity than those corresponding to catalysts with higher Ce content (15 wt%). Activity measurements coupled with catalysts characterization suggest that the improvement in the reducibility of the support with lower Ce content was associated with the presence of CeO{sub x} clusters of high reducibility that improve the chemical activity of the oxide-metal interfaces at which the WGS reaction takes place.

Rodriguez J. A.; Barrio, L.; Zhou, G.; Gonzalez, I.D.; Estrella, M.; Hanson, J.; Navarro, R.M.; Fierro, J.L.G.

2012-01-01

366

Multicolor Holography With Phase Shifting  

NASA Technical Reports Server (NTRS)

Prototype apparatus constructed to test feasibility of two-color holographic interferometric scheme in which data for reconstructing holographic wavefront obtained with help of phase-shifting technique. Provides two sets of data needed to solve equations for effects of temperature and concentration. Concept extended to holography at three or more wavelengths to measure three or more phenomena associated with significant variations in index of refraction

Vikram, Chandra S.

1996-01-01

367

Considerations Based on Reaction Rate on Char Gasification Behavior in Two-stage Gasifier for Biomass  

NASA Astrophysics Data System (ADS)

In order to develop a small-scale gasifier in which biomass can be converted to energy with high efficiency, we planned a gasification process that consists of two parts: pyrolysis part (rotary kiln) and gasification part (downdraft gasifier). We performed fundamental experiments on gasification part and discussed the appropriate conditions such as air supply location, air ratio, air temperature and hearth load. We considered the results by calculating reaction rates of representative reactions on char gasification part and found that water gas reaction is dominant in the reduction area and its behavior gives important information to decide the adequate length of the char layer.

Taniguchi, Miki; Nishiyama, Akio; Sasauchi, Kenichi; Ito, Yusuke; Akamatsu, Fumiteru

368

Nonlocality in Deuteron Stripping Reactions  

NASA Astrophysics Data System (ADS)

We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by ˜40MeV from the “Ed/2” value frequently used in the analysis of experimental data, where Ed is the incident deuteron energy. The “Ed/2” rule lies at the heart of all three-body analyses of (d, p) reactions performed so far with the aim of obtaining nuclear structure properties such as spectroscopic factors and asymptotic normalization coefficients that are crucial for our understanding of nuclear shell evolution in neutron- and proton-rich regions of the nuclear periodic table and for predicting the cross sections of stellar reactions. The large predicted shift arises from the large relative kinetic energy of the neutron and proton in the incident deuteron in those components of the n+p+A wave function that dominate the (d, p) reaction amplitude. The large shift reduces the effective d-A potentials and leads to a change in predicted (d, p) cross sections, thus affecting the interpretation of these reactions in terms of nuclear structure.

Timofeyuk, N. K.; Johnson, R. C.

2013-03-01

369

Frequency shift discrimination: Can homing pigeons locate infrasounds by Doppler shifts?  

Microsoft Academic Search

Summary Homing pigeons can detect small shifts in sound frequency at 1, 2, 5, 10, and 20 Hz. Their thresholds range from a 1% shift at 20 Hz to a 7% shift at 1 Hz. The frequency shifts used were designed to simulate the natural Doppler shifts resulting from changes in flight path. Their ability was sufficiently sensitive to make

Douglas B. Quine; Melvin L. Kreithen

1981-01-01

370

Incoherent and coherent tune shifts  

SciTech Connect

The longitudinal and transverse microwave instabilities are the two important limiting factors for the performance of an accelerator. Comparing with the fairly unified approach for the longitudinal microwave instabilities, different approaches have been used to define the transverse microwave instabilities. One reason of this is related to the role played by the space charge incoherent and coherent tune shifts. In this article, the transverse microwave instabilities will be discussed by defining separately the roles of the space charge incoherent and coherent tunes, which are represented by the space charge transverse impedances. Preliminary results for the AGS as proton driver are presented by using this approach.

Zhang, S.Y. [Brookhaven National Lab., Upton, NY (United States). AGS Dept.

1995-12-31

371

Incoherent and coherent tune shifts  

SciTech Connect

The longitudinal and transverse microwave instabilities are the two important limiting factors for the performance of an accelerator. Comparing with the fairly unified approach for the longitudinal microwave instabilities, different approaches have been used to define the transverse microwave instabilities. One reason of this is related to the role played by the space charge incoherent and coherent tune shifts. In this article, the transverse microwave instabilities will be discussed by defining separately the roles of the space charge incoherent and coherent tunes, which are represented by the space charge transverse impedances. Preliminary results for the AGS as proton driver are presented by using this approach. {copyright} {ital 1996 American Institute of Physics.}

Zhang, S.Y. [AGS Department, BNL, Upton, New York 11973 (United States)

1996-05-01

372

Paradigm shifts in corneal transplantation.  

PubMed

Conventional corneal transplantation, in the form of penetrating keratoplasty (PK), involves full-thickness replacement of the cornea, and is a highly successful procedure. However, the cornea is anatomically a multi-layered structure. Pathology may only affect individual layers of the cornea, hence selective lamellar surgical replacement of only the diseased corneal layers whilst retaining unaffected layers represents a new paradigm shift in the field. Recent advancements in surgical techniques and instrumentation have resulted in several forms of manual, microkeratome and femto-second laser-assisted lamellar transplantation procedures. Anterior lamellar keratoplasty (ALK) aims at replacing only diseased or scarred corneal stroma, whilst retaining the unaffected corneal endothelial layer, thus obviating the risk of endothelial allograft rejection. Posterior lamellar keratoplasty/endothelial keratoplasty (PLK/EK) involves the replacement of the dysfunctional endothelial cell layer only. Whilst significant technical and surgical challenges are involved in performing lamellar micro-dissection of a tissue which is only 0.5 mm thick, the benefits of a more controlled surgical procedure and improved graft survival rates have resulted in a shift away from conventional PK. This review details the current advances in emerging lamellar corneal surgical procedures and highlights the main advantages and disadvantages of these new lamellar corneal procedures. PMID:19434336

Tan, Donald T H; Anshu, Arundhati; Mehta, Jodhbir S

2009-04-01

373

SHIFT: Shared Information Framework and Technology Concept.  

National Technical Information Service (NTIS)

Shared Information Framework and Technology (SHIFT) was originally created for MNE 5 covering the aspects of information sharing as a concept and its supporting tools within a comprehensive approach framework. SHIFT is used in MNE 5 to experiment with inf...

S. Vesterinen

2009-01-01

374

Shift register generators and applications to coding  

NASA Technical Reports Server (NTRS)

The most important properties of shift register generated sequences are exposed. The application of shift registers as multiplication and division circuits leads to the generation of some error correcting and detecting codes.

Morakis, J. C.

1968-01-01

375

Reaction Time  

NSDL National Science Digital Library

In this activity, learners explore reaction time and challenge themselves to improve their coordination. Do you want to move faster? Catch that ball that you never seem to see in time? Use a simple test to help you improve your reaction (or response) time.

Science, New Y.

1999-01-01

376

Lasers with internal frequency-shifted feedback  

SciTech Connect

Properties of lasers with frequency-shifted feedback are discussed. The analysis concentrates on the passive characteristics of the cavity. Particular emphasis is given to the case in which the frequency shift is small compared to the free spectral range of a normal Fabry-Perot cavity with no frequency shift.

Kowalski, F.V. (Colorado School of Mines, Golden, CO (United States). Dept. of Physics); Balle, S.; Littler, I.C.M.; Bergmann, K. (Fachbereich Physik der Univ., Kaiserslautern (Germany))

1994-04-01

377

Combined-Phase-Shift Waveguide Polarizer  

Microsoft Academic Search

A waveguide polarizer exploiting two different phase shift phenomena is presented in this letter. Iris-type discontinuities are in fact introduced in a waveguide structure having different propagation constants for the two principal polarizations. In this way, the required 90 differential phase shift is obtained combining the iris phase shift with the waveguide one. Several operative conditions arise from the combination

Giuseppe Virone; Riccardo Tascone; Oscar Antonio Peverini; Giuseppe Addamo; Renato Orta

2008-01-01

378

Mean Shift, Mode Seeking, and Clustering  

Microsoft Academic Search

Abstract-Mean shift, a simple iterative procedure that shifts each data point to the average of data points in its neighborhood, is generalized and analyzed in this paper. This generalization makes some k-means like clustering algorithms its special cases. It is shown that mean shift is a mode-seeking process on a surface constructed with a \\

Yizong Cheng

1995-01-01

379

Combined Shift-Methanation Processes. Final Report.  

