Note: This page contains sample records for the topic mordenite from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Benzene adsorption and desorption in mordenite  

Microsoft Academic Search

The zeolite-catalyzed synthesis of cumene from benzene and propene is an industrially important reaction. We used small mordenite crystals to study benzene adsorption and desorption behaviour for sodium, proton and nitric acid treated mordenite. Adsorption of benzene was for all samples fast and completed within 25 seconds at a benzene partial pressure of 0.12 bar in nitrogen at 423 K.

A. N. C. van Laak; K. P. de Jong; P. E. de Jongh

2007-01-01

2

Catalytic degradation of expandable polystyrene waste (EPSW) over mordenite and modified mordenites  

Microsoft Academic Search

The performance of the several different modified mordenite zeolites in the degradation of expandable polystyrene waste (EPSW) was investigated in this study. The composition of the degradation products, especially the liquid fraction was compared to understand the role of H-mordenite and the effect of its modification through framework dealumination and metal impregnation. The degradation was carried out in a batch

Vilas Ramdas Chumbhale; Jun-Sik Kim; Sang-Bong Lee; Myoung-Jae Choi

2004-01-01

3

Chemical Resistivity of Silver Mordenite and Berl Sadles  

SciTech Connect

This report discusses results of testing to determine the chemical resistance of pellets of silver mordenite and silver mordenite, reduced form. For comparison Berl saddles were tested under similar conditions. Silver mordenite has been proposed as a replacement for the saddles that remove iodine in the off-gas treatment system from the canyon dissolvers.

Holcomb, H.P.

2001-05-17

4

Shape Selective Chemistries with Modified Mordenite Zeolites  

Microsoft Academic Search

This is a review of work carried at Dow Chemical on the design and characterization of novel mordenite catalysts with a unique\\u000a micro and meso-porous structure characterized by a variety of methods including, TEM, BET surface area and pore size distribution,\\u000a and n-decane hydro-conversion. The catalytic performance of these catalysts in shape selective reactions is illustrated with results\\u000a from n-decane

Juan M. Garcés; Michael M. Olken; G. John Lee; Garry R. Meima; Pierre A. Jacobs; Johan A. Martens

2009-01-01

5

n-Butane Isomerization over Acidic Mordenite  

Microsoft Academic Search

Conversion of n-butane was studied between 523 K and 623 K over acidic mordenites with SiO2\\/Al2O3 ratios between 10 and 20. The main products were iso-butane, propane, and pentane. The selectivity to olefins, methane, ethane, C6 paraffins, and aromatics was lower than 4 mol% under all reaction conditions. Isomerization and disproportionation were identified to be the dominating reactions. At 523

Raymond A. Asuquo; Gabriele Eder-Mirth; J. A. Lercher

1995-01-01

6

Process for catalytic dewaxing with mordenite  

Microsoft Academic Search

The method of catalytically dewaxing a hydrocarbon base lubricating oil, charge containing a wax fraction, is described consists of: passing a hydrocarbon base lubricating oil charge, at anhydrous dewaxing catalytic conditions, into contact with a dewaxing catalyst, a hydrogen mordenite catalyst, which catalyst has been calcined at 1300°F-1500°F after contact with water for the last time, having a silica-to-alumina mole

1986-01-01

7

Preparation of mordenite membranes for dehydration of water–UDMH  

Microsoft Academic Search

Mordenite membranes were prepared on the outer surface of ceramic tubular tubes via hydrothermal synthesis and evaluated for dehydration pervaporation of water unsymmetrical dimethylhydrazine UDMH mixtures. Highly water-selective mordenite membranes were prepared and the optimum reaction condition was found to be 24h crystallization time and 170°C crystallization temperature. Effect of gel composition on separation factor and water flux of the

Mansoor Kazemimoghadam; Toraj Mohammadi

2010-01-01

8

Cesium-mordenite solid electrolyte as a cesium ion source  

Microsoft Academic Search

A novel solid state Cs{sup +} ion source has been developed which combines the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a cesium-mordenite solid electrolyte pellet whose emitting surface is coated with a porous tungsten film. Cesium supply to the emitting electrode is controlled by a voltage applied across the solid

1989-01-01

9

n-Butane isomerization over H-mordenite: role of the monomolecular mechanism  

Microsoft Academic Search

Isomerization of n-butane over several H-mordenite and Pd\\/H-mordenite samples with different Si\\/Al ratios is studied. 1,1,1,3,3,3-Hexamethyldisilazane was injected to obtain catalysts with poisoned external Brönsted acid sites. In the absence of metal, isomerization activity was virtually suppressed for the poisoned non-dealuminated mordenite catalysts. However, dealuminated samples were more resistant to the poisoning, and showed a higher selectivity to isobutane. For

P Cañizares; A de Lucas; F Dorado

2000-01-01

10

Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites  

Microsoft Academic Search

Dehydration of fructose to 5-hydroxymethylfurfural was performed in a batch mode in the presence of a series of dealuminated H-form mordenites as catalysts, at 165°C, and in a solvent mixture consisting of water and methyl isobutyl ketone (1:5 by volume).Under the operating conditions used, the reaction was not controlled by external or internal diffusional limitations. Fructose conversion and selectivity to

Claude Moreau; Robert Durand; Sylvie Razigade; Jean Duhamet; Pierre Faugeras; Patrick Rivalier; Pierre Ros; Gérard Avignon

1996-01-01

11

Adsorption of lanthanides on mordenite from nitrate medium  

Microsoft Academic Search

The adsorption of lanthanides (except for Pm) on mordenite was investigated under various solution conditions of nitrate ion concentrations ([NO?3]: 0.001–2 mol\\/dm3) and total lanthanide concentrations (0.0005 mol\\/dm3). Solutions of lanthanide nitrates were equilibrated with zeolite samples at 296 K. A concave tetrad effect was evident in the change of logKd values within the lanthanide series and an explanation by

Agnieszka G?adysz-P?aska; Marek Majdan; Stanis?aw Pikus

2008-01-01

12

Organic iodine removal from simulated dissolver off-gas systems utilizing silver-exchanged mordenite  

Microsoft Academic Search

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The adsorption of methyl iodide on silver mordenite was examined for the effect of NO\\/sub x\\/, humidity, iodine concentration, filter temperature, silver loadings and filter pretreatment. The highest iodine loading achieved in these

Jubin

1981-01-01

13

Organic iodine removal from simulated dissolver off-gas streams using partially exchanged silver mordenite  

SciTech Connect

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide adsorption of partially exchanged silver mordenite was examined for the effects of NO/sub x/, humidity, filter temperature, and degree of silver exchange. Partially exchanged silver mordenite, in general, achieved significantly higher silver utilizations than the fully exchanged material. Silver utilizations of > 95% were achieved, assuming the formation of AgI. The experimental results indicate that CH/sub 3/I loadings increase proportionally with silver loading up to 5 wt % silver and then appear to level off. Tests conducted to determine the effect of temperature on the loading showed higher loadings at 200/sup 0/C than at either 150 or 250/sup 0/C. The presence of NO, NO/sub 2/, and H/sub 2/O vapor showed negligible effects on the loading of CH/sub 3/I. In contrast to iodine loaded onto fully exchanged silver mordenite, the iodine loaded onto the partially exchanged silver mordenite could not be stripped by either 4.5% hydrogen or 100% hydrogen at temperatures up to 500/sup 0/C. A study of the regeneration characteristics of fully exchanged silver mordenite indicates a decreased adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500/sup 0/C. The loss of adsorbent capacity was much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing. A cost evaluation for the use of the partially exchanged silver mordenite shows that the cost of the silver mordenite on a once-through basis is < $10/h of operation for a 0.5-t/d reprocessing plant.

Jubin, R.T.

1982-01-01

14

Recycle of iodine-loaded silver mordenite by hydrogen reduction  

SciTech Connect

In 1977 and 1978, workers at Idaho National Engineering Laboratory (INEL) developed and tested a process for the regeneration and reuse of silver mordenite, AgZ, used to trap iodine from the dissolver off-gas stream of a nuclear fuel reprocessing plant. We were requested by the Airborne Waste Management Program Office of the Department of Energy to perform a confirmatory recycle study using repeated loadings at about 150/sup 0/C with elemental iodine, each followed by a drying step at 300/sup 0/C, then by iodine removal using elemental hydrogen at 500/sup 0/C. The results of our study show that AgZ can be recycled. There was considerable difficulty in stripping the iodine at 500/sup 0/C.; however, this step went reasonably well at 550/sup 0/C or slightly higher, with no apparent loss in the iodine-loading capacity of the AgZ. Large releases of elemental iodine occurred during the drying stage and the early part of the stripping stage. Lead zeolite, which was employed in the original design to trap the HI produced, is ineffective in removal of I/sub 2/. The process needs modification to handle the iodine. Severe corrosion of the stainless steel components of the system resulted from the HI-I/sub 2/-H/sub 2/O mixture. Monel or other halogen-resistant materials need to be examined for this application. Because of difficulty with the stripping stage and with corrosion, the experiments were terminated after 12 cycles. Thus, the maximum lifetime (cycles) of recycle AgZ has not been determined. Mechanistic studies of iodine retention by silver zeolites and of the behavior of silver atoms on the reduction stage would be of assistance in optimizing silver mordenite recycle.

Burger, L.L.; Scheele, R.D.

1982-11-01

15

Catalytic cracking of polyethylene over zeolite mordenite with enhanced textural properties  

Microsoft Academic Search

Catalytic cracking of low density polyethylene (LDPE) has been investigated using different samples of mordenite zeolite as catalyst. In order to obtain materials with different textural properties, a new synthesis method based on the functionalization of the zeolite seeds with an organosilane was employed. Mordenite samples with BET and external surface areas in the range 385–485 and 9–57m2\\/g, respectively, were

J. Aguado; D. P. Serrano; J. M. Escola; A. Peral

2009-01-01

16

Improving the Stability of H–Mordenite for n-Butane Isomerization  

Microsoft Academic Search

The conversion ofn-butane over mordenite-based catalysts in the presence of hydrogen and water was investigated for reaction temperatures between 523 and 623 K. Special attention was given to the influence of Pt upon catalytic activity, selectivity, and stability. With parent mordenite the catalytic activity forn-butane conversion decreased markedly after a short time on stream. Deactivation can be minimized by hydrogen

R. A. Asuquo; G. Eder-Mirth; K. Seshan; J. A. Z. Pieterse; J. A. Lercher

1997-01-01

17

Development of modified mordenite-zirconia catalysts active at low-temperature in n-butane isomerization  

Microsoft Academic Search

Activity of mordenite-zirconia catalysts in n-butane isomerization depends on the dealumination degree of H-mordenite, the concentration of zirconium dioxide, the preparation method of samples, the nature and the concentration of different promoters. The modification of dealuminated H-mordenite with ratio Si\\/Al=8.5 (HM8.5) by zirconyl nitrate, sulfate ions and cobalt results in a considerable increase in the catalyst activity and a decrease

2008-01-01

18

Adsorption of hexane isomers on ion-exchanged mordenite  

SciTech Connect

To remove lead from petrol and thereby promote a cleaner environment, other means must be found to keep the octane number or anti-knock qualities of the petrol high. It is found that this can be accomplished by increasing the proportion of highly branched chain hydrocarbon isomers in the fuel. This in turn promotes processes for the separation of the hydrocarbon isomers and in the case of hexane, it is an easy matter to separate out n-hexane from the more substituted isomers but it is difficult to separate out the mono- from the di-branched isomers. This work addresses itself to such challenging separations using modified zeolites as the separating agent, and by studying the heats of sorption of these isomers on zeolites using gas chromatographic techniques to find a trend in the potential abilities of these modified zeolites to effect a good separation. In this work mordenite zeolite was modified by a range of double cation exchanges and the resulting modified zeolites were investigated for their ability to sorb the hexane isomers 3-methylpentane and 2,3-dimethylbutane. These two isomers are closely related in size as they both have the same kinetic diameter of 0.56 nm. In this work only heats of sorption have been investigated and measurement of the diffusion coefficients, which also affect the ability of the modified zeolites to act as good separating agents, is currently under investigation.

Huddersman, K. [DeMonfort Univ., Leicester (United Kingdom)

1996-10-01

19

The effect of iron on the biological activities of erionite and mordenite.  

PubMed

Epidemiological data has demonstrated that environmental and/or occupational exposure to mineral particulates may result in the development of pulmonary fibrosis, bronchogenic carcinoma and malignant mesothelioma many years following exposure. It has been suggested that the genotoxic effects of fibrous particulates, such as asbestos, is due in part to the generation of reactive oxygen species (ROS) from iron associated with the particulates. However, the molecular mechanisms by which mineral particulates induce ROS that results in genotoxic damage remains unclear. The naturally occurring zeolites, erionite and mordenite share several physiochemical properties but they elicit very different biological responses, with erionite, a fibrous particulate, being highly toxic, and mordenite, a nonfibrous particulate, being relatively benign. We are using these natural zeolites as a model system to determine what physicochemical properties of these zeolites are responsible for their biological response(s) and to evaluate the parameters that influence these responses. The purpose of the present study was to determine the mutagenic potential of erionite and mordenite and to determine whether this mutagenic potential was modulated by iron. The results of this study using the Chinese hamster ovary cell line AS52 demonstrated that erionite was more cytotoxic than mordenite. However, the cytotoxicity of both zeolites was increased in the presence of physiological concentrations of ferrous chloride. Ferrous ions (5-20 microM) significantly (p<0.001) increased the cytotoxicity of mordenite, but only at the highest concentration (16 microg/cm(2)) of mordenite tested. Conversely, only the highest concentration (20 microM) of ferrous ion significantly (p<0.001) increased the cytotoxicity of erionite, but this enhanced cytotoxicity occurred over a wider concentration range (6-16 microg/cm(2)) of erionite. Mordenite was not mutagenic at any of the concentrations tested, and the mutagenic potential of mordenite was not enhanced by the addition of ferrous ion. Conversely, erionite was mutagenic in a dose-response manner at concentrations greater than 6 microg/cm(2) and the mutagenic potential of erionite was significantly enhanced by the addition of ferrous ions. These results suggest that while the cytotoxicity of mordenite and erionite may be related to the ability of these fibers to transport iron into a cell, the different coordination state of iron associated with the two fiber surfaces is critical for inducing genotoxic damage. PMID:12705942

Fach, Estelle; Kristovich, Robert; Long, John F; Waldman, W James; Dutta, Prabir K; Williams, Marshall V

2003-07-01

20

Paraffin isomerization and disproportionation catalyzed by Pd-loaded fluorided mordenites  

SciTech Connect

Fluorided, Pd-loaded ({approximately}1.1 wt% Pd) mordenites, with 8, 12, 28, and 100% replacement of {minus}OH groups, were synthesized from H-mordenite. These materials were characterized by IR, XRD, SEM, the adsorption of N{sub 2} and 2-methylpentane, and their activity for paraffin reactions. Except in the case of 100% nominal fluoridation, the fluorided mordenites retained their crystallinity, displayed enhanced acid strengths and adsorption capacities for paraffinic hydrocarbons, and were catalytically active (at 533-573 K and {approximately}0.1 bar hydrocarbon partial pressure) for the transformation of n-butane to isobutane and products of both higher and lower molecular weights. The presence of a small amount of isobutene in the feed greatly accelerated these transformations and increase yields to the pentane isomers. The primary reactions were apparently acid-catalyzed, with the role of Pd confined to activity maintenance. The mildly fluorided zeolites in some cases proved more active overall than the parent zeolites H-mordenite and Pd-mordenite and were especially selective for the formation of the pentane isomers, apparently through a combination of disproportionation reactions and secondary alkylation reactions involving light hydrocarbon primary products.

Maness, J.A. Jr.; Dooley, K.M. (Louisiana State Univ., Baton Rouge (USA))

1989-06-01

21

Photophysical properties of pyrene in zeolites: Adsorption and distribution of pyrene molecules on the surfaces of zeolite L and mordenite  

SciTech Connect

Adsorption of pyrene on the surfaces of zeolites L and mordenite is investigated using photophysical techniques. Although the internal surfaces of both zeolites are polar, their external surfaces may not be the same. A difference is observed for mordenite. No pyrene excimers can be produced in mordenite, while excimers are readily formed in zeolite L. Due to structural constraints, 30-35% of pyrene adsorbed in mordenite cannot be quenched by O{sub 2}. Rotational movement of pyrene molecules in mordenite is also restricted by the zeolite structure. Laser photolysis produces pyrene cation and anion radicals, the former having a larger yield than the latter in both zeolites. 31 refs., 5 figs., 2 tabs.

Liu, Xinsheng; Thomas, J.K. [Univ. of Notre Dame, IN (United States)

1994-12-01

22

Improving the stability of H-mordenite for n-butane isomerization  

SciTech Connect

The conversion of n-butane over mordenite-based catalysts in the presence of hydrogen and water was investigated for reaction temperatures between 523 and 623 K. Special attention was given to the influence of Pt upon catalytic activity, selectivity, and stability. With parent mordenite the catalytic activity for n-butane conversion decreased markedly after a short time on stream. Deactivation can be minimized by hydrogen (in the presence of Pt) and water addition. Both measures are thought to reduce the concentration of intermediate olefins in the zeolite pores. The best results with respect to selective conversion of n-butane to isobutane were obtained for 0.25 wt% Pt on mordenite in the presence of hydrogen. Higher concentrations of Pt in the catalyst are shown to be detrimental for n-butane isomerization, because of increasing selectivity to hydrogenolysis. A detailed mechanistic scheme for n-butane conversion over Pt-containing mordenites is presented. n-Butane conversion is concluded to occur via a bimolecular mechanism involving a complex network of hydrogen transfer, oligomerization/cracking, isomerization, hydrogenation/dehydrogenation, and hydrogenolysis. 23 refs., 14 figs., 5 tabs.

Asuquo, R.A.; Eder-Mirth, G.; Lercher, J.A. [Catalysis Univ. of Twente, Enschede (Netherlands)] [and others

1997-06-01

23

Adsorption mechanism of 1,2-dichloroethane into an organophilic zeolite mordenite: A combined diffractometric and gas chromatographic study  

Microsoft Academic Search

We investigated the 1,2-dichloroethane (DCE) adsorption process into an organophilic zeolite mordenite. A combined diffractometric, thermogravimetric and gas chromatographic approach enabled to obtain clear evidence of DCE adsorption in mordenite channels as well as to pinpoint the exact location of the organic species found in the structure. Rietveld refinement revealed the incorporation of 2.5 DCE molecules and approximately 4 water

Annalisa Martucci; Luisa Pasti; Marianna Nassi; Alberto Alberti; Rossella Arletti; Roberto Bagatin; Rodolfo Vignola; Rosalba Sticca

24

Characterization of Se-loaded molecular sieves A, X, Y, AlPO-5, and mordenite  

SciTech Connect

Selenium has been successfully loaded into molecular sieves A, X, Y, AlPO-5, and mordenite, and the products were characterized by using EXAFS, solid-state NMR, and diffuse-reflectance techniques. This study reveals selenium is predominantly of the trigonal (helical chains) form in all but the A sample, where only the Se/sub 8/-crown ring form is found. A mixture of allotropes and helical chains occupy the large 3D-pore and channel systems of molecular sieves X and Y; however, a single, probably fixed-pitch helical-chain allotrope occupies the more constrained 12-membered-ring channels found in mordenite and AlPO-5. The high degree of order in these last two sieves is reflected in a strong second-shell feature in the EXAFS spectra. 22 refs., 12 figs., 3 tabs.

Parise, J.B.; MacDougall, J.E.; Herron, N.; Farlee, R.; Sleight, A.W.; Ying Wang; Bein, T.; Moller, K.; Moroney, L.M.

1988-01-27

25

Dealumination of proton form mordenite with high aluminum content in atmosphere  

Microsoft Academic Search

A proton form mordenite with Si\\/Al2=10 was prepared by heating of an ammonium type sample at 813 K in a nitrogen flow and transferred into an NMR (nuclear magnetic resonance) cell in a dry box filled with a controlled atmosphere, and the framework aluminum content was measured by means of 29Si NMR. It was estimated that almost all the aluminum

Naonobu Katada; Takahide Kanai; Miki Niwa

2004-01-01

26

Electrical conductivity response and sensitivity of ZSM-5, Y, and mordenite zeolites towards ethanol vapor  

Microsoft Academic Search

This work is an attempt to search for highly selective sensing materials for ethanol vapor. The electrical conductivity response\\u000a of ZSM-5, Y, and mordenite zeolites towards ethanol vapor have been investigated for the effects of the framework, the charge\\u000a balancing cation type, and the Si\\/Al ratio. All zeolites were characterized using XRD, FT-IR, SEM, TGA, BET, and NH3-TPD techniques. For

Intira Yimlamai; Sumonman Niamlang; Pojjawan Chanthaanont; Ruksapong Kunanuraksapong; Sairung Changkhamchom; Anuvat Sirivat

27

Standardization of catalyst preparation using reference catalyst: ion exchange of mordenite type zeolite  

Microsoft Academic Search

A joint study was organized to establish a standard set of conditions for the ion exchange of zeolite from sodium into proton-form. The sodium-form mordenite with Si\\/Al2=ca. 15 was ion exchanged into an NH4-form, followed by calcination according to various recipes. Then various advanced techniques for characterization (ICP, TG, XPS, SEM, XRD, N2 adsorption, 29Si and 27Al NMR, benzene diffusion,

Naonobu Katada; Tatsuya Takeguchi; Tatsuya Suzuki; Toshihisa Fukushima; Kinya Inagaki; Setsuo Tokunaga; Hiromichi Shimada; Koichi Sato; Yasunori Oumi; Tsuneji Sano; Kohichi Segawa; Kazuyuki Nakai; Hiroshi Shoji; Peng Wu; Takashi Tatsumi; Takayuki Komatsu; Takao Masuda; Kazunari Domen; Eisuke Yoda; Junko N. Kondo; Toshio Okuhara; Yasuyoshi Kageyama; Miki Niwa; Masaru Ogura; Masahiko Matsukata; Eiichi Kikuchi; Noriyasu Okazaki; Motoi Takahashi; Akio Tada; Shogo Tawada; Yoshihiro Kubota; Yoshihiro Sugi; Yasuhiko Higashio; Masahiko Kamada; Yukiyo Kioka; Kohei Yamamoto; Takayuki Shouji; Yusaku Arima; Yasuaki Okamoto; Hideyuki Matsumoto

2005-01-01

28

Plasmonic photocatalyst system using Ag/AgBr/mordenite nanocrystal under visible light  

NASA Astrophysics Data System (ADS)

In this paper, plasmonic photocatalyst nanostructure system was investigated on Ag/AgBr/mordenite nanocrystal under visible light. Silver nanoparticles were readily prepared using dispersing agent and calcinations. The X-ray diffraction analysis (XRD) and diffuse-reflectance spectroscopy (DRS) demonstrated that silver bromide were introduced on the surface of mordenite nanocrystal and then Ag nanostructured photocatalytic materials were successfully synthesized. The silver nanoparticles plasmonic photocatalysts exhibited the enhanced photocatalytic performance over mordenite nanocrystal. The photocatalytic activity and stability of the synthesized catalysts were evaluated for methylene blue (MB) degradation in aqueous solution in the presence of 60 W tungsten filament Philips lamp. Several parameters were examined, catalyst amount, pH and initial concentration of MB, AgBr loading. The support size was obtained about 100-150 nm. In the same way, the average size of silver nanoparticles was obtained about 8 nm, before visible radiation. After visible radiation the average size of Ag nanoparticles was about 30 nm.

Sohrabnezhad, Sh.; Rezaei, A.

2013-03-01

29

Ab initio density functional investigation of the (001) surface of mordenite  

NASA Astrophysics Data System (ADS)

Structural and acidic properties of the (001) surface of mordenite have been studied using density functional theory including generalized gradient corrections to the exchange-correlation functional. Our calculations, in agreement with experimental results, show that the surface structure of mordenite differs only moderately from the bulk structure, no reconstruction of the surface has been found. Part of the terminal silanol groups form weak hydrogen bonds with other framework oxygen sites, the lengths of hydrogen bonds vary in the range 1.9-2.6 Å depending on the position of the Al site. The OH-stretching frequencies for various acid sites in the mordenite framework have been calculated. In agreement with experiment, calculated OH-stretching frequencies of terminal silanol groups are shifted by about 100 cm-1 with respect to the Brønsted acid sites. Those silanol groups whose OH-stretching frequencies are modified by the presence of hydrogen bonds are shown to absorb in the region typical for the Brønsted acid sites.

Bucko, T.; Benco, L.; Demuth, Th.; Hafner, J.

2002-10-01

30

Selective catalytic reduction of nitrogen oxide by hydrocarbons over mordenite-type zeolite catalysts  

Microsoft Academic Search

The reduction of NO by hydrocarbons such as C2H4, C2H6, C3H6, and C3H8 has been investigated over mordenite-type zeolite catalysts including HM, CuHM, NZA (natural zeolite), and CuNZA prepared by an ion-exchange method in a continuous flow fixed-bed reactor. NO conversion over CuNZA catalyst reaches about 94% with 2000 ppm of C3H6 at 500°C. As reductants, alkenes seem to exhibit

Moon Hyeon Kim; In-Sik Nam; Young Gul Kim

1995-01-01

31

Removal of free fatty acid in Azadirachta indica (Neem) seed oil using phosphoric acid modified mordenite for biodiesel production.  

PubMed

In this study free fatty acids present in Azadirachta indica (Neem) oil were esterified with our synthesized phosphoric acid modified catalyst. During the esterification, the acid value was reduced from 24.4 to 1.8 mg KOH/g oil. Synthesized catalyst was characterized by NH(3) TPD, XRD, SEM, FTIR and TGA analysis. During phosphoric acid modification hydrophobic character and weak acid sites of the mordenite were increased, which lead to better esterification when compared to H-mordenite. A kinetic study demonstrates that the esterification reaction followed pseudo-first order kinetics. Thermodynamic studies were also done based on the Arrhenius model. PMID:20346652

SathyaSelvabala, Vasanthakumar; Varathachary, Thiruvengadaravi Kadathur; Selvaraj, Dinesh Kirupha; Ponnusamy, Vijayalakshmi; Subramanian, Sivanesan

2010-03-25

32

Effect of cation exchange on hydrogen adsorption property of mordenite for isotope separation  

NASA Astrophysics Data System (ADS)

Zeolite easily exchanges its cation to another. As a result, pore size changes easily. Cation-exchanged mordenite type zeolite (MOR) has been reported to have comparatively good isotope separation capability at temperatures higher than 77 K. However, correlations between adsorption capacities, adsorption rate, cation variety, and cation exchange ratio have not been clearly indicated. In this work, the cation (Na+) of synthetic mordenite type zeolite (Na-MOR) was exchanged by alkaline metal ion or alkaline earth ion (e.g., Li+, K+, Mg2+ and Ca2+). Then, adsorption capacities of H2 and D2 were investigated at 77 K, 159 K, 175 K and 195 K. Adsorption capacities on Li-MOR and Ca-MOR became larger than that of Na-MOR at a low-pressure range, while that of K-MOR became smaller. Micro-pore size indicated that only K-MOR was clearly shifting to smaller size. In the case of alkaline metal, cations with lower atomic numbers may lead to increased adsorption capacities.

