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1

The glmS ribozyme cofactor is a general acid-base catalyst.  

PubMed

The glmS ribozyme is the first natural self-cleaving ribozyme known to require a cofactor. The d-glucosamine-6-phosphate (GlcN6P) cofactor has been proposed to serve as a general acid, but its role in the catalytic mechanism has not been established conclusively. We surveyed GlcN6P-like molecules for their ability to support self-cleavage of the glmS ribozyme and found a strong correlation between the pH dependence of the cleavage reaction and the intrinsic acidity of the cofactors. For cofactors with low binding affinities, the contribution to rate enhancement was proportional to their intrinsic acidity. This linear free-energy relationship between cofactor efficiency and acid dissociation constants is consistent with a mechanism in which the cofactors participate directly in the reaction as general acid-base catalysts. A high value for the Brønsted coefficient (? ~ 0.7) indicates that a significant amount of proton transfer has already occurred in the transition state. The glmS ribozyme is the first self-cleaving RNA to use an exogenous acid-base catalyst. PMID:23113700

Viladoms, Júlia; Fedor, Martha J

2012-11-21

2

Arginine as a General Acid Catalyst in Serine Recombinase-mediated DNA Cleavage*  

PubMed Central

Members of the serine family of site-specific DNA recombinases use an unusual constellation of amino acids to catalyze the formation and resolution of a covalent protein-DNA intermediate. A recent high resolution structure of the catalytic domain of Sin, a particularly well characterized family member, provided a detailed view of the catalytic site. To determine how the enzyme might protonate and stabilize the 3?O leaving group in the strand cleavage reaction, we examined how replacing this oxygen with a sulfur affected the cleavage rate by WT and mutant enzymes. To facilitate direct comparison of the cleavage rates, key experiments used suicide substrates that prevented religation after cleavage. The catalytic defect associated with mutation of one of six highly conserved arginine residues, Arg-69 in Sin, was partially rescued by a 3? phosphorothiolate substrate. We conclude that Arg-69 has an important role in stabilizing the 3?O leaving group and is the prime candidate for the general acid that protonates the 3?O, in good agreement with the position it occupies in the high resolution structure of the active site of Sin. PMID:23970547

Keenholtz, Ross A.; Mouw, Kent W.; Boocock, Martin R.; Li, Nan-Sheng; Piccirilli, Joseph A.; Rice, Phoebe A.

2013-01-01

3

Arginine as a general acid catalyst in serine recombinase-mediated DNA cleavage.  

PubMed

Members of the serine family of site-specific DNA recombinases use an unusual constellation of amino acids to catalyze the formation and resolution of a covalent protein-DNA intermediate. A recent high resolution structure of the catalytic domain of Sin, a particularly well characterized family member, provided a detailed view of the catalytic site. To determine how the enzyme might protonate and stabilize the 3'O leaving group in the strand cleavage reaction, we examined how replacing this oxygen with a sulfur affected the cleavage rate by WT and mutant enzymes. To facilitate direct comparison of the cleavage rates, key experiments used suicide substrates that prevented religation after cleavage. The catalytic defect associated with mutation of one of six highly conserved arginine residues, Arg-69 in Sin, was partially rescued by a 3' phosphorothiolate substrate. We conclude that Arg-69 has an important role in stabilizing the 3'O leaving group and is the prime candidate for the general acid that protonates the 3'O, in good agreement with the position it occupies in the high resolution structure of the active site of Sin. PMID:23970547

Keenholtz, Ross A; Mouw, Kent W; Boocock, Martin R; Li, Nan-Sheng; Piccirilli, Joseph A; Rice, Phoebe A

2013-10-01

4

Polypyrrole based strong acid catalyst for acetalization  

NASA Astrophysics Data System (ADS)

Novel polypyrrole based acid catalyst has been synthesized through the neutralization reaction of polypyrrole and sulfuric acid. The polypyrrole based acid owned the acidity as high as 6.0 mmol/g, which was much higher than that of the traditional solid acids such as Nafion and Amberlyst-15 (0.8 mmol/g). The catalytic activities of the novel solid acid were investigated through the acetalization. The results showed that the novel solid acid held high activities for the reactions. Furthermore, the recycled activities of the catalyst indicated that the solid acid owned high stability during the catalytic process and little acid sites dropped from polypyrrole. The high acidity and stability made the novel polypyrrole based acid hold great potential for the green chemical processes.

Liang, Xuezheng; Cheng, Yuxiao; Qi, Chenze

2011-09-01

5

Calcium-based Lewis acid catalysts.  

PubMed

Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf?)?, Ca(OTf)?, CaF? and Ca[OCH(CF?)?]? have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare-earth metals or strong Brønsted acids. PMID:23712417

Begouin, Jeanne-Marie; Niggemann, Meike

2013-06-17

6

Biochar based solid acid catalyst for biodiesel production  

Microsoft Academic Search

A promising catalyst based on a biomass pyrolysis by-product, biochar, has been developed for the production of biodiesel. Two carbon-based solid acid catalysts were prepared by sulfonating pyrolysis char with concentrated or fuming sulfuric acids. Prepared catalysts were studied for their ability to catalyze transesterification of vegetable oils and esterification of free fatty acids. The catalyst sulfonated with the concentrated

Amir Mehdi Dehkhoda; Alex H. West; Naoko Ellis

2010-01-01

7

Dehydration of glycerol over niobia-supported silicotungstic acid catalysts.  