National Technical Information Service (NTIS)

This study compares three combined shift and methanation processes with the separate shift and methanation process used by Braun in the commercial concept design. The three combined shift and methanation processes are the ICI-Krupp Koppers, R M Parsons, a...

N. G. Kertamus

1978-01-01

380

Physical origin of the Gouy phase shift  

Microsoft Academic Search

We show explicitly that the well-known Gouy phase shift of any focused beam originates from transverse spatial confinement, which, through the uncertainty principle, introduces a spread in the transverse momenta and hence a shift in the expectation value of the axial propagation constant. A general expression is given for the Gouy phase shift in terms of expectation values of the

Simin Feng; Herbert G. Winful

2001-01-01

381

Strong Shift Equivalence of $C^*$-correspondences  

Microsoft Academic Search

We define a notion of strong shift equivalence for $C^*$-correspondences and show that strong shift equivalent $C^*$-correspondences have strongly Morita equivalent Cuntz-Pimsner algebras. Our analysis extends the fact that strong shift equivalent square matrices with non-negative integer entries give stably isomorphic Cuntz-Krieger algebras.

PAUL S. MUHLY; David Pask; Mark Tomforde

2005-01-01

382

Strong shift equivalence of C *-correspondences  

Microsoft Academic Search

We define a notion of strong shift equivalence for C*-correspondences and show that strong shift equivalent C*-correspondences have strongly Morita equivalent Cuntz-Pimsner algebras. Our analysis extends the fact that strong shift\\u000a equivalent square matrices with non-negative integer entries give stably isomorphic Cuntz-Krieger algebras.

Paul S. Muhly; David Pask; Mark Tomforde

2008-01-01

383

Reaction Kinetics  

NASA Astrophysics Data System (ADS)

Detonation, which is the result of a reacting high explosive, is not a simple chemical reaction. Instead it is a complex process of rapid chemical changes that give rise to equally rapid mechanical and physical changes. Initially, as the explosive is initiated or Subscriptjected to a stimulus such as a shock wave, energy is transferred to the material causing mechanical deformation and heating. The transferred energy and heating produce chemically excited species, leading to initial bond-breaking or reaction initiation. These processes are thought to occur in a Hot-Molecule Zone (HMZ). Once reaction is initiated, sequences of chemical reactions follow resulting in the liberation of chemical energy and the production of gaseous reaction products.

Peiris, Suhithi M.

384

Gold, Copper and Platinum Nanoparticles Dispersed on CeOx\\/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level  

Microsoft Academic Search

At small coverages of ceria on TiOâ(110), the CeOâ nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of CeâOâ dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42{sup o} with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on

J. A. Rodriguez; Jesus Graciani; Dario Stacchiola; S. D. Senanayake; L. Barrio; Javier Fdez. Sanz

2010-01-01

385

Sensitivity of Fischer-Tropsch Synthesis and Water-Gas Shift Catalysts to Poisons from High-Temperature High-Pressure Entrained-Flow (EF) Oxygen-Blown Gasifier Gasification of Coal\\/Biomass Mixtures  

Microsoft Academic Search

The successful adaptation of conventional cobalt and iron-based Fischer-Tropsch synthesis catalysts for use in converting biomass-derived syngas hinges in part on understanding their susceptibility to byproducts produced during the biomass gasification process. With the possibility that oil production will peak in the near future, and due to concerns in maintaining energy security, the conversion of biomass-derived syngas and syngas derived

Burtron Davis; Gary Jacobs; Wenping Ma; Khalid Azzam; Dennis Sparks; Wilson Shafer

2010-01-01

386

Amplitude dependent shift of betatron oscillation center  

NASA Astrophysics Data System (ADS)

We have analytically calculated and measured the amplitude-dependent shift of the betatron oscillation center at the electron storage ring, NewSUBARU. The shift is due to nonzero average horizontal deflections at the normal sextupole magnets. The shifted center forms a displaced closed orbit and is measured by a closed orbit distortion measurement system, although no single electron runs on this orbit. The measured shifts by betatron oscillations agreed with the theoretical calculation except the variation of data points, which did not obey the ring symmetry. Additional measurements, whose results included the effect of the circumference shift, experimentally proved the amplitude dependent circumference shift for the first time. We also discuss some applications of the shift, which has never been previously analyzed.

Shoji, Yoshihiko; Takao, Masaru; Nakamura, Takeshi

2014-06-01

387

The Modality Shift Experiment in Adults and Children with High Functioning Autism  

PubMed Central

This study used the modality shift experiment, a relatively simple reaction time measure to visual and auditory stimuli, to examine attentional shifting within and across modalities in 33 children and 42 adults with high-functioning autism as compared to matched numbers of age- and ability-matched typical controls. An exaggerated “modality shift effect” relative to the TD children occurred for the children with autism in conditions involving the reaction time when shifting from sound to light but not from light to sound. No exaggerated MSE was found for the adults with autism; rather, their responses were characterized by a generalized slowness relative to the adults with TD. These results suggest a lag in maturational development in autism in basic information processing mechanisms.

Williams, Diane L.; Goldstein, Gerald; Minshew, Nancy J.

2012-01-01

388

[Periosteal reaction].  

PubMed

The periosteal membrane covers the cortical bone except for the articular surface. The deep layer of the periosteum contains bone-forming mesenchymal cells, capillaries, and nerves. This layer is more active in infants than in adults. Prostaglandin osteopathy, infantile cortical hyperostosis, hypervitaminosis A, and congenital syphilis are examples of periostitis in infants. Incidental asymptomatic periosteal reactions are usually either physiological changes or cortical bone irregularities simulating periostitis. On the other hand, symptomatic periosteal reactions of single bone, such as bone tumor, tumor-like lesion, infection, and trauma, are always pathologic. Careful radiological analysis of periosteal reactions is needed to evaluate the activity and aggressiveness of the lesions. Periosteal reactions of multiple bones usually show solid smooth or undulating patterns. They include pachydermoperiostosis, secondary hypertrophic osteoarthropathy, vascular insufficiency, renal osteodystrophy, and thyroid acropachy. These are usually skeletal manifestations of systemic disorders. PMID:10429428

Fukuda, K

1999-06-01

389

Drug Reactions  

MedlinePLUS

... can also cause unwanted reactions. One problem is interactions, which may occur between Two drugs, such as ... and diseases, such as aspirin and peptic ulcers Interactions can change the actions of one or both ...

390

Recovery and detachment between shifts, and fatigue during a twelve-hour shift.  

PubMed

The study investigated the role of recovery and detachment in the break period between two shifts for fatigue in the current shift. A time-based paper-and-pencil diary study was carried out observing sixty-four railway controllers over ten consecutive working shifts. The results demonstrated that fatigue in the current shift was not only affected by recovery and psychological detachment during break phases before a shift, but also by fatigue at shift onset and perceived workload during the shift. PMID:22317209

Korunka, Christian; Kubicek, Bettina; Prem, Roman; Cvitan, Antonio

2012-01-01

391

Red Shifts and Existing Speculations  

NASA Astrophysics Data System (ADS)

There are many current flaws, mysteries, and errors in the standard model of the universe - all based upon speculative interpretation of many excellent and verified observations. The most serious cause of some errors is the speculation about the meaning of the redshifts observed in the 1930s by Hubble. He ascribed the redshifts as due to ``an apparent Doppler effect''. This led to speculation that the remote stars were receding, and the universe was expanding -- although without observational proof of the actual receding velocity of the stars. The age of the universe, based upon the Hubble constant is pure speculation because of lack of velocity demonstration. The belief in expansion, the big bang, and of inflation should be reexamined. Also, the redshift cannot always be used as a distance measure, particularly for photons from quasars containing massive black holes that can reduce photon energy through gravitational attraction. If the linear Hubble constant is extrapolated to the most remote super novae and beyond, it would eventually require that the corresponding photon energy go to zero or become negative -- according to Hubble linear relationship. This should require a reexamination of the meaning of the red shift and the speculative consequences and give a model with fewer mysteries.