Kawamura, Yoshinori; Iwai, Yasunori; Munakata, Kenzo; Yamanishi, Toshihiko

2013-11-01

33

Molecular simulation of the adsorption of MTBE in silicalite, mordenite, and zeolite beta.  

PubMed

The use of methyl tertiary butyl ether (MTBE) as a gasoline additive has resulted in serious environmental problems following spills and leaks, primarily due to MTBE's high solubility in water. Remediation technologies have involved air stripping, advanced oxidation, and sorption on granular activated carbons (GAC). Hydrophobic zeolites, such as silicalite, dealuminated Y, mordenite, and beta, have been of interest in recent studies for the removal of MTBE from water. Some of these materials have shown a better performance than GAC particularly in the microg/L range. We made Monte Carlo and molecular dynamics simulations of the adsorption of pure MTBE in silicalite, mordenite, and zeolite beta with different Na+ loadings at room temperature to reveal the factors affecting the adsorption process. The results show that although the three zeolites studied here have similar pore volumes, the pore structure of zeolite beta causes a significant difference on the predicted amount of MTBE adsorbed. It was found that the position of the Na+ cations has an important effect at lower pressures. Within the range of [Na+] studied, the amount of Na+ was not found to be critical on the adsorption capacity of any of the zeolites studied, except at very low pressures in silicalite and zeolite beta. PMID:16854156

Yazaydin, A Ozgur; Thompson, Robert W

2006-07-27

34

Mordenite and montmorillonite alteration of glass structures in a rhyolite pipe, northern Black Hills, South Dakota  

SciTech Connect

Green structures, 0.5 to 1.5 in. across, occur in a Tertiary rhyolite pipe in the northern Black Hills, South Dakota. The structures are of two types: angular to ellipsoidal masses and stretched or smeared structures. Thin section analysis revealed that those of the first type are massive, with no internal structure, and those of the second type are cellular and have classic flame structure characteristics. XRD indicated the composition to be a mixture of secondary mordenite (a zeolite) and montmorillonite. The first type is interpreted to be deuterically altered vitrophyre clasts and the second type to be altered vesicular structures produced by degassing of the magma in the pipe. Chemical analysis of the alteration material indicates a loss of alkalies and silica, with an increase in water, CaO, MgO and ferric iron when compared to the composition of fresh vitrophyre from the same pipe. The changes are in agreement with experimental work on the alteration of rhyolitic glass by a number of researchers. This is the first occurrence of mordenite reported for the Black Hills.

Kirchner, J.G. (Illinois State Univ., Normal (United States))

1991-10-01

35

Kinetic and equilibrium studies of the removal of ammonium ions from aqueous solution by rice husk ash-synthesized zeolite Y and powdered and granulated forms of mordenite.  

PubMed

The removal of ammonium from aqueous solutions using zeolite NaY prepared from a local agricultural waste, rice husk ash waste was investigated and a naturally occurring zeolite mordenite in powdered and granulated forms was used as comparison. Zeolite NaY and mordenite were well characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis and the total cation exchange capacity (CEC). CEC of the zeolites were measured as 3.15, 1.46 and 1.34 meq g(-1) for zeolite Y, powdered mordenite and granular mordenite, respectively. Adsorption kinetics and equilibrium data for the removal of NH(4)(+) ions were examined by fitting the experimental data to various models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The equilibrium pattern fits well with the Langmuir isotherm compared to the other isotherms. The monolayer adsorption capacity for zeolite Y (42.37 mg/g) was found to be higher than that powdered mordenite (15.13 mg/g) and granular mordenite (14.56 mg/g). Thus, it can be concluded that the low cost and economical rice husk ash-synthesized zeolite NaY could be a better sorbent for ammonium removal due to its rapid adsorption rate and higher adsorption capacity compared to natural mordenite. PMID:19879040

Yusof, Alias Mohd; Keat, Lee Kian; Ibrahim, Zaharah; Majid, Zaiton Abdul; Nizam, Nik Ahmad

2009-09-19

36

The use of cyclohexanol dehydration, isobutane cracking and 2,6-dipn synthesis over dealuminated mordenite to probe acidity  

Microsoft Academic Search

The title probe reactions provided information on the strength and location of acid sites formed after hydrothermal and acid treatment of Mordenite. A generally good correlation was observed between the isobutane cracking activity and the concentration of non-sodium-charge-balanced framework aluminium but certain treatments showed a significant positive deviation from this. Mild self steaming (“deep bed” calcination) resulted in a significant

A. W. O'Donovan; C. T. O'Connor

1997-01-01

37

Characterization and fuel cell performance analysis of polyvinylalcohol–mordenite mixed-matrix membranes for direct methanol fuel cell use  

Microsoft Academic Search

Polyvinylalcohol–mordenite (PVA–MOR) mixed matrix membranes were synthesized for direct methanol fuel cell (DMFC) use. For the structural and the morphological characterization, Scanning Electron Microscopy and Thermal Gravimetric Analysis methods were used. Zeolite distribution within the polymer matrix was found to be homogeneous. An impedance spectroscope was used to measure the proton conductivity. In order to obtain information about methanol permeation

Fehmi Görkem Üçtu?; Stuart M. Holmes

2011-01-01

38

Location of MTBE and toluene in the channel system of the zeolite mordenite: Adsorption and host-guest interactions  

NASA Astrophysics Data System (ADS)

This paper reports a study of the location of Methyl Tertiary Butyl Ether (MTBE) and toluene molecules adsorbed in the pores of the organophylic zeolite mordenite from an aqueous solution. The presence of these organic molecules in the zeolite channels was revealed by structure refinement performed by the Rietveld method. About 3 molecules of MTBE and 3.6 molecules of toluene per unit cell were incorporated into the cavities of mordenite, representing 75% and 80% of the total absorption capacity of this zeolite. In both cases a water molecule was localized inside the side pocket of mordenite. The saturation capacity determined by the adsorption isotherms, obtained by batch experiments, and the weight loss given by thermogravimetric (TG) analyses were in very good agreement with these values. The interatomic distances obtained after the structural refinements suggest MTBE could be connected to the framework through a water molecule, while toluene could be bonded to framework oxygen atoms. The rapid and high adsorption of these hydrocarbons into the organophylic mordenite zeolite makes this cheap and environmental friendly material a suitable candidate for the removal of these pollutants from water.

Arletti, Rossella; Martucci, Annalisa; Alberti, Alberto; Pasti, Luisa; Nassi, Marianna; Bagatin, Roberto

2012-10-01

39

A study involving mordenite, titanate nanotubes, perfluoroalkoxy polymers, and ammonia borane  

NASA Astrophysics Data System (ADS)

Zeolites and molecular sieves are finding applications in many areas of catalysis due to appreciable acid activity, shape selectivity, and ion-exchange capacity, as they possess an unbalanced framework charge. For catalytic applications, zeolites become more valuable as the ratio of SiO2/Al2O 3 increases. Acid resistance and thermal stability of zeolite are both improved with increasing SiO2/Al2O3. This part of the thesis deals with the control of morphology focused on decreasing the crystal diameter of mordenite zeolite and to increase the SiO2/Al 2O3 ratio by changing synthesis conditions. A high SiO 2/Al2O3 ratio (SAR15) of mordenite was prepared in a very short reaction time. We studied the role of hydroxide in the crystallization of the mordenite as a structure director, nucleation time modifier, and crystallite aggregate enhancer. The formation of nano-aggregates of mordenites was greatly enhanced using a combination of alcohol additives and conventional heating. Mordenite nucleation was also increased without using alcohols when microwave heating was employed, but the alcohols further accelerated the nucleation process. The different heating techniques affected the morphology; microwave heating produced crystallites of ˜40 nm, while the conventional hydrothermal method formed larger size crystallites of ˜88 nm. We controlled the size and shape of the mordenite crystals because they have important implications in hydrocarbon conversion and separation processes. Mordenite synthesized showed jellyfish, acicular, flower, and wheat grain like structures. In the second part of this thesis, a phase transition was successfully achieved from TiO2 particles to titanate nanotubes by the breakage of Ti-O bonds and the creation of oxygen vacancies without using expensive precursors, high temperatures, high chemical concentrations of alkaline solutions, and long synthesis times. A combination of anatase nano-particles/titanate nano-tubes was synthesized using TiO2 (anatase) and a temperature of only 100°C. When TiO2 (P-25) was used with the same concentration of alkaline solution (1 molar NaOH), the same processing time of 12 hours, and a higher temperature at 110°C, only titanate nano-tubes were observed. The linkages of 'Ti-O' play a very important role in the structural features of different phases. Two crystalline phases (tetragonal and monoclinic) were synthesized as products in the case of TiO 2 (anatase) and one crystalline phase (monoclinic) for products of TiO 2 (P-25). The third part of the thesis concerns surface modification of hydrophobic fluoropolymers that have low surface energies and are very difficult to metallize. Surface modification was done to enhance surface roughness and hence to boost surface energy for metallization processes. We used low impact, environmentally friendly non-thermal plasmas at atmospheric pressure to strip off F - ions and replace them with reactive unsaturated hydrocarbon functionalities such as CH=CH2 on the surface of a polymer. As these hydrocarbon functionalities are reactive with metals, they form composites that have good adhesion between layers of polymer. Due to surface modification, polymeric chains were broken by the loss of fluorine atoms (F/C = 0.33) and the gain of oxygen atoms (O/C = 0.17) using methane/argon plasmas. Methane/hydrogen/argon plasmas on the other hand produced extensive loss of fluorine atoms (F/C = 0.07-0.33) and gain of oxygen atoms (O/C = 0.08-0.16) that was far better than pristine PFA. The surface of PFA was modified by defluorination and oxidation. Further enhancement of COF and COO groups revealed that the surface was modified to a hydrophilic membrane that can further be easily hydrolyzed to COOH in the presence of atmospheric humidity. The last part of the thesis deals with ammonia borane which was studied as a potential source of hydrogen for fuel cells. We analyzed the viability of ammonia borane as a hydrogen carrier compound for fuel cell applications using a thermolysis method. Ammonia borane is an attractive source for hydrogen productio

Nosheen, Shaneela

40

Use of dielectric relaxation for measurements of surface energy variations during adsorption of water on mordenite.  

PubMed

This paper tries to assess simply and quantitatively the link between classical adsorption theories and dielectric spectroscopy, in order to demonstrate that dielectric spectroscopy can be used as a tool of determination of surface energy variations due to movements of charge carriers at the surface of solids. A simple theory is developed to analyze hops of cations at the surface of mordenite, which are detected by complex impedance spectroscopy during adsorption of water. An energy of extraction of the cation can be determined from measurements and its dependence on the quantity of water molecules adsorbed is shown and qualitatively and quantitatively explained, using relationships developed in order to interpret adsorption phenomena generally. The agreement with other determinations of the adsorption energies and solid surface energy is correct. PMID:17126849

Douillard, J M; Maurin, G; Henn, F; Devautour-Vinot, S; Giuntini, J C

2006-11-28

41

Comparative study of transformation of linear alkanes over modified mordenites and sulphated zirconia catalysts: Influence of the zeolite acidity on the performance of n-butane isomerization  

Microsoft Academic Search

Zeolite mordenite was dealuminated by steam treatment followed by acid leaching and further impregnated with 1wt.% of iron or sulphated. The various solids were characterized by XRD, 29Si and 27Al NMR, IR of adsorbed pyridine as well as ammonia adsorption calorimetry and evaluated in n-butane isomerization. BET surface area of non-dealuminated mordenite was 462m2g?1 and this value showed marked decreases

Alcineia C. Oliveira; Nadine Essayem; Alain Tuel; Jean-Marc Clacens; Younes Ben Tâarit

2008-01-01

42

Role of Lewis acidity in the isomerization of n-pentane and o-xylene on dealuminated H-mordenites  

SciTech Connect

n-Pentane and o-xylene isomerizations have been studied at 285 and 150{degrees}C, respectively, on seven dealuminated H-mordenites containing different amounts of framework and nonframework aluminum which were prepared by steaming or calcining NH{sub 4}-mordenite. The number of Bronsted and Lewis sites were known beforehand from {sup 29}Si high-resolution magnetic resonance and infrared study of low-temperature CO adsorption. In addition, the availability of the acid sites to the reactants was estimated from the ratios of the liquid monolayer volume of the reactant (n-pentane or o-xylene) to that of N{sub 2}, the availability of the active sites to N{sub 2} and CO being the same. A synergistic enhancement of the acidity by the interaction between Bronsted and Lewis acid centers is suggested. Other aspects related with the product distribution are also discussed. 32 refs., 9 figs., 5 tabs.

Hong, Y.; Gruver, V.; Fripiat, J.J. [Univ. of Wisconsin, Milwaukee, WI (United States)

1994-12-01

43

Ethyl tert-butyl ether (ETBE) synthesis on H-Mordenite: Gas-phase kinetics and DRIFTS studies  

SciTech Connect

The ethyl tert-butyl ether (ETBE) formation between 313 and 363 K over an H-mordenite catalyst was studied in a packed-bed flow catalytic reactor at atmospheric pressure. An activation energy of 82 kJ/mol and reaction orders in isobutene and ethanol of 0.8 and -0.8 were found. In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to study the state of the catalyst under reaction conditions. The IR studies, coupled with the reaction kinetics information, are consistent with the idea that the stability of the H-mordenite catalyst requires the protective action of ethanol to prevent the occurrence of isobutene oligomerization products. The high ethanol concentrations found in the zeolite pores under the temperature and pressure conditions employed is also responsible for reaction inhibition. 27 refs., 13 figs., 1 tab.

Larsen, G.; Lotero, E.; Marquez, M. [Univ. of Nebraska-Lincoln, NB (United States)] [and others

1995-12-01

44

Deactivation of sulfated-zirconia and H-mordenite catalysts during n-butane and isobutane isomerization  

Microsoft Academic Search

The catalytic properties of sulfated-zirconia and H-mordenite for isomerization of n-butane and isobutane were studied at temperatures near 450K. Both catalysts showed rapid deactivation (deactivation constant kdeact near 0.02min?1) during isomerization of n-butane when olefins were present in the feed stream. Removal of olefins from the feed decreased the rate of catalyst deactivation over sulfated-zirconia (kdeact near 0.007min?1), while removal

K. B. Fogash; Z. Hong; J. M. Kobe; J. A. Dumesic

1998-01-01

45

Multiple adsorption of NO on cobalt-exchanged chabazite, mordenite, and ferrierite zeolites: A periodic density functional theory study  

Microsoft Academic Search

The adsorption of NO on Co(II)-exchanged chabazite (CHA), mordenite (MOR), and ferrierite (FER) has been investigated by periodic density functional theory calculations. The most stable configurations of Co(II) in alpha and beta sites of the zeolites with two framework Al\\/Si substitutions at short distances and Al-(Si)n>1-Al ordering are used for calculating the adsorption energy of NO molecules on Co(II) cations

Ivelina Georgieva; Lubomir Benco; Daniel Tunega; Natasha Trendafilova; Jürgen Hafner; Hans Lischka

2009-01-01

46

Isomerization of C{sub 8} aromatics over a Pt/mordenite catalyst: A statistical model  

SciTech Connect

A statistical approach was used to analyze the behavior of the isomerization of the C{sub 8} aromatics fraction on a commercial Pt/mordenite catalyst. In particular, the effects that the operating variables, temperature, pressure, space velocity, and hydrogen to hydrocarbon ratio had on the yield of p-xylene and loss of xylenes were studied. To this end, a sequential experimental design with a linear model in the first stage and a quadratic model in the second stage was used. The results of the linear model indicated that the temperature, pressure, and space velocity were the most influential factors for the yield of p-xylene, while for the loss of xylenes, pressure and space velocity were 2 times more important than temperature. The results from the quadratic model indicate the existence of an important curvature effect, especially with respect to the space velocity, and therefore the linear model by itself cannot describe adequately the behavior of the reaction system in the whole range of operating conditions.

Gonzalex, H.; Rodriguez, A.; Cedeno, L.; Ramirez, J. [UNAM, Mexico City (Mexico). Dept. de Ingenieria Quimica; Aracil, J. [Univ. Complutense, Madrid (Spain). Dept. de Ingenieria Quimica

1996-11-01

47

Determination of temperature-induced changes in the structure of the nearest environment of aluminum in mordenite zeolites from x-ray absorption near-edge structure spectra  

NASA Astrophysics Data System (ADS)

The structure of the nearest environment of aluminum in mordenite zeolites was investigated at temperatures up to 1000 K using the Al K x-ray absorption near-edge structure (XANES) spectra. The interatomic Al-O distances and the number of coordinating oxygen atoms were determined by Fourier transformation of Al K-XANES spectra and fitting of the contribution of the nearest oxygen atoms. The exactness and stability of the obtained values of structural parameters were verified using the Al K-XANES spectrum of the model Na-mordenite zeolite. To determine the coordination of aluminum in H-mordenites in the temperature range under study, fitting of the contribution of coordinating oxygen atoms was performed using both the single-sphere model of the nearest environment of aluminum and two-sphere fitting for the most probable structural models of the nearest environment of aluminum. Such models were chosen based on the analysis of the specific preedge features and fine structure of the XANES spectra, as well as NMR data. With this approach, the simultaneous presence of tetra-and hexacoordinated aluminum in H-mordenite at T = 300 K was established and the concentrations of such mixed states were determined. The presence of strong distortions of the oxygen tetrahedron coordinating the aluminum atom in dehydrated H-mordenite at 575 K was shown and the Al-O distances for such distortions were determined. The simultaneous presence of tri-and tetracoordinated aluminum in H-mordenite at 985 K was established and the fraction of tricoordinated aluminum was estimated quantitatively.

Bugaev, L. A.; Latokha, Ya. V.; Avakyan, L. A.; van Bokhoven, E. A.

2006-04-01

48

Effect of Temperature on the Pb (II) Removal from Single Aqueous Solutions by a Locally Natural Mordenite: Equilibrium and Kinetic Modeling  

Microsoft Academic Search

Zeolites have been shown to be effective adsorbents for the removal of heavy metals from aqueous solutions. In this study, mordenite (a natural zeolite) has been used for the removal of lead ions to evaluate its potential use as a low?cost adsorbent. Batch experiments have been conducted to evaluate the equilibrium and process kinetics at different temperatures. The equilibrium experimental

Xue Song Wang; Lei He; Hai Qiong Hu; Jin Wang

2008-01-01

49

Calorimetric study of the acidity of decationized mordenite according to the adsorption of ammonia at 30 and 300/sup 0/C  

SciTech Connect

The heats of adsorption of NH/sub 3/ at 30 and 300/sup 0/C on decationized mordenites have been studied by the method of adsorption calorimetry. It has been found that the heat of adsorption on the strong acid sites increases with increasing temperature, the highest initial heat of adsorption of NH/sub 3/, 170 kJ/mole, being discovered on the dehydroxylated zeolite. Acidity spectra obtained at different temperatures have been compared.

Kapustin, G.I.; Brueva, T.R.; Klyachko, A.L.; Rukhadze, A.D.; Rubinshtein, A.M.

1983-02-01

50

A study of copper-exchanged mordenite natural and ZSM-5 zeolites as SCR–NO x catalysts for diesel road vehicles: Simulation by neural networks approach  

Microsoft Academic Search

Copper-catalysts, based on the ZSM-5 (CuZSM5) and Cuban natural Mordenite (CuMORD) zeolites have been prepared by a conventional ion-exchange method and their catalytic activity in the selective catalytic reduction (SCR) of NO was studied using ammonia in presence of H2O and SO2. A commercial catalyst SCR (CATCO) based on V2O5–WO3–TiO2, was also studied as reference. This paper presents experimental results

Mona Lisa Moura de Oliveira; Carla Monteiro Silva; Ramon Moreno-Tost; Tiago Lopes Farias; Antonio Jiménez-López; Enrique Rodríguez-Castellón

2009-01-01

51

A TPD and IR study of the surface species formed from ammonia on zeolite H-ZSM-5, H-mordenite and H-beta  

Microsoft Academic Search

Ammonia was found to react with the Brönsted acid sites of H-zeolites forming NH4+ ions, coordinate to Lewis acid sites and, at higher coverage, to NH4+ ions forming protonated ammonia associations, such as, NH4+(NH3)n. Besides the Lewis acid NH4+ ions, one kind of strong Lewis acid site was detected in zeolite H-ZSM-5 and H-mordenite, while strong and weak Lewis acid

F Lónyi; J Valyon

2001-01-01

52

Reduction of nitrogen dioxide by propene over acidic mordenites: influence of acid site concentration, formation of by-products and mechanism  

Microsoft Academic Search

The reduction of nitrogen dioxide to nitrogen by propene was studied over a variety of acidic mordenite zeolites differing in their Si:Al ratio and thus, in their concentration of acid sites. The formation of by-products was monitored applying an ion–molecule reaction (IMR) mass spectrometer. It was found that at fixed conditions the yield of nitrogen increases with increasing concentration of

Till Gerlach; Uta Illgen; Michael Bartoszek; Manfred Baerns

1999-01-01

53

Characterization of the acidity of ultrastable Y, mordenite, and ZSM-12 via NH 3stepwise temperature programmed desorption and Fourier transform infrared spectroscopy  

Microsoft Academic Search

The acidity of ultrastable Y (USY), mordenite, and ZSM-12 of variable Si\\/Al ratios has been characterized by coupling NH3-stepwise temperature programmed desorption (STPD) and FT-IR. The former technique allows us to quantify accurately the ammonia chemisorbed on acid sites of different strengths. In contrast to other acidic oxide catalysts, it was found that protonated zeolites possess distinct limits of acid

Wenmin Zhang; Eric C. Burckle; Panagiotis G. Smirniotis

1999-01-01

54

Multiple adsorption of NO on cobalt-exchanged chabazite, mordenite, and ferrierite zeolites: A periodic density functional theory study  

NASA Astrophysics Data System (ADS)

The adsorption of NO on Co(II)-exchanged chabazite (CHA), mordenite (MOR), and ferrierite (FER) has been investigated by periodic density functional theory calculations. The most stable configurations of Co(II) in ? and ? sites of the zeolites with two framework Al/Si substitutions at short distances and Al-(Si)n>1-Al ordering are used for calculating the adsorption energy of NO molecules on Co(II) cations and at Al framework sites. The less stable configurations of ?-Co(II)-MOR/FER show larger adsorption energies for one and two NO molecules. The bonding of one, two (and three) NO molecules to ?/?-Co(II) sites in CHA/MOR/FER induces a shortening of the N-O bond lengths because electron density is withdrawn from the antibonding orbital of the adsorbed NO molecule. The calculated ?(NO) stretching frequencies of mono- and dinitrosyl complexes at ?/?-Co(II)-MOR/FER are in good agreement with the experimental data. NO molecules adsorbed on ?-Co(II)-MOR and on ?-Co(II)-FER show similar NO stretching frequencies as nitrosyl complexes in Co(II)-MOR/-FER/-ZSM-5. Mononitrosyl complexes of ?/?-Co(II)-MOR/FER display ?(NO) frequencies blueshifted relative to the free NO, while in dinitrosyl complexes both the symmetric and asymmetric components are redshifted compared to the mononitrosyl frequency. The analysis of the vibrational spectra suggests that mononitrosyls are formed by adsorption at cation in both ? and ? sites in MOR, FER, and ZSM-5, while dinitrosyl complexes exist only at ?-type Lewis sites. This is important for the understanding of the reduction mechanism of NO to N2. A larger adsorption capacity of ?-Co(II)-FER compared to ?-Co(II)-MOR is predicted.

Georgieva, Ivelina; Benco, Lubomir; Tunega, Daniel; Trendafilova, Natasha; Hafner, Jürgen; Lischka, Hans

2009-08-01

55

High catalytic performance of PtFe alloy nanoparticles supported in mordenite pores for preferential CO oxidation in H 2-rich gas  

Microsoft Academic Search

Catalytic performance of Pt-Fe\\/mordenite for preferential CO oxidation (PROX) was tested in comparison with that of Pt-Fe\\/Al2O3. The former catalyst pretreated at 300°C (Pt-Fe\\/M-300) showed extremely high reactivity and selectivity for the PROX reaction but the catalyst treated at 500°C (Pt-Fe\\/M-500) showed the inferior performances as well as Pt-Fe\\/Al2O3. Characterization of the catalysts indicated that most of metallic particles at

Masashi Kotobuki; Akiko Watanabe; Hiroyuki Uchida; Hisao Yamashita; Masahiro Watanabe

2006-01-01

56

Structural investigations of zeolites ERS-7, mordenite, and sodalite using a combination of powder diffraction and computer simulation techniques  

NASA Astrophysics Data System (ADS)

The framework structure of dehydrated template-free ERS-7 was determined by a combination of synchrotron X-ray powder diffraction and the simulated annealing approach of Deem and Newsam. The orthorhombic unit cell ( a = 9.79976(4) A, b = 12.41163(6) A, c = 22.86063(11) A) contains 6 tetrahedral framework atoms (Si/Al = 8.4), all on general positions, and 14 bridging oxygens. It can be constructed as a network of purely face-sharing 17-sided (465 46582) "picnic-basket"-shaped cages that are stacked so as to form a 1D 8-ring channel system (3.5 A x 4.7 A) that runs through the handles of the baskets. Three Bronsted acid sites were then identified via a multi-dataset Rietveld refinement against both PXD and PND data. Previous reports of correlations between diffracted intensities and aluminum content in as-synthesized Na mordenites (Si/Al = 5 to 10) are shown to be explained as a selective suppression of the (h, k,? = 2n + 1) reflections caused by linear faulting along the main channel axis. Computer generated structures with up to 500,000 atoms were used to simulate the diffuse scattering patterns for several different correlated defect models, which were then compared to previously reported experimental results. The regions of faulted material are shown to consist of c-axis chains of shifted framework 4-rings, such that neighboring pairs of chains along the a-axis shift together. The intensity of odd-? reflections is suppressed by a factor of (1 - 2po) 2 where po is the fraction of fault-shifted material, the intensity of the diffusely scattered sheets in the odd-? planes perpendicular to c* increases in proportion to po(1 - po), and the in-plane modulations of these sheets are shown to have the form sin 2(pih/2). Variable-temperature synchrotron PXD data from dehydrated sodium sodalite, Na6[Al6Si6O24], reveals a structural phase transition at 500 K that involves both a commensurate ordering of the extra-framework Na cations and a one-dimensional incommensurate modulation of the framework. Peak splittings and superlattice reflections implicate an orthorhombically distorted supercell which is related to the original 9.1 A cubic cell by a 45° rotation about a 4-fold axis and a doubling of the volume (?2 a x ?2a x a). The incommensurate modulation vector is then shown to be [211]/8.9 on the commensurate supercell basis. The 88 unique orderings of the 12 Na cations of the supercell among its 16 available sites were enumerated, and each configuration was subjected to lattice energy minimization using an empirical interatomic potential. A unique solution was identified that minimizes the structural energy and also matches the experimental diffraction data. The high-temperature phase (Pm3¯n) is well described by dynamical disorder among the cation sites and also between opposite framework "partial collapse" angles.