PubMed

Liquid-phase dehydration of glycerol to acrolein over nanosized niobia-supported silicotungstic acid catalysts was performed to investigate the effect of the silicotungstic acid loading on the catalytic performance of the catalysts. The catalysts were prepared by following an impregnation method with different HSiW loadings in the range of 10-50 wt%. The prepared catalysts were characterized by N2 physisorption, XRD, FT-IR, TPD of ammonia, and TGA. Dehydration of glycerol was conducted in an autoclave reactor under the conditions of controlled reaction temperatures under corresponding pressure. Increasing HSiW loading rapidly increased the acidity of HSiW/Nb205 catalyst and rate of glycerol conversion, but acrolein selectivity decreased due to enhanced deactivation of the catalyst by carbon deposit. Consequently, it was confirmed that catalytic activity for the dehydration of glycerol to acrolein was dependant on the acidity of catalyst and can be controlled by HSiW loading. PMID:23646735

Lee, Young Yi; Ok, Hye Jeong; Moon, Dong Ju; Kim, Jong Ho; Park, Nam Cook; Kim, Young Chul

2013-01-01

8

Acid monolayer functionalized iron oxide nanoparticle catalysts  

NASA Astrophysics Data System (ADS)

Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80° and starch at 130°, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide nanoparticle syntheses and functionalizations for biomedical and catalytic applications, affecting understandings of surface charge and other material properties.

Ikenberry, Myles

9

Alumino-rhenium-sulphide catalysts in hydrogenation of carboxylic acids  

SciTech Connect

Alumino-rhenium sulfide catalysts containing 1.5, 5 and 8% rhenium are active in hydrogenation of mono-, dicarboxylic acids (isobutyric, valeric, pelargonic and succinic) and a fraction of synthetic fatty acids to corresponding alcohols at 210 to 270/sup 0/C and a partial pressure of hydrogen of 25 MPa. These catalysts appear to be more selective and are more stable than other well-known oxide catalysts. 2 tables.

Ryashentseva, M.A.; Minachev, Kh.M.; Yunusov, M.P.; Serodzhev, A.T.

1982-01-01

10

Mesoporous Silica Supported Solid Acid Catalysts  

SciTech Connect

In this brief proceedings paper, we summarize the results of recent studies of the preparation and characterization of mesoporous silica supported tungstophosphoric acid (TPA/MS) and Cs-substituted tungstophosphoric acid salt (Cs-TPA/MS). In particular, we demonstrate that we have synthesized MS-supported Cs-substituted catalysts having significantly improved dispersion of the active clusters compared to materials described previously in the literature. Transmission electron micrographs and the activity results for a model reaction, the alkylation of 1,3,5-trimethylbenzene by cyclohexene are presented as evidence for the enhanced dispersion and performance. In addition, we demonstrate improvements in the physical and thermal stability of these materials with Cs substitution using various characterization techniques. Finally, we also briefly describe the characterization and catalytic activity of TPA/MS materials, providing evidence for shape selectivity that is likely imparted by the structure of the MS support. The promising results with TPA/MS and Cs-TPA/MS catalysis indicate that they have potential applications in a variety of acid-catalyzed organic reactions involving large-sized reacting, intermediate, and/or product molecules with desired shape selectivity to products and/or intermediates.

Choi, Saemin (ASSOC WESTERN UNIVERSITY); Wang, Yong (BATTELLE (PACIFIC NW LAB)); Nie, Zimin (BATTELLE (PACIFIC NW LAB)); Khmbapati, D (N/A); Liu, Jun (BATTELLE (PACIFIC NW LAB)); Peden, Charles HF (BATTELLE (PACIFIC NW LAB)); A. Corma, F.Melo, S. Mendioroz et al

2000-01-01

11

A microalgae residue based carbon solid acid catalyst for biodiesel production.  

PubMed

Biodiesel production from microalgae is recognized as one of the best solutions to deal with the energy crisis issues. However, after the oil extraction from the microalgae, the microalgae residue was generally discarded or burned. Here a novel carbon-based solid acid catalyst derived from microalgae residue by in situ hydrothermal partially carbonization were synthesized. The obtained catalyst was characterized and subjected to both the esterification of oleic acid and transesterification of triglyceride to produce biodiesel. The catalyst showed high catalytic activity and can be regenerated while its activity can be well maintained after five cycles. PMID:23953130

Fu, Xiaobo; Li, Dianhong; Chen, Jie; Zhang, Yuanming; Huang, Weiya; Zhu, Yi; Yang, Jun; Zhang, Chengwu

2013-10-01

12

EPA'S CATALYST RESEARCH PROGRAM: ENVIRONMENTAL IMPACT OF SULFURIC ACID EMISSIONS  

EPA Science Inventory

A sulfuric acid review conference sponsored by EPA's automotive Catalyst Research Program was held recently at Hendersonville, NC, for researchers whose work is funded by EPA. Emissions characterization research indicated that in-use catalyst-equipped vehicles emit low levels of ...