Aisenberg, Sol

2009-03-01

392

Eigenpolarizations for Giant Transverse Optical Beam Shifts  

NASA Astrophysics Data System (ADS)

We show how careful control of the incident polarization of a light beam close to the Brewster angle gives a giant transverse spatial shift on reflection. This resolves the long-standing puzzle of why such beam shifts transverse to the incident plane (Imbert-Fedorov shifts) tend to be an order of magnitude smaller than the related Goos-Hänchen shifts in the longitudinal direction, which are largest close to critical incidence. We demonstrate that with the proper initial polarization the transverse displacements can be equally large, which we confirm experimentally near Brewster incidence. In contrast to the established understanding, these polarizations are elliptical and angle dependent. We explain the magnitude of the Imbert-Fedorov shift by an analogous change of the symmetry properties for the reflection operators as compared to the Goos-Hänchen shift.

Götte, Jörg B.; Löffler, Wolfgang; Dennis, Mark R.

2014-06-01

393

VERIFICATION OF THE SHIFT MONTE CARLO CODE  

Microsoft Academic Search

Shift is a new hybrid Monte Carlo\\/deterministic radiation transport code being developed at Oak Ridge National Laboratory. At its current stage of development, Shift includes a fully-functional parallel Monte Carlo capability for simulating eigenvalue and fixed-source multigroup transport problems. This paper focuses on recent efforts to verify Shift s Monte Carlo component using the two-dimensional and three-dimensional C5G7 NEA benchmark

Nicholas Sly; Mervin Brenden Mervin; Scott W Mosher; Thomas M Evans; G. Ivan Maldonado

2012-01-01

394

[Occupational diseases and night-shift work].  

PubMed

Shift and night work concern every year more and more workers, specifically women. Recent recommendations on good practice for the medical surveillance of shift and night workers have been edited in France. They confirmed that this kind of organisation, unavoidable in some economical sectors is associated with a significant higher risk of sleep and wake disorders, cardiovascular disorders, overweight and obesity, breath cancer. Specific surveillance of shift and night workers is recommended in occupational health. PMID:24851373

Bayon, Virginie; Léger, Damien

2014-03-01

395

Can sunlight shift the Earth onto a different orbit?  

NASA Astrophysics Data System (ADS)

This article comes from a question asked by a student of mine: if the Sun radiates energy in the form of electromagnetic waves, could they shift the Earth from its current orbit on a suitable timescale? The answer to such a question is apparently obvious and trivial. Nevertheless, it requires an instructive reasoning and interesting estimates of orders of magnitude. Given the particularly positive reaction of my students to the solution given to the question, I think it is useful to report it here for the possible benefit of other students.

Esposito, S.

2011-09-01

396

Exercise, Energy Balance and the Shift Worker  

PubMed Central

Shift work is now common in society and is not restricted to heavy industry or emergency services, but is increasingly found amongst ‘white collar’ occupations and the growing number of service industries. Participation in shift work is associated with increased body mass index, prevalence of obesity and other health problems. We review the behavioural and biological disturbances that occur during shift work and discuss their impact on leisure-time physical activity and energy balance. Shift work generally decreases opportunities for physical activity and participation in sports. For those shift workers who are able to exercise, subjective and biological responses can be altered if the exercise is taken at unusual times of day and/or if the shift worker is sleep-deprived. These altered responses may in turn impact on the longer-term adherence to an exercise programme. The favourable effects of exercise on body mass control and sleep quality have not been confirmed in shift workers. Similarly, recent reports of relationships between sleep duration and obesity have not been examined in a shift work context. There is no evidence that exercise can mediate certain circadian rhythm characteristics (e.g. amplitude or timing) for improved tolerance to shift work. Total energy intake and meal composition do not seem to be affected by participation in shift work. Meal frequency is generally reduced but snacking is increased on the night shift. Unavailability of preferred foods in the workplace, a lack of time, and a reduced desire to eat at night explain these findings. ‘Normal’ eating habits with the family are also disrupted. The metabolic responses to food are also altered by shift work-mediated disruptions to sleep and circadian rhythms. Whether any interactions on human metabolism exist between timing or content of food intake and physical activity during shift work is not known at present. There are very few randomised controlled studies on the efficacy of physical activity or dietary interventions during shift work. Some favourable effects of such interventions on fatigue levels at work have been reported, but biological and behavioural outcomes relevant to long-term health and energy balance have not been studied adequately. In addition, recruitment and retention of research participants for randomised controlled trials of physical activity or dietary interventions has been very difficult. We present a model of the various behavioural and biological factors relevant to exercise and energy balance during shift work as a framework for future research.

Atkinson, Greg; Fullick, Sarah; Grindey, Charlotte; Maclaren, Don; Waterhouse, Jim

2009-01-01

397

Exercise, energy balance and the shift worker.  

PubMed

Shift work is now common in society and is not restricted to heavy industry or emergency services, but is increasingly found amongst 'white collar' occupations and the growing number of service industries. Participation in shift work is associated with increased body mass index, prevalence of obesity and other health problems. We review the behavioural and biological disturbances that occur during shift work and discuss their impact on leisure-time physical activity and energy balance. Shift work generally decreases opportunities for physical activity and participation in sports. For those shift workers who are able to exercise, subjective and biological responses can be altered if the exercise is taken at unusual times of day and/or if the shift worker is sleep deprived. These altered responses may in turn impact on the longer-term adherence to an exercise programme. The favourable effects of exercise on body mass control and sleep quality in shift workers have not been confirmed. Similarly, recent reports of relationships between sleep duration and obesity have not been examined in a shift work context. There is no evidence that exercise can mediate certain circadian rhythm characteristics (e.g. amplitude or timing) for improved tolerance to shift work. Total energy intake and meal composition do not seem to be affected by participation in shift work. Meal frequency is generally reduced but snacking is increased on the night shift. Unavailability of preferred foods in the workplace, a lack of time, and a reduced desire to eat at night explain these findings. 'Normal' eating habits with the family are also disrupted. The metabolic responses to food are also altered by shift work-mediated disruptions to sleep and circadian rhythms. Whether any interactions on human metabolism exist between timing or content of food intake and physical activity during shift work is not known at present. There are very few randomized controlled studies on the efficacy of physical activity or dietary interventions during shift work. Some favourable effects of such interventions on fatigue levels at work have been reported, but biological and behavioural outcomes relevant to long-term health and energy balance have not been studied adequately. In addition, recruitment and retention of research participants for randomized controlled trials of physical activity or dietary interventions have been very difficult. We present a model of the various behavioural and biological factors relevant to exercise and energy balance during shift work as a framework for future research. PMID:18620467

Atkinson, Greg; Fullick, Sarah; Grindey, Charlotte; Maclaren, Don

2008-01-01

398

In-line phase shift tomosynthesis  

SciTech Connect

Purpose: The purpose of this work is to (1) demonstrate laboratory measurements of phase shift images derived from in-line phase-contrast radiographs using the attenuation-partition based algorithm (APBA) of Yan et al.[Opt. Express 18(15), 16074–16089 (2010)], (2) verify that the APBA reconstructed images obey the linearity principle, and (3) reconstruct tomosynthesis phase shift images from a collection of angularly sampled planar phase shift images.Methods: An unmodified, commercially available cabinet x-ray system (Faxitron LX-60) was used in this experiment. This system contains a tungsten anode x-ray tube with a nominal focal spot size of 10 ?m. The digital detector uses CsI/CMOS with a pixel size of 50 × 50 ?m. The phantoms used consisted of one acrylic plate, two polystyrene plates, and a habanero pepper. Tomosynthesis images were reconstructed from 51 images acquired over a ±25° arc. All phase shift images were reconstructed using the APBA.Results: Image contrast derived from the planar phase shift image of an acrylic plate of uniform thickness exceeded the contrast of the traditional attenuation image by an approximate factor of two. Comparison of the planar phase shift images from a single, uniform thickness polystyrene plate with two polystyrene plates demonstrated an approximate linearity of the estimated phase shift with plate thickness (?1600 rad vs ?2970 rad). Tomographic phase shift images of the habanero pepper exhibited acceptable spatial resolution and contrast comparable to the corresponding attenuation image.Conclusions: This work demonstrated the feasibility of laboratory-based phase shift tomosynthesis and suggests that phase shift imaging could potentially provide a new imaging biomarker. Further investigation will be needed to determine if phase shift contrast will be able to provide new tissue contrast information or improved clinical performance.