Campbell, Branton J.

57

Use of isotopic labeling for mechanistic studies of the methanol-to-hydrocarbons reaction. Methylation of toluene with methanol over H-ZSM-5, H-mordenite and H-beta  

Microsoft Academic Search

Methylation of toluene (in one case benzene) with methanol has been investigated over four different zeolites: Small and large crystal ZSM-5, dealuminated mordenite and zeolite beta. The feed ratio methanol\\/arene was varied over a wide range, mostly >1, using nitrogen or helium as carrier gas. A rather high space velocity was employed (WHSV (methanol+arene): 5–35 h?1). The reaction temperature was

Øyvind Mikkelsen; Per Ola Rønning; Stein Kolboe

2000-01-01

58

Review of the thermal stability and cation exchange properties of the zeolite minerals clinoptilolite, mordenite, and analcime; applications to radioactive waste isolation in silicic tuff  

SciTech Connect

Silicic tuffs of the southern Great Basin and basalts of the Columbia River Plateau are under investigation as potential host rocks for high- and intermediate-level radioactive wastes. Nonwelded and partially welded tuffs may contain major amounts (> 50%) of the zeolite minerals clinoptilolite, mordenite, and analcime. Densely welded tuffs and some basalt flows may contain clinoptilolite as fracture filling that limits the permeability of these rocks. The cation exchange properties of these zeolite minerals allow them to pose a formidable natural barrier to the migration of cationic species of various radionuclides in aqueous solutions. However, these minerals are unstable at elevated temperatures and at low water-vapor pressures and may break down either by reversible dehydration or by irreversible mineralogical reactions. All the breakdown reactions occurring at increased temperature involve a net volume reduction and evolution of fluids. Thus, they may provide a pathway (shrinkage fractures) and a driving force (fluid pressure) for release of radionuclides to the biosphere. These reactions may be avoided by keeping zeolite-bearing horizons saturated with water and below about 85{sup 0}C. This may restrict allowable gross thermal loadings in waste repositories in volcanic rocks.

Smyth, J.R.; Caporuscio, F.A.

1981-06-01

59

Molecular adsorption and metal-support interaction for transition-metal clusters in zeolites: NO adsorption on Pdn (n=1-6) clusters in mordenite  

NASA Astrophysics Data System (ADS)

The adsorption of NO molecules on Pdn clusters of varying size (n=1-6) located in the main channel of mordenite and the interaction of the metallic clusters with the zeolitic framework were investigated using ab initio density-functional calculations under periodic boundary conditions. The supported clusters are created by binding Pdn2+ cations to the inner cavity of a deprotonated Al-exchanged zeolite with an Al/Si ratio of 1/11, such that a charge-neutral system is created. Compared to the highly symmetric structures of the gas-phase clusters, the clusters bound to the zeolitic framework undergo appreciable geometric distortions lowering their symmetry. The distortions are induced by strong interactions with ``activated'' framework oxygens located close to the charge-compensating Al/Si substitution sites, but the cluster forms also weaker bonds to ``nonactivated'' oxygen atoms. The interaction with the framework also affects the electronic and magnetic properties of the clusters. While in the gas phase all clusters (except the isolated Pd atom with a closed d10 ground state) have a paramagnetic moment of 2?B, in the zeolite clusters with two to four atoms have zero magnetic moment, while the Pd5 cluster has a magnetic moment of 2?B and for the Pd6 cluster, it is even enhanced to 4?B (but the magnetic energy differences relative to low-spin configurations are modest). Analysis of the magnetization densities shows that in all clusters with zero total moment (singlet ground state), there are sites with excess spin densities of opposite sign. The influence of the cluster-support interaction on the chemical properties of the clusters has been tested by the adsorption of NO molecules. The results demonstrate the interplay between the molecule-cluster and cluster-framework interactions, which can lead to an increase or decrease in the adsorption energy compared to NO on a gas-phase cluster. While on the gas-phase cluster adsorption in low-coordination sites (vertex or bridge) is preferred, for the cluster in the zeolite adsorption in threefold coordinated hollow or twofold bridge sites is preferred. The magnetic properties of the clusters and of the paramagnetic NO molecule play an important role. For the supported clusters with zero magnetic moment, upon adsorption the spin of the molecule is transferred to the cluster (and induces also a modest polarization of the framework). For magnetic clusters, spin pairing induces a reduced magnetic moment of the NO-Pdn complex. The redshift of the NO stretching frequencies is reduced compared to the free clusters by the cluster-support interaction for the smaller clusters, while it remains essentially unchanged for the larger clusters. A detailed electronic analysis of the cluster-support interactions and of the adsorption properties is presented.

Grybos, Robert; Benco, Lubomir; Bu?ko, Tomas; Hafner, Jürgen

2009-03-01

60

Matrix-assisted laser desorption ionization using lithium-substituted mordenite surface  

NASA Astrophysics Data System (ADS)

An efficient matrix for matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) has been developed. The use of 2,4,6-trihydroxyacetophenone (THAP) on lithium-substituted zeolite has enabled ionization of low-molecular-weight compounds that are not detectable by conventional MALDI-MS. IR measurements and quantum-chemical calculations have also been carried out to understand the adsorption structure of THAP on zeolite. The mechanism of Li+ adduction from zeolite to THAP is also discussed. The important role of the water molecules adsorbed on the zeolite surface for the Li+ adduction from zeolite to THAP has been clarified.

Suzuki, Junya; Sato, Asami; Yamamoto, Ryo; Asano, Takashi; Shimosato, Taku; Shima, Hisashi; Kondo, Junko N.; Yamashita, Ken-ichi; Hashimoto, Kenro; Fujino, Tatsuya

2012-09-01

61

K/AR dating of clinoptilolite, mordenite, and associated clays from Yucca Mountains, Nevada.  

National Technical Information Service (NTIS)

Zeolites are abundant in the geologic record in both continental and marine environments. The purpose of the present study is to evaluate the utility of K-bearing zeolites for dating by the K/Ar method to determine the time of zeolite diagenesis at Yucca ...

G. WoldeGabriel

1993-01-01

62

A study involving mordenite, titanate nanotubes, perfluoroalkoxy polymers, and ammonia borane  

Microsoft Academic Search

Zeolites and molecular sieves are finding applications in many areas of catalysis due to appreciable acid activity, shape selectivity, and ion-exchange capacity, as they possess an unbalanced framework charge. For catalytic applications, zeolites become more valuable as the ratio of SiO2\\/Al2O 3 increases. Acid resistance and thermal stability of zeolite are both improved with increasing SiO2\\/Al2O3. This part of the

Shaneela Nosheen

2009-01-01

63

Experimental and computational study of beta, ZSM-12, Y, mordenite and ERB-1 in cumene synthesis  

Microsoft Academic Search

The catalytic performance of zeolite ? in the liquid phase alkylation of benzene with propylene is compared with that of other zeolites: MOR, ERB-1, USY, MTW. The comparison is carried out both by catalytic tests and by computational evaluation of the energy barriers for diffusion of the product molecules and of the binding energies (BE's) of the same molecules, inside

C. Perego; S. Amarilli; R. Millini; G. Bellussi; G. Girotti; G. Terzoni

1996-01-01

64

Selective oxidation of methane by the bis(mu-oxo)dicopper core stabilized on ZSM-5 and mordenite zeolites.  

PubMed

This work reports on the capability of the O2-activated Cu-ZSM-5 and Cu-MOR zeolites to selectively convert methane into methanol at a temperature of 398 K. A strong correlation between (i) the activity and (ii) the intensity of the 22 700 cm-1 UV-vis band, assigned to the bis(mu-oxo)dicopper core, is found (i) as a function of the reaction temperature, (ii) as a function of the Cu loading of the zeolite, and (iii) in comparison to other Cu materials. These three lines of evidence firmly support the key role of the bis(mu-oxo)dicopper core in this selective, low-temperature hydroxylation of methane. PMID:15686370

Groothaert, Marijke H; Smeets, Pieter J; Sels, Bert F; Jacobs, Pierre A; Schoonheydt, Robert A

2005-02-01

65

Influence of modified mordenite on hydrodesulfurization activity of alumina-cobalt-molybdenum and alumina-nickel-molybdenum catalysts  

Microsoft Academic Search

UDC 661.183.004.14 Middle distillates and vacuum gasoils are hydrotreated on alumina--cobalt-molybdenum (ACM) and alumina-nickel-molybdenum (ANM) catalyst [1-3]. These catalysts will reduce the sulfur eontent indiesel fuel cuts from 1-1..2% to 0ol-0.2% (temperature 360-3809C, pressure 3-4 MPa, and feedstock mass velocity 4-4.5 h-Z), and in vacumm gasoil from 1.5-7% to0.25-0.3% (temperature 370-380~ pressure 4-5 MPa, and feedstock mass velocity i-1.5 h-~).

L. V. Vasilenko; B. K. Nefedov

1985-01-01

66

Cyclohexanol conversion as a test reaction for acid properties of solids investigation of faujasites, mordenites and MCM-41  

Microsoft Academic Search

The goal of this study was to find an universal test reaction for the properties of both weak and strong acid sites. Cyclohexanol conversion was found to be such test reaction. It has been found that in the presence of weak Bronsted sites (such as Si-OHB in HBoralites or (AlO)3 Si-OH-Al (SiO)3 in NaHX) only dehydration occured. More acidic sites

J. Datka; B. Gil; O. Vog; J. Rakoczy

1999-01-01

67

Comparison absorption of new methylene blue dye in zeolite and nanocrystal zeolite  

Microsoft Academic Search

Mordenite and mordenite nanocrystal, were employed as effective adsorbents for new methylene blue (NMB) from an aqueous solution. The adsorption kinetics was investigated. The adsorption capacity of mordenite nanocrystal zeolite for NMB dye is more than that of the mordenite zeolite. Kinetic and adsorption isotherm studies demonstrate that the adsorption follows the pseudo second-order kinetics. The intraparticle diffusion rate coefficient

Sh. Sohrabnezhad; A. Pourahmad

2010-01-01

68

Aluminosilicates as Carriers of Phosphate-accumulating Bacteria  

Microsoft Academic Search

Five different aluminosilicate materials: natural altered tuff, synthetic mordenite, ammonium-exchanged mordenite, synthetic perlite and zeolite A were used for the immobilisation of metabolically active P-accumulating bacteria A. ju- nii. After 24 h of bacterial cultivation in reactors containing different carriers, one part of the total cell population was immobilised onto the carriers by means of adsorptive growth while the other

Jasna Hrenovic; Darko Tibljas; Lavoslav Sekovanic

69

ESTUDIO COMPARATIVO DE LA HIDROCONVERSIÓN DE AROMÁTICOS C8 SOBRE CATALIZADORES Pt\\/MORDENITA Y Pt\\/SiO2Al2O3 COMPARATIVE STUDY OF THE HYDROCONVERSION OF C8 AROMATICS OVER Pt\\/MORDENITE AND Pt\\/SiO2Al2O3 CATALYSTS  

Microsoft Academic Search

The C8 aromatics fraction in a refinery consists mainly of four isomers i.e. ortho-, meta-, para-xylene and ethylbenzene, being para-xylene the one with major industrial importance. Since the equilibrium amount of para- xylene at the outlet of the catalytic reformer is only ?24 %, a separation of this isomer is performed, and the ortho- and meta- rich fraction is selectively

H. González-Rodríguez; E. Ramírez-Álvarez; J. Ramírez-Solís; J. L. Rico-Cerda; J. Lara-Romero; Facultad de Ingeniería Química

2006-01-01

70

Benzylation of benzene with benzyl alcohol on zeolite catalysts  

Microsoft Academic Search

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl alcohol (BnOH) was investigated over various zeolite catalysts (HSZ 600 mordenite, CBV 20A mordenite, H-beta zeolites with Si\\/Al of 10.8 and 35.8, respectively) at 353–423K and under atmospheric pressure, using three reaction methodologies: (A) by adding all benzyl alcohol at the beginning of the reaction, (B) by dropwise

N. Candu; M. Florea; S. M. Coman; V. I. Parvulescu

2011-01-01

71

Environmentally friendly, heterogeneous acid and base catalysis for the methylation of catechol: Chances for the control of chemo-selectivity  

Microsoft Academic Search

The properties of catalysts with (i) Brønsted-type acidity (H-mordenite and Al\\/P mixed oxide), (ii) Lewis-type acidity (Al trifluoride) or (iii) basic characteristics (Mg\\/Fe mixed oxide) were investigated in the gas-phase methylation of catechol. When methanol was used as the methylating agent, H-mordenite and AlF3 gave high selectivities to guaiacol (the product of O-methylation) under mild reaction conditions, that is at

M. Ardizzi; N. Ballarini; F. Cavani; E. Chiappini; L. Dal Pozzo; L. Maselli; T. Monti

2007-01-01

72

Efficient removal of cesium from low-level radioactive liquid waste using natural and impregnated zeolite minerals  

Microsoft Academic Search

The objective of the proposed work was focused to provide promising solid-phase materials that combine relatively inexpensive and high removal capacity of some radionuclides from low-level radioactive liquid waste (LLRLW). Four various zeolite minerals including natural clinoptilolite (NaNCl), natural chabazite (NaNCh), natural mordenite (NaNM) and synthetic mordenite (NaSM) were investigated. The effective key parameters on the sorption behavior of cesium

E. H. Borai; R. Harjula; Leena malinen; Airi Paajanen

2009-01-01

73

Influence of alkaline earth metals on the activity and sulfur stability of zeolites in the No x ?C 3 ?C 4 hydrocarbon selective reduction of no to nitrogen (SKV) process  

Microsoft Academic Search

The results of the influence of alkaline earth metal and magnesium cations on the activity and sulfur stability of catalysts\\u000a based on synthetic mordenites and high-silicon zeolites with pentasil structures on the selective reduction of nitrogen oxides\\u000a with C3?C4 hydrocarbons are presented. Doping the H-form of mordenite and pentasils with Ca, Sr, Ba, and Mg cations increased their\\u000a activity and

M. G. Martsenyuk-Kukharuk; V. L. Struzhko; V. P. Stasevich; S. N. Orlik

1999-01-01

74

Fenten chemistry of Fe(III)-exchanged zeolitic minerals treated with antioxidants.  

PubMed

Respirable mineral fibers, such as asbestos, are known to cause pleural mesothelioma, pulmonary fibrosis, and bronchial carcinoma, often years after exposure. Erionite and mordenite, two mineral aluminosilicates (zeolites) with different toxicities, can be used as models to help understand asbestos toxicity. Erionite is carcinogenic, while mordenite is relatively benign. No iron is typically present in erionite or mordenite, but because of their ion-exchange properties they can acquire iron after inhalation. The iron is typically in the Fe(III) form and will need to be reduced prior to any Fenton activity. Lung lining fluid contains antioxidants, such as glutathione (GSH) and ascorbic acid (AA), which can reduce Fe(III) to Fe(II). In this study, we have compared the Fenton reactivity of Fe(III)-exchanged erionite and mordenite after treatment with antioxidants. The Fenton assay involved the reaction of hydroxyl radicals with dimethyl sulfoxide. Fenton reactivity was most marked with AA followed by GSH, and hydrogen peroxide also exhibited minor reactivity. Erionite generated an order of magnitude greater hydroxyl radicals than mordenite, normalized to the surface iron content, providing support for the hypothesis that the iron coordination at the mineral surface plays a significant role in bioactivity. PMID:16173575

Ruda, Toni A; Dutta, Prabir K

2005-08-15

75

Catalytic removal of carbon monoxide from gases at low temperatures  

SciTech Connect

A study was made of the low-temperature oxidation of carbon monoxide using both heavy catalysts (manganese oxide, manganese-palladium, manganese-silver, hopcalite), and catalysts deposited onto mordenite (manganese oxide, cobalt oxide, palladium). It was found that when carbon monoxide reacted with atmospheric oxygen at room temperature the cobalt oxide and palladium catalysts deposited on mordenite were considerably more active than hopcalite, even in the presence of water vapor. By introducing small quantities of ozone into the gaseous reaction mixture it was possible to intensify the carbon monoxide oxidation process with these catalysts.

Solov`ev, S.A.; Belokleitseva, G.M.; Vlasenko, V.M.

1993-02-20

76

Ion exchange properties of Japanese natural zeolites in seawater.  

PubMed

Ion exchange properties of five different Japanese natural zeolites in seawater were examined. Sodium ions could be reduced by all zeolites, although anions, Cl(-) and SO(4)(2-), in seawater showed barely changes. Natural zeolite desalination treatment mainly depends on the ion exchange between Na(+), K(+) and Mg(2+) in seawater and Ca(2+) in natural zeolite. This study found that mordenite is superior to clinoptilolite for use in Na(+) reduction. Mordenite with high cation exchange capacity containing Ca(2+) resulted in the highest Na(+) reduction from seawater. PMID:23303099

Wajima, Takaaki

2013-01-01

77

An infrared spectral reflectance study of hydrothermal alteration minerals from the Te Mihi sector of the Wairakei geothermal system, New Zealand  

Microsoft Academic Search

Hydrothermal alteration minerals and their zoning with depth in the Te Mihi sector of the Wairakei geothermal field have been characterised in this study by using field portable short-wave infrared spectroscopy. Observed variations in the spectral reflectance of hydrothermally altered volcanic and sedimentary rocks indicate a downward gradation in the dominant alteration minerals from mordenite, smectite, illite, to illite +

Kai Yang; Jonathan F. Huntington; Patrick R. L. Browne; Chi Ma

2000-01-01

78

Catalytic pyrolysis of woody biomass in a fluidized bed reactor: Influence of the zeolite structure  

Microsoft Academic Search

Catalytic pyrolysis of biomass from pine wood was carried out in a fluidized bed reactor at 450°C. Different structures of acidic zeolite catalysts were used as bed material in the reactor. Proton forms of Beta, Y, ZSM-5, and Mordenite were tested as catalysts in the pyrolysis of pine, while quartz sand was used as a reference material in the non-catalytic

A. Aho; N. Kumar; K. Eränen; T. Salmi; M. Hupa; D. Yu. Murzin

2008-01-01

79

Molecule sieving catalysts for NO reduction with hydrocarbons in exhaust of lean burn gasoline and diesel engines  

Microsoft Academic Search

NO oxidation catalysts with small pores and low hydrocarbon oxidation activity owing to molecular sieving were prepared by dispersing platinum in the pores of ferrierite and chabazite zeolites. These small pore platinum zeolite crystals were physically mixed with large pore silver mordenite zeolite crystals and evaluated as HC-SCR catalysts for selective catalytic reduction of NO in a synthetic gas mixture

J. A Martens; A Cauvel; F Jayat; S Vergne; E Jobson

2001-01-01

80

Zeolite-supported Ni and Mo catalysts for hydrotreatments. 2. HRTEM observations  

SciTech Connect

Calcined and sulfided Ni-Mo catalysts supported on ultrastable Y zeolite (USY), NaY zeolite, mordenite, and ZSM-5 were studied by high-resolution electron transmission microscopy (HRTEM) with selected-area electron diffraction (SAED) and energy-dispersive spectroscopy (EDS). Ni and Mo oxide aggregates were rarely observed in the USY-supported Ni-Mo catalyst, indicating that most of Ni and Mo may be incorporated into USY, e.g., supercavities and possibly sodalite cages. However, there were a large number of {alpha}-NiMoO{sub 4} aggregates of different particle sizes in NaY-, mordenite-, and ZSM-5-supported catalysts, and the mordenite-supported catalyst also contained MoO{sub 3} crystals. The {alpha}-NiMoO{sub 4} may be attached to the surface of substrates as individual particles or needle aggregates, it may be disseminated into mordenite particles, or it may even form an isolated sphere (in Ni-Mo/NaY) or a needle (in Ni-Mo/ZSM-5) aggregates. Thus, most of Ni and Mo in NaY-, mordenite-, and ZSM-5-supported catalysts preferentially formed aggregates, although some Mo may have been incorporated into NaY and ZSM-5. After sulfidation, small MoS{sub 2} aggregates containing some Ni were rarely but occasionally found on the surface of USY zeolite; however, there were a large number of such MoS{sub 2} aggregates on the surface of NaY. Separate and intergrown MoS{sub 2} and Ni sulfides aggregates were observed on the surface of mordenite and ZSM-5. The Ni sulfide might be identified by SAED and high-magnification images as troilite-like NiS and/or Ni{sub 9}S{sub 8}, but definitely not as NiS with millerite structure or Ni{sub 3}S{sub 2}. These results indicated that sulfidation does not extensively affect Ni and Mo that have been incorporated into the supercavity and/or sodalite cage of USY in calcined Ni-Mo/USY. The USY-supported Ni-Mo catalyst had a much higher hydrodesulfurization (HDS) activity than the other zeolite-supported catalysts.

Li, D.; Xu, H.; Guthrie, G.D. Jr.

2000-01-25

81

Dual-catalyst system to broaden the window of operability in the reduction of NO/sub chi/ with ammonia  

SciTech Connect

The objective of the research discussed in this paper was to determine if a dual-catalyst system for NO reduction with NH/sub 3/ can achieve a given percent NO reduction over a wider range of temperatures and space velocities than either catalyst used alone in the same total reactor volume. Hydrogen mordenite (20/32 mesh) and copper-ion-exchanged hydrogen mordenite (2.2% Cu) were used in series at temperatures from 200 to 600 {sup 0}C and space velocities from 1000000 to 450000 h/sup -1/ (STP). The superiority of the dual-catalyst system was demonstrated experimentally, and a model was developed which predicted its performance very well from data on the individual catalysts. A technique was then developed for predicting quantitatively the dual-catalyst enhancement of the space velocity versus temperature window for achieving a given percent NO conversion.

Medros, F.G. (Thermedics, Inc., Woburn, MA (US)); Eldridge, J.W. (Massachusetts Univ., Amherst, MA (USA). Dept. of Chemical Engineering); Kittrell, J.R. (KSE, Inc., Amherst, MA (US))

1989-08-01

82

Ring opening of methylcyclohexane over platinum-loaded zeolites.  

PubMed

The activity of different platinum-loaded zeolites (Mordenite, ZSM-12, ZSM-5, ZSM-23) was investigated in the hydroconversion of methylcyclohexane (MCH), in the context of upgrading highly aromatic distillates for fuel blending. In all cases, conversion of MCH proceeds according to a pathway where the primary products are a mixture of dimethylcyclopentanes and ethylcyclopentane formed by isomerization and ring contraction of MCH. The primary products undergo consecutive ring-opening reactions with formation of n- and isoheptanes. The latter further react to form lower-molecular-weight n- and isoalkanes. The selectivity and distribution of products deriving from ring-contraction and ring-opening reactions are strongly affected by the pore size and topology of the zeolites. ZSM-5 exhibits a strong reactant shape-selectivity effect on ring-opening products. The evaluated zeolites show the following order of activity in the conversion of methylcyclohexane: Mordenite>ZSM-12>ZSM-5>ZSM-23. PMID:18702154

Calemma, Vincenzo; Carati, Angela; Flego, Cristina; Giardino, Roberto; Gagliardi, Federica; Millini, Roberto; Bellussi, Giuseppe

2008-01-01

83

Isomerization of ethylbenzene and m-xylene on zeolites  

SciTech Connect

Simultaneous isomerizstion of ethylbenzene and m-xylene on zeolite catalysts, including Pt/mordenite, Pt/USY, Pt/ZSM-5, and Pd/ZSM-5, was studied. Experimental results indicated that Pt/ZSM-5 was the superior catalyst for these reactions. Pd/ZSM-5 is better than Pt/USY, although, both are good enough for the reactions, in comparison with Pt/mordenite. A kinetic model with plausible reaction paths was proposed for the isomerization. The estimated reaction rate constants and activation energies indicated that the transformation of m-xylene to o- or p-xylene might be limited by the mass-transfer rate of the diphenylmethane-type intermediate, and the formation of o-xylene from ethylbenzene could be restricted by the smaller protonated cyclopropane intermediate.

Hsu, Y.S.; Lee, T.Y.; Hu, H.C.

1988-06-01

84

An Investigation of the Effects of Zeolites on the Thermal Degradation and Charring of APP–PER by TGA–XPS  

Microsoft Academic Search

The effects of zeolites 4A, 13X, mordenite, and ZSM-5 on the thermal degradation and charring of intumescent ammonium polyphosphate (APP)–pentaerythritol (PER) systems were explored by X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analyses (TGA). The weight loss rate of the third main degradation step (corresponding to the maximum degradation rate of APP–PER) was remarkably decreased for all systems with addition

Ping Wei; Pingkai Jiang; Zhidong Han; Jianqi Wang

2005-01-01

85

Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution  

Microsoft Academic Search

An Australian natural zeolite was collected, characterised and employed for basic dye adsorption in aqueous solution. The natural zeolite is mainly composed of clinoptiloite, quartz and mordenite and has cation-exchange capacity of 120meq\\/100g. The natural zeolite presents higher adsorption capacity for methylene blue than rhodamine B with the maximal adsorption capacity of 2.8×10?5 and 7.9×10?5mol\\/g at 50°C for rhodamine B

Shaobin Wang; Z. H. Zhu

2006-01-01

86

Comparison of thermodesorption and calorimetric methods of investigation of acidity of zeolites  

SciTech Connect

The thermodesorption of NH/sub 3/ from Na- and H-forms of different types of zeolites (A, Y, mordenite) in the temperature range of 30-440/sup 0/C was studied by the gravimetric method. A correlation was discovered between the temperature-dependent desorption and the calorimetrically measured heat of adsorption. It was shown that thermodesorption data can be used for rapid approximate determination of heats of adsorption of NH/sub 3/ on zeolites.

Kapustin, G.I.; Brueva, T.R.; Kutateladze, G.M.; Klyachko, A.P.