13

Cyclobutane amino acids and peptidomimetics, parallel catalyst screening for aziridination  

E-print Network

This thesis describes two projects: (i) syntheses and conformational studies of cyclobutane amino acids and peptidomimetics; and, (ii) parallel screening of catalysts for asymmetric aziridination. Syntheses and conformational studies of nonnatural...

Li, Shih-ming

2012-06-07

14

A novel Brønsted acid catalyst for Friedel–Crafts acylation  

Microsoft Academic Search

Bis(trifluoroalkylsulfonylimino)trifluoromethanesulfonic acid has demonstrated remarkable catalytic ability in the electrophilic acylation of aromatic substrates. Various perfluoroalkyl substituted aroyl chlorides are employed in Friedel–Crafts acylation typically using 1mol% of catalyst.

Anna G. Posternak; Romute Yu. Garlyauskayte; Lev M. Yagupolskii

2009-01-01

15

Method for producing iron-based acid catalysts  

SciTech Connect

A method for preparing an acid catalyst with a long shelf-life is described. Crystalline iron oxides are doped with lattice compatible metals which are heated with halogen compounds at elevated temperatures.

Farcasiu, M.; Kathrein, H.; Kaufman, P.B.; Diehl, J.R.

1998-04-01

16

Solid acid catalysts: Stain and shine  

NASA Astrophysics Data System (ADS)

Catalyst particles for fluid catalytic cracking are vital for the oil-refinery industry, but their activity is hard to diagnose because of their inter- and intra-particle structural inhomogeneity. With fluorescence confocal microscopy and selective staining, one can now pinpoint the catalytic activity within single catalyst particles from an industrial reactor.

Chen, Peng

2011-11-01

17

Staining of fluid-catalytic-cracking catalysts: localising Brønsted acidity within a single catalyst particle.  

PubMed

A time-resolved in situ micro-spectroscopic approach has been used to investigate the Brønsted acidic properties of fluid-catalytic-cracking (FCC) catalysts at the single particle level by applying the acid-catalysed styrene oligomerisation probe reaction. The reactivity of individual FCC components (zeolite, clay, alumina and silica) was monitored by UV/Vis micro-spectroscopy and showed that only clay and zeolites (Y and ZSM-5) contain Brønsted acid sites that are strong enough to catalyse the conversion of 4-fluorostyrene into carbocationic species. By applying the same approach to complete FCC catalyst particles, it has been found that the fingerprint of the zeolitic UV/Vis spectra is clearly recognisable. This almost exclusive zeolitic activity is confirmed by the fact that hardly any reactivity is observed for FCC particles that contain no zeolite. Confocal fluorescence microscopy images of FCC catalyst particles reveal inhomogeneously distributed micron-sized zeolite domains with a highly fluorescent signal upon reaction. By examining laboratory deactivated FCC catalyst particles in a statistical approach, a clear trend of decreasing fluorescence intensity, and thus Brønsted acidity, of the zeolite domains is observed with increasing severity of the deactivation method. By comparing the average fluorescence intensities obtained with two styrenes that differ in reactivity, it has been found that the Brønsted acid site strength within FCC catalyst particles containing ZSM-5 is more uniform than within those containing zeolite Y, as confirmed with temperature-programmed desorption of ammonia. PMID:22161809

Buurmans, Inge L C; Ruiz-Martínez, Javier; van Leeuwen, Sanne L; van der Beek, David; Bergwerff, Jaap A; Knowles, William V; Vogt, Eelco T C; Weckhuysen, Bert M

2012-01-23

18

Lewis acid-assisted formic acid dehydrogenation using a pincer-supported iron catalyst.  

PubMed

Formic acid (FA) is an attractive compound for H2 storage. Currently, the most active catalysts for FA dehydrogenation use precious metals. Here, we report a homogeneous iron catalyst that, when used with a Lewis acid (LA) co-catalyst, gives approximately 1,000,000 turnovers for FA dehydrogenation. To date, this is the highest turnover number reported for a first-row transition metal catalyst. Preliminary studies suggest that the LA assists in the decarboxylation of a key iron formate intermediate and can also be used to enhance the reverse process of CO2 hydrogenation. PMID:24999607

Bielinski, Elizabeth A; Lagaditis, Paraskevi O; Zhang, Yuanyuan; Mercado, Brandon Q; Würtele, Christian; Bernskoetter, Wesley H; Hazari, Nilay; Schneider, Sven

2014-07-23

19

Organometallic catalysts for primary phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

A continuing effort by the U.S. Department of Energy to improve the competitiveness of the phosphoric acid fuel cell by improving cell performance and/or reducing cell cost is discussed. Cathode improvement, both in performance and cost, available through the use of a class of organometallic cathode catalysts, the tetraazaannulenes (TAAs), was investigated. A new mixed catalyst was identified which provides improved cathode performance without the need for the use of a noble metal. This mixed catalyst was tested under load for 1000 hr. in full cell at 160 to 200 C in phosphoric acid H3PO4, and was shown to provide stable performance. The mixed catalyst contains an organometallic to catalyze electroreduction of oxygen to hydrogen peroxide and a metal to catalyze further electroreduction of the hydrogen peroxide to water. Cathodes containing an exemplar mixed catalyst (e.g., Co bisphenyl TAA/Mn) operate at approximately 650 mV vs DHE in 160 C, 85% H3PO4 with oxygen as reactant. In developing this mixed catalyst, a broad spectrum of TAAs were prepared, tested in half-cell and in a rotating ring-disk electrode system. TAAs found to facilitate the production of hydrogen peroxide in electroreduction were shown to be preferred TAAs for use in the mixed catalyst. Manganese (Mn) was identified as a preferred metal because it is capable of catalyzing hydrogen peroxide electroreduction, is lower in cost and is of less strategic importance than platinum, the cathode catalyst normally used in the fuel cell.