Hammonds, Jeffrey C.; Price, Ronald R.; Pickens, David R.; Donnelly, Edwin F. [Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232 (United States)] [Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232 (United States)

2013-08-15

399

Reaction Time  

NSDL National Science Digital Library

In this activity, learners conduct an experiment to test how fast they can react. Learners try to catch a piece of paper with a ruler printed on it (or a ruler) as quickly as they can. Learners collect data and compare the reaction times of friends and family.

Boston, Wgbh

2003-01-01

400

Reaction time  

Microsoft Academic Search

Reviews the studies on RT by H. E. Burtt, A. T. Poffenberger, T. Topciu, and H. Woodrow (1915-1916). It was found that the with shorter intervals, the time of the 1st reaction was lengthened through the inhibiting and distracting influence of the 2nd stimulus. The RT to the cessation of sound and light stimuli and to beginning of the stimuli

V. A. C. Henmon

1916-01-01

401

Categorization of some oscillatory enzymatic reactions  

SciTech Connect

We investigate the categorization of two or more proposed reaction mechanisms for each of the following oscillatory enzymatic reactions: (1) the peroxidase-oxidase reaction; (2) glycolytic oscillations; (3) oscillations of cyclic AMP in smile mold cells; (4) enzymatic pH oscillations; (5) calcium spiking in cytosol. We use prior work in stoichiometric network analysis and categorization of oscillatory reactions to identify in each proposed reaction mechanism essential and nonessential species, the specific role of each essential species, the connectivity of the essential species, including the identification of the reactions leading to oscillatory instabilities, and the category. For each model, we predict the result of several experiments including relative amplitudes, quench amplitudes, phase shifts, and sign symbolic concentration shifts and compare them with those from available experiments. These and several other experiments such as bifurcation analysis, phase response curves, entrainment experiments, qualitative and quantitative pulsed species response, delay experiments, and external periodic perturbation provide stringent tests of proposed reaction mechanisms, and appropriate ones are suggested to discriminate among competing mechanisms for a given reaction. We find the necessity for introducing a new subcategory in our categorization of oscillatory reactions. 45 refs., 6 figs., 6 tabs.

Schreiber, I. [Prague Inst. of Chemical Technology (Czechoslovakia)] [Prague Inst. of Chemical Technology (Czechoslovakia); Hung, Y.F.; Ross, J. [Stanford Univ., CA (United States)] [Stanford Univ., CA (United States)

1996-05-16

402

A Short History of Three Chemical Shifts  

ERIC Educational Resources Information Center

A short history of chemical shifts in nuclear magnetic resonance (NMR), electron spectroscopy for chemical analysis (ESCA) and Mossbauer spectroscopy, which are useful for chemical studies, is described. The term chemical shift is shown to have originated in the mistaken assumption that nuclei of a given element would all undergo resonance at the…

Nagaoka, Shin-ichi

2007-01-01

403

Shift Work: Is There a Better Way.  

National Technical Information Service (NTIS)

Rotating shift work causes fatigue and other physical problems in many Air Force personnel. If Air Force supervisors and workers were more aware of their daily body rhythms and what effect rotating shift work has on those rhythms, they could better plan t...

M. F. Fukey

1985-01-01

404

Shifting and Focusing Auditory Spatial Attention  

Microsoft Academic Search

Auditory spatial attention was investigated by manipulating spatial and temporal relations between an auditory spatial cue and an auditory target. The principal findings were that performance improved as time available to shift attention to a cued spatial position increased, accurate spatial cues facilitated performance more than inaccurate cues, performance was virtually identical for shifts of attention ranging from 0° and

Todd A. Mondor; Robert J. Zatorre

1995-01-01

405

Lamb Shift in Nonrelativistic Quantum Electrodynamics.  

ERIC Educational Resources Information Center

The bound electron self-energy or Lamb shift is calculated in nonrelativistic quantum electrodynamics. Retardation is retained and also an interaction previously dropped in other nonrelativistic approaches is kept. Results are finite without introducing a cutoff and lead to a Lamb shift in hydrogen of 1030.9 MHz. (Author/JN)

Grotch, Howard

1981-01-01

406

Frequency shift by optical coherent control  

SciTech Connect

We report the experimental observation of an optically controllable shift of the central frequency of a laser pulse, using a scheme based on dynamical electromagnetically induced transparency. This is evidence of frequency shift controllable by a coherent process. Original theoretical results are in agreement with the experimental data.

Ignesti, Emilio [Dipartimento di Fisica, Universita di Siena, Via Roma 56, I-53100 Siena (Italy); Buffa, Roberto [Dipartimento di Fisica, Universita di Siena, Via Roma 56, I-53100 Siena (Italy); CNISM, Unita di Siena, Via Roma 56, I-53100 Siena (Italy); Fini, Lorenzo; Sali, Emiliano; Cavalieri, Stefano [Dipartimento di Fisica, Universita di Firenze and CNISM, Via G. Sansone 1, I-50019 Sesto Fiorentino, Firenze (Italy); European Laboratory for Non-linear Spectroscopy (LENS), Universita di Firenze, Via N. Carrara 1, I-50019 Sesto Fiorentino, Firenze (Italy); Tognetti, Marco V. [CNISM, Unita di Siena, Via Roma 56, I-53100 Siena (Italy)

2010-02-15

407

Changes in psychophysiological functions during night shift in nurses  

Microsoft Academic Search

The effects of changing from a full-day to a half-day shift work before a night duty shift on physiological and psychological\\u000a functions during the night shift were investigated in 12 healthy unmarried nurses working on the same ward of a university\\u000a hospital. Three shift patterns, i.e., a day shift following a day shift, a night shift following a day shift,

Fumio Kobayashi; Hikari Furui; Yasuhiro Akamatsu; Takemasa Watanabe; Hiroshi Horibe

1996-01-01

408

SPONTANEOUS AND CATALYZED HYDROGEN SHIFTS IN RADICAL CATIONS HAVING A PHOSPHORYL OR CARBONYL GROUP  

Microsoft Academic Search

Intermolecular and intramolecular hydrogen shifts represent a key component of a vast number of chemical reactions. This is particularly true for radical cations, whose high reactivity makes them prone to isomerization and dissociation reactions. In the context of the experimental work in this thesis, hydrogen transfers involved in both the intra-and inter-molecular isomerization of radical cations containing a phosphoryl (P=O)

Lisa Natasha Heydorn

2003-01-01

409

Rainbow-shift mechanism behind discrete optical-potential ambiguities  

SciTech Connect

Some years ago, Drisko {ital et} {ital al}. suggested that the discrete ambiguity often encountered for elastic scattering optical potentials could be understood as being due to the interior or small-{ital l} {ital S}-matrix elements for two equivalent'' potentials differing in phase by 2{pi}, {ital l}-by-{ital l}. We point out that the {ital absence} of this phase change for peripheral partial waves is equally essential, and suggest that a deeper understanding of the ambiguity may be achieved by viewing it as a consequence of a farside interference between interior and peripheral partial waves. It is this interference which produces the broad Airy maxima'' of a nuclear rainbow, and we show that a Drisko-type phase-shift increment {delta}{sub {ital l}}{r arrow}({delta}{sub {ital l}}+{pi}) for low-{ital l} phases relative to the high-{ital l} ones is exactly what is needed to shift a farside rainbow pattern by one Airy maximum, thus providing an equivalent rainbow-shift'' interpretation of the discrete ambiguity. The physical importance of both interpretations lies in the fact that the existence of discrete ambiguities (as well as of nuclear rainbows) is explicit evidence for low-{ital l} transparency in nucleus-nucleus collisions. The essential role played by low partial waves explains why peripheral reactions have generally not proven helpful in resolving this ambiguity.