1987-12-01

87

The role of acid sites in cobalt zeolite catalysts for selective catalytic reduction of NO x  

Microsoft Academic Search

The role of the acidic support in ion-exchanged cobalt-zeolite, lean NOx catalysts has been determined by studying the individual steps in the selective reduction pathway. At a GHSV of 10,000 and\\u000a reaction temperatures below 400C, NO oxidation is not sufficiently rapid to obtain equilibrium over, for example, 1–4 wt%\\u000a Co-mordenite catalysts. The NO oxidation rate increases in the order H+Co2+

J. T. Miller; E. Glusker; R. Peddi; T. Zheng; J. R. Regalbuto

1998-01-01

88

Photodegradation of aromatic pollutants in water over TiO 2 supported on molecular sieves  

Microsoft Academic Search

TiO2 was supported on porous materials, including NaY and Na-mordenite zeolites, as well as mesoporous MCM-41 molecular sieve by using impregnation method with organic solvents. The products were characterized with powder XRD, BET surface area measurement, TEM, IR, Raman and UV–VIS spectroscopies. The supported TiO2 was crystallized in anatase structure and the intensity of its X-ray diffraction peaks increased with

Yu-Hsiang Hsien; Chi-Fu Chang; Yu-Huang Chen; Soofin Cheng

2001-01-01

89

Dehydration of cyclohexanol as a test reaction for zeolite acidity  

Microsoft Academic Search

Dehydration of cyclohexanol was investigated using a fixed-bed continuous flow reactor with acidic mordenite-type, clinoptilolite-type, and faujasite-type (Y) zeolites as catalysts. The surface acidity of the catalysts employed was studied by IR using pyridine or 2,6-di-tert. butylpyridine as probe molecules. A correlation between the acidity and the rates of dehydration was clearly shown.

H. G. Karge; H. Kosters; Y. Wada

1984-01-01

90

Methane Combustion over Pd Catalysts Loaded on Medium and Large Pore Zeolites  

Microsoft Academic Search

Methane combustion was conducted over Pd catalysts supported on medium (ZSM-5, ferrierite, TNU-9, TNU-10) and large (USY,\\u000a mordenite, beta) pore zeolites. Among the catalysts studied here, Pd\\/H-TNU-10 exhibited the highest combustion activity, together\\u000a with excellent durability in the presence of water vapor. A combination of TEM and Pd K-edge XAFS measurements reveals the\\u000a formation of highly dispersed PdO particles within

Jung-Hyun Park; Bokie Kim; Chae-Ho Shin; Gon Seo; Seok Han Kim; Suk Bong Hong

2009-01-01

91

A new selective route to 5-hydroxymethylfurfural from furfural and furfural derivatives over microporous solid acidic catalysts  

Microsoft Academic Search

Hydroxymethylation of furfural and its 1,3 dithiolane derivative with aqueous formaldehyde was performed in a batch mode in the presence of dealuminated mordenites as catalysts, at 363 K. Starting from furfural, the selectivity to 5-hydroxymethylfurfural is about 30% whatever the catalysts. However, the selectivity can rise up to 50% if an organic co-solvent is used for simultaneous extraction of 5-hydroxymethylfurfural

Jérôme Lecomte; Annie Finiels; Claude Moreau

1999-01-01

92

Occlusion potential of zeolites for mixed and non-nitrate salts  

Microsoft Academic Search

Occluded salts in the form of salt complexes exhibit the interesting properties unattainable in bulk state. In this study, occlusion of non-nitrate salts and co-occlusion of mixed nitrate salts were attempted to further expand occlusion potential of zeolites. The non-nitrate salts such as KClO3 and KH2PO4 were occluded by mordenite, although they do not establish stable molten state. Their occlusions

Man Park; Choong Lyeal Choi; Jong Soo Kim; Dong Hoon Lee; Kwang Seop Kim; Nam Ho Heo; Jyung Choi

2003-01-01

93

Selective catalytic reduction of NO with methane on gallium catalysts  

Microsoft Academic Search

Gallium species supported on H-ZSM-5 and on H-mordenite are active catalysts for NO reduction with methane in the presence of excess O[sub 2]. Over Ga-H-ZSM-5, the NO reduction rate is first order in NO with a variable, fractional order in CH[sub 4]. The distinct feature of these gallium-based catalysts is their very high CH[sub 4] selectivities for NO[sub x] reduction.

Yuejin Li; J. N. Armor

1994-01-01

94

Adsorption of cobalt on some natural zeolites occurring in ?SFR  

Microsoft Academic Search

The subject of this paper was to study Co2+-ion removal from aqueous solutions by means of natural mordenite and clinoptilolite. The mentioned zeolites were of Slovak origin (SFR). The static and dynamic equilibrium adsorption of Co2+-ions by zeolites, the influence of pH, quality and quantity of interfering ions on adsorbate\\/adsorbent system were investigated. The influence of flow rate, activation and

E. Chmielewská-Horváthová; J. Lesný

1992-01-01

95

The interaction mechanisms between aqueous solutions of 137 Cs and 134 Ba radionuclides and local natural zeolites for an deactivation scenario  

Microsoft Academic Search

137Cs and134Ba were removed from synthetic aqueous solutions by means of natural zeolites of Slovakian origin. The equilibrium sorption\\u000a behavior of Cs and Ba ions onto clinoptilolite and mordenite were studied under static as well as dynamic experimental conditions.\\u000a Both Freundlich and Langmuir isotherms describe satisfactory by Cs and Ba adsorption on the zeolites studied. The elution\\u000a of Cs and

E. Chmielewská-Horváthová

1998-01-01

96

Environmental Applications of Natural Zeolitic Materials Based on Their Ion Exchange Properties  

Microsoft Academic Search

\\u000a Present and potential use of natural zeolites as cation exchangers in environmental protection is reviewed. Siliceous zeolites,\\u000a such as chabazite, clinoptilolite, mordenite and phillipsite, exhibit good selectivities for cations with low charge density,\\u000a e.g., Cs+ and NH4\\u000a +, and for cations with low hydration energy, such as Pb2+. Zeolitised tuffs, containing the mentioned zeolites, may therefore be utilised for removing

C. Colella; Piazza Ie; V. Tecchio

97

An electron paramagnetic resonance spectroscopy investigation of the retention mechanisms of Mn and Cu in the nanopore channels of three zeolite minerals  

SciTech Connect

The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium sized nanopore channels or smaller.

Ferreira, Daniel R.; Schulthess, Cristian P.; Amonette, James E.; Walter, Eric D.

2012-12-01

98

Iron ion-exchanged zeolite: the most active catalyst at 473 K for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere  

Microsoft Academic Search

Among various metal ion-exchanged zeolites, metal loading alumina, and oxides, iron ion-exchanged mordenite was the most active for the selective reduction of nitrogen monoxide to nitrogen by ethene in the presence of oxygen at the temperature as low as 473 K. The catalytic activities of iron ion-exchanged zeolites depended on the zeolite structure and the iron ion exchange level. The

Shinya Sato; Hiroshi Hirabayashi; Hidenori Yahiro; Noritaka Mizuno; Masakazu Iwamoto

1992-01-01

99

On the exceptional time-on-stream stability of HZSM-12 zeolite: relation between zeolite pore structure and activity  

Microsoft Academic Search

ZSM-12 and several other 12-membered ring large-pore zeolites have been tested for the reforming of naphthenic hydrocarbon\\u000a mixtures. It was found that ZSM-12 possesses a surprisingly higher coking resistance than other large pore zeolites tested\\u000a such as USY, L-zeolite, mordenite, and ?=zeolite for reforming of hydrocarbon mixtures. This superior performance is due to\\u000a the unique non-interconnecting tubular-like linear channels of

Wenmin Zhang; Panagiotis G. Smirniotis

1999-01-01

100

Isobutane\\/2Butene Alkylation Using Large-Pore Zeolites: Influence of Pore Structure on Activity and Selectivity  

Microsoft Academic Search

The alkylation of isobutane with 2-butene was performed in the liquid phase at 80°C and 300 psi. This study constitutes a detailed comparison under identical conditions of 12-membered pore zeolites with different dimensionalities, namely USY, mordenite, beta, LTL, and ZSM-12 zeolite. Particular attention was paid to the role of the structural characteristics of the catalysts. In the mechanism studies, very-low-olefin

Kyesang Yoo; Eric C. Burckle; Panagiotis G. Smirniotis

2002-01-01

101

Factors affecting isomer yield for n-heptane hydroisomerization over as-synthesized and dealuminated zeolite catalysts loaded with platinum  

Microsoft Academic Search

Pt loaded Y, USY, beta, mordenite, ZSM-12, and ZSM-5 zeolites with different Si\\/Al ratios and a USY and ZSM-12 sample having enhanced activity were studied for the hydroisomerization of n-heptane. All the possible heptane isomers were obtained over Pt\\/H-ZSM-12 and the product distribution was closer to that over Y and beta catalysts, but very different from that over Pt\\/H-ZSM-5. Shape-selective

Srikant Gopal; Panagiotis G. Smirniotis

2004-01-01

102

Effect of Zeolite Structure and Acidity on the Product Selectivity and Reaction Mechanism for n-Octane Hydroisomerization and Hydrocracking  

Microsoft Academic Search

The activity, product selectivity, and stability of a series of bifunctional zeolite catalysts, primary ZSM-12, USY, and ?-zeolite, with different Si\\/Al ratios were compared for the hydroisomerization and hydrocracking ofn-octane. The performance of L-zeolite and mordenite was examined to a lesser extent as well. It was found that the activity per acidic site decreases at the initial stage (1 h

Wenmin Zhang; Panagiotis G. Smirniotis

1999-01-01

103

Deactivation Behavior of Bifunctional Pt\\/H-Zeolite Catalysts during Cyclopentane Hydroconversion  

Microsoft Academic Search

Cyclopentane hydroconversion was used as a probe reaction to study the coking behavior of selected large-pore zeolites loaded with 0.5% Pt under identical conditions. The zeolites studied, namely, Y zeolite, zeolite beta, mordenite, LTL, and ZSM-12, were also tested at several different Si\\/Al ratios. The zeolite pore structure was the most important factor determining the deactivation behavior. Zeolites like Y

Srikant Gopal; Panagiotis G. Smirniotis

2002-01-01

104

Adsorption and separation of ?, ?-dimethylnaphthalene isomers on various large-pore zeolites having 12-oxygen-member-ring structure  

Microsoft Academic Search

Different types of large-pore zeolites with 12-oxygen-member-ring structure were synthesized by a hydrothermal method and used for adsorbing and separating mixtures of ?,?-DMN isomers. Among all the zeolites tested, zeolites Y and BEA which possess three-dimensional pore channels were found to adsorb ?,?-DMN isomers effectively. On the other hand, SAPO-5, Mordenite and ZSM-12 scarcely adsorbed ?,?-DMN molecules because of the

S. B. Pu; Y. Tanaka; T. Inui

1996-01-01

105

Conversion of ethane over zeolite catalysts in the presence of oxygen and nitrogen(I) oxide  

Microsoft Academic Search

1.A study has been made of the relationship between the catalytic properties of pentasils and mordenite in the oxidative conversion of ethane and the concentration of acid-base and one-electron sites in the decomposition of nitrogen(I) oxide.2.A linear correlation was found in the C2H6-N2O system between the activity of the zeolites and the number of charge-transfer sites. The high activity of

S. N. Vereshchagin; L. I. Baikalova; A. G. Anshits

1988-01-01

106

Removal of tar base from coal tar aromatics employing solid acid adsorbents  

Microsoft Academic Search

Aromatic compounds from coal tar generally contain a small amount of tar bases, such as quinoline and isoquinoline. These nitrogen-containing compounds can poison the acid-type catalysts and downgrade the aromatic products because of stinking odor. Four solid acid catalysts, silica-alumina, HY, NH4-mordenite, and ?-alumina are used to remove tar bases by adsorption. Wash oil (WO), refined naphthalene (RN), and an

Jeffrey Chi-Sheng Wu; Hsueh-Chang Sung; Yu-Fu Lin; Shi-Long Lin

2000-01-01

107

Preparation for Size-Controlled MOR Zeolite Nanocrystal Using Water\\/Surfactant\\/Organic Solvent  

Microsoft Academic Search

Recently, the synthesis of nanometer-sized zeolite crystals has attracted considerable attention from many researchers. In\\u000a this study, the preparation of Mordenite (MOR zeolite) nanocrystals via hydrothermal synthesis in water\\/surfactant\\/organic\\u000a solvent was carried out. Polyoxyethylene-(15)-oleylether (O-15, non-ionic surfactant) and cyclohexane were employed as a surfactant\\u000a and organic solvent, respectively. Interestingly, it was found that the crystal sizes and morphology of MOR

Teruoki Tago; Daichi Aoki; Kazuyuki Iwakai; Takao Masuda

2009-01-01

108

Infrared, microcalorimetric, and electron spin resonance investigations of the acidic properties of the H-ZSM-5 zeolite  

Microsoft Academic Search

Infrared, microcalorimetric, and electron spin resonance investigations of the acidic properties of the H-ZSM-5 zeolite showed that two types of hydroxyls were present which were similar to those of mordenite but stronger, and that dehydroxylation above 675°K yielded Lewis acid sites in an irreversible process which was accompanied by partial dealumination (15 3< dea;i,omatopm as the outgassing temperature increased from

J. C. Vedrine; E. G. Derouane; J. H. C. Hooff; A. Aurouxt; V. Bolis; P. Dejaifve; C. Naccache; P. Wierzchowski; J. B. Nagy; J. P. Gilson

1979-01-01

109

[Effect of chrysotile-asbestos and zeolites dust on generations of reactive oxygen species by alveolar macrophages and granulocytes].  

PubMed

Different characteristics of the influence of dusts of chrysotile--asbestos, mordenite, erionite and klinoptilolite on the total generation of the active forms of oxygen by the alveolar macrophages and the generation of O2- and H2O2 by the granulocytes give the possibility to connect some of these characteristics with the peculiarity of biological action these dusts. It is discovered the most strong activating properties has the dust of chrysotile--asbestos, and the most cytotoxic effect has the dust of klinoptilolite. PMID:9273777

Gusev, V A; Lomonosova, O S; Velichkovskií, B T

110

Supercritical n -butane isomerization  

Microsoft Academic Search

Supercritical n-butane isomerization over the solid acid catalysts sulfated zirconia, TiO2-supported H4[Si(W3O10)4] · xH2O (Keggin-type heteropoly acid), and H-mordenite is studied in a flow reactor. The critical parameters of n-butane are calculated for a wide range of reaction conditions. Changing from gaseous n-butane to supercritical n-butane markedly extends the lifetime of the catalysts. Under supercritical conditions, the activity and selectivity

V. I. Bogdan; T. A. Klimenko; L. M. Kustov; V. B. Kazanskii

2004-01-01

111

Supercritical n-butane isomerization on solid acid catalysts  

Microsoft Academic Search

n-Butane isomerization was investigated at the supercritical state in a flow type reactor. Sulfated zirconia (SZ), heteropolyacids (HPA) of the Keggin type H3PW12O40 (HPWO), H4SiW12O40 (HSiWO) supported on titania, H-mordenite (HM) were studied as catalysts at 488, 533 and 573K and 6.1, 11.0 and 13.8MPa, respectively. Gas-phase isomerization was carried out on the same catalysts for comparison. Rapid deactivation of

V. I Bogdan; T. A Klimenko; L. M Kustov; V. B Kazansky

2004-01-01

112

Zeolite catalysis: technology  

SciTech Connect

Zeolites have been used as catalysts in industry since the early nineteen sixties. The great majority of commercial applications employ one of three zeolite types: zeolite Y; Mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. This paper reviews the rapid development of zeolite catalysis and its application in industries such as: the production of gasoline by catalytic cracking of petroleum; isomerization of C/sub 5/ and C/sub 6/ paraffin hydrocarbons; alkylation of aromatics with olefins; xylene isomerization; and conversion of methanol to gasoline.

Heinemann, H.

1980-07-01

113

Dehydration of aldoximes on rare earth exchanged (La 3+ , Ce 3+ , RE 3+ , Sm 3+ ) Na–Y zeolites: A facile route for the synthesis of nitriles  

Microsoft Academic Search

Rare earth exchanged Na–Y zeolites, H-mordenite, K-10 montmorillonite clay and amorphous silica-alumina were effectively employed\\u000a for the continuous synthesis of nitriles. Dehydration of benzaldoxime and 4-methoxybenzaldoxime were carried out on these\\u000a catalysts at 473 K. Benzonitrile (dehydration product) was obtained in near quantitative yield with benzaldoxime whereas;\\u000a 4-methoxybenzaldoxime produces both Beckmann rearrangement (4-methoxyphenylformamide) as well as dehydration products (4-methoxy\\u000a benzonitrile) in

Bejoy Thomas; S. Sugunan

2007-01-01

114

Effective catalysts for decomposition of aqueous ozone  

Microsoft Academic Search

Activities of a series of oxide supports and dozens of supported metal catalysts toward the decomposition of aqueous ozone have been investigated. Under reaction conditions, active carbon (AC) showed comparatively high activity, while zeolite (HY and mordenite), Al2O3, SiO2, SiO2·Al2O3 and TiO2 showed no or negligible activity. Noble metals showed high activity. Among four kinds (Al2O3, SiO2, SiO2·Al2O3 and TiO2)

Jianjun Lin; Akimasa Kawai; Tsuyoshi Nakajima

2002-01-01

115

Catalytic Reduction of Nitrogen Oxides by Propene in the Presence of Oxygen over Cerium Ion-Exchanged Zeolites  

Microsoft Academic Search

The mechanism of catalytic reduction of NOxby propene in the presence of oxygen, NO (or NO2)+C3H6+O2reaction, over Ce-supported catalysts was studied, focusing on the relative activities of catalysts and carriers for several relevant reactions. The rate of N2formation in the NO+C3H6+O2reaction was very much dependent on the kinds of carriers, the rate being in the order of Ce-ZSM-5>Ce-mordenite?Ce-Y zeolite>Ce\\/SiO2. This

Chikafumi Yokoyama; Makoto Misono

1996-01-01

116

Selective reduction of nitric oxide by methane on H-form zeolite catalysts in oxygen-rich atmosphere  

Microsoft Academic Search

Selective reduction of NO by CH4 in the presence of excess oxygen was investigated using H-form zeolite catalysts. H-ZSM-5, H-ferrierite, and H-mordenite showed high catalytic activity and selectivity. On the contrary, H-USY and Al2O3 were not effective for this reaction. Both NO-CH4 and O2-CH4 reaction hardly proceeded on H-ZSM-5. Higher NOx conversion was obtained in the NO2-O2-CH4 and NO2-CH4 systems

Katsunori Yogo; Michiaki Umeno; Hirotake Watanabe; Eiichi Kikuchi

1993-01-01

117

Encapsulation of lead sulfide molecular clusters into solid matrices. Structural analysis with x-ray absorption spectroscopy  

Microsoft Academic Search

Molecular-size PbS species have been stabilized in the open-pore structure of zeolite Y and mordenite via ion exchange with Pb(II) and subsequent treatment with HâS at 295 K. Detailed analysis of synchrotron x-ray absorption data of the Pb L{sub III}-edge shows that intrazeolite PbOâ(O{sub z} = zeolite oxygen) species in zeolite Y react with HâS to form monomolecular SâPb(I{sub z})â

Karin Moller; Thomas Bein; Norman Herron; Walter Mahler; Ying Wang

1989-01-01

118

Shape-selective hydrogenation of naphthalene over zeolite-supported Pt and Pd catalysts  

Microsoft Academic Search

Zeolite-supported Pt and Pd catalysts were used to effect naphthalene hydrogenation with high trans\\/cis decahydronaphthalene (DeHN) isomer selectivity. Four zeolites were studied: three hydrogen-mordenites (HM) with different SiO2\\/A12O3 ratios (17, 21 and 38) and HY (SiO2\\/A12O3 of 5.0). Catalytic selectivity was found to depend on both the metal and the zeolite. Consequently, the catalyst composition could be tailored for selective

Andrew D. Schmitz; Grainne Bowers; Chunshan Song

1996-01-01

119

Diagenesis of basalts from the Pasco Basin, Washington. I. Distribution and composition of secondary mineral phases  

SciTech Connect

The principal components of secondary mineral assemblages found in Pasco Basin basalts are iron-rich smectite (nontronite), clinoptilolite, and silica. Silica occurs as quartz, cristobalite, tridymite, and opal-CT. Extractable iron within the nontronite suggests the presence of an iron-bearing oxyhydroxide phase intercalated with the nontronite. Other components present in minor or trace amounts are mordenite, celadonite, apatite, pyrite, phillipsite, gypsum, crionite, and chabazite. The generalized precipitation sequence with time and/or depth was found to be clay (usually nontronite) ..-->.. clinoptilolite ..-->.. silica and/or clay. Nontronite, the first phase to form, is present at nearly all sampled depths. Clinoptilolite is apparently restricted to depths below about 350 m. Quartz is ubiquitous whereas opal and cristobalite appear to be abundant only below 600 m. Mordenite occurs only at depths below about 900 m, which correlates roughly with the first occurrence of dissolution-etched clinoptilolite. These observations as well as comparisons with data on secondary minearl assemblages from other basaltic and felsic systems suggest that the geochemical evolution of Pasco Basin basalts probably occurred under conditions similar to those existing today.

Benson, L.V.; Teague, L.S.

1982-01-01

120

Clay mineral assemblages and analcime formation in a Palaeogene fluvial lacustrine sequence (Maíz Gordo Formation Palaeogen) from northwestern Argentina  

NASA Astrophysics Data System (ADS)

The Palaeogene Maíz Gordo Formation is one of the main lacustrine events recorded in northwestern Argentina. It consists of sandstone, mudstone, and limestone beds 200 m thick, deposited in a brackish alkaline lake and braided alluvial systems. The Maíz Gordo Lake evolved mainly as a closed system, with brief periods as an open one. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study samples from seven sites, corresponding respectively to proximal, intermediate, and transitional positions of the fluvial environment and marginal and inner-lake environment, focusing on the clay mineralogy and analcime formation. The basinward zonation of diagenetic minerals identified in the Maíz Gordo Lake was: mordenite ? analcime ? K-feldspar. Although not a typical zonation of saline alkaline lakes, it does indicate an increase in salinity and alkalinity towards the centre. In proximal fluvial settings, smectite predominates at the base of the sequence, with scarce kaolinite. Towards the top, a striking increase in kaolinite content suggests a change from a relatively arid climate with alternating humid and dry seasons, towards a warm and humid climate. Kaolinite content clearly decreases in a basinward direction. Such a variation is attributable to changes in hydro-geochemistry, denoting the progressive influence of the brackish and alkaline lake water on interstitial pores. SEM images of intermediate fluvial samples reveal authigenesis of illite at the expense of kaolinite booklets. In littoral and inner-lake settings the clay fraction is composed of muscovite, sometimes with subordinate smectite. Analcime occurs in variable amounts in all sedimentary facies, in rock pores or filling veins. It forms subhedral square to hexagonal, or anhedral rounded crystals, denoting that they coarsened at low to moderate degrees of supersaturation. Although the mordenite identified in a fluvial level would have been the precursor of analcime in the Maíz Gordo Basin, no textural evidence of analcime formation through replacement of mordenite or other precursor zeolite was found. Hence it is more probable that analcime formation took place by direct authigenic precipitation or through the reaction between interstitial brines and clay minerals or plagioclase.

Do Campo, M.; Del Papa, C.; Jiménez-Millán, J.; Nieto, F.

2007-09-01

121

Removal of toxic heavy metal ions from waste water by functionalized magnetic core-zeolitic shell nanocomposites as adsorbents.  

PubMed

Functionalized magnetic core-zeolitic shell nanocomposites were prepared via hydrothermal and precipitation methods. The products were characterized by vibrating sample magnetometer, X-ray powder diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, and transmission electron microscopy analysis. The growth of mordenite nanocrystals on the outer surface of silica-coated magnetic nanoparticles at the presence of organic templates was well approved. The removal performance and the selectivity of mixed metal ions (Pb(2+) and Cd(2+)) in aqueous solution were investigated via the sorption process. The batch method was employed to study the sorption kinetic, sorption isotherms, and pH effect. The removal mechanism of metal ions was done by chem-phys sorption and ion exchange processes through the zeolitic channels and pores. The experimental data were well fitted by the appropriate kinetic models. The sorption rate and sorption capacity of metal ions could be significantly improved by optimizing the parameter values. PMID:23184130

Padervand, Mohsen; Gholami, Mohammad Reza

2012-11-27

122

Activated cation motions in zeolites  

NASA Astrophysics Data System (ADS)

We apply a Monte Carlo technique specialized for the simulation of rare events to study the activated counterions motions in the aluminosilicate Na+-mordenite. Mean activation barriers are obtained from minimum energy paths calculated on realistic potential energy surfaces by using a Metropolis algorithm. Energy barriers for Na+ hops calculated for lattices with various Si/Al ratio are found in good agreement with the Na+ detrapping energies measured by thermally stimulated current spectroscopy. One shows that the dielectric activated motions of Na+ proceed between degenerated many-body ground states with different dipolar moment by either sequential or collective hopping motions. This provides a first microscopic description of dielectric relaxation measured in zeolites.

Maurin, G.; Devautour, S.; Henn, F.; Giuntini, J. C.; Senet, P.

2002-07-01

123

Hydrolysis of cellulose by amorphous carbon bearing SO3H, COOH, and OH groups.  

PubMed

The hydrolysis of cellulose into saccharides using a range of solid catalysts is investigated for potential application in the environmentally benign saccharification of cellulose. Crystalline pure cellulose is not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, H-mordenite, Nafion and Amberlyst-15, whereas amorphous carbon bearing SO 3H, COOH, and OH function as an efficient catalyst for the reaction. The apparent activation energy for the hydrolysis of cellulose into glucose using the carbon catalyst is estimated to be 110 kJ mol (-1), smaller than that for sulfuric acid under optimal conditions (170 kJ mol (-1)). The carbon catalyst can be readily separated from the saccharide solution after reaction for reuse in the reaction without loss of activity. The catalytic performance of the carbon catalyst is attributed to the ability of the material to adsorb beta-1,4 glucan, which does not adsorb to other solid acids. PMID:18759399

Suganuma, Satoshi; Nakajima, Kiyotaka; Kitano, Masaaki; Yamaguchi, Daizo; Kato, Hideki; Hayashi, Shigenobu; Hara, Michikazu

2008-08-29

124

Evidence for the presence of a bimolecular pathway in the isomerization of xylene on some large-pore zeolites  

SciTech Connect

Using deuterated para-xylene as a reactant, the authors have found that more than 20% of the meta- and ortho-xylenes, obtained when using a HY zeolite as catalyst, are formed via a bimolecular mechanism. This involves, as an intermediate complex, a molecule of trimethylbenzene and another of xylene. The bimolecular process is less important in the case of mordenite, and does not occur in Zeolite Beta at low levels of conversion. The relative proportion of uni- to bimolecular mechanism depends on: reaction conditions, zeolite composition, and zeolite structure. Some of the mechanistic conclusions, reached when using xylene isomerization and transalkylation as a test reaction on faujasite zeolites, should be revised in light of these results. Finally, transalkylation between trimethylbenzenes and xylenes is proposed as a test reaction for 12 membered-ring (MR) zeolites since structural differences can be better established than when the conventional xylene isomerization-transalkylation reaction is used.