Walsh, Fraser

1987-01-01

20

Hydrolysis of oligosaccharides over solid acid catalysts: a review.  

PubMed

Mild fractionation/pretreatment processes are becoming the most preferred choices for biomass processing within the biorefinery framework. To further explore their advantages, new developments are needed, especially to increase the extent of the hydrolysis of poly- and oligosaccharides. A possible way forward is the use of solid acid catalysts that may overcome many current drawbacks of other common methods. In this Review, the advantages and limitations of the use of heterogeneous catalysis for the main groups of solid acid catalysts (zeolites, resins, carbon materials, clays, silicas, and other oxides) and their relation to the hydrolysis of model soluble disaccharides and soluble poly- and oligosaccharides are presented and discussed. Special attention is given to the hydrolysis of hemicelluloses and hemicellulose-derived saccharides into monosaccharides, the impact on process performance of potential catalyst poisons originating from biomass and biomass hydrolysates (e.g., proteins, mineral ions, etc.). The data clearly point out the need for studying hemicelluloses in natura rather than in model compound solutions that do not retain the relevant factors influencing process performance. Furthermore, the desirable traits that solid acid catalysts must possess for the efficient hemicellulose hydrolysis are also presented and discussed with regard to the design of new catalysts. PMID:24616436

Vilcocq, Léa; Castilho, Paula C; Carvalheiro, Florbela; Duarte, Luís C

2014-04-01

21

A functionally stable manganese oxide oxygen evolution catalyst in acid.  

PubMed

First-row metals have been a target for the development of oxygen evolution reaction (OER) catalysts because they comprise noncritical elements. We now report a comprehensive electrochemical characterization of manganese oxide (MnOx) over a wide pH range, and establish MnOx as a functionally stable OER catalyst owing to self-healing, is derived from MnOx redeposition that offsets catalyst dissolution during turnover. To study this process in detail, the oxygen evolution mechanism of MnOx was investigated electrokinetically over a pH range spanning acidic, neutral, and alkaline conditions. In the alkaline pH regime, a ?60 mV/decade Tafel slope and inverse first-order dependence on proton concentration were observed, whereas the OER acidic pH regime exhibited a quasi-infinite Tafel slope and zeroth-order dependence on proton concentration. The results reflect two competing mechanisms: a one-electron one-proton PCET pathway that is dominant under alkaline conditions and a Mn(3+) disproportionation process, which predominates under acidic conditions. Reconciling the rate laws of these two OER pathways with that of MnOx electrodeposition elucidates the self-healing characteristics of these catalyst films. The intersection of the kinetic profile of deposition and that of water oxidation as a function of pH defines the region of kinetic stability for MnOx and importantly establishes that a non-noble metal oxide OER catalyst may be operated in acid by exploiting a self-healing process. PMID:24669981

Huynh, Michael; Bediako, D Kwabena; Nocera, Daniel G

2014-04-23

22

Role of solid acid catalysts in bio diesel production.  

PubMed

Biodiesel is gaining importance as an alternate source of attractive fuel because of depleting fossil fuel resources. It is produced by trans-esterification, in which oil or fat reacts with a monohydric alcohol in presence of a catalyst. In the present work, trans-esterification of sunflower oil with methanol is carried out by using zirconia supported isopoly and heteropoly tungstates (HPAs) as catalysts. Effects of reaction parameters, such as catalyst types and its concentration, molar ratio of sunflower oil to methanol, reaction temperature and time, have been optimized to get higher conversion of sunflower oil and the product distribution of fatty acid methyl esters (FAME) in the trans-esterfication reaction. PMID:21117436

Shivayogimath, C B; Sunita, G; Manoj Kumar, B

2009-07-01

23

Phase transitions in a bed of vanadium catalyst for sulfuric acid production: experiment and modeling  

Microsoft Academic Search

Sulfur dioxide oxidation on vanadium catalysts in sulfuric acid production may cause phase transitions in the catalyst active component. These phase transitions involve crystallization of vanadium(IV), and may influence catalyst activity. In the present study, we show that reaction mixture flow through a fixed catalyst bed is accompanied by the moving front of crystal phase, which decreases SO2 conversion at

B. S. Bal’zhinimaev; N. P. Belyaeva; S. I. Reshetnikov; E. S. Yudina; A. A. Ivanov

2001-01-01

24

[Experimental and kinetic modeling of acid/base and redox reactions over oxide catalysts  

SciTech Connect

The research has involved the characterization of catalyst acidity, [sup 2]D NMR studies of Bronsted acid sites, and kinetic, calorimetric, and spectroscopic studies of methylamine synthesis and related reactions over acid catalysts. Approach of this work was to explore quantitative correlations between factors that control the generation, type, strength, and catalytic properties of acid sites on zeolite catalysts. Microcalorimetry, thermogravimetric analysis, IR spectroscopy, and NMR spectroscopy have provided information about the nature and strength of acid sites in zeolites. This was vital in understanding the catalytic cycles involved in methylamine synthesis and related reactions over zeolite catalysts.