Brandan, M.E. (Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Distrito Federal Mexico (Mexico)); McVoy, K.W. (Department of Physics, University of Wisconsin, Madison, Wisconsin (USA))

1991-03-01

410

Total Antioxidant Capacity and Malondialdehyde in Depressive Rotational Shift Workers  

PubMed Central

Shift work is associated with sleep deprivation, occupational stress, and increased risk of depression. Depressed patients show increased oxidative stress. During excessive oxidative stress, Malondialdehyde (MDA) increases and total antioxidant capacity (TAC) decreases in body. This cross-sectional study was conducted to determine the serum level of TAC and MDA among depressed rotational shift workers in Shahid Tondooyan Tehran Oil Refinery. 21-item Beck Depression Inventory was used to measure depression level. The level of TAC and MDA was measured by 8 mL fasting blood sample. MDA was determined by thiobarbituric acid reaction. Serum total antioxidants were measured using the ABTS. Results of this study showed that TAC mean and standard deviation concentration was 2.451 (±0.536)?mg/dL and MDA was 3.725 (±1.098)?mic·mol/L, and mean and standard deviation of depression score and BMI were 14.07 (±3.84) and 24.92 (±3.65)?kg/m2, respectively. Depression score had a positive correlation with rotational shift work experience and work experience (r = 0.218 and r = 0.212), respectively, (P < 0.05).

Khajehnasiri, Farahnaz; Mortazavi, Seyed Bagher; Allameh, Abdolamir; Akhondzadeh, Shahin; Hashemi, Hassan

2013-01-01

411

A calcium oxide sorbent process for bulk separation of carbon dioxide  

SciTech Connect

This projects described a study of the simultaneous water-gas shift reaction and carbon dioxide removal to prove the technical feasibility of an alternate process for hydrogen production from coal derived gases. Results have been favorable.

Harrison, D.P.; Han, C.; Lee, G.

1995-11-01

412

[1,5]Sigmatropic shift of hydrogen in amination of 3-pyrrolidino-1,2,4-triazine 4-oxide  

Microsoft Academic Search

The reaction of 3-pyrrolidino-1,2,4-triazine 4-oxide with ammonia leads to the product of tele-substitution of pyrrolidine - 5-amino-1,2,4-triazine 4-oxide. Sigmatropic shift of hydrogen postulated for such reactions has been proved by isolation of key intermediates.

Oleg N. Chupakhin; Valery N. Kozhevnikov; Dmitry N. Kozhevnikov; Vladimir L. Rusinov

1999-01-01

413

Shifting timing indicating system for a vehicle  

SciTech Connect

A shifting timing indicating system is described for a vehicle comprising a control means having an engine rpm detecting means for detecting the engine rpm and a rpm determination means which receives the output of the engine rpm detecting means and determines whether the engine rpm exceeds a preset value. The control means outputs a shift-up signal when the engine rpm exceeds the preset value, and a shift-up indicating means which receives the shift-up signal from the control means and makes a shift-up indication to direct the operator of the vehicle to shift up. The improvement comprises an engine load detecting means for detecting the engine load; and acceleration detecting means responsive to the engine load detecting means to detect the rate of increase in engine load and restricting means responsive to the acceleration detecting means to inhibit the means from making the shift-up indication when the rate of increase in engine load is greater than a predetermined positive value.

Kido, Y.; Yamada, T.

1987-07-28

414

Metabolic Shifts in Immunity and Inflammation  

PubMed Central

Sites of ongoing inflammation and triggered immune responses are characterized by significant changes in metabolic activity. Recent studies have indicated that such shifts in tissue metabolism result from a combination of profound recruitment of inflammatory cells (neutrophils and monocytes) and high proliferation rates among lymphocyte populations. The resultant shifts in energy supply and demand can result in metabolic acidosis and diminished delivery and/or availability of oxygen, leading to hypoxia extensive enough to trigger transcriptional and translation changes in tissue phenotype. Such phenotypic shifts can imprint fundamental changes to tissue metabolism. Here, we review recent work addressing metabolic changes and metabolic control of inflammation and immunity.

Kominsky, Douglas J.; Campbell, Eric L.; Colgan, Sean P.

2014-01-01

415

Production of synthesis gas by partial oxidation and high-pressure shift conversion  

SciTech Connect

A fifteen-year history account of process improvements at the BASF ammonia plant at Ludwigshafen, West Germany is presented. Heavy fuel oil with a sulfur content of 1.75% (by weight) and with an ash content of about 0.015% (by weight) is used as feedstock at the plant. The fuel oil is converted with oxygen and steam to synthesis gas at a pressure of 80 bar. The synthesis gas generation is followed by raw-gas preheater, a two-step water-gas shift conversion, and a subsequent waste heat recovery. Sulfur compounds and CO/sub 4/ are removed from converted gas in a combination of a TEA- and an Alkazid-scrubber. Final purification and nitrogen enrichment is achieved in a liquid-nitrogen scrubber. The NH/sub 3/ synthesis operated at 350-430 bar, at which pressure NH/sub 3/-refrigeration of the recycle loop and purge gas removal are not necessary. (JMT)

Balz, D.F.; Gettert, H.F.; Gruendler, K.H.

1983-01-01

416

Adaptation to Shift Work: Physiologically Based Modeling of the Effects of Lighting and Shifts' Start Time  

PubMed Central

Shift work has become an integral part of our life with almost 20% of the population being involved in different shift schedules in developed countries. However, the atypical work times, especially the night shifts, are associated with reduced quality and quantity of sleep that leads to increase of sleepiness often culminating in accidents. It has been demonstrated that shift workers’ sleepiness can be improved by a proper scheduling of light exposure and optimizing shifts timing. Here, an integrated physiologically-based model of sleep-wake cycles is used to predict adaptation to shift work in different light conditions and for different shift start times for a schedule of four consecutive days of work. The integrated model combines a model of the ascending arousal system in the brain that controls the sleep-wake switch and a human circadian pacemaker model. To validate the application of the integrated model and demonstrate its utility, its dynamics are adjusted to achieve a fit to published experimental results showing adaptation of night shift workers (n?=?8) in conditions of either bright or regular lighting. Further, the model is used to predict the shift workers’ adaptation to the same shift schedule, but for conditions not considered in the experiment. The model demonstrates that the intensity of shift light can be reduced fourfold from that used in the experiment and still produce good adaptation to night work. The model predicts that sleepiness of the workers during night shifts on a protocol with either bright or regular lighting can be significantly improved by starting the shift earlier in the night, e.g.; at 21?00 instead of 00?00. Finally, the study predicts that people of the same chronotype, i.e. with identical sleep times in normal conditions, can have drastically different responses to shift work depending on their intrinsic circadian and homeostatic parameters.

Postnova, Svetlana; Robinson, Peter A.; Postnov, Dmitry D.

2013-01-01

417

Adaptation to shift work: physiologically based modeling of the effects of lighting and shifts' start time.  