Corma, A. (Universidad Politecnica de Valencia (Spain)); Sastre, E. (Instituto de Catalisis y Petroleoquimica, Madrid (Spain))

1991-05-01

125

Removal of trimethylamine by adsorption over zeolite catalysts and deodorization of fish oil.  

PubMed

Trimethylamine (TMA) is the main agent for the odor often associated with fouling fish, some infections, and bad breath. This study focused on the adsorption of TMA over various microporous zeolites for application in the low-temperature deodorization of fishy odor from raw fish oil. The faujasite (Si/Al=3) zeolite exhibited the high adsorption ability, which, in combination with its wide surface area and pore volume, may have induced the high adsorption ability. The H-mordenite (Si/Al=10) zeolite exhibited a large TMA adsorption. It was considered to have generated more attractive adsorption with TMA ions, because TMA interacted briskly with cations of acid sites on the zeolites. The fishy odor of raw fish oil was considerably reduced by low-temperature adsorption on the zeolites. The surface area of the zeolites retained most of the TMA adsorption ability, and their acid strength further enhanced the adsorption ability. PMID:19692177

Chung, Kyong-Hwan; Lee, Ki-Young

2009-07-28

126

Binding and catalytic reduction of NO by transition metal aluminosilicates  

SciTech Connect

The objective of this research is to provide the scientific understanding of processes that actively and selectively reduce NO in dilute exhaust streams, as well as in concentrated streams, to N{sub 2}. Experimental studies of NO chemistry in transition metal-containing aluminosilicate catalysts are being carried out with the aim of determining the chemical rules for NO reduction on non- precious metals. The catalysts supports chosen for this investigation are A and Y zeolites, mordenite, and monoliths based on cordierite. The supported transition metal cations that will be examined are principally the first row redox metals, e.g. Cr(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cu(I). The reactions of interest are the reductions of NO by H{sub 2} CO, and CH{sub 4} as well as the disproportionation of NO.

Klier, K.; Herman, R.G.; Hou, S.

1991-12-01

127

Binding and catalytic reduction of NO by transition metal aluminosilicates. Technical progress report, September 1991--November 1991  

SciTech Connect

The objective of this research is to provide the scientific understanding of processes that actively and selectively reduce NO in dilute exhaust streams, as well as in concentrated streams, to N{sub 2}. Experimental studies of NO chemistry in transition metal-containing aluminosilicate catalysts are being carried out with the aim of determining the chemical rules for NO reduction on non- precious metals. The catalysts supports chosen for this investigation are A and Y zeolites, mordenite, and monoliths based on cordierite. The supported transition metal cations that will be examined are principally the first row redox metals, e.g. Cr(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cu(I). The reactions of interest are the reductions of NO by H{sub 2} CO, and CH{sub 4} as well as the disproportionation of NO.

Klier, K.; Herman, R.G.; Hou, S.

1991-12-01

128

Experimental and simulated propene isotherms on porous solids  

NASA Astrophysics Data System (ADS)

The lack of treatment capacity of hydrocarbons by three-way catalysts during the "cold start" period creates an important environmental problem. During this period, the temperature of the three-way catalyst is too low for effective operation and cannot convert the hydrocarbons in the exhaust. 50-80% of the total hydrocarbon emissions are produced in this phase that accomplishes the first 60-120 s of the engine operation. In this study, the technology chosen to treat these emissions is the use of HC-traps, and molecular simulations are tested as a tool to reproduce the experimental adsorption behaviour of porous solids. Therefore, experimental and simulated adsorption isotherms of propene (model hydrocarbon) have been obtained for four different crystalline materials with distinctive framework structures (3D and 1D) and a variety of Si/Al ratios and cations (three zeolites: ZSM-5, BETA and Mordenite; and a silicoaluminophosphate molecular sieve: SAPO-5).

Navarro, M. V.; Puértolas, B.; García, T.; Murillo, R.; Mastral, A. M.; Varela-Gandía, F. J.; Lozano-Castelló, D.; Cazorla-Amorós, D.; Bueno-López, A.

2010-06-01

129

Efficient isomerization of glucose to fructose over zeolites in consecutive reactions in alcohol and aqueous media.  

PubMed

Isomerization reactions of glucose were catalyzed by different types of commercial zeolites in methanol and water in two reaction steps. The most active catalyst was zeolite Y, which was found to be more active than the zeolites beta, ZSM-5, and mordenite. The novel reaction pathway involves glucose isomerization to fructose and subsequent reaction with methanol to form methyl fructoside (step 1), followed by hydrolysis to re-form fructose after water addition (step 2). NMR analysis with (13)C-labeled sugars confirmed this reaction pathway. Conversion of glucose for 1 h at 120 °C with H-USY (Si/Al = 6) gave a remarkable 55% yield of fructose after the second reaction step. A main advantage of applying alcohol media and a catalyst that combines Brønsted and Lewis acid sites is that glucose is isomerized to fructose at low temperatures, while direct conversion to industrially important chemicals like alkyl levulinates is viable at higher temperatures. PMID:23506200

Saravanamurugan, Shunmugavel; Paniagua, Marta; Melero, Juan A; Riisager, Anders

2013-04-02

130

Peculiarities of the conversion of n-butane on metal-containing zeolites  

SciTech Connect

The conversions of n-butane on metal-containing zeolites of the ultrasil and mordenite types were studied in the range 230-400/sup 0/ C, and the possibility of joint production of isoparaffin C/sub 4/-C/sub 5/ hydrocarbons from n-butane was demonstrated. It was established that at a low metal content (0.5% by weight), the activity of platinum-containing samples in the formation of isoparaffins is higher than that of palladium-containing samples. The method of introduction of the metal has virtually no effect on the activity of palladium-containing samples. Under optimum conditions the yield of C/sub 4/-C/sub 5/ isomers reaches 40% by weight, with the selectivity of their formation 83.7% by weight.

Dorogochinskii, A.Z.; Krupina, N.N.; Proskurnin, A.L.

1985-06-01

131

Multiple zeolite structures from one ionic liquid template.  

PubMed

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis. PMID:23255393

Martínez Blanes, José María; Szyja, Bart?omiej M; Romero-Sarria, Francisca; Centeno, Miguel Ángel; Hensen, Emiel J M; Odriozola, José Antonio; Ivanova, Svetlana

2012-12-19

132

The assay of acid sites on zeolites as measured by ammonia poisoning  

SciTech Connect

The decomposition of neopentane was studied with and without selective site poisoning with NH{sub 3}. The lethal dose, which was just sufficient to kill the catalytic activity, was estimated for each of a series of H-mordenites, H-Y and H-ZSM-5 zeolites, all with Si/Al ratios higher than 7.0 i.e., over silica-rich compositions where ideally all the sites are supposedly identical. It was found that poisoning no more than 10% of the sites (counted as lattice aluminum ions) was sufficient to eliminate the activity. Some ramifications of these observations are discussed. Unpoisoned and partially poisoned zeolites were investigated using {sup 13}C-MASNMR following adsorption of isopropanol-2-{sup 13}C. These findings clearly show the efficacy of adsorbed NH{sub 3} in repressing formation of polymeric surface residues. 29 refs.

Lombardo, E.A.; Sill, G.A.; Hall, W.K. (Univ. of Pittsburgh, PA (USA))

1989-10-01

133

NMR study of reactions of alcohols on solid acids  

SciTech Connect

Contradictory evidence currently exists concerning the stability of small aliphatic carbenium ions on the surfaces of various zeolites. This question has been investigated using triphenylmethanol-{sup 13}COH, 2-propanol-2-{sup 13}C and propene-2-{sup 13}C on a silica-alumina catalyst and H-Y, H-ZSM-5, and H-M (mordenite) zeolites using the {sup 13}C MASNMR technique. The stable (C{sub 6}H{sub 5}){sub 3}C{sup +} cation was used as a calibration standard and a test was devised (bleaching with NH{sub 3} or H{sub 2}O) to discriminate between carbenium ions and other nonionic species present. The data indicate that whereas carbenium ions have evidently been formed from 2-propanol and propene, they are not stabilized on these materials. Instead they react with olefin released from other sites to produce polymeric residues, some of which may be ionic. 16 refs.

Lombardo, E.A.; Dereppe, J.M.; Marcelin, G.; Hall, W.K. (Univ. of Pittsburgh, PA (USA))

1988-11-01

134

Studies on transition metals and alloy Fischer-Tropsch catalysts, their electronic and bulk properties. (I: Fe/MnO; II: Fe/TiO/sub 2/; III: Fe/Mord. ). Final report, July 1, 1982-September 30, 1983  

SciTech Connect

The objectives were: (1) to characterize samples D1, 10% FeO/90% MnO, and D2, 48% FeO/52% MnO, under varying conditions of reduction (at 250/sup 0/C or 350/sup 0/C in H/sub 2/) and of syngas reaction 1:1 of CO:H/sub 2/ at 290/sup 0/C) and in some cases use CO only for reduction and to identify species by Moessbauer Spectroscopy and Magnetization (sigma/sub s) measurement; (2) similarly, to see if there is any metal (oxide)/support (Mordenite) interaction by the same techniques. The characterization was carried out with above techniques and the kinetic results for syngas were obtained on the above systems mostly at PETC. During reduction of Fe-oxide/Mn-oxide an intermediate Mn-ferrite phase was detected. After reduction, species such as Fe/sup 0/+Fe/sup 3 +/+Fe/sup 2 +/ in varying total proportions (45% at 290/sup 0/C and Fe/sup 0/+Fe/sup 2 +/ 75% were found at 350/sup 0/C). Syngas conversion showed Fe-carbides (Fe/sub 2/C/sub 2/+Fe/sub 3/C) depending on the reaction conditions, and the composition of D/sub 1/ and D/sub 2/. With the fresh ..gamma..-Fe/sub 2/O/sub 3/ (identified by Moessbauer) on Mordenites with varying ratios of SiO/sub 2//Al/sub 2/O/sub 3/, a decrease in (sigma/sub s/) was found with lowering of the ratios from 60 to 17. At 17% ratio (sigma/sub s/) was smallest and the change in the isomer shift was maximum, which established an interaction with the Broensted cities. 24 figures.

Mulay, L.N.

1983-11-01

135

Tabulation and evaluation of ion exchange data on smectites, certain zeolites and basalt  

SciTech Connect

An extensive search of the literature has been made for ion exchange data on smectites, certain zeolites and basalt. The data are in the form of thermodynamic equilibrium constants, corrected selectivity coefficients, and distribution coefficients. Room temperature alkali and alkaline earth metal cation ion exchange data for smectites are extensive. Correlation between the exchange free energies of alkali metal cations on Camp Berteau montmorillonite values with their Debeye-Hueckel parameter was found. Significant differences in values of exchange constants for the same reaction on different smectites were noted. While this in part may be attributable to differences in experimental procedures, much of the variance is probably due to differences in charge densities and the effective field strengths of the smectites. Differences in field strength are related to the type and amount of substitution on intercrystalline octahedral and tetrahedral sites. Data on smectites suggest that cation exchange selectivities are very strong functions of temperature. Experiments on the exchange properties of clinoptilolite and mordenite have been generally confined to alkali and alkaline earth cations although data for certain transition metal ions are also available for synthetic mordenite. The temperature dependences of zeolite exchange selectivities remain largely unknown. Distribution coefficients for groundwater-basalt systems have been measured for a variety of elements at temperatures up to 150/sup 0/C. Steady state concentrations are often never achieved either from the sorption or the desorption side. Classical models of ion exchange have been applied successfully to zeolite and smectite exchange reactions. The sorption behavior of a basalt is better treated with models of the interface which take surface ionization and complexation into account.

Benson, L.V.

1980-05-01

136

Analysis of the biological and chemical reactivity of zeolite-based aluminosilicate fibers and particulates.  

PubMed

Environmental and/or occupational exposure to minerals, metals, and fibers can cause lung diseases that may develop years after exposure to the agents. The presence of toxic fibers such as asbestos in the environment plus the continuing development of new mineral or vitreous fibers requires a better understanding of the specific physical and chemical features of fibers/particles responsible for bioactivity. Toward that goal, we have tested aluminosilicate zeolites to establish biological and chemical structure-function correlations. Zeolites have known crystal structure, are subject to experimental manipulation, and can be synthesized and controlled to produce particles of selected size and shape. Naturally occurring zeolites include forms whose biological activity is reported to range from highly pathogenic (erionite) to essentially benign (mordenite). Thus, we used naturally occurring erionite and mordenite as well as an extensively studied synthetic zeolite based on faujasite (zeolite Y). Bioactivity was evaluated using lung macrophages of rat origin (cell line NR8383). Our objective was to quantitatively determine the biological response upon interaction of the test particulates/fibers with lung macrophages and to evaluate the efficacy of surface iron on the zeolites to promote the Fenton reaction. The biological assessment included measurement of the reactive oxygen species by flow cytometry and chemiluminescence techniques upon phagocytosis of the minerals. The chemical assessment included measuring the hydroxyl radicals generated from hydrogen peroxide by iron bound to the zeolite particles and fibers (Fenton reaction). Chromatography as well as absorption spectroscopy were used to quantitate the hydroxyl radicals. We found that upon exposure to the same mass of a specific type of particulate, the oxidative burst increased with decreasing particle size, but remained relatively independent of zeolite composition. On the other hand, the Fenton reaction depended on the type of zeolite, suggesting that the surface structure of the zeolite plays an important role. PMID:12417479

Fach, Estelle; Waldman, W James; Williams, Marshall; Long, John; Meister, Richard K; Dutta, Prabir K

2002-11-01

137

Molecular modeling of heterogeneous catalysis  

NASA Astrophysics Data System (ADS)

A novel method for modeling heterogeneous catalysis was developed to further facilitate the understanding of catalytic reactor mechanisms. The method employs molecular dynamics simulations, statistical mechanical, and Unity Bond Index - Quadratic Exponential Potential (UBI-QEP) calculations to calculate the rate constants for reactions on metal surfaces. The primary difficulty of molecular dynamics simulations on metal surfaces has been the lack of reliable reactive potential energy surfaces. We have overcome this through the development of the Normalized Bond Index - Reactive Potential Function (NBI-RPF), which can accurately describe the reaction of adsorbates on metal surfaces. The first calculations of rate constants for a reaction on a metal surface using molecular dynamics simulations are presented. This method is applied to the determination of the mechanism for selective hydrogenation of acetylene in an ethylene rich flow. It was determined that the selectivity for acetylene hydrogenation is attributable to the higher reactivity of acetylene versus ethylene with respect to hydrogenation by molecular hydrogen. It was shown that hydrogen transfer from the carbonaceous layer to acetylene or ethylene is insignificant in the hydrogenation process. Molecular dynamics simulations and molecular mechanics calculations were used to determine the diffusion rate constants for dimethylnaphthalene isomers is mordenite. 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene were found to have similar diffusion rate constants. Grand canonical Monte Carlo calculations were performed on the competitive adsorption of 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene in type X zeolites exchanged individually with barium, calcium, potassium, and rubidium ions, calcium exchanged MCM-22, and hydrogen form mordenite (MOR), X zeolite, Y zeolite, hypBEB, ZSM- 12, and MCM-22. These calculations showed that barium exchanged X zeolite was the most selective toward 2,6- dimethylnaphthalene adsorption.

Gislason, Jason Joseph

138

Hydrothermal alteration in research drill hole Y-3, Lower Geyser Basin, Yellowstone National Park, Wyoming  

USGS Publications Warehouse

Y-3, a U.S. Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, Wyoming, reached a depth of 156.7 m. The recovered drill core consists of 42.2 m of surficial (mostly glacial) sediments and two rhyolite flows (Nez Perce Creek flow and an older, unnamed rhyolite flow) of the Central Plateau Member of the Pleistocene Plateau Rhyolite. Hydrothermal alteration is fairly extensive in most of the drill core. The surficial deposits are largely cemented by silica and zeolite minerals; and the two rhyolite flows are, in part, bleached by thermal water that deposited numerous hydrothermal minerals in cavities and fractures. Hydrothermal minerals containing sodium as a dominant cation (analcime, clinoptilolite, mordenite, Na-smectite, and aegirine) are more abundant than calcium-bearing minerals (calcite, fluorite, Ca-smectite, and pectolite) in the sedimentary section of the drill core. In the volcanic section of drill core Y-3, calcium-rich minerals (dachiardite, laumontite, yugawaralite, calcite, fluorite, Ca-smectite, pectolite, and truscottite) are predominant over sodium-bearing minerals (aegirine, mordenite, and Na-smectite). Hydrothermal minerals that contain significant amounts of potassium (alunite and lepidolite in the sediments and illitesmectite in the rhyolite flows) are found in the two drill-core intervals. Drill core y:.3 also contains hydrothermal silica minerals (opal, [3-cristobalite, chalcedony, and quartz), other clay minerals (allophane, halloysite, kaolinite, and chlorite), gypsum, pyrite, and hematite. The dominance of calcium-bearing hydrothermal minerals in the lower rhyolitic section of the y:.3 drill core appears to be due to loss of calcium, along with potassium, during adiabatic cooling of an ascending boiling water.

Bargar, Keith E.; Beeson, Melvin H.

1985-01-01

139

Environmental effect and genetic influence: a regional cancer predisposition survey in the Zonguldak region of Northwest Turkey  

NASA Astrophysics Data System (ADS)

The Cretaceous-Eocene volcano-sedimentary units of the Zonguldak region of the western Black Sea consist of subalkaline andesite and tuff, and sandstone dominated by smectite, kaolinite, accessory chlorite, illite, mordenite, and analcime associated with feldspar, quartz, opal-CT, amphibole, and calcite. Kaolinization, chloritization, sericitization, albitization, Fe-Ti-oxidation, and the presence of zeolite, epidote, and illite in andesitic rocks and tuffaceous materials developed as a result of the degradation of a glass shards matrix, enclosed feldspar, and clinopyroxene-type phenocrysts, due to alteration processes. The association of feldspar and glass with smectite and kaolinite, and the suborientation of feldspar-edged, subparallel kaolinite plates to fracture axes may exhibit an authigenic smectite or kaolinite. Increased alteration degree upward in which Al, Fe, and Ti are gained, and Si, Na, K, and Ca are depleted, is due to the alteration following possible diagenesis and hydrothermal activities. Micromorphologically, fibrous mordenite in the altered units and the presence of needle-type chrysotile in the residential buildings in which cancer cases lived were detected. In addition, the segregation pattern of cancer susceptibility in the region strongly suggested an environmental effect and a genetic influence on the increased cancer incidence in the region. The most likely diagnosis was Li-Fraumeni syndrome, which is one of the hereditary cancer predisposition syndromes; however, no mutations were observed in the p53 gene, which is the major cause of Li-Fraumeni syndrome. The micromorphology observed in the altered units in which cancer cases were detected may have a role in the expression of an unidentified gene, but does not explain alone the occurrence of cancer as a primary cause in the region.

Kadir, Selahattin; Önen-Hall, A. Piril; Aydin, S. Nihal; Yakicier, Cengiz; Akarsu, Nurten; Tuncer, Murat

2008-03-01

140

Analysis of the biological and chemical reactivity of zeolite-based aluminosilicate fibers and particulates.  

PubMed Central

Environmental and/or occupational exposure to minerals, metals, and fibers can cause lung diseases that may develop years after exposure to the agents. The presence of toxic fibers such as asbestos in the environment plus the continuing development of new mineral or vitreous fibers requires a better understanding of the specific physical and chemical features of fibers/particles responsible for bioactivity. Toward that goal, we have tested aluminosilicate zeolites to establish biological and chemical structure-function correlations. Zeolites have known crystal structure, are subject to experimental manipulation, and can be synthesized and controlled to produce particles of selected size and shape. Naturally occurring zeolites include forms whose biological activity is reported to range from highly pathogenic (erionite) to essentially benign (mordenite). Thus, we used naturally occurring erionite and mordenite as well as an extensively studied synthetic zeolite based on faujasite (zeolite Y). Bioactivity was evaluated using lung macrophages of rat origin (cell line NR8383). Our objective was to quantitatively determine the biological response upon interaction of the test particulates/fibers with lung macrophages and to evaluate the efficacy of surface iron on the zeolites to promote the Fenton reaction. The biological assessment included measurement of the reactive oxygen species by flow cytometry and chemiluminescence techniques upon phagocytosis of the minerals. The chemical assessment included measuring the hydroxyl radicals generated from hydrogen peroxide by iron bound to the zeolite particles and fibers (Fenton reaction). Chromatography as well as absorption spectroscopy were used to quantitate the hydroxyl radicals. We found that upon exposure to the same mass of a specific type of particulate, the oxidative burst increased with decreasing particle size, but remained relatively independent of zeolite composition. On the other hand, the Fenton reaction depended on the type of zeolite, suggesting that the surface structure of the zeolite plays an important role.

Fach, Estelle; Waldman, W James; Williams, Marshall; Long, John; Meister, Richard K; Dutta, Prabir K

2002-01-01

141

Fracture-coating minerals in the Topopah Spring Member and upper tuff of Calico Hills from drill hole J-13  

SciTech Connect

Fracture-lining minerals from drill core in the Topopah Spring Member of the Paintbrush Tuff and the tuff of Calico Hills from water well J-13 were studied to identify the differences between these minerals and those seen in drill core USW G-4. In USW G-4 the static water level (SWL) occurs below the tuff of Calico Hills, but in J-13 the water table is fairly high in the Topopah Spring Member. There are some significant differences in fracture minerals between these two holes. In USW G-4 mordenite is a common fracture-lining mineral in the Topopah Spring Member, increasing in abundance with depth. Euhedral heulandite >0.1 mm in length occurs in fractures for about 20 m above the lower vitrophyre. In J-13, where the same stratigraphic intervals are below the water table, mordenite is uncommon and euhedral heulandite is not seen. The most abundant fracture coating in the Topopah Spring Member in J-13 is drusy quartz, which is totally absent in this interval in USW G-4. Though similar in appearance, the coatings in the vitrophyre have different mineralogy in the two holes. In USW G-4 the coatings are extremely fine grained heulandite and smectite. In J-13 the coatings are fine-grained heulandite, chabazite, and alkali feldspar. Chabazite has not been identified from any other hole in the Yucca Mountain area. Fractures in the tuff of Calico Hills have similar coatings in core from both holes. In J-13, as in USW G-4, the tuff matrix of the Topopah Spring Member is welded and devitrified and that of the tuff of Calico Hills is zeolitic. 11 refs., 10 figs., 5 tabs.

Carlos, B.

1989-02-01

142

Radium-thorium disequilibrium and zeolite-water ion exchange in a Yellowstone hydrothermal environment  

SciTech Connect

Whole rock samples of hydrothermally altered Biscuit Basin rhyolite from Yellowstone drill cores Y-7 and Y-8 were analyzed for {sup 226}Ra and {sup 230}Th to determine the extent of radioactive disequilibrium and its relation to the rates and mechanisms of element transport in the shallow portion of an active hydrothermal system. The ({sup 226}Ra/{sup 230}Th) activity ratios range from 0.73 to 1.46 and are generally correlated with Th-normalized Ba concentrations (Ba{sub N}). Compositions of clinoptilolite and mordenite in these samples are consistent with ion exchange equilibrium between zeolites and coexisting thermal waters. Average K{sup Ba}{sub d mineral-water} values are 1.0 {center dot} 10{sup 5} mL/g for clinoptilolite and 1.4 {center dot} 10{sup 4} mL/g for mordenite. Apparent diffusivities through matrix porosity estimated for R and Ba range from {approximately}10{sup {minus}12} to {approximately}10{sup {minus}10} cm{sup 2} s{sup {minus}1} in thoroughly zeolitic rhyolite; these rates of diffusion are too low to account for the observed distance scale of ({sup 226}Ra/{sup 230}Th) disequilibrium. The correlated values of ({sup 226}Ra/{sup 230}Th) disequilibrium and Ba{sub N} represent zeolite-water ion exchange equilibrium that is caused by porous flow of water through the rock matrix and by the relatively rapid diffusion of cations within the zeolite lattices. A water flux of at least {approximately}2.5 (cm{sup 3}{sub water}/cm{sup 3}{sub rock}) yr{sup {minus}1} is required to produce measurable ({sup 226}Ra/{sup 230}Th) disequilibrium, whereas at least {approximately}23 (cm{sup 3}{sub water}/cm{sup 3}{sub rock}) yr{sup {minus}1} is required for the sample exhibiting the most extreme ({sup 226}Ra/{sup 230}Th) disequilibrium; these fluxes are much higher than those that can be inferred from net mass transfers of stable species.

Sturchio, N.C.; Bohlke, J.K. (Argonne National Laboratory, IL (USA)); Binz, C.M. (Loras College, Dubuque, IA (USA))

1989-05-01

143

Alteration history studies in the Exploratory Studies Facility, Yucca Mountain, Nevada, USA  

SciTech Connect

By mid-1995, the Exploratory Studies Facility (ESF) extended about 1. 1 km from Exile Hill westward toward Yucca Mountain, mostly within densely welded, devitrfied Tiva Canyon Tuff. Secondary mineral occurrences in this unit include breccia cements of mordenite, a fibrous zeolite, and vapor-phase deposits of silica, alkali feldspar, apatite, hollandite, amphibole, and zircon. Calcite is also a common secondary mineral in faults and fractures. Studies of water and gas contents in fluid inclusions in calcites from a fault in nonwelded tuff and a fracture in densely welded tuff suggest mineral deposition under transient locally saturated conditions. Calcite in the nonwelded tuff incorporated air from the unsaturated tuff adjacent to the fault. A highly altered interval within pre-Pah Canyon tuffs just above the top of the Topopah Spring Tuff may be a fossil fumarole or other hydrothermal feature associated with cooling pyroclastic deposits, overprinted by later zeolitic alteration. The observed quartz, cristobalite, opal-CT, and fluorite have been widely identified as products of syngenetic devitrification and vapor-phase alteration in and above the Topopah Spring Tuff. Smectite, also an abundant secondary mineral at the ESF site, has been observed elsewhere at this stratigraphic level. Zeolitic alteration of nonwelded tuffs above the Topopah Spring Tuff, as seen in the ESF, has also been noted in drill core and outcrop at northeastern Yucca Mountain. The hydrologic and geochemical conditions that favored zeolitization only in certain areas of this stratigraphic interval have yet to be determined.