Not Available

1993-01-01

25

Matrix acidity determination: A bench scale method for predicting resid cracking of FCC catalysts  

SciTech Connect

Novel methods for determination of matrix acidity of cracking catalysts are discussed. Virgin matrix acidity is determined after complete destruction of the zeolite phase by acid treating the catalyst at pH 2. Properties of acid-treated catalyst closely approximate those of pure matrix. However, the virgin matrix acidity does not correlate with resid cracking performance of the catalyst under commercial or pilot plant conditions. A second method has been developed that facilitates the measurement of matrix acidity on a laboratory deactivated sample with properties similar to that in the commercial cracking unit. The approach is based on total destruction of the zeolite by steaming at 870 C for 5 h. Acidity of the steamed catalyst closely resembles that of steamed pure matrix and has a good correlation with the resid cracking activity in the pilot plant testing. Preservation of matrix acid sites during hydrothermal deactivation was shown to be an important requirement for achieving high resid cracking activity.

Alerasool, S.; Doolin, P.K.; Hoffman, J.F. (Ashland Petroleum Co., KY (United States). Research and Development Dept.)

1995-02-01

26

Metal extraction from spent sulfuric acid catalyst through alkaline and acidic leaching  

Microsoft Academic Search

Spent catalyst from manufacture of sulfuric acid production (main elemental composition: 3.5% V, 0.63% Ni, 7.9% Fe and 9.64% Si) can be used as a secondary source of vanadium and nickel. Extraction of these metals was studied using two different leaching systems (alkaline and acidic). Statistical design of the experiments and ANOVA (analysis of variance) were performed in order to

A. Ognyanova; A. T. Ozturk; I. De Michelis; F. Ferella; G. Taglieri; A. Akcil; F. Vegliò

2009-01-01

27

Polymerization of Fatty Acid Methyl Ester Using Acidic Ionic Liquid as Catalyst  

Microsoft Academic Search

The polymerization of fatty acid methyl ester was investigated using biodiesel as the feed in the presence of a Brönsted-Lewis acidic ionic liquid (IL). A synergetic effect of Brönsted and Lewis acid sites enhanced the catalytic performance of the IL. 1-(3-Sulfonic acid)-propyl-3-methylimidazole chlorozincinate ([HO3S-(CH2)3-mim]Cl-ZnCl2, molar fraction of ZnCl2 was 0.67) was an efficient catalyst for the polymerization. The effects of

Shiwei LIU; Lu LI; Shitao YU; Congxia XIE; Fusheng LIU; Zhanqian SONG

2010-01-01

28

Wet oxidation of acid brown dye by hydrogen peroxide using heterogeneous catalyst Mn-salen-Y zeolite: A potential catalyst  

Microsoft Academic Search

Catalytic wet hydrogen peroxide oxidation of acid dye has been explored in this study. Manganese(III) complex of N,N?-ethylene bis(salicylidene-aminato) (salenH2) has been encapsulated in super cages of zeolite-Y by flexible ligand method. The catalyst has been characterized by FT-IR, XRD, TG\\/DTA and nitrogen adsorption studies. The effects of various parameters such as pH, catalyst and hydrogen peroxide concentration on the

Rathinam Aravindhan; Nishtar Nishad Fathima; Jonnalagadda Raghava Rao; Balachandran Unni Nair

2006-01-01

29

Sulfamic Acid as a Green, Efficient, Recyclable and Reusable Catalyst for Direct Addition of Aliphatic Acid with Cyclic Olefins  

Microsoft Academic Search

Sulfamic acid has been used as a catalyst for esterification of cyclic olefins with aliphatic acids, and good olefins conversion as well as excellent esters selectivity was obtained. The catalyst could be recycled easily by filtration and directly reused in the next run with satisfactory results.

Bo Wang; Yanlong Gu; Liming Yang; Jishuan Suo; Okamoto Kenichi

2004-01-01

30

Acid properties of silica-alumina catalysts and catalytic degradation of polyethylene  

Microsoft Academic Search

A relationship between the acid strengths and amounts of silica-alumina catalysts and the compositions of products formed by the catalytic degradation of polyethylene at 673 K was studied. The acid strengths and amounts were varied with SiOâ\\/AlâOâ weight ratio in the catalysts. Although the resulting products and amounts were varied with SiOâ\\/AlâOâ weight ratio in the catalysts. Although the resulting

Hironobu Ohkita; Ryuji Nishiyama; Yoshihisa Tochihara; Takanori Mizushima; Noriyoshi Kakuta; Yoshio Morioka; Akifumi Ueno; Yukihiko Namiki; Susumu Tanifuji; Hiroshi Katoh; Hideo Sunazuka; Reikichi Nakayama; Takashi Kuroyanagi

1993-01-01

31

Acidic and basic surface sites of zirconia-based biomass gasification gas clean-up catalysts  

Microsoft Academic Search

The surface structures of ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 catalysts were studied in relation to their basicity and acidity, and the relationship between surface structure and gasification gas clean-up activity was evaluated. The physical properties of the catalysts were characterized by BET, XRD and Raman spectroscopy. The basicity and acidity of the catalysts were measured by CO2-TPD and NH3-TPD, respectively. The