PubMed

Shift work has become an integral part of our life with almost 20% of the population being involved in different shift schedules in developed countries. However, the atypical work times, especially the night shifts, are associated with reduced quality and quantity of sleep that leads to increase of sleepiness often culminating in accidents. It has been demonstrated that shift workers' sleepiness can be improved by a proper scheduling of light exposure and optimizing shifts timing. Here, an integrated physiologically-based model of sleep-wake cycles is used to predict adaptation to shift work in different light conditions and for different shift start times for a schedule of four consecutive days of work. The integrated model combines a model of the ascending arousal system in the brain that controls the sleep-wake switch and a human circadian pacemaker model. To validate the application of the integrated model and demonstrate its utility, its dynamics are adjusted to achieve a fit to published experimental results showing adaptation of night shift workers (n?=?8) in conditions of either bright or regular lighting. Further, the model is used to predict the shift workers' adaptation to the same shift schedule, but for conditions not considered in the experiment. The model demonstrates that the intensity of shift light can be reduced fourfold from that used in the experiment and still produce good adaptation to night work. The model predicts that sleepiness of the workers during night shifts on a protocol with either bright or regular lighting can be significantly improved by starting the shift earlier in the night, e.g.; at 21:00 instead of 00:00. Finally, the study predicts that people of the same chronotype, i.e. with identical sleep times in normal conditions, can have drastically different responses to shift work depending on their intrinsic circadian and homeostatic parameters. PMID:23308206

Postnova, Svetlana; Robinson, Peter A; Postnov, Dmitry D

2013-01-01

418

Metal Reactions  

NSDL National Science Digital Library

This is written as a static display, but can easily be adapted to a hands-on experiment for learners to conduct. Sodium phosphate, a clear colorless solution, is combined with six different metal ion solutions. Each metal (copper, nickel, iron, silver, cobalt, and barium) forms a different color and texture precipitate. Learners discover that a chemical reaction can be identified by a color change, and formation of a precipitate. They also learn that metals can be identified by their precipitates. For safety reasons, this activity should be conducted as a demonstration for younger audiences.

Industry, Oregon M.

1997-01-01

419

Red Shifts with Obliquely Approaching Light Sources.  

ERIC Educational Resources Information Center

Refutes the Doppler effect as the explanation of large red shifts in the spectra of distant galaxies and explains the relativistic effects in which the light sources approach the observer obliquely. Provides several diagrams and graphs. (YP)

Head, C. E.; Moore-Head, M. E.

1988-01-01

420

Doppler Shift Methods for Plasma Diagnostics,  

National Technical Information Service (NTIS)

Work to develop novel advanced laser spectroscopy plasma diagnostic methods is described. The methods are based on observing the doppler shift in the absorption liners of ionic species. Two methods under study are Velocity Modulated Laser Spectroscopy and...

M. Sassi J. W. Daily

1987-01-01

421

Integral equations, fractional calculus and shift operator  

Microsoft Academic Search

We present an extension of a previously developed method employing the formalism of the fractional derivatives to solve new classes of integral equations. This method uses different forms of integral operators that generalizes the exponential shift operator.

D. Babusci; G. Dattoli; D. Sacchetti

2010-01-01

422

Stabilizing windings for tilting and shifting modes  

SciTech Connect

This invention provides simple, inexpensive, independent and passive, conducting loops for stabilizing a plasma ring having externally produced equilibrium fields on opposite sides of the plasma ring and internal plasma currents that interact to tilt and/or shift the plasma ring relative to the externally produced equilibrium field so as to produce unstable tilting and/or shifting modes in the plasma ring. More particularly this invention provides first and second passive conducting loops for containing first and second induced currents in first and second directions corresponding to the amplitude and directions of the unstable tilting and/or shifting modes in the plasma ring. To this end, the induced currents provide additional magnetic fields for producing restoring forces and/or restoring torques for counteracting the tilting and/or shifting modes when the conducting loops are held fixed in stationary positions relative to the externally produced equilibrium fields on opposite sides of the plasma ring.

Jardin, S.C.; Christensen, U.R.

1982-02-26

423

[Medical surveillance for shift and night work].  

PubMed

Shift and night work are recognized as risk factors for health and safety; they are related to a wide range of public health problems ranging from cardiovascular disease and cancer to mental disorders and accidents. Occupational health physicians should evaluate workers' fitness for shift and night work before their assignment, at regular intervals, and if health problems connected with shift work occur. The evaluation should be accompanied by a careful job analysis to ensure that shift schedules are arranged according to ergonomic criteria. This arrangement can reduce health problems and make coping with irregular working hours possible, even for people suffering from contraindicative illnesses. Both health disorders representing absolute or relative contraindication and actual work conditions should be taken into account. Health checks should be aimed at detecting early signs of intolerance, such as sleeping and digestive trouble, drug consumption, accidents, and female reproductive function problems. PMID:23405656

Roscelli, F

2012-01-01

424

Stage-shift cancer screening model.  

PubMed

A stage-shift cancer screening model is developed in the context of a randomized controlled trial (RCT) of cancer screening. In the model, detection by screening causes the time of diagnosis of the cancer to be advanced so that either the stage at diagnosis is shifted from one stage to the next lower one or the stage of diagnosis is unchanged but the cancer is diagnosed earlier in the stage. These are called external and internal stage shifts, respectively. At each stage the extent of the external and internal shifts and any associated mortality benefits are estimated. Further, the model allows the interrelationships of these benefits within and between stages to be delineated. This then allows us to better understand the results of the RCT. Data from a completed breast cancer screening RCT are used to illustrate the application of the model and its value in improving our understanding of the trial's results. PMID:2681551

Connor, R J; Chu, K C; Smart, C R

1989-01-01

425

Tracking a phase-shift-keyed signal  

NASA Technical Reports Server (NTRS)

In detector, phase shifter is used to generate negative phase shift opposing detected phase angle. This produces converted series sideband and component carrier, with residual carrier signal and converted series sideband and component carrier added together to produce tracking signal.

Villarreal, S.; Lenett, S. D.; Kobayashi, H. S.; Pawlowski, J. F.

1977-01-01

426

Phase shifts in gravitationally evolving density fields  

Microsoft Academic Search

The phases of the Fourier components of an initially Gaussian density field are examined to see how the phases are shifted away from their initial values as the field evolves gravitationally. The analytic expression for the phase shift, in second-order perturbation theory, is presented. To investigate the fully nonlinear regime, 2D N-body simulations were run. The power spectra used were

Barbara S. Ryden; Mirt Gramann

1991-01-01

427

The Knight shift of francium in mercury  

Microsoft Academic Search

For Fr in Hg an extremely small Knight shift has been found as compared to the shift known for an alkali metal host. It indicates\\u000a an almost complete loss of the outer s-electron of the alkali atom Fr when embedded in liquid mercury. This may be understood\\u000a as a consequence of the small ionization energy of the Fr atom in

H. Haas; Ch. Stenzel; H.-E. Mahnke; B. Spellmeyer; W.-D. Zeitz

1990-01-01

428

Relativistic Correction to the Lamb Shift  

Microsoft Academic Search

The relativistic corrections to the Lamb shift, i.e., terms of order alpha(Zalpha)5mc2, are calculated. For this purpose, the Lamb shift is separated into one term in which the Coulomb potential acts only once, and another term in which it acts two or more times (Sec. II). The one-potential term is shown to be equal to the expression calculated in previous

M. Baranger; H. A. Bethe; R. P. Feynman

1953-01-01

429

Hierarchical Surface Abstraction Using Adaptive Mean Shift  

Microsoft Academic Search

This paper presents a novel hierarchical surface abstraction technique based on Mean Shift for 3D shape matching. The automatically generated statistical modes and their associated geometric properties from Mean Shift-based surface analysis are further integrated into an Attributed Relational Graph (ARG). Therefore, the ARG can be used as an abstract represen- tation of the 3D surface object for 3D shape

Chang Liu; Jiaxi Hu; Jing Hua

430

Isotope shift in a beryllium atom  

NASA Astrophysics Data System (ADS)

We calculate the isotope shift of 21P0-21S0, 31S0-21S0 transitions and of the 21S0 ionization potential in the four-electron beryllium atom. The achieved precision is high enough to make possible the accurate determination of the nuclear charge radii from the experimental isotope shifts. This calls for corresponding measurements and opens the window for the determination of charge radii of heavier nuclei.

Puchalski, Mariusz; Pachucki, Krzysztof; Komasa, Jacek

2014-01-01

431

Centralizing physician office functions. A paradigm shift.  