Levy, S.S; Chipera, S.J. [Los Alamos National Lab., NM (United States); Norman, D.I. [New Mexico Inst. of Mining and Technology, Socorro, NM (United States). Dept. of Geoscience

1996-04-01

144

AGING AND IODINE LOADING OF SILVER-FUNCTIONALIZED AEROGELS  

SciTech Connect

Engineered silver-functionalized silica aerogels are being investigated for their application in off-gas treatment at a used nuclear fuel reprocessing facility. Reprocessing will release several key volatile radionuclides, including iodine-129. To achieve regulatory compliance, iodine-129 must be removed from any off-gas stream prior to environmental discharge. Silver-functionalized aerogels have been demonstrated to have high iodine capture capacity, high porosity and potential for conversion into a waste form. Capture materials used in off-gas treatment may be exposed to a heated, high humidity, acidic gas stream for months. Extended exposure to this stream could affect sorbent performance. It was the aim of this study to evaluate what impacts might be observed when Ag0-functionalized aerogels prepared at Pacific Northwest National Laboratory were contacted with a dry air stream for up to 6 months and then used to adsorb iodine from a synthetic off-gas stream. Results demonstrate that there is some loss of iodine capture capacity caused by aging, but that this loss is not as marked as for aging of more traditional iodine sorbents, such as silver-impregnated mordenite. Specifically, aging silver-functionalized aerogel under a dry air stream for up to 6 months can decrease its iodine capacity from 41wt% to 32wt%.

Bruffey, Stephanie H [ORNL; Jubin, Robert Thomas [ORNL; Anderson, Kaara K [ORNL; Walker Jr, Joseph Franklin [ORNL

2013-01-01

145

Support effects on CO hydrogenation over Ru/zeolite catalysts  

SciTech Connect

Hydrogenation of carbon monoxide at 101.3 kPa has been studied over a series of ion-exchanged Ru catalysts supported on NaX, NaY, KL, Na mordenite, and HY zeolites. The type of zeolite had pronounced effects on the activity and selectivity of the Ru. The specific activity would appear to be related to the dispersion of reduced ruthenium in the zeolite. Methane selectivity, however, seems to be strongly influenced by the type and concentration of alkali cations remaining in the ion-exchanged zeolite. These cations appear to promote chain growth much as traditional alkali promoters would, though perhaps more indirectly. Due to bifunctional properties of the zeolite-supported catalysts, a significant fraction of C/sub 4/ was in the form of isobutane. Formation of isobutane seems to be related to either the Si/Al ratio in the zeolites or the concentration of the remaining alkali cations, but not to the OH concentration. In addition, H/sub 2/ chemisorption at 25/sup 0/C was increasingly suppressed as the Se/Al ratio of the zeolite support increased. Both the formation of isobutane and the suppression of H/sub 2/ chemisorption may be related to the acid strength of the OH groups present, which is a function of the Si/Al ratio of the zeolite.

Chen, Y.W.; Wang, H.T.; Goodwin, J.G. Jr.

1984-02-01

146

Probing the structure of complex solids using a distributed computing approach—Applications in zeolite science  

NASA Astrophysics Data System (ADS)

We demonstrate the viability of distributed computing techniques employing idle desktop computers in investigating complex structural problems in solids. Through the use of a combined Monte Carlo and energy minimisation method, we show how a large parameter space can be effectively scanned. By controlling the generation and running of different configurations through a database engine, we are able to not only analyse the data "on the fly" but also direct the running of jobs and the algorithms for generating further structures.As an exemplar case, we probe the distribution of Al and extra-framework cations in the structure of the zeolite Mordenite. We compare our computed unit cells with experiment and find that whilst there is excellent correlation between computed and experimentally derived unit cell volumes, cation positioning and short-range Al ordering (i.e. near neighbour environment), there remains some discrepancy in the distribution of Al throughout the framework. We also show that stability-structure correlations only become apparent once a sufficiently large sample is used.

French, Samuel A.; Coates, Rosie; Lewis, Dewi W.; Catlow, C. Richard A.

2011-06-01

147

Ion exchange in a zeolite-molten chloride system  

SciTech Connect

Electrometallurgical treatment of spent nuclear fuel results in a secondary waste stream of radioactive fission products dissolved in chloride salt. Disposal plans include a waste form that can incorporate chloride forms featuring one or more zeolites consolidated with sintered glass. A candidate method for incorporating fission products in the zeolites is passing the contaminated salt over a zeolite column for ion exchange. To date, the molten chloride ion-exchange properties of four zeolites have been investigated for this process: zeolite A, IE95{reg_sign}, clinoptilolite, and mordenite. Of these, zeolite A has been the most promising. Treating zeolite 4A, the sodium form of zeolite A , with the solvent salt for the waste stream-lithium-potassium chloride of eutectic melting composition, is expected to provide a material with favorable ion-exchange properties for the treatment of the waste salt. The authors constructed a pilot-plant system for the ion-exchange column. Initial results indicate that there is a direct relationship between the two operating variable of interest, temperature, and initial sodium concentration. Also, the mass ratio has been about 3--5 to bring the sodium concentration of the effluent below 1 mol%.

Woodman, R.H.; Pereira, C. [Argonne National Lab., IL (United States). Chemical Technology Div.

1997-07-01

148

Status of radioiodine control for nuclear fuel reprocessing plants  

SciTech Connect

This report summarizes the status of radioiodine control in a nuclear fuel reprocessing plant with respect to capture, fixation, and disposal. Where possible, we refer the reader to a number of survey documents which have been published in the last four years. We provide updates where necessary. Also discussed are factors which must be considered in developing criteria for iodine control. For capture from gas streams, silver mordenite and a silver nitrate impregnated silica (AC-6120) are considered state-of-the-art and are recommended. Three aqueous scrubbing processes have been demonstrated: Caustic scrubbing is simple but probably will not give an adequate iodine retention by itself. Mercurex (mercuric nitrate-nitric acid scrubbing) has a number of disadvantages including the use of toxic mercury. Iodox (hyperazeotropic nitric acid scrubbing) is effective but employs a very corrosive and hazardous material. Other technologies have been tested but require extensive development. The waste forms recommended for long-term storage or disposal are silver iodide, the iodates of barium, strontium, or calcium, and silver loaded sorbents, all fixed in cement. Copper iodide in bitumen (asphalt) is a possibility but requires testing. The selection of a specific form will be influenced by the capture process used.

Burger, L.L.; Scheele, R.D.

1983-07-01

149

NO decomposition in non-reducing atmospheres. Final report, September 1993--February 1997  

SciTech Connect

Co(II)NH{sub 4}-erionite zeolites with cobalt contents varying from 0.002 to 8.2 wt% of Co(II) were prepared, and the samples were studied via diffuse reflectance spectroscopy in the UV-VIS-NIR region and measurement of magnetic moments of the Co ions. Samples of Co(II)-ZSM-5 zeolites were also prepared and studied via diffuse reflectance spectroscopy after being dehydrated at 350 and 525 C and after adsorption of carbon monoxide, water, and ethylene. NO adsorption/desorption studies were carried out, and diffuse reflectance spectroscopy was utilized to monitor the spectral changes that occurred during adsorption of NO on the Co(II) cations, which was observed to occur after dehydration treatments at 350 C and 525 C. In selective catalytic reduction of NO by methane, it was observed that Co-mordenite and Co-ferrierite exhibited the highest % NO converted to products and selectivity toward N{sub 2} formation, but Co-A zeolite and Co-erionite yielded the highest selectivities to NO{sub 2} formation. Co-ZSM-5 zeolite exhibited an intermediate behavior.

NONE

1997-12-31

150

Simultaneous SO{sub 2}/NO{sub x} abatement using zeolite-supported copper. Progress report, April 1--June 30, 1995  

SciTech Connect

Several catalysts for NO decomposition have been reported in the literature to include the following: Cu/ZSM-5; Cu/Zeolite-Y; Cu/mordenite; Cu/{beta} zeolite; Cu/alumina; and Cu/silica which have been studied less than Cu/ZSM-5. The catalytic properties for NO conversion are found to be different on these samples with the ZSM-5 supported catalysts showing the highest activity in a dry environment free from sulfur oxides. One of the goals of this study is to have a better fundamental understanding on the different roles of Cu and the support in the catalytic reaction. The authors use stable, cationic metal complexes in non-aqueous solvents as sources of the Cu ions in producing model catalysts for which the fate of the source molecule is known and is controlled during the ion exchange/impregnation. Molecular models of these systems can be used to identify the possible configurations of the metal complexes within the zeolite support. The authors compare the performance of the model catalysts to one prepared by aqueous impregnation of ZSM-5 zeolite. The performance of the dinuclear metal complex on silica is compared to the same complex in ZSM-5 and Y-zeolites.

Mitchell, M.B.; White, M.G.

1995-12-31

151

Assignment of Nonclassical [Cu(CO)(n)](+) (n = 1, 2) Complex Ions in Zeolite Cages.  

PubMed

A time-resolved FT-IR technique combined with an isotopic tracer method has been applied to study CO adsorbates on Cu(+) ions in copper ion-exchanged zeolites. Three kinds of monocarbonyl species were found to adsorb strongly on Cu-zeolite samples after admission and subsequent evacuation of gas phase CO at room temperature. Their absorption bands were observed at 2146-2160, 2128-2150, and 2097-2129 cm(-1), respectively, dependent on the zeolite structures. In the presence of gaseous CO, the monocarbonyl species at 2146-2160 cm(-1) (so called nonclassical [Cu(CO)](+) complexes) could react with a CO molecule to form a dicarbonyl species [Cu(CO)(2)](+) with nu(sym) bands at 2169-2180 cm(-1). The reactivity of the nonclassical [Cu(CO)](+) complexes was dependent on the zeolite structures, ferrierite > mordenite > ZSM-5 > X-type left harpoon ovet right harpoon offretite/erionite left harpoon ovet right harpoon Y-type > L-type. The remaining two types of monocarbonyl species have little been affected by gas phase CO. PMID:11666867

Iwamoto, Masakazu; Hoshino, Yasuyuki

1996-11-20

152

Diffusion of radionuclides in brine-saturated backfill barrier materials  

SciTech Connect

The diffusion of cesium (I), strontium (II), pertechnetate and europium in brine-saturated backfill materials was measured. Plastic diffusion cells containing cylindrical diffusion columns were used for low density backfill materials. The diffusion of gamma-emitters was followed by a gamma scanning technique. Metal diffusion cells constructed entirely from Hastelloy C-276 were used for the diffusion of pertechnetate in highly compacted bentonite. Apparent distribution coefficients calculated from diffusion data are (a) 0.02 m/sup 3//kg for cesium (I) in 40 wt.% mordenite and 60 wt.% bentonite; (b) 0.04 m/sup 3//kg for strontium (II) in 10 wt.% sodium titanate and 90 wt.% bentonite; (c) 0.5 m/sup 3//kg for pertechnetate in 70 wt.% charcoal and 30 wt.% bentonite; and (d) 3 m/sup 3//kg for europium in 100% bentonite. Backfill effectiveness estimates based on batch sorption measurements were supported by these results; however, the diffusion results for europium did not agree well with a model for diffusion retarded by linear sorption. First measurements of pertechnetate diffusion in highly compacted bentonite suggest that anion exclusion may play a role in reducing mass transport rates of anions in this material. Needs for diffusion measurements that take into account site-specific materials interactions are described. 8 figures, 2 tables.

Nowak, E.J.

1982-01-01

153

Effect of benzene on the isomerization of n-pentane on palladium-zeolite catalysts  

SciTech Connect

An investigation has been made of the effect of benzene on the isomerization of n-pentane on palladium catalysts based on Y, mordenite and TsVM zeolites. The palladium content of the catalysts was varied form 0.001 to 0.5 wt.%. It was shown that, in the presence of benzene, there is a reduction in the isopentane yield, and isomerization is less selective. The activity of catalysts in isomerization and cracking increases with their palladium content. The hydrogenation of benzene begins with palladium contents of 0.05-0.1 wt.%. It was established that hydrocarbon cracking and isomerization occurs on acid centres of the catalyst. Here, in the case of catalysts based on HTsVM, the state of the acid centres is such that the intermediate carbonium ions on them act like radicals. This is indicated by the magnitude of the isobutane/n-butane ratio in the cracking products. The results obtained are explained on the basis of the bifunctional mechanism of action of the catalyst and by movement of the isomerization of n-pentane in the presence of benzene to acid centres of lower strength. 11 refs., 7 figs., 2 tabs.

Minachev, Kh.M.; Kharlamov, V.V.; Fomin, A.S.; Shkitov, A.M. [N.D. Zelinskii Institute of Organic Chemistry, Moscow (Russian Federation)

1993-12-31

154

Mineral precipitation on modern siliciclastic tidal flats colonized by microbial mats  

NASA Astrophysics Data System (ADS)

The preservation and cementation of sedimentary structures under the influence of microorganisms in siliciclastic environments have been poorly studied in contrast to carbonatic settings, where they have been extensively investigated. Whereas in carbonatic environments, microbial mat-induced precipitation of calcium carbonate results in a cementation process producing a quick lithification, in siliciclastic environments other minerals would act as cement. The focus of this paper is to document the presence of authigenic minerals within a biosedimentary fabrics and the possible link of these minerals with the extensive microbial mats that colonize the tidal flat of the temperate Bahía Blanca estuary. "Anoxic" minerals (e.g. pyrite) and authigenic zeolites such as analcime, clinoptilolite, mordenite, phillipsite and chabazite were recognized through SEM and EDX analyses. These minerals were most likely formed by alteration of volcanic ash, which is present in this tidal flat and also silica may result from dissolution of frustules of benthic diatoms. Minerals precipitated in this setting are significant as they would act as early cement in the eogenesis, enhancing the preservation of sedimentary and biogenic structures.

Cuadrado, Diana G.; Carmona, Noelia B.; Bournod, Constanza N.

2012-10-01

155

MOLECULAR SIEVES AS CATALYSTS FOR METHANOL DEHYDRATION IN THE LPDMEtm PROCESS  

SciTech Connect

Several classes of molecular sieves were investigated as methanol dehydration catalysts for the LPDME{trademark} (liquid-phase dimethyl ether) process. Molecular sieves offer a number of attractive features as potential catalysts for the conversion of methanol to DME. These include (1) a wide range of acid strengths, (2) diverse architectures and channel connectivities that provide latitude for steric control, (3) high active site density, (4) well-investigated syntheses and characterization, and (5) commercial availability in some cases. We directed our work in two areas: (1) a general exploration of the catalytic behavior of various classes of molecular sieves in the LPDME{trademark} system and (2) a focused effort to prepare and test zeolites with predominantly Lewis acidity. In our general exploration, we looked at such diverse materials as chabazites, mordenites, pentasils, SAPOs, and ALPOs. Our work with Lewis acidity sought to exploit the structural advantages of zeolites without the interfering effects of deleterious Broensted sites. We used zeolite Ultrastable Y (USY) as our base material because it possesses a high proportion of Lewis acid sites. This work was extended by modifying the USY through ion exchange to try to neutralize residual Broensted acidity.

Andrew W. Wang

2002-04-01

156

Probing the structure of complex solids using a distributed computing approach-Applications in zeolite science  

SciTech Connect

We demonstrate the viability of distributed computing techniques employing idle desktop computers in investigating complex structural problems in solids. Through the use of a combined Monte Carlo and energy minimisation method, we show how a large parameter space can be effectively scanned. By controlling the generation and running of different configurations through a database engine, we are able to not only analyse the data 'on the fly' but also direct the running of jobs and the algorithms for generating further structures. As an exemplar case, we probe the distribution of Al and extra-framework cations in the structure of the zeolite Mordenite. We compare our computed unit cells with experiment and find that whilst there is excellent correlation between computed and experimentally derived unit cell volumes, cation positioning and short-range Al ordering (i.e. near neighbour environment), there remains some discrepancy in the distribution of Al throughout the framework. We also show that stability-structure correlations only become apparent once a sufficiently large sample is used. - Graphical Abstract: Aluminium distributions in zeolites are determined using e-science methods. Highlights: > Use of e-science methods to search configurationally space. > Automated control of space searching. > Identify key structural features conveying stability. > Improved correlation of computed structures with experimental data.

French, Samuel A.; Coates, Rosie [Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ (United Kingdom); Lewis, Dewi W., E-mail: d.w.lewis@ucl.ac.uk [Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ (United Kingdom); Catlow, C. Richard A. [Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ (United Kingdom)

2011-06-15

157

Evaluation of factors affecting performance of a zeolitic rock barrier to remove zinc from water.  

PubMed

This study examined the factors affecting the performance of zeolitic rocks as reactive media in a permeable reactive barrier (PRB) used to remediate groundwater contaminated with Zn. Serial batch kinetic and sorption tests were conducted on zeolitic rock samples under a variety of conditions (i.e., reaction time, pH, initial Zn concentration, and particle size) using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on zeolitic rock samples at various flow rates. The removal of Zn increased approximately from 20-60 to 70-100% with increasing pH from 2 to 4 and decreasing initial Zn concentration from 434 to 5mg/L. Zn removal was not affected by the particle size, regardless of the zeolitic rock samples used in this study. The Zn removal increased approximately from 20-70 to 60-100% with increasing the cation exchange capacity (CEC) from 124.9 to 178.5meq/100g and increasing zeolite (i.e., clinoptilonite and mordenite) and montmorillonite contents from 53.7 to 73.2%. The results from the column and batch tests were comparable. Increasing the flow rate caused the earlier breakthrough of Zn (sorbing cation) and a rapid decrease in the concentration of Na, Ca, and Mg (desorbing cations). The hydraulic conductivities of the samples were unaffected by the particle size and mineral components. PMID:19880248

Lee, Se-Hoon; Jo, Ho Young; Yun, Seong-Taek; Lee, Young Jae

2009-10-06

158

Effects of long-term exposure of tuffs to high-level nuclear waste repository conditions. Final report  

SciTech Connect

We have performed exploratory tests to investigate the effects of extended exposure of tuffs from Yucca Mountain, Nevada, to temperatures and pressures similar to those that will be encountered in a high-level nuclear waste repository. In a preliminary report we described statistically significant changes in strength properties and generally minor changes in porosity and grain density. In the present report we describe additional measurements that indicate possible changes in permeability (in one tuff type) after exposure for 2 to 6 months at temperatures from 80 to 180 C, confining pressures of 9.7 and 19.7 MPa, and water pore pressures of 0.5 and 19.7 MPa. Mineralogic examinations have established reactions involving dissolution of silica and feldspar minerals and possible conversion of clinoptilolite to mordenite. We conclude that rock properties important to the operation of a nuclear waste repository in tuff are likely to change over time when exposed to simulated repository conditions, and the details of these time-dependent processes should be investigated further.

Blacic, J.D.; Vaniman, D.T.; Bish, D.L.; Duffy, C.J.; Gooley, R.C.

1986-08-01

159

Investigation on NOx adsorption in [M?]-MAPO-5 (M = Si, Ti; M? = Ag, Cu) by density functional theory calculation  

NASA Astrophysics Data System (ADS)

NO, N2O and NO2 adsorption in [M?]-MAPO-5 (M = Si, Ti; M? = Ag, Cu) models of the modified aluminophosphate molecular sieves was investigated by density functional theory (DFT) method. The equilibrium structural parameters and adsorption energies were obtained and compared. The structural parameters of NO and NO2 in the adsorbed state had a distinct change than that of N2O compared to their free gas state. [M?]-MAPO-5 was more effective for the activation of NOx molecule compared to [M?]-AlMOR (M? = Ag, Cu) models of the modified mordenite in our previous studies. The adsorption energies data indicated that adsorption strength of NOx followed the decreasing order of NO2 > NO > N2O. And adsorption complexes in ?1-N mode were much stabler than that in ?1-O mode, which was similar to that in [M?]-AlMOR. [Cu]-MAPO-5 had a much stronger adsorption for NOx than [Ag]-MAPO-5. And [M?]-SiMOR had a little stronger adsorption for NOx than [M?]-TiMOR. Furthermore, the resistance capabilities of [M?]-MAPO-5 to SO2, H2O and O2 were studied and analyzed. The interaction mechanism of NOx adsorption in [M?]-MAPO-5 was also discussed by natural bond orbital (NBO) analysis, which was in reasonable agreement with the adsorption interaction strengths.

Liu, Jiexiang; Zhang, Xiaoguang

2013-01-01

160

Association of Indigo with Zeolites for Improved Color Stabilization  

NASA Astrophysics Data System (ADS)

The durability of an organic colour and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidising conditions, using Raman and UV-visible spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high colour stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.

Dejoie, Catherine; Martinetto, Pauline; Dooryhée, Eric; van Elslande, Elsa; Blanc, Sylvie; Bordat, Patrice; Brown, Ross; Porcher, Florence; Anne, Michel

2010-10-01

161

Mechanism of neopentane cracking over solid acids  

SciTech Connect

Neopentane was used as a probe to test whether catalyst protons can attack the C-C and/or the C-H sigma-bonds in the cracking of alkanes. Over a variety of solid acids approximately one CH/sub 4/ molecule was formed for every neopentane reacted. Moreover, in most cases nearly as much isobutene was formed. With H-Y zeolite (H-Y) and particularly with H-mordenite (H-M), however, hydride transfer leading to paraffin formation became important or dominant. Generally, the results conformed to (CH/sub 3/)/sub 3/C-H/sup +/-CH/sub 3/ ..-->.. CH/sub 4/ + (CH/sub 3/)/sub 3/C/sup +/ with the t-butyl ion either decomposing to isobutene or else undergoing secondary reactions. The latter tended to increase with the intensive factor of the acidity, i.e., with the strength of the acid-base interaction. The fraction of neopentane converted to CH/sub 4/, when plotted in the Arrhenius fashion against T/sup -1/, produced straight lines from which apparent activation energies could be calculated. Values obtained fell between 30 kcal/mol for silica-alumina and 14 kcal/mol for H-M (the most acidic and active catalyst investigated). Controversial views found in current literature are discussed in light of the present results.

Lombardo, E.A.; Pierantozzi, R.; Hall, W.K.

1988-03-01

162

Specificity of sites within eight-membered ring zeolite channels for carbonylation of methyls to acetyls.  

PubMed

The acid-catalyzed formation of carbon-carbon bonds from C1 precursors via CO insertion into chemisorbed methyl groups occurs selectively within eight-membered ring (8-MR) zeolite channels. This elementary step controls catalytic carbonylation rates of dimethyl ether (DME) to methyl acetate. The number of O-H groups within 8-MR channels was measured by rigorous deconvolution of the infrared bands for O-H groups in cation-exchanged and acid forms of mordenite (M,H-MOR) and ferrierite (H-FER) after adsorption of basic probe molecules of varying size. DME carbonylation rates are proportional to the number of O-H groups within 8-MR channels. Na+ cations selectively replaced protons within 8-MR channels and led to a disproportionate decrease in carbonylation turnover rates (per total H+). These conclusions are consistent with the low or undetectable rates of carbonylation on zeolites without 8-MR channels (H-BEA, H-FAU, H-MFI). Such specificity of methyl reactivity upon confinement within small channels appears to be unprecedented in catalysis by microporous solids, which typically select reactions by size exclusion of bulkier transition states. PMID:17397162

Bhan, Aditya; Allian, Ayman D; Sunley, Glenn J; Law, David J; Iglesia, Enrique

2007-03-31

163

Electronic and Lattice Structures of Isolated Se Chains and Defects in Them. II  

NASA Astrophysics Data System (ADS)

Electronic and lattice structures of terminal and internal defects in a Se chain are systematically studied with the semi-empirical model developed previously. Structures of the defects are as follows: negative ion 1C1-, a little altered helix; neutral radical 2C10, and positive singlet ion 1C1+, planer structures with four atoms; positive triplet ion 3C1+, an acute triangle; n-type polaron 2P-, locally relaxed helix; p-type polaron 2P+ and self-trapped triplet exciton 3Ex, planer zig-zag structures with five atoms; intimate valence alternation pair (IVAP), a ramification of a Se atom. The IVAP is of C3+-C1- type. Interactions of a Se chain with Li, H and O are studied as a model of the effects of the wall on a Se chain enclosed in a mordenite channel (M-Se). A Se chain makes unusual charge transfer complexes with Li. Hydrogen binds to an internal Se making it C3+ type or blocks a terminal Se. Based on these calculations we propose a model for photo-induced events in M-Se.

Ikawa, Atsushi; Fukutome, Hideo

1990-03-01

164

Sorption of cesium and strontium from concentrated brines by backfill barrier materials  

SciTech Connect

The sorption of radionuclides from potentially intruding groundwater at a nuclear waste repository is a major chemical function of backfill barriers. In this study, various materials (including clays, zeolites and an inorganic ion exchanger) were screened for the sorption of the fission products cesium and strontium in concentrated brines. Representative brines A and B for the Waste Isolation Pilot Plant (WIPP), a proposed radioactive waste repository and test facility in bedded salt were used. Sorption properties were quantified using empirical distribution coefficients, k/sub d/. Of the materials examined, sodium titanate had the highest k/sub d/ for the sorption of Sr(II) in both brine A (k/sub d/ = 125 ml/g) and brine B(k/sub d/ = 500 to 600 ml/g). A mordenite-type zeolite was the most effective getter for Cs(I) in brine A (k/sub d = 27 ml/g), while illite yielded the highest k/sub d/ for Cs(I) in brine B (k/sub d/ = 115 ml/g). The relative merit of these k/sub d/ values is evaluated in terms of calculated estimates of breakthrough times for a backfill barrier containing the getter. Results show that a backfill mixture containing these getters is potentially an effective barrier to the migration of Sr(II) and Cs(I), although further study (especially for the sorption of cesium from brine A) is recommended. Initial mechanistic studies revealed competing ion effects which would support an ion exchange mechanism. K/sub d/'s were constant over a Sr(II) concentration range of 10/sup -11/ to 10/sup -5/ M and a Cs(I) concentration range of 10/sup -8/ to 10/sup -5/ M, supporting the choice of a linear sorption isotherm as a model for the results. Constant batch composition was shown to be attained within one week.

Winslow, C D

1981-03-01

165

Malignant mesothelioma induced by asbestos and zeolite in the mouse peritonenal cavity  

SciTech Connect

The carcinogenicity of asbestos (amosite and chrysotile) and zeolite (fibrous erionite, mordenite, and synthetic zeolite 4A) were studied in the peritoneum of 586 BALB/C male mice after a single intraperitoneal or intraabdominal wall injection. Tumors developed in 93 of 394 animals (23.6%) treated with asbestos or fibrous erionite 7 months or more after administration. All of the induced peritoneal tumors were intimately associated with marked peritoneal fibrosis, in which asbestos or erionite fibers were regularly detected. Histopathologically, 83 of 93 were consistent with malignant mesotheliomas. Other tumors consisted of 6 plasmacytomas, 1 histiocytoma, 1 liposarcoma, 1 osteosarcoma, and 1 adenocarcinoma of the pancreas. Two of the cases of mesotheliomas were associated with plasmacytoma. In many instances, the primary site of the mesotheliomas seemed to be multiple, the favorite sites being the omentum, mesentery, serosae of the gastrointestinal and genital organs, the diaphragm, the capsule of the liver and spleen, and the abdominal wall peritoneum. In addition to the 93 peritoneal tumors, 3 extraperitoneal tumors (1 fibrosarcoma and 2 rhabdomyosarcomas) were induced by amosite which was probably accidentally injected into the extraperitoneal connective tissue and the striated muscle tissue of the abdominal wall, respectively. These three tumors were also intimately associated with focal fibrosis in which amosite fibers were detected. Among the three different types of zeolite, only fibrous erionite showed striking carcinogenicity and marked fibrogenicity. The erionite-induced mesotheliomas were similar to those induced by asbestos in exhibiting long latency, in gross appearance, in histology, and in close association with fibrosis.