Tiia Viinikainen; Hanne Rönkkönen; Heather Bradshaw; Hazel Stephenson; Sanna Airaksinen; Matti Reinikainen; Pekka Simell; Outi Krause

2009-01-01

32

Reaction of 5-ethylidene-2-norbomene with formic acid: cation exchange resins as catalysts  

Microsoft Academic Search

The esterification of formic acid with ethylidene norbornene (ENB), i.e. 5-ethylidene bicyclo[2.2.1]hept 2-ene was carried out with and without cation exchange resins as catalysts. The effect of various parameters e.g. speed of agitation, catalyst loading, mole ratio of the reactants, temperature, concentration of formic acid in aqueous solutions were studied to optimise the reaction conditions; the reusability of catalysts was

Basudeb Saha

1998-01-01

33

Solid acids and their use as environmentally friendly catalysts in organic synthesis  

Microsoft Academic Search

Tightening environmental legislation is driving the fine and speciality chemicals industries to consider alternative processes that avoid the use of conventional mineral acids. The use of heterogeneous catalysts in these processes would vastly simplify catalyst removal, minimizing the amount of waste formed. However, diffusion limitation of liquids within porous solids dictates that effective solid acids for liquid-phase reactions require the

Karen Wilson; James H. Clark

2000-01-01

34

Manipulating catalytic pathways: deoxygenation of palmitic acid on multifunctional catalysts.  

PubMed

The mechanism of the catalytic reduction of palmitic acid to n-pentadecane at 260 °C in the presence of hydrogen over catalysts combining multiple functions has been explored. The reaction involves rate-determining reduction of the carboxylic group of palmitic acid to give hexadecanal, which is catalyzed either solely by Ni or synergistically by Ni and the ZrO2 support. The latter route involves adsorption of the carboxylic acid group at an oxygen vacancy of ZrO2 and abstraction of the ?-H with elimination of O to produce the ketene, which is in turn hydrogenated to the aldehyde over Ni sites. The aldehyde is subsequently decarbonylated to n-pentadecane on Ni. The rate of deoxygenation of palmitic acid is higher on Ni/ZrO2 than that on Ni/SiO2 or Ni/Al2O3, but is slower than that on H-zeolite-supported Ni. As the partial pressure of H2 is decreased, the overall deoxygenation rate decreases. In the absence of H2, ketonization catalyzed by ZrO2 is the dominant reaction. Pd/C favors direct decarboxylation (-CO2), while Pt/C and Raney Ni catalyze the direct decarbonylation pathway (-CO). The rate of deoxygenation of palmitic acid (in units of mmol moltotal metal(-1) h(-1)) decreases in the sequence r(Pt black) ?r(Pd black) >r(Raney Ni) in the absence of H2 . In situ IR spectroscopy unequivocally shows the presence of adsorbed ketene (C=C=O) on the surface of ZrO2 during the reaction with palmitic acid at 260 °C in the presence or absence of H2. PMID:23519964

Peng, Baoxiang; Zhao, Chen; Kasakov, Stanislav; Foraita, Sebastian; Lercher, Johannes A

2013-04-01

35

A general and efficient copper catalyst for the double carbonylation reaction.  

PubMed

The use of (NHC)CuI complex in combination with a N-heterocyclic carbene precursor as catalyst for the double carbonylation of aryl Iodides and secondary amines solves the problem of using the precious metal Pd and phosphine ligands. The new protocol requires a nonprecious metal catalyst and has greater generality than those previously reported. PMID:19220013

Liu, Jianming; Zhang, Rongzhao; Wang, Shoufeng; Sun, Wei; Xia, Chungu

2009-03-19

36

Dimerization of fatty acid methyl ester using Brönsted–Lewis acidic ionic liquid as catalyst  

Microsoft Academic Search

The dimerization of fatty acid methyl ester was investigated using Brönsted–Lewis acidic ionic liquids (ILs) as catalysts. It is found that IL (3-sulfonic acid)-propyl-triethylammonium chlorozincinate [HO3S–(CH2)3–NEt3]Cl–ZnCl2 (x=0.64, x: molar fraction of ZnCl2, x=moles of ZnCl2\\/(moles of ZnCl2+moles of ammonium salt) was of good catalytic performance. Under the optimum conditions m(biodiesel):m(IL) 15:1, biodiesel 15g, reaction temperature 240°C, and reaction time 5h,

Shiwei Liu; Hongxia Zhou; Shitao Yu; Congxia Xie; Fusheng Liu; Zhanqian Song

2011-01-01

37

Vapor phase nitration of benzene over solid acid catalysts IV. Nitration with nitric acid (3); supported sulfuric acid catalyst with co-feeding of a trace amount of sulfuric acid  

Microsoft Academic Search

In the vapor phase nitration of benzene with diluted nitric acid, we have succeeded in keeping a high nitration activity of the supported sulfuric acid catalyst for more than 2 months by co-feeding a trace amount of sulfuric acid (H2SO4\\/HNO3=1\\/5000 (wt. ratio)). The results after 60 days on-stream over 10wt.%–H2SO4\\/SiO2 catalyst are as follows: yield of nitrobenzene (NB), 93% based

H Sato; K Nagai; H Yoshioka; Y Nagaoka

1999-01-01

38

Efficient solid acid catalyst containing Lewis and Brønsted Acid sites for the production of furfurals.  