PubMed

Recent trends show that organizations that once thought business office centralization was beneficial are re-thinking their strategies and decentralizing business office functions. This article focuses on the paradigm shift from business office centralization to decentralization and the political factors effecting this shift. It provides actual case summaries to demonstrate what has transpired, and presents an alternative strategy to establishing successful business office functions, a hybrid business office. PMID:10662475

Croopnick, J G

1999-01-01

432

Multiple shift patient classification: is it necessary?  

PubMed

Efficient, cost-effective patient classification systems are an essential component of information needed for staffing projections, budgeting, productivity monitoring, and determining the cost of nursing services. Data collection on every shift is typical of GRASP-based patient classification systems. In this study, comparisons among multiple shift measurements showed that no relevant information was being gained by multiple daily assessments of patient care requirements. PMID:3102705

Kinley, J; Cronenwett, L R

1987-02-01

433

The pacemaker of major climate shifts  

NASA Astrophysics Data System (ADS)

Models and data suggest that the interplay of major climate modes may result in climate shifts. More specifically it has been shown that when the network of North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), El Nino/Southern Oscillation (ENSO) and North Pacific Index (NPI) synchronizes, an increase in the coupling between these oscillations destroys the synchronous state and leads the climate system to a new state. These shifts are associated with significant changes in global temperature trend and in ENSO variability. Here we probe the details of this network's dynamics to investigate if a certain oscillation is the culprit in these shifts. From a total of 12 synchronization events observed in three climate simulations and in observations we find that the instigator of these shifts is NAO. Without exception only when NAO's coupling with the Pacific increases a shift will occur. Our results suggest a dynamical sequence of events in the evolution of climate shifts which is consistent with recent independent empirical and modeling studies.

Wang, Geli; Swanson, Kyle L.; Tsonis, Anastasios A.

2009-04-01

434

Shifts in global vegetation activity dynamics?  

NASA Astrophysics Data System (ADS)

Vegetation belongs to the components of the Earth surface, which are most extensively studied using historic and present satellite records. Recently, these records exceeded a 30-year time span composed of pre-processed fortnightly observations (1981-2011). The existence of monotonic changes and trend shifts present in such records has previously been demonstrated. However, information on timing and type of such trend shifts was lacking at global scale. We detected major shifts in vegetation activity trends and their associated type (either interruptions or reversals) and timing. It appeared that the trend shifts have, over time, increased in frequency, confirming recent findings of increased turnover rates in vegetated areas. Signs of greening-to-browning reversals around the millennium transition were found in many regions (Patagonia, the Sahel, northern Kazakhstan, among others), as well as negative interruptions--'setbacks'--in greening trends (southern Africa, India, Asia Minor, among others). A minority (26%) of all significant trends appeared monotonic, illustrating the importance of shift detection and characterisation. Examples for specific locations of major shifts detected in NDVI3g time series are discussed.

Verbesselt, J.; de Jong, R.; Herold, M.

2013-12-01

435

Regime shifts in models of dryland vegetation.  

PubMed

Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity of stable states and fronts separating domains of alternative stable states. Pattern dynamics, induced by droughts or disturbances, can result in desertification shifts from patterned vegetation to bare soil. Pattern formation theory suggests various scenarios for such dynamics: an abrupt global shift involving a fast collapse to bare soil, a gradual global shift involving the expansion and coalescence of bare-soil domains and an incipient shift to a hybrid state consisting of stationary bare-soil domains in an otherwise periodic pattern. Using models of dryland vegetation, we address the question of which of these scenarios can be realized. We found that the models can be split into two groups: models that exhibit multiplicity of periodic-pattern and bare-soil states, and models that exhibit, in addition, multiplicity of hybrid states. Furthermore, in all models, we could not identify parameter regimes in which bare-soil domains expand into vegetated domains. The significance of these findings is that, while models belonging to the first group can only exhibit abrupt shifts, models belonging to the second group can also exhibit gradual and incipient shifts. A discussion of open problems concludes the paper. PMID:24471267

Zelnik, Yuval R; Kinast, Shai; Yizhaq, Hezi; Bel, Golan; Meron, Ehud

2013-12-13

436

[Comparison of shift work and night shifts: impacts on health and wellbeing among sanitary workers].  

PubMed

The generally agreed view is that there is no ideal shift system, and that most systems will have both advantages and disadvantages. As such, attention has been placed on trying to identify good and bad features of shift systems, with a view to minimising the possible ill health as a consequence of shiftwork. The present study focuses on the quality of the shift and looks at the implications for individual health and wellbeing, during the wellbeing, during the shift. Three groups of sanitary workers, one working in the morning, one working two shifts, and the other working three, took part. All completed a version of the standard shiftwork index (SSI), a set of self reported questionnaires related to health and wellbeing. The three groups differed on many outcome measures, although the differences that did exist didn't suggested advantages for one shift system over the others. PMID:23393869

Della Betta, F; Martinellit, R; Del Re, C; Tarquini, M; Fantasia, D; Paoletti, A

2011-01-01

437

Shift Work and Circadian Dysregulation of Reproduction  

PubMed Central

Health impairments, including reproductive issues, are associated with working nights or rotating shifts. For example, shift work has been associated with an increased risk of irregular menstrual cycles, endometriosis, infertility, miscarriage, low birth weight or pre-term delivery, and reduced incidence of breastfeeding. Based on what is known about circadian regulation of endocrine rhythms in rodents (and much less in humans), the circadian clock is an integral regulatory part of the reproductive system. When this 24-h program is disordered by environmental perturbation (such as shift work) or genetic alterations, the endocrine system can be impaired. The purpose of this review is to explore the hypothesis that misalignment of reproductive hormones with the environmental light-dark cycle and/or sleep-wake rhythms can disrupt menstrual cycles, pregnancy, and parturition. We highlight the role of the circadian clock in regulating human reproductive physiology and shift work-induced pathology within each step of the reproductive axis while exploring potential mechanisms from the animal model literature. In addition to documenting the reproductive hazards of shift work, we also point out important gaps in our knowledge as critical areas for future investigation. For example, future studies should examine whether forced desynchronization disrupts gonadotropin secretion rhythms and whether there are sleep/wake schedules that are better or worse for the adaptation of the reproductive system to shift work. These studies are necessary in order to define not only whether or not shift work-induced circadian misalignment impairs reproductive capacity, but also to identify strategies for the future that can minimize this desynchronization.

Gamble, Karen L.; Resuehr, David; Johnson, Carl Hirschie

2013-01-01

438

Phase-shift algorithm for white-light interferometry insensitive to linear errors in phase shift  

Microsoft Academic Search

White-light interference has changes in fringe contrast. When phase-shift techniques are applied to white-light interference,\\u000a the phase-shift algorithm which can extract the phase accurately under the contrast changes is required. There is often another\\u000a requirement that the phase shift between frames should not be restricted to ?\\/2. Computer simulations show that the well-known algorithms have non-negligible errors under both requirements.

Masaaki Adachi

2008-01-01

439

Nozzle Aerodynamic Stability During a Throat Shift  

NASA Technical Reports Server (NTRS)

An experimental investigation was conducted on the internal aerodynamic stability of a family of two-dimensional (2-D) High Speed Civil Transport (HSCT) nozzle concepts. These nozzles function during takeoff as mixer-ejectors to meet acoustic requirements, and then convert to conventional high-performance convergent-divergent (CD) nozzles at cruise. The transition between takeoff mode and cruise mode results in the aerodynamic throat and the minimum cross-sectional area that controls the engine backpressure shifting location within the nozzle. The stability and steadiness of the nozzle aerodynamics during this so called throat shift process can directly affect the engine aerodynamic stability, and the mechanical design of the nozzle. The objective of the study was to determine if pressure spikes or other perturbations occurred during the throat shift process and, if so, identify the caused mechanisms for the perturbations. The two nozzle concepts modeled in the test program were the fixed chute (FC) and downstream mixer (DSM). These 2-D nozzles differ principally in that the FC has a large over-area between the forward throat and aft throat locations, while the DSM has an over-area of only about 10 percent. The conclusions were that engine mass flow and backpressure can be held constant simultaneously during nozzle throat shifts on this class of nozzles, and mode shifts can be accomplished at a constant mass flow and engine backpressure without upstream pressure perturbations.