Suzuki, Y.; Kohyama, N.

1984-10-01

166

A test and demonstration unit for concentrating sulfur dioxide from flue gas  

SciTech Connect

A bench-scale system to continuously separate and concentrate SO{sub 2} from flue gas has been developed and tested. The separation is accomplished due to the relative adsorption strengths of SO{sub 2} and water on a synthetic mordenite, a phenomenon known as rollup. The continuous concentration system (CCS) is comprised of two pairs of packed beds that cycle between cleaning, roll-up, and regeneration modes. The bed pairs behave identically, with cycles staggered by half of one adsorption-desorption-regeneration period. The cycle for each pair involves regeneration of one bed with dry air, while the other is cleaning the flue gas and subsequently rolling up the SO{sub 2}. This bench-scale CCS is able to split a 6 standard liters per minute (SLPM) gas stream containing 2,000 ppm SO{sub 2} into two streams of equal flowrate, one containing 3,400 ppm SO{sub 2} and the other 70 ppm SO{sub 2}. The influence of water is strong, with the rollup being optimal at 13% moisture in the flue gas. Adsorption starting with the bed at 75 C is optimal, and air regeneration at 200 C and 8 SLPM for 76 min is adequate. An economic analysis of an industrial-scaled CCS capable of treating a 1,000,000 scfm flue gas stream containing 2,000 ppm SO{sub 2} (typical of a 400-MW coal-fired power plant) was conducted. The CCS installation permits smaller flue gas scrubbers to be installed and can potentially save a 400-MW power plant $2.6 million in annual operating costs.

Dunn, J.P.; Cai, Y.; Liebmann, L.S.; Stenger, H.G. Jr.; Simpson, D.R. [Lehigh Univ., Bethlehem, PA (United States)

1996-04-01

167

Fracture coatings in Topopah Spring Tuff along drill hole wash  

SciTech Connect

Fracture-lining minerals are being studied as part of site characterization to determine the suitability of Yucca Mountain, Nevada as a potential high level nuclear waste repository. Fracture coatings in the Paintbrush Group provide information on potential flow paths above the water table both toward and away from the potential repository and provide information on the distribution of fracture-lining minerals needed to model thermal effects of waste emplacement. Fracture coatings within the predominantly non-zeolitic Paintbrush Group vary both with depth and laterally across Yucca Mountain, whereas fracture coatings in tuffs below the Paintbrush Group are related to the mineralogy of the tuffs and follow a consistent pattern of distribution with predominantly quartz, calcite, and manganese oxides in the devitrified intervals and mordenite and clinoptilolite in the zeolitic intervals. The zeolites stellerite and heulandite are more abundant in fractures in the Topopah Spring Tuff in drill holes USW G-1 and UE-25 a{number_sign}l, located along Drill Hole Wash (at the northern end of Yucca Mountain) than in core from other parts of Yucca Mountain. Buesch et al. (2) present evidence for a complex fault system along Drill Hole Wash. To investigate the possibility that the abundant fracture-lining zeolites in USW G-1 and UE-25 a{number_sign} 1 are related to the Drill Hole Wash fault, the Topopah Spring Tuff was examined in drill cores from USW UZ-14, USW G-1, USW NRG-7/7a, and UE-25 a{number_sign}l.

Carlos, B.A.; Chipera, S.J.; Bish, D.L.

1994-12-01

168

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

SciTech Connect

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar during organic heavy-liquid treatment and cleaning using acetone and deionized water does occur, as indicated by comparing the amounts of radiogenic Ar of treated and untreated fractions. Moreover, a regular decrease in radiogenic Ar contents was noted in clinoptilolite fractions during dehydration experiments at different temperatures for 16 hours. Comparable losses do not occur from saturated samples that were heated in 100 C for more than five months. Water appears to play a vital role in stabilizing the clinoptilolite framework structure and in the retention of Ar. The radiogenic Ar depletion pattern noted in clinoptilolite fractions dehydrated in unsaturated environment at different temperatures is similar to variations in the amount of radiogenic Ar observed in clinoptilolite samples from the unsaturated zone of an altered tuff. These results can be used to evaluate the extent of zeolitic water (and hence Ar) retention in unsaturated geologic settings. The utility of alkali zeolites (e.g., phillipsite, clinoptilolite, and mordenite) from low-temperature, open-hydrologic alteration as potential dateable minerals was evaluated using the K/Ar method as part of the Yucca Mountain Site Characterization Project, which is evaluating Yucca Mountain, Nevada, as a potential high-level radioactive waste repository site.

WoldeGabriel, G.

1995-02-01

169

Distribution of Components in Ion Exchange Materials Taken from the K East Basin and Leaching of Ion Exchange Materials by Nitric/Hydrofluoric Acid and Nitric/Oxalic Acid  

SciTech Connect

Laboratory tests were performed to examine the efficacy of mixed nitric/hydrofluoric acid followed by mixed nitric/oxalic acid leach treatments to decontaminate ion exchange materials that have been found in a number of samples retrieved from K East (KE)Basin sludge. The ion exchange materials contain organic ion exchange resins and zeolite inorganic ion exchange material. Based on process records, the ion exchange resins found in the K Basins is a mixed-bed, strong acid/strong base material marketed as Purolite NRW-037. The zeolite material is Zeolon-900, a granular material composed of the mineral mordenite. Radionuclides sorbed or associated with the ion exchange material can restrict its disposal to the Environmental Restoration Disposal Facility (ERDF). The need for testing to support development of a treatment process for K Basin sludge has been described in Section 4.2 of ''Testing Strategy to Support the Development of K Basins Sludge Treatment Process'' (Flament 1998). Elutriation and washing steps are designed to remove the organic resins from the K Basin sludge. To help understand the effects of the anticipated separation steps, tests were performed with well-rinsed ion exchange (IX) material from KE Basin floor sludge (sample H-08 BEAD G) and with well-rinsed IX having small quantities of added KE canister composite sludge (sample KECOMP). Tests also were performed to determine the relative quantities of organic and inorganic IX materials present in the H-08 K Basin sludge material. Based on chemical analyses of the separated fractions, the rinsed and dry IX material H-08 BEAD G was found to contain 36 weight percent inorganic material (primarily zeolite). The as-received (unrinsed) and dried H-08 material was estimated to contain 45 weight percent inorganic material.

Delegard, C.H.; Rinehart, D.E.; Hoopes, F.V.

1999-04-02

170

Synthesis, crystal structure, characterization, and catalytic properties of TNU-9.  

PubMed

The synthesis, crystal structure, characterization, and catalytic properties of the novel medium-pore zeolite TNU-9 (framework type TUN), one of the most crystallographically complex zeolites known to date, are described. TNU-9 was found to crystallize under hydrothermal conditions at the expense of a lamellar precursor over a very narrow range of SiO(2)/Al(2)O(3) and NaOH/SiO(2) ratios and in the presence of 1,4-bis(N-methylpyrrolidinium)butane and Na+ ions as structure-directing agents. A combination of molecular modeling and Rietveld refinement using synchrotron powder diffraction data confirms the proposed topology of as-made TNU-9 and suggests three or possibly four different sites for the organic within the complex pore structure. The proton form (H-TNU-9) of this new medium-pore zeolite exhibits exceptionally high hydrothermal stability, as well as very strong acidity. When compared to H-ZSM-5, H-MCM-22, H-mordenite, and H-Beta, H-TNU-9 displays unique shape selectivities for the acid-catalyzed reactions of monoaromatic hydrocarbons such as the disproportionation of toluene and the isomerization and disproportionation of m-xylene. In particular, for the isomerization of m-xylene, the ratio of isomerization to disproportionation increases steadily to values in excess of 50 with prolonged time on stream and a high p/o xylene ratio is observed in the products, achieving a value of ca. 6 after only a short time on stream. These results are rationalized on the basis of the unique pore topology of TNU-9. PMID:17696433

Hong, Suk Bong; Min, Hyung-Ki; Shin, Chae-Ho; Cox, Paul A; Warrender, Stewart J; Wright, Paul A

2007-08-15

171

Hydrothermal alteration in research drill hole Y-2, Lower Geyser Basin, Yellowstone National Park, Wyoming  

SciTech Connect

Y-2, a US Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, was drilled to a depth of 157.4 meters. The hole penetrated interbedded siliceous sinter and travertine to 10.2 m, glacial sediments of the Pinedale Glaciation interlayered with pumiceous tuff from 10.2 to 31.7 m, and rhyolitic lavas of the Elephant Back flow of the Central Plateau Member and the Mallard Lake Member of the Pleistocene Plateau Rhyolite from 31.7 to 157.4 m. Hydrothermal alteration is pervasive in most of the nearly continuous drill core. Rhyolitic glass has been extensively altered to clay and zeolite minerals (intermediate heulandite, clinoptilolite, mordenite, montmorillonite, mixed-layer illite-montmorillonite, and illite) in addition to quartz and adularia. Numerous veins, vugs, and fractures in the core contain these and other minerals: silica minerals (opal, ..beta..-cristobalite, ..cap alpha..-cristobalite, and chalcedony), zeolites (analcime, wairakite, dachiardite, laumontite, and yugawaralite), carbonates (calcite and siderite), clay (kaolinite and chlorite), oxides (hematite, goethite, manganite, cryptomelane, pyrolusite, and groutite), and sulfides (pyrhotite and pyrite) along with minor aegirine, fluorite, truscottite, and portlandite. Interbedded travertine and siliceous sinter in the upper part of the drill core indicate that two distinct types of thermal water are responsible for precipitation of the surficial deposits, and further that the water regime has alternated between the two thermal waters more than once since the end of the Pinedale Glaciation (approx. 10,000 years B.P.). Alternation of zones of calcium-rich and sodium- and potassium-rich hydrothermal minerals also suggests that the calcium-rich and sodium- and potassium-rich hydrothermal minerals also suggests that the water chemistry in this drill hole varies with depth.

Bargar, K.E.; Beeson, M.H.

1981-05-01

172

Single-column-based absorption process for treating dissolver off-gas  

SciTech Connect

The fluorocarbon absorption process for krypton and xenon removal from dissolver off-gas is based on exploitation of solubility differences which exist among noble gases and other gas-phase constituents in the fluorocarbon solvent dichlorofluoromethane (refrigerant-12). Process performance and reliability have been demonstrated on an engineering scale with over 10 years of pilot plant operation, including testing with /sup 85/Kr, /sup 133/Xe, and /sup 131/I. The culmination of this work is a single-column design which results in a simplified process with improved reliability and lower cost. Data are presented summarizing recent single-column development activities. These include data plots depicting decontamination factor vs feed gas flow rate, DF vs process absorption factor (kG/L), and location of the concentration peak via the solvent flow rate. In general, 99% removal is easily obtainable for Kr, Xe, and CO/sub 2/ while attaining concentration factors on the order of 10/sup 3/ to 10/sup 4/. Further concentration of the Kr product is investigated using solid sorbent and cold trapping technologies. Effective removal of entrained fluorocarbon solvent and CO/sub 2/ from the single-column product stream is demonstrated using 13X and 5A molecular sieves, respectively. Additional separation of Xe is studied using a silver mordenite bed and compared to existing methods using cryogenic charcoal beds or selective cold trap sublimation. Regardless of the method for Xe removal, Kr is ultimately concentrated via a simple cold trap to > 90% purity from a feed gas containing 10 ppM. 14 figures.

Eby, R.S.; Little, D.K.; Merriman, J.R.; Stephenson, M.J.

1982-05-21

173

Test results from the GA technologies engineering-scale off-gas treatment system  

SciTech Connect

One method for reducing the volume of HTGR fuel prior to reprocessing or spent fuel storage is to crush and burn the graphite fuel elements. The burner off-gas (BOG) contains radioactive components, principally H-3, C-14, Kr-85, I-129, and Rn-220, as well as chemical forms such as CO/sub 2/, CO, O/sub 2/, and SO/sub 2/. The BOG system employs components designed to remove these constitutents. Test results are reported for the iodine and SO/sub 2/ adsorbers and the CO/HT oxidizer. Silver-based iodine adsorbents were found to catalyze the premature conversion of CO to CO/sub 2/. Subsequent tests showed that iodine removal could not be performed downstream of the CO/HT oxidizer since iodine in the BOG system rapidly deactivated the Pt-coated alumina CO catalyst. Lead-exchanged zeolite (PbX) was found to be an acceptable alternative for removing iodine from BOG without CO conversion. Intermittent and steady-state tests of the pilot-plant SO/sub 2/ removal unit containing sodium-exchanged zeolite (NaX) demonstrated that decontamination factors greater than or equal to 100 could be maintained for up to 50 h. In a reprocessing flowsheet, the solid product from the burners is dissolved in nitric or Thorex acid. The dissolver off-gas (DOG) contains radioactive components H-3, Kr-85, I-129, Rn-220 plus chemical forms such as nitrogen oxides (NO/sub x/). In the pilot-scale system at GA, iodine is removed from the DOG by adsorption. Tests of iodine removal have been conducted using either silver-exchanged mordenite (AgZ) or AgNO/sub 3/-impregnated silica gel (AC-6120). Although each sorbent performed well in the presence of NO/sub x/, the silica gel adsorbent proved more efficient in silver utilization and, thus, more cost effective.

Jensen, D.D.; Olguin, L.J.; Wilbourn, R.G.

1984-06-01

174

Chemistry and morphology of coal liquefaction. Annual report, October 1, 1982-September 30, 1983  

SciTech Connect

The kinetics of Fischer-Tropsch synthesis over a potassium-promoted, fused-iron catalyst were studied as a function of catalyst reduction conditions. Severe reduction leads to a very active catalyst, which deactivates rapidly. Milder reduction conditions give a less active but more stable catalyst. Differences in the order of dependence on H/sub 2/ and CO and the fact that activation energies are independent of reduction condition suggest that different fractions of the surface are brought into an active state. A study of potential support-metal interaction was undertaken. There are significant differences in the product spectrum between fused Fe/sub 2/O/sub 3/ and precipated Fe/sub 2/O/sub 3/ catalysts. Supported iron on silica, mordenite, y-zeolite and ZSM-5 indicated that chain growth probability is the same for all these supports. Olefin to paraffin ratio increases with increasing Al/Si ratio. Dependencies of rates of formation of individual products on H/sub 2/ and CO partial pressure are different for each support. Powdered graphite samples loaded with various amounts of KOH have been reacted with atmospheric pressure of steam in the temperature range 700 to 900/sup 0/K. The reaction proceeds via two successive stages. During Stage 1, hydrogen and hydrocarbons are evolved at a high rate but no CO or CO/sub 2/. During Stage 2, gasification proceeds catalytically at a much reduced rate with the production of one CO molecule per equivalent H/sub 2/ molecule. While the results with graphite described indicate a stoichiometric reaction, recent work with an Illinois No. 5 char shows that hydrocarbon production does not stop when all potassium hydroxide has been converted. It appears that an ash component catalytically decomposes the phenolate at reaction temperature, reconstitutes the potassium hydroxide and permits a continuous hydrocarbon production.

Heinemann, H.

1983-09-01

175

Adsorption Model for Off-Gas Separation  

SciTech Connect

The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed in gPROMS software. Inputs include gas stream constituents, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. It models dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions for a multiple component gas stream. The simulation outputs component concentrations along the column length as a function of time from which the breakthrough data is obtained. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data will be input into the adsorption model to develop a model specific for iodine adsorption on silver mordenite as well as model(s) specific for krypton and xenon adsorption. The model will be validated with experimental breakthrough curves. Another future off-gas modeling goal is to develop a model for the unit operation absorption. The off-gas models will be made available via the server or web for evaluation by customers.

Veronica J. Rutledge

2011-03-01

176

Electron transfer reactions in microporous solids  

SciTech Connect

We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

Mallouk, T.E.

1992-05-01

177

Electron transfer reactions in microporous solids. Progress report, June 1991--May 1992  

SciTech Connect

We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently ``dry`` powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center_dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

Mallouk, T.E.

1992-05-01

178

NO decomposition in non-reducing atmospheres. Technical progress report, December 1994--February 1995  

SciTech Connect

The overall goal of this research is to establish the fundamental science needed to develop catalysts that will exhibit high activity and selectivity in the decomposition of NO into N{sub 2} and O{sub 2}. This project is centered on the preparation, characterization, and testing of transition metal exchanged catalysts, especially Co(III) zeolites. Additional Co(II) exchanged A zeolite samples have been prepared in aqueous solution at pH = 5.0-6.1 that contain different exchange levels of Co(II). Some of these have been analyzed for Na and Co contents by chemical methods and by X-ray photoelectron spectroscopy. It was shown that preparation of the samples by ion exchange between pH {approx}6 and 7 tended to give stoichiometric ion exchange of Co(II) for Na{sup +}. However, ion exchange at lower pH tended to lead to exchange with H{sup +} while ion exchange at higher pH tended to lead to the presence of excess Co(H), probably by precipitation of a basic Co phase. Systematic analyses of Na A zeolite, CO(II) A zeolites, and Co(II)/Ce(III) A zeolites, as well as Na X zeolite, Na Y zeolite, and Na mordenite for comparison purposes, have been carried out by X-ray photoelectron spectroscopy and Auger spectroscopy methods. Complete data analysis has not yet been carried out, but trends in some parameters have been noted, e.g. the relative intensity of the O KL{sub 2,3}L{sub 2,3} line in the O ls spectral region increases as the Si Al ratio of the Na zeolites increases.

Klier, K.; Herman, R.G.; Jirka, I.

1995-05-01

179

Minerals produced during cooling and hydrothermal alteration of ash flow tuff from Yellowstone drill hole Y-5  

USGS Publications Warehouse

A rhyolitic ash-flow tuff in a hydrothermally active area within the Yellowstone caldera was drilled in 1967, and cores were studied to determine the nature and distribution of primary and secondary mineral phases. The rocks have undergone a complex history of crystallization and hydrothermal alteration since their emplacement 600,000 years ago. During cooling from magmatic temperatures, the glassy groundmass underwent either devitrification to alkali feldspar + ??-cristobalite ?? tridymite or granophyric crystallization to alkali feldspar + quartz. Associated with the zones of granophyric crystallization are prismatic quartz crystals in cavities similar to those termed miarolitic in plutonic rocks. Vapor-phase alkali feldspar, tridymite, magnetite, and sporadic ??-cristobalite were deposited in cavities and in void spaces of pumice fragments. Subsequently, some of the vapor-phase alkali feldspar crystals were replaced by microcrystalline quartz, and the vapor-phase minerals were frosted by a coating of saccharoidal quartz. Hydrothermal minerals occur primarily as linings and fillings of cavities and fractures and as altered mafic phenocrysts. Chalcedony is the dominant mineral related to the present hydrothermal regime and occurs as microcrystalline material mixed with various amounts of hematite and goethite. The chalcedony displays intricate layering and was apparently deposited as opal from silica-rich water. Hematite and goethite also replace both mafic phenocrysts and vapor-phase magnetite. Other conspicuous hydrothermal minerals include montmorillonite, pyrite, mordenite, calcite, and fluorite. Clinoptilolite, erionite, illite, kaolinite, and manganese oxides are sporadic. The hydrothermal minerals show little correlation with temperature, but bladed calcite is restricted to a zone of boiling in the tuff and clearly was deposited when CO2 was lost during boiling. Fractures and breccias filled with chalcedony are common throughout Y-5 and may have been produced by rapid disruption of rock caused by sudden decrease of fluid pressure in fractures, most likely a result of fracturing during resurgent doming in this part of the Yellowstone caldera. The chalcedony probably was deposited as opal or ??-cristobalite from a pre-existing silica floc that moved rapidly into the fractures and breccias immediately after the sudden pressure drop. ?? 1978.

Keith, T. E. C.; Muffler, L. J. P.

1978-01-01

180

Adsorption of Amino Acids (Ala, Cys, His, Met) on Zeolites: Fourier Transform Infrared and Raman Spectroscopy Investigations  

NASA Astrophysics Data System (ADS)

Minerals adsorb more amino acids with charged R-groups than amino acids with uncharged R-groups. Thus, the peptides that form from the condensation of amino acids on the surface of minerals should be composed of amino acid residues that are more charged than uncharged. However, most of the amino acids (74%) in today's proteins have an uncharged R-group. One mechanism with which to solve this paradox is the use of organophilic minerals such as zeolites. Over the range of pH (pH 2.66-4.50) used in these experiments, the R-group of histidine (His) is positively charged and neutral for alanine (Ala), cysteine (Cys), and methionine (Met). In acidic hydrothermal environments, the pH could be even lower than those used in this study. For the pH range studied, the zeolites were negatively charged, and the overall charge of all amino acids was positive. The conditions used here approximate those of prebiotic Earth. The most important finding of this work is that the relative concentrations of each amino acid (X=His, Met, Cys) to alanine (X/Ala) are close to 1.00. This is an important result with regard to prebiotic chemistry because it could be a solution for the paradox stated above. Pore size did not affect the adsorption of Cys and Met on zeolites, and the Si/Al ratio did not affect the adsorption of Cys, His, and Met. ZSM-5 could be used for the purification of Cys from other amino acids (Student-Newman-Keuls test, p<0.05), and mordenite could be used for separation of amino acids from each other (Student-Newman-Keuls test, p<0.05). As shown by Fourier transform infrared (FT-IR) spectra, Ala interacts with zeolites through the group, and methionine-zeolite interactions involve the COO, , and CH3 groups. FT-IR spectra show that the interaction between the zeolites and His is weak. Cys showed higher adsorption on all zeolites; however, the hydrophobic Van der Waals interaction between zeolites and Cys is too weak to produce any structural changes in the Cys groups (amine, carboxylic, sulfhydryl, etc.); thus, the FT-IR and Raman spectra are the same as those of solid Cys.

Carneiro, Cristine E. A.; de Santana, Henrique; Casado, Clara; Coronas, Joaquin; Zaia, Dimas A. M.

2011-06-01

181

Carbon dioxide-krypton separation and radon removal from nuclear-fuel-reprocessing off-gas streams  

SciTech Connect

General Atomic Company (GA) is conducting pilot-plant-scale tests that simulate the treatment of radioactive and other noxious volatile and gaseous constituents of off-gas streams from nuclear reprocessing plants. This paper reports the results of engineering-scale tests performed on the CO/sub 2//krypton separation and radon holdup/decay subsystems of the GA integrated off-gas treatment system. Separation of CO/sub 2/ from krypton-containing gas streams is necessary to facilitate subsequent waste processing and krypton storage. Molecular sieve 5A achieved this separation in dissolver off-gas streams containing relatively low krypton and CO/sub 2/ concentrations and in krypton-rich product streams from processes such as the krypton absorption in liquid carbon dioxide (KALC) process. The CO/sub 2//krypton separation unit is a 30.5-cm-diameter x 1.8-m-long column containing molecular sieve 5A. The loading capacity for CO/sub 2/ was determined for gas mixtures containing 250 ppM to 2.2% CO/sub 2/ and 170 to 750 ppM krypton in either N/sub 2/ or air. Gas streams rich in CO/sub 2/ were diluted with N/sub 2/ to reduce the temperature rise from the heat of adsorption, which would otherwise affect loading capacity. The effluent CO/sub 2/ concentration prior to breakthrough was less than 10 ppM, and the adsorption capacity for krypton was negligible. Krypton was monitored on-line with a time-of-flight mass spectrometer and its concentration determined quantitatively by a method of continuous analysis, i.e., selected-ion monitoring. Radon-220 was treated by holdup and decay on a column of synthetic H-mordenite. The Rn-220 concentration was monitored on-line with flow-through diffused-junction alpha detectors. Single-channel analyzers were utilized to isolate the 6.287-MeV alpha energy band characteristic of Rn-220 decay from energy bands due to daughter products.

Hirsch, P.M.; Higuchi, K.Y.; Abraham, L.

1982-07-01

182

Geological, mineralogical and geochemical characteristics of zeolite deposits associated with borates in the Bigadiç, Emet and Kirka Neogene lacustrine basins, western Turkey  

NASA Astrophysics Data System (ADS)

The Bigadiç, Emet and Kirka lacustrine basins of western Turkey may be considered as Tibet-type graben structures that were developed during the Miocene within the Izmir-Ankara suture zone complex. The volcanic-sedimentary successions of these basins are made up of mudstone, carbonate (limestone and dolomite) and detrital rocks, and also of crystal or vitric tuffs about 135 to 200 m thick. The Degirmenli (Bigadiç), Emirler (Bigadiç) Köpenez (Emet) and Karaören (Kirka) tuffs constituting the zeolite deposits are situated beneath four borate deposits (colemanite, ulexite, borax). The most abundant diagenetic silicate minerals are K- and Ca-clinoptilolites in the zeolite deposits, and Li-rich trioctahedral smectites (stevensite, saponite and hectorite) and K-feldspar in the borate deposits. In the Degirmenli, Emirler, Köpenez and Karaören deposits, the following diagenetic facies were developed from rhyolitic glasses rich in K and poor in Na: (glass+smectite), (K-clinoptilolite+opal-CT), (Ca-clinoptilolite+K-feldspar±analcime± quartz) and (K-feldspar+analcime+quartz). K-feldspar which is also rarely associated with phillipsite (Karaören) and heulandite (Degirmenli and Karaören), succeeds clinoptilolite and precedes analcime in these diagenetic facies where dioctahedral smectites, opal-CT and quartz are the latest minerals. No diagenetic transformations exist between clinoptilolite, K-feldspar and analcime that were formed directly from glass. The lateral facies distributions resulted from the differences in salinity and pH of pore water trapped during deposition of the tuffs, but vertical distributions in vitric tuffs seem to have been controlled by the glass/liquid ratio of the reacting system and the permeability or diffusion rate of alkali elements. The Bigadiç, Emet and Kirka zeolite deposits which were formed in saline basins rich in Ca and Mg ions, show similar chemical changes, i.e. loss of alkalis and gain in alkaline-earth elements that have taken place during the diagenetic transformation of rhyolitic glasses to dioctahedral smectites or clinoptilolite. The absence of sodic zeolites such as mordenite, erionite, chabazite and silica-rich phillipsite is mainly due to the very high K/Na ratio of the starting materials rather than initial alkaline conditions or high Na content in lake waters.

Gündogdu, M. N.; Yalçin, H.; Temel, A.; Clauer, N.

1996-09-01

183

Structure-property relationship of metal-organic frameworks (MOFs) and physisorbed off-gas radionuclides.  