PubMed

Self-assembled nanoparticulates of porous sulfonated carbonaceous TiO2 material that contain Brønsted and Lewis acidic sites were prepared by a one-pot synthesis method. The material was characterized by XRD, FTIR spectroscopy, NH3 temperature-programmed desorption, pyridine FTIR spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, N2 -sorption, atomic absorbance spectroscopy, and inductively coupled plasma optical emission spectroscopy. The carbonaceous heterogeneous catalyst (Glu-TsOH-Ti) with a Brønsted-to-Lewis acid density ratio of 1.2 and more accessible acid sites was effective to produce 5-hydroxymethylfurfural and furfural from biomass-derived mono- and disaccharides and xylose in a biphasic solvent that comprised water and biorenewable methyltetrahydrofuran. The catalyst was recycled in four consecutive cycles with a total loss of only 3?% activity. Thus, Glu-TsOH-Ti, which contains isomerization and dehydration catalytic sites and is based on a cheap and biorenewable carbon support, is a sustainable catalyst for the production of furfurals, platform chemicals for biofuels and chemicals. PMID:24807741

Mazzotta, Michael G; Gupta, Dinesh; Saha, Basudeb; Patra, Astam K; Bhaumik, Asim; Abu-Omar, Mahdi M

2014-08-01

39

Acid\\/epoxy reaction catalyst screening for low temperature (120 °C) powder coatings  

Microsoft Academic Search

This paper describes efforts to identify and screen suitable acid\\/epoxy reaction catalysts for low temperature curing (?120°C) powder coatings including tertiary amines, ammonium compounds, and metal complexes. Thermal analysis techniques were developed to aid evaluation of catalyst efficacy and a statistical design of experiments was carried out to study several commercially available catalysts. In three different resin\\/crosslinker systems, the effect

Glen Merfeld; Chris Molaison; Rainer Koeniger; A. Ersin Acar; Steve Mordhorst; Joe Suriano; Pat Irwin; Ron Singh Warner; Ken Gray; Mark Smith; Kevin Kovaleski; Greg Garrett; Steve Finley; Debora Meredith; Mike Spicer; Tom Naguy

2005-01-01

40

Catalysts  

NSDL National Science Digital Library

There are two types of catalysis reactions: homogeneous and heterogeneous. In a homogeneous reaction, the catalyst is in the same phase as the reactants. In a heterogeneous reaction, the catalyst is in a different phase from the reactants. This activity addresses homogeneous catalysis.

Consortium, The C.

2011-12-11

41

A solid acid esterification catalyst which reduces waste and increases yields  

SciTech Connect

Recent research on polymeric catalysts has led to the development of a new solid acid esterification catalyst which is highly active for the esterification of fatty acids and maleic anhydride at elevated temperatures. The use of this catalyst eliminates the need for a final neutralization step which is required when using traditional homogenous acid (H{sub 2}SO{sub 4} and HCl) catalysts. This neutralization step generates large amounts of waste salts and hurts efficiency since unconsumed organic acid reactants are also neutralized. In the high temperature esterification reactions studied here, the production of dialkyl ether by-products from the acid catalyzed self-condensation of alcohol is also greatly reduced allowing for both high activity and selectivity.

Lundquist, E.G. [Rohm and Haas Co., Spring House, PA (United States)

1993-12-31

42

Gallium(III) triflate: an efficient and a sustainable Lewis acid catalyst for organic synthetic transformations.  

PubMed

Green chemical processes play a crucial role in sustainable development, and efficient recyclable catalysts that can be conveniently applied in various chemical reactions are the key elements for the development of sustainable synthetic processes. Many organic transformations rely on Lewis and Brønsted acid catalysts, and such molecules have been widely studied in organic synthesis. Over the years, researchers have looked for Lewis acid catalysts that provide high selectivity and high turnover frequency but are also stable in aqueous media and recoverable. Since the first preparation of trifluoromethanesulfonic acid by Hazeldine (triflic acid, HOTf), researchers have synthesized and used numerous metal triflates in a variety of organic reactions. Even though the rare earth metal triflates have played a major role in these studies, the majority of rare earth triflates lack one or more of the primary properties of sustainable catalysts: low cost and easy availability of the metals, easy preparation of triflates, aqueous/thermal stability, recyclability, and catalytic efficiency. In this Account, we describe the synthetic applications of Ga(OTf)(3) and its advantages over similar catalysts. Ga(OTf)(3) can be conveniently prepared from gallium metal or gallium chloride in excess of trifluoromethanesulfonic acid (triflic acid) under reflux. Among many Lewis acid catalysts recently studied, Ga(OTf)(3) is water tolerant and soluble and requires very low catalyst loading to drive various acid-catalyzed reactions including Friedel-Crafts alkylation, hydroxyalkylation, and acylation selectively and efficiently. In many reactions Ga(OTf)(3) demonstrated high chemo- and regioselectivity, high yields, excellent stability, and recyclability. We successfully synthesized many biologically active heterocycles and their fluoroanalogs under mild conditions. Many challenging reactions such as the ketonic Strecker reactions proceed efficiently via Ga(OTf)(3) catalysis. Because it is stable in water, this catalyst provides the opportunity to study substrates and develop new synthetic protocols in aqueous media, significantly reducing the production of hazardous waste from organic solvents and toxic catalyst systems. PMID:22148160