Kawecki, Edwin J.; Ribeiro, Gregg L.

2005-01-01

440

Beam Propagation and Shift-Variant Optics.  

NASA Astrophysics Data System (ADS)

The goal of the research described in this dissertation is to be able to model propagation of light through shift -variant optics. Shift-variant optical elements have a point spread function which is a function of the transverse coordinates. This shift-variance can be caused by aberration or by the first order properties of the optical system. In this work the latter is emphasized. Specifically, this dissertation discusses propagation through lenses and prisms and between tilted planes or a plane and a spherical surface. Extension to other types of shift-variant optical elements is possible. Two methods for performing the propagation are described. One, the beam division model, divides the beam into isoplanatic patches, separately propagates the patches and recombines them on the observation surface. The second method, the mapping model, maps the beam into a space in which the propagation is shift-invariant, propagates and then maps back into real space. Experimental verification of these methods is demonstrated by means of the Talbot effect. The setup consists of a collimated laser beam passing through a Ronchi ruling of about ten cycles per millimeter. With no intervening optics, Talbot images of the ruling are formed which are parallel to the wavefronts. When a prism at minimum deviation is placed in the outgoing beam, it causes the Talbot images to be tilted with respect to the wavefronts. If a stigmatic unit magnification telescope replaces the prism, the Talbot images are formed on surfaces congruent to the Petzval surface.

Eckhardt, Stephen Karl

1990-08-01

441

Chemical Shift Prediction for Denatured Proteins  

PubMed Central

While chemical shift prediction has played an important role in aspects of protein NMR that include identification of secondary structure, generation of torsion angle constraints for structure determination, and assignment of resonances in spectra of intrinsically disordered proteins, interest has arisen more recently in using it in alternate assignment strategies for crosspeaks in 1H-15N HSQC spectra of sparsely labeled proteins. One such approach involves correlation of crosspeaks in the spectrum of the native protein with those observed in the spectrum of the denatured protein, followed by assignment of the peaks in the latter spectrum. As in the case of disordered proteins, predicted chemical shifts can aid in these assignments. Some previously developed empirical formulas for chemical shift prediction have depended on basis data sets of 20 pentapeptides. In each case the central residue was varied among the 20 amino common acids, with the flanking residues held constant throughout the given series. However, previous choices of solvent conditions and flanking residues make the parameters in these formulas less than ideal for general application to denatured proteins. Here, we report 1H and 15N shifts for a set of alanine based pentapeptides under the low pH urea denaturing conditions that are more appropriate for sparse label assignments. New parameters have been derived and a Perl script was created to facilitate comparison with other parameter sets. A small, but significant, improvement in shift predictions for denatured ubiquitin is demonstrated.

Sahu, Sarata C.; Nkari, Wendy K.; Morris, Laura C.; Live, David; Gruta, Christian

2013-01-01

442

How automatic is manual gear shifting?  

PubMed

Manual gear shifting is often used as an example of an automated (vs. controlled) process in driving. The present study provided an empirical evaluation of this assumption by evaluating sign detection and recall performance of novice and experienced drivers driving manual shift and automatic transmission cars in a downtown area requiring frequent gear shifting. The results showed that manual gear shifting significantly impaired sign detection performance of novice drivers using manual gears compared with novice drivers using an automatic transmission, whereas no such differences existed between the two transmission types for experienced drivers. The results clearly demonstrate that manual gear shifting is a complex psychomotor skill that is not easily (or quickly) automated and that until it becomes automated, it is an attention-demanding task that may impair other monitoring aspects of driving performance. Actual or potential applications of this research include a reevaluation of the learning process in driving and the need for phased instruction in driving from automatic gears to manual gears. PMID:9974234

Shinar, D; Meir, M; Ben-Shoham, I

1998-12-01

443

5 CFR 532.505 - Night shift differentials.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 2009-01-01 false Night shift differentials. 532.505 Section...and Differentials § 532.505 Night shift differentials. (a) Employees shall be entitled to receive night shift differentials in accordance with...

2009-01-01

444

5 CFR 532.505 - Night shift differentials.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Night shift differentials. 532.505 Section...and Differentials § 532.505 Night shift differentials. (a) Employees shall be entitled to receive night shift differentials in accordance with...

2010-01-01

445

Dielectronic resonance method for measuring isotope shifts.  

PubMed

Long standing problems in the comparison of very accurate hyperfine-shift measurements to theory were partly overcome by precise measurements on few-electron highly charged ions. Still the agreement between theory and experiment is unsatisfactory. In this Letter, we present a radically new way of precisely measuring hyperfine shifts, and demonstrate its effectiveness in the case of the hyperfine shift of 4s1/2 and 4p1/2 in 207Pb53+. It is based on the precise detection of dielectronic resonances that occur in electron-ion recombination at very low energy. This allows us to determine the hyperfine constant to around 0.6 meV accuracy which is on the order of 10%. PMID:16383901

Schuch, R; Lindroth, E; Madzunkov, S; Fogle, M; Mohamed, T; Indelicato, P

2005-10-28

446

Multiscale regime shifts and planetary boundaries.  

PubMed

Life on Earth has repeatedly displayed abrupt and massive changes in the past, and there is no reason to expect that comparable planetary-scale regime shifts will not continue in the future. Different lines of evidence indicate that regime shifts occur when the climate or biosphere transgresses a tipping point. Whether human activities will trigger such a global event in the near future is uncertain, due to critical knowledge gaps. In particular, we lack understanding of how regime shifts propagate across scales, and whether local or regional tipping points can lead to global transitions. The ongoing disruption of ecosystems and climate, combined with unprecedented breakdown of isolation by human migration and trade, highlights the need to operate within safe planetary boundaries. PMID:23769417

Hughes, Terry P; Carpenter, Stephen; Rockström, Johan; Scheffer, Marten; Walker, Brian

2013-07-01

447

Age Related Shift in Visceral Fat  

PubMed Central

Fat distribution, especially increased visceral fat, may be as important as overall obesity in increasing risk of heart disease, type 2 diabetes and certain cancers. Risk of disease, as well as visceral fat, increases dramatically with age. Cross-sectional data suggests that increased risk of disease may be largely prevented if the age related increase in visceral fat does not occur. The objective of this short review is to present data that shows visceral fat increasing over 200% in men and 400% in women between the 3rd and 7th decades, show that a combination of weight gain, loss of muscle, and a shift from peripheral to central fat patterning contributes to this increase, and identify hormones that may be responsible for the shift. Finally, the review will show how participation in exercise can slow the age related shift in visceral fat.

Hunter, Gary R.; Gower, Barbara A.; Kane, Brandon L.

2011-01-01

448

Polarization phase shifting lateral shearing interferometer  

NASA Astrophysics Data System (ADS)

A polarization phase shifting lateral shearing interferometer based on a polarization beam splitting plate(PBSP) is proposed. The front surface of the PBSP is coated with polarization beam splitting film and its back surface is coated with total reflection film. The beam to be tested is split by the PBSP with an incidence angle of 45° and divided into two mutually perpendicular linearly polarization beams. Phase shifting can be introduced to the interferometer when the PBSP is combined with a polarzation temporal or spatial phase shifter. A polarizaiton temporal phase shifting lateral shearing interferometer system is built up both with the ASAP software and the experiments. The usefulness of the interferometer is verified.

Liu, Lei; Zeng, Aijun; Zhu, Linglin; Song, Qiang; Huang, Huijie

2013-08-01

449

Liquid crystal display for phase shifting  

NASA Astrophysics Data System (ADS)

This work arises based on the idea proposed by Millered et al. in 2004, where they show how to get in one shot interferograms with phase shift using a mask with micro-polarizers, in this work we pretend to obtain phase shift in localized areas of an interferogram using the properties of polarization and the pixelated configuration of a liquid crystal display (LCD) for testing optical surfac