SciTech Connect

We report on the host-guest interactions between metal-organic frameworks (MOFs) with various profiles and highly polarizable molecules (iodine), with emphasis on identifying preferential sorption sites in these systems. Radioactive iodine 129I, along with other volatile radionuclides (3H, 14C, Xe and Kr), represents a relevant component in the off-gas resulted during nuclear fuel reprocessing. Due to its very long half-life, 15.7 x 106 years, and potential health risks in humans, its efficient capture and long-term storage is of great importance. The leading iodine capture technology to date is based on trapping iodine in silver-exchanged mordenite. Our interests are directed towards improving existent capturing technologies, along with developing novel materials and alternative waste forms. Herein we report the first study that systematically monitors iodine loading onto MOFs, an emerging new class of porous solid-state materials. In this context, MOFs are of particular interest as: (i) they serve as ideal high capacity storage media, (ii) they hold potential for the selective adsorption from complex streams, due to their high versatility and tunability. This work highlights studies on both newly developed in our lab, and known highly porous MOFs that all possess distinct characteristics (specific surface area, pore volume, pore size, and dimension of the window access to the pore). The materials were loaded to saturation, where elemental iodine was introduced from solution, as well as from vapor phase. Uptakes in the range of {approx}125-150 wt% I2 sorbed were achieved, indicating that these materials outperform all other solid adsorbents to date in terms of overall capacity. Additionally, the loaded materials can be efficiently encapsulated in stable waste forms, including as low temperature sintering glasses. Ongoing studies are focused on gathering qualitative information with respect to localizing the physisorbed iodine molecules within the frameworks: X-ray single-crystal analyses, in conjunction with high pressure differential pair distribution function (d-PDF) studies aimed to identify preferential sites in the pores, and improve MOFs robustness. Furthermore, durability studies on the iodine loaded MOFs and subsequent waste forms include thermal analyses, SEM/EDS elemental mapping, and leach-durability testing. We anticipate for this in-depth analysis to further aid the design of advanced materials, capable to address major hallmarks: safe capture, stability and durability over extended timeframes.

Nenoff, Tina Maria; Chupas, Peter J. (Argonne National Laboratory); Garino, Terry J.; Rodriguez, Mark Andrew; Chapman, Karena W. (Argonne National Laboratory); Sava, Dorina Florentina

2010-11-01

184

FINAL REPORT REGULATORY OFF GAS EMISSIONS TESTING ON THE DM1200 MELTER SYSTEM USING HLW AND LAW SIMULANTS VSL-05R5830-1 REV 0 10/31/05  

SciTech Connect

The operational requirements for the River Protection Project - Waste Treatment Plant (RPP-WTP) Low Activity Waste (LAW) and High Level Waste (HLW) melter systems, together with the feed constituents, impose a number of challenges to the off-gas treatment system. The system must be robust from the standpoints of operational reliability and minimization of maintenance. The system must effectively control and remove a wide range of solid particulate matter, acid mists and gases, and organic constituents (including those arising from products of incomplete combustion of sugar and organics in the feed) to concentration levels below those imposed by regulatory requirements. The baseline design for the RPP-WTP LAW primary off-gas system includes a submerged bed scrubber (SBS), a wet electrostatic precipitator (WESP), and a high efficiency particulate air (HEPA) filter. The secondary off-gas system includes a sulfur-impregnated activated carbon bed (AC-S), a thermal catalytic oxidizer (TCO), a single-stage selective catalytic reduction NOx treatment system (SCR), and a packed-bed caustic scrubber (PBS). The baseline design for the RPP-WTP HLW primary off-gas system includes an SBS, a WESP, a high efficiency mist eliminator (HEME), and a HEPA filter. The HLW secondary off-gas system includes a sulfur-impregnated activated carbon bed, a silver mordenite bed, a TCO, and a single-stage SCR. The one-third scale HLW DM1200 Pilot Melter installed at the Vitreous State Laboratory (VSL) was equipped with a prototypical off-gas train to meet the needs for testing and confirmation of the performance of the baseline off-gas system design. Various modifications have been made to the DM1200 system as the details of the WTP design have evolved, including the installation of a silver mordenite column and an AC-S column for testing on a slipstream of the off-gas flow; the installation of a full-flow AC-S bed for the present tests was completed prior to initiation of testing. The DM1200 system was reconfigured to enable testing of the baseline HLW or LAW off-gas trains to perform off-gas emissions testing with both LAW and HLW simulants in the present work. During 2002 and 2003, many of these off-gas components were tested individually and in an integrated manner with the DM1200 Pilot Melter. Data from these tests are being used to support engineering design confirmation and to provide data to support air permitting activities. In fiscal year 2004, the WTP Project was directed by the Office of River Protection (ORP) to comply with Environmental Protection Agency (EPA) Maximum Achievable Control Technology (MACT) requirements for organics. This requires that the combined melter and off-gas system have destruction and removal efficiency (DRE) of >99.99% for principal organic dangerous constituents (PODCs). In order to provide confidence that the melter and off-gas system are able to achieve the required DRE, testing has been directed with both LAW and HLW feeds. The tests included both 'normal' and 'challenge' WTP melter conditions in order to obtain data for the potential range of operating conditions for the WTP melters and off-gas components. The WTP Project, Washington State Department of Ecology, and ORP have agreed that naphthalene will be used for testing to represent semi-volatile organics and allyl alcohol will be used to represent volatile organics. Testing was also performed to determine emissions of halides, metals, products of incomplete combustion (PICs), dioxins, furans, coplanar PCBs, total hydrocarbons, and COX and NOX, as well as the particle size distribution (PSD) of particulate matter discharged at the end of the off-gas train. A description of the melter test requirements and analytical methods used is provided in the Test Plan for this work. Test Exceptions were subsequently issued which changed the TCO catalyst, added total organic emissions (TOE) to exhaust sampling schedule, and allowing modification of the test conditions in response to attainable plenum temperatures as well as temperature increases in the sulfur impr

KRUGER AA; MATLACK KS; GONG W; BARDAKCI T; D'ANGELO NA; BRANDYS M; KOT WK; PEGG IL

2011-12-29

185

Megabreccias, Early Lakes, and Duration of Resurgence Recorded in Valles Caldera, New Mexico  

NASA Astrophysics Data System (ADS)

New 1:24,000 scale geologic mapping combined with previous and ongoing geoscientific studies are revealing significant new findings on intracaldera stratigraphy and structure, initial development of intracaldera lakes, and the duration of resurgence within the ca. 1.25 Myr Valles caldera. The caldera is about 22 km in diameter and contains a resurgent dome that is a northeast-trending oval roughly11 x 9 km in dimension. Maximum resurgence (uplift) was more than 1000 m, during which the dome split into three principal segments herein named the Redondo Peak, Redondo Border, and Valle San Luis segments. These segments are separated from each other by long, narrow grabens herein called the Redondo Creek, Jaramillo Creek, and San Luis Creek grabens. Differential uplift accompanied by intense faulting has exposed large, rootless megabreccia (Mbx) blocks composed of precaldera rocks submerged in densely welded, intracaldera upper Bandelier Tuff. The largest Mbx blocks are roughly 0.2 to 2.0 km long and consist primarily of Abo Fm (Permian), Gallisteo Fm (?) (Eocene), Santa Fe Group (Miocene), Paliza Canyon Fm (late Miocene) and lower Bandelier Tuff (ca. 1.62 Ma). Deep geothermal wells drilled within the Redondo Creek graben from 1970 to 1983 penetrate as much as 2032 m of intracaldera Bandelier Tuff and post-Bandelier rocks before intersecting caldera floor rocks (average = 1646 m, n = 23 wells). Evidence that a lake developed within the caldera depression is preserved in finely laminated lacustrine beds and rhyolitic, hydromagmatic tuffs that overlie intracaldera Bandelier Tuff on the resurgent dome. The lacustrine rocks contain organic remains and the hydromagmatic tuffs contain accretionary lapilli. In some locations, lacustrine and hydromagmatic rocks are interbedded. Earliest post-caldera rhyolite lavas (Deer Canyon Member) display occasional pepperite and pillow textures. Many lavas contain significant amounts of fine, opalized flow breccia indicating interaction with water. Associated Deer Canyon tuffs are altered to variable mixtures of silica, smectite, clinoptilolite, mordenite and other phases. Slightly younger rhyolite lava flows (Redondo Creek Member) occasionally display upper flow surfaces in which cracks are filled with zeolitized mud. The combined geologic evidence indicates that the initial Valles lake was widespread and relatively shallow, containing waters with neutral to alkaline pH and relatively high K/Na ratios. 40Ar/39Ar dating of sanidine separates from Deer Canyon and Redondo Creek rhyolites yields ages that are statistically indistinguishable from the age of underlying upper Bandelier Tuff. These results indicate that the intracaldera lake developed immediately after the caldera formed and that the resurgent dome rose out of a lake. Most resurgence occurred after Redondo Creek rhyolite was erupted because the unit is intensely faulted and associated lacustrine beds are now as much as 500 m above the undeformed caldera moat. In contrast, rhyolite lavas of the first post-caldera moat complex, Cerro del Medio (about 1.22 Ma) show no apparent deformation or uplift due to resurgence. Within the errors of the various 40Ar/39Ar dates, the apparent duration of resurgence was no longer than about 50,000 years yielding a minimum resurgence rate of about 2 cm/y.

Goff, F.; Goff, C. J.; Phillips, E. H.; Kyle, P. R.; McIntosh, W. C.; Chipera, S.; Gardner, J. N.

2003-12-01

186

Geothermometry, geochronology, and mass transfer associated with hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy  

USGS Publications Warehouse

A rhyolitic hyaloclastite from Ponza Island, Italy, was hydrothermally altered, producing four distinct alteration zones based on X-ray diffraction mineralogy and field textures: (1) nonpervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the nonpervasive argillic zone, characterized by smectite and disordered opal-CT. The other three zones exhibit more complete alteration of the hyaloclastite. The propylitic zone is characterized by mixed-layer illite-smectite (I-S) with 10 to 85% I, mordenite, opal-C, and authigenic K-feldspar (akspar). The silicic zone is characterized by I-S with ???90% I, pure illite, quartz, akspar, and occasional albite. The sericitic zone consists primarily of I-S with ???66% I, pure illite, quartz, and minor akspar and pyrite. K/Ar dates of I-S indicate hydrothermal alteration occurred at 3.38 ?? 0.08 Ma. Oxygen isotope compositions of I-S systematically decrease from zones 1 to 4. In the argillic zone, smectite has ??18 O values of 21.7 to 22.0??? and I-S from the propylitic, silicic, and sericitic zones ranges from 14.5 to 16.3???, 12.5 to 14.0???, and 8.6 to 11.9???, respectively. ??18 O values for quartz from the silicic and sericitic zones range from 12.6 to 15.9???. By use of isotope fractionation equations and data from authigenic quartz-hosted primary fluid inclusions, alteration temperatures ranged from 50 to 65 ??C for the argillic zone, 85 to 125 ??C for the propylitic zone, 110 to 210 ??C for the silicic zone, and 145 to 225 ??C for the sericitic zone. Fluid inclusion data and calculated ??18 O water values indicate that hydrothermal fluids were seawater dominated. Mass-transfer calculations indicate that hydrothermal alteration proceeded in a relatively open chemical system and alteration in the sericitic zone involved the most extensive loss of chemical species, especially Si. Systematic gains in Mg occur in all alteration zones as a result of I-S clay mineral formation, and systematic losses of Na, Ca, and K occur in most zones. With the exception of Ca, calculations of mass transfer associated with hydrothermal alteration on Ponza agree with chemical fluxes observed in laboratory experiments involving hydrothermal reactions of rhyolite and seawater. The anomalous Ca loss at Ponza may be due to hydrothermal formation of anhydrite and later low-temperature dissolution. On the basis of Mg enrichments derived from circulating seawater, we estimate the following minimum water/rock ratios: 9, 3, 6, and 9 for the argillic, propylitic, silicic, and sericitic zones, respectively. Hydrothermal fluid pH for the propylitic and silicic zones was neutral to slightly basic and relatively acidic for the sericitic zone as a result of condensation of carbonic and perhaps other acids. Copyright ?? 2003 Elsevier Science Ltd.

Altaner, S. P.; Ylagan, R. F.; Savin, S. M.; Aronson, J. L.; Belkin, H. E.; Pozzuoli, A.

2003-01-01

187

Erionite and other fibrous zeolites in volcanic environments: the need for a risk assessment in Italy  

NASA Astrophysics Data System (ADS)

In many European countries in the '90s there was a significant increase in mortality linked to mesothelioma, a cancer of the lung, involving pleural, pericardial and peritoneal mesothelial cells, which unfortunately has no cure at present. Though most of these cases have been attributed to t asbestos, in Italy at least 17% of cases of mesothelioma is still not fully explained. In the years between 1990 and 2000, it was discovered that the inhalation of erionite fibers (a zeolite group mineral, that can be found in altered volcanic rocks) was the cause of a regional epidemic of mesothelioma in some villages of Cappadocia (Turkey). Erionite, in fact, was recently included in Class 1 (highly carcinogenic) by the World Health Organization, up to 800 times more carcinogenic than asbestos; on the other hand, little is known about the toxicity of other fibrous zeolites, commonly intergrown with erionite, such as offretite and mordenite. Erionite was reported in different regions of Italy; nevertheless, a systematic mapping of its distribution, the quantification of its presence in rocks and data about airborne fibers are still missing. We carried out first preliminary sampling in Veneto, in Tertiary volcanic rocks, mainly hydrothermally altered basalts. The first mineralogical investigations by means of XRPD, SEM-EDS and OM confirmed the presence of small amounts of erionite and abundant fibrous offretite, in vugs of basaltic rocks. Intergrowths and overgrowths with other fibrous minerals are quite common, and the morphological-chemical similarities among these zeolites pose a special analytical problem, with the need of combining different techniques. Our first findings, combined with the fact that zeolites are important industrial minerals, emphasize the need of a risk assessment in Italy and Europe, because there are no systematic studies on the distribution of erionite or similar fibrous zeolites in the environment. The knowledge of the epidemiology of mesothelioma linked to erionite in Italy is extremely scarce: INAIL, through its database of occupational diseases, can provide essential information for epidemiological research. An effective risk assessment in Italy will require coordinated actions from government agencies, local health authorities, Universities and research centers, in order to record the actual presence of fibrous zeolites, recognizing mineral species and quantifying their abundance in rock deposits. The different geological conditions through time of volcanic deposits will be compared with an updated "database" on the physical-chemical-geological conditions of formation of zeolites. In sites where the presence of fibrous zeolites has been validated by laboratory tests, we will proceed with accurate field surveys and sampling campaigns, in order to determine detailed geological-stratigraphic and structural features, and resolving precisely the thickness, areal extent and volume of lithostratigraphic units containing these minerals. These data will be entered into a GIS to produce a result that can be used immediately and in the long-period by research institutes, local authorities and regional agencies for environmental protection. In sites where the presence of hazardous fibrous minerals has been validated, we will plan airborne fibers sampling campaigns, and we will assess the extent of airborne dispersion produced by natural agents and by man activity. In the case that these sites host active mining or quarrying activities, we will quantify the airborne fibers contamination at workplaces and propose measures for environmental risk mitigation.

Cavallo, A.; Rimoldi, B.

2012-04-01

188

Final report on the safety assessment of aluminum silicate, calcium silicate, magnesium aluminum silicate, magnesium silicate, magnesium trisilicate, sodium magnesium silicate, zirconium silicate, attapulgite, bentonite, Fuller's earth, hectorite, kaolin, lithium magnesium silicate, lithium magnesium sodium silicate, montmorillonite, pyrophyllite, and zeolite.  

PubMed

This report reviews the safety of Aluminum, Calcium, Lithium Magnesium, Lithium Magnesium Sodium, Magnesium Aluminum, Magnesium, Sodium Magnesium, and Zirconium Silicates, Magnesium Trisilicate, Attapulgite, Bentonite, Fuller's Earth, Hectorite, Kaolin, Montmorillonite, Pyrophyllite, and Zeolite as used in cosmetic formulations. The common aspect of all these claylike ingredients is that they contain silicon, oxygen, and one or more metals. Many silicates occur naturally and are mined; yet others are produced synthetically. Typical cosmetic uses of silicates include abrasive, opacifying agent, viscosity-increasing agent, anticaking agent, emulsion stabilizer, binder, and suspending agent. Clay silicates (silicates containing water in their structure) primarily function as adsorbents, opacifiers, and viscosity-increasing agents. Pyrophyllite is also used as a colorant. The International Agency for Research on Cancer has ruled Attapulgite fibers >5 microm as possibly carcinogenic to humans, but fibers <5 microm were not classified as to their carcinogenicity to humans. Likewise, Clinoptilolite, Phillipsite, Mordenite, Nonfibrous Japanese Zeolite, and synthetic Zeolites were not classified as to their carcinogenicity to humans. These ingredients are not significantly toxic in oral acute or short-term oral or parenteral toxicity studies in animals. Inhalation toxicity, however, is readily demonstrated in animals. Particle size, fibrogenicity, concentration, and mineral composition had the greatest effect on toxicity. Larger particle size and longer and wider fibers cause more adverse effects. Magnesium Aluminum Silicate was a weak primary skin irritant in rabbits and had no cumulative skin irritation in guinea pigs. No gross effects were reported in any of these studies. Sodium Magnesium Silicate had no primary skin irritation in rabbits and had no cumulative skin irritation in guinea pigs. Hectorite was nonirritating to the skin of rabbits in a Draize primary skin irritation study. Magnesium Aluminum Silicate and Sodium Magnesium Silicate caused minimal eye irritation in a Draize eye irritation test. Bentonite caused severe iritis after injection into the anterior chamber of the eyes of rabbits and when injected intralamellarly, widespread corneal infiltrates and retrocorneal membranes were recorded. In a primary eye irritation study in rabbits, Hectorite was moderately irritating without washing and practically nonirritating to the eye with a washout. Rats tolerated a single dose of Zeolite A without any adverse reaction in the eye. Calcium Silicate had no discernible effect on nidation or on maternal or fetal survival in rabbits. Magnesium Aluminum Silicate had neither a teratogenic nor adverse effects on the mouse fetus. Female rats receiving a 20% Kaolin diet exhibited maternal anemia but no significant reduction in birth weight of the pups was recorded. Type A Zeolite produced no adverse effects on the dam, embryo, or fetus in either rats or rabbits at any dose level. Clinoptilolite had no effect on female rat reproductive performance. These ingredients were not genotoxic in the Ames bacterial test system. In primary hepatocyte cultures, the addition of Attapulgite had no significant unscheduled DNA synthesis. Attapulgite did cause significant increases in unscheduled DNA synthesis in rat pleural mesothelial cells, but no significant increase in sister chromosome exchanges were seen. Zeolite particles (<10 microm) produced statistically significant increase in the percentage of aberrant metaphases in human peripheral blood lymphocytes and cells collected by peritoneal lavage from exposed mice. Topical application of Magnesium Aluminum Silicate to human skin daily for 1 week produced no adverse effects. Occupational exposure to mineral dusts has been studied extensively. Fibrosis and pneumoconiosis have been documented in workers involved in the mining and processing of Aluminum Silicate, Calcium Silicate, Zirconium Silicate, Fuller's Earth, Kaolin, Montmorillonite, Pyrophyllite, and Zeolite. The Cosmetic Ingre

Elmore, Amy R

2003-01-01

189

Impact Materials of Takamatsu Crater in Japan  

NASA Astrophysics Data System (ADS)

Shocked quartz materials have been found in Japanese K.T boundary (Hokkaido) and mountains of middle main-islands of Japan, though there are few direct evidence of "natural circular structure" on the surface in Japan. However circular structure has been recently found as a buried crater(up to 150m deep) [1] which is ca. 4km in diameter with -10 mgal of Bouguer gravity anomaly from surrounding Rhyoke granitic region of the southern part of Takamatsu City, Kagawa Prefecture, northeast Shikoku, Japan [1,2,3]. Two boring cores of 300m deep near small mountains inside the crater could not reach the bottom of the crater so far. From model calculation of the negative gravity anomaly, the Takamatsu crater shows deep basin structure up to 1.4km. If the Takamatsu crater is considered to be only impact crater, it is difficult to discuss only surface materials on the crater. But anomalous minerals are found only around small volcanic intrusions inside the crater, which the mixed minerals are clearly different with those of other volcanic intrusions of the Yashima and Goshikidai outside the crater [1,2,3]. The small volcanic intrusions are not origin of large Takamatsu crater, because the small volcanic intrusions are found on whole areas of Kagawa Prefecture. Major different activity of the small intrusions inside the crater is to bring the brecciated materials of the interior (esp. crater sediments). The xenolith materials around only volcanic intrusion of andesite are divided into the following four major mineral materials:(a) round pebble fragments from the Rhyoke granitic basement (Sampling No.15), (b) rock fragments from intruded biotite andesites (Nos. 2,15), (c) impact-induced fragments of shocked Quartz grains (Nos. 2,3,6,15), diaplectic feldspars (Nos. 2,3,6,15), silica glasses (Nos. 2,15) and small Fe-Ni metallic grains (No.15), and (d) small sedimentary fragments of halite and mordenite, as listed in Table 1. Table I, showing the characterization of surface samples around small intrusions of the Takamatsu crater, appears here in the hard copy. The following anomalous mixed materials are considered to be impact-induced origin: 1) Fe-Ni grains: Black glassy rocks at Jissojiyama (No. 15) contain irregularly Fe-Ni grains of 10 to 100 micrometers in diameter. Chemical composition of the small Fe+Ni grains varies from ca. 18~90 atom. % mixed with the major granitic components. Atomic ratios of Fe/Ni are the same of kamacite as 3.4 to 68.7, but differ from those of awaruite (Fe/Ni<0.5) from the deep seated rock of the interior of the Earth [4]. The similar tiny Fe grains are found on the Wolf Creek and Ries impact craters. 2) Shocked quartz with high-density and shock lamellae: Anomalous quartz grains with undulatory anomalous extinction and shock lamellae are found at the Hiyama (Nos. 2,3,6 in whitish fine rocks) and Jissoiiyama (No. 15 in black glass) as brecciated xenolith from the interior of crater sediments. Typical shocked quartz grain shows with two sets of shock lamellae along pi (102) crystallographic planes [5]. The main X-ray diffraction peaks of each Miller plane show high Bragg angle and X-ray density (Delta rho=+0.9+/-0.3%) and lower values (ca.- 0.4%) of each plane-distance of all shock-generated Plane deformation features (PDFs). The structural data of high density are the same of shocked quartz grains in terrestrial impact craters [6,7]. 3) Diaplectic feldspars: Shock-generated diaplectic feldspars with compositions of albite plagioclases with undulatory extinction are observed with dark or partly dark (i.e. diaplectic) glassy materials under cross-polarized microscope (Nos. 2,3,6,15). Crushed plagioclases with circular or ellipsoidal shape are also found at Hiyama (No. 6) and Hiraike (No. ll). Diffuse and irregular textures of feldspar fragments are different with other localities outside the crater [2,3]. 4) G1asses of potassium feldspar compositions: Many glassy fragments with flow texture are observed from fine-grained sediments around Hiyama (Nos. 2,3,6), which have potassium feldspars compos

Miura, Y.; Okamoto, M.; Fukuchi, T.

1995-09-01

190

A thermodynamic and structural study of atomistic, nano and bulk systems  

NASA Astrophysics Data System (ADS)

Atomistic and nanocrystalline materials exhibit significantly different properties than bulk materials. This work aims to compare thermodynamic and structural properties of atomistic, nanocrystalline and bulk materials using high temperature oxide melt drop solution calorimetry, high energy synchrotron X-ray diffraction and computational techniques using molecular mechanics modelling. Oxidative drop solution calorimetry is being developed as a general method for sulfide thermochemistry. Enthalpies of formation (kJ/mol) from the elements (DeltaH°f) are determined for sphalerite (ZnS) (-206.53 +/- 4.03 kJ/mol), galena (PbS) (-98.12 +/- 4.37 kJ/mol), greenockite (hexagonal CdS) (-148.79 +/- 4.13 kJ/mol) and hawleyite (cubic CdS) (-147.65 +/- 4.28 kJ/mol). The enthalpy of formation of hawleyite was determined for the first time. Oxide melt drop solution calorimetry was also developed for selenides. Enthalpies of formation (kJ/mol) from the elements (DeltaH°f) are determined for zinc selenide (ZnSe) (-160.13 +/- 2.91 kJ/mol), lead selenide (PbSe) (-100.83 +/- 4.39 kJ/mol), and cadmium selenide (CdSe) (-138.99 +/- 8.70 kJ/mol). The values for CdSe and PbSe match published data, the DeltaH°f value for CdSe from direct calorimetry is reported for the first time, and a more reliable value for ZnSe is proposed as available data for ZnSe are quite scattered. High-temperature oxide melt solution calorimetry was used to determine the dehydration enthalpy and the formation enthalpy of cationic variants of zeolite beta (Li-BEA, Na-BEA, K-BEA, Rb-BEA and Cs-BEA) from the constituent oxides. The dehydration enthalpy per mole of water decreases in the order Li-BEA > Na-BEA >Cs-BEA > K-BEA >Rb-BEA. Molecular mechanics was used to investigate location of the alkali cations and bonding of water molecules in BEA zeolites. The somewhat smaller dehydration enthalpy of K-BEA can be attributed to weaker cation-water interaction, weaker cation-framework interaction, and absence of framework-water interaction. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25°C are 25.6 +/- 1.7 kJ/mol TO2 for the dehydrated zeolite and -8.45 +/- 0.94 kJ/mol TO2 for the fully hydrated zeolite; for Na-BEA they are -2.4 +/- 0.6 kJ/mol TO2 for the dehydrated and -17.8 +/- 1.0 kJ/mol TO2 for the fully hydrated zeolite. The integral dehydration enthalpy at 25°C is 33.2 +/- 1.8 kJ/mol H2O for Li-BEA and 16.5 +/- 1.1 kJ/mol H2O for Na-BEA. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents. This study presents an analysis of the role of structural water in stabilization of bulk synthetic akaganeite (beta-FeOOH) and compare the structural behavior of bulk and nano akaganeite. Rietveld refinements using synchrotron X-ray powder diffraction data are presented. Akaganeite is, indeed, monoclinic with the Cl atoms located at the center of the tunnels and filling only ˜2.8% of the tunnel sites (0,0,0) in this sample. Structural water and vacancies occupy the remaining tunnel sites. There is no evidence of ordering of water molecules in the tunnels. In nanophase akaganeite, the diffraction pattern shows a mixture of akaganeite and a goethite-like phase. The destruction of the tunnel structure, because of the large fraction of tunnels exposed at the surface of the small particles, leads to the formation of this goethite-like phase, possibly a surface reconstruction on the akaganeite particles. As the particle size increases, the formation of the tunnel structure is complete and the goethite-like phase disappears. The closely balanced energetics of akaganeite and goethite permit this complex crossover in stability, with goethite or goethite-like phases present at small and large, but not intermediate, particle size. The localization and arrangement of thionin blue (C12H 10N3S+) dye molecules in the zeolite mordenite frame

Deore, Suraj Waman