Prakash, G K Surya; Mathew, Thomas; Olah, George A

2012-04-17

43

Heterogeneous catalysts for the transformation of fatty acid triglycerides and their derivatives to fuel hydrocarbons  

NASA Astrophysics Data System (ADS)

The results of studies devoted to the catalysts for transformation of fatty acid triglycerides and their derivatives to fuel hydrocarbons are presented and described systematically. Various approaches to the use of heterogeneous catalysts for the production of biofuel from these raw materials are considered. The bibliography includes 134 references.

Yakovlev, Vadim A.; Khromova, Sofia A.; Bukhtiyarov, Valerii I.

2011-10-01

44

Synthesis of biodiesel from a model waste oil feedstock using a carbon-based solid acid catalyst: Reaction and separation  

Microsoft Academic Search

A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt. The structure of these catalysts was characterized by a variety of

Qing Shu; Zeeshan Nawaz; Jixian Gao; Yuhui Liao; Qiang Zhang; Dezheng Wang; Jinfu Wang

2010-01-01

45

Acidic ionic liquid as "quasi-homogeneous" catalyst for controllable synthesis of cellulose acetate.  

PubMed

In this paper, we demonstrated that acidic ionic liquids (ILs) can be used as "quasi-homogeneous" catalysts for the efficient acetylation of cellulose. Unlike existing techniques that use large amount of ILs as solvent to dissolve and acetylate cellulose, a small amount of acidic ILs was used as catalyst in this study to overcome the low efficiency associated with relatively high viscosity and costs of ILs during homogeneous acetylation. Fully substituted cellulose acetate with a conversion of 88.8% was obtained by using only 9mol% IL 1-vinyl-3-(3-sulfopropyl) imidazolium hydrogen sulfate as catalyst, which is much higher than that of common commercialized solid acid catalysts. The degree of substitution and solubility of the obtained cellulose acetate can be facilely controlled by varying the concentration of ILs and reaction time. The dual function of swelling and catalyzing of acidic ILs for the acetylation of cellulose is responsible for the excellent catalytic performance. PMID:25256462

Tian, Dong; Han, Yangyang; Lu, Canhui; Zhang, Xinxing; Yuan, Guiping

2014-11-26

46

Topics in Catalysis 6 (1998) 8799 87 Solid acid catalysts based on supported tungsten oxides  

E-print Network

clusters are active and stable catalysts for isomerization, dehydration, and cracking reactions. Brønsted slightly during catalytic reactions. WOx clusters of intermediate size provide the balance between acid sites during catalytic reactions on WOx clusters. Keywords: tungsten oxides, solid acids, acid

Iglesia, Enrique

47

Synthesis of biodiesel from waste vegetable oil with large amounts of free fatty acids using a carbon-based solid acid catalyst  

Microsoft Academic Search

A carbon-based solid acid catalyst was prepared by the sulfonation of carbonized vegetable oil asphalt. This catalyst was employed to simultaneously catalyze esterification and transesterification to synthesis biodiesel when a waste vegetable oil with large amounts of free fatty acids (FFAs) was used as feedstock. The physical and chemical properties of this catalyst were characterized by a variety of techniques.

Qing Shu; Jixian Gao; Zeeshan Nawaz; Yuhui Liao; Dezheng Wang; Jinfu Wang

2010-01-01

48

Direct production of biodiesel from high-acid value Jatropha oil with solid acid catalyst derived from lignin  

PubMed Central

Background Solid acid catalyst was prepared from Kraft lignin by chemical activation with phosphoric acid, pyrolysis and sulfuric acid. This catalyst had high acid density as characterized by scanning electron microscope (SEM), energy-dispersive x-ray spectrometry (EDX) and Brunauer, Emmett, and Teller (BET) method analyses. It was further used to catalyze the esterification of oleic acid and one-step conversion of non-pretreated Jatropha oil to biodiesel. The effects of catalyst loading, reaction temperature and oil-to-methanol molar ratio, on the catalytic activity of the esterification were investigated. Results The highest catalytic activity was achieved with a 96.1% esterification rate, and the catalyst can be reused three times with little deactivation under optimized conditions. Biodiesel production from Jatropha oil was studied under such conditions. It was found that 96.3% biodiesel yield from non-pretreated Jatropha oil with high-acid value (12.7 mg KOH/g) could be achieved. Conclusions The catalyst can be easily separated for reuse. This single-step process could be a potential route for biodiesel production from high-acid value oil by simplifying the procedure and reducing costs. PMID:22145867

2011-01-01

49

Synthesis of aliphatic polyesters by polycondensation using inorganic acid as catalyst  

PubMed Central

An effective route for the synthesis of aliphatic polyesters made from adipic or sebacic acid and alkanediols, using inorganic acid as a catalyst is reported. The monomer composition, reaction time, catalyst type, and reaction conditions were optimized to yield polyesters with weight average molecular weights of 23,000 for adipic acid and 85,000 for sebacic acid-based polyesters. The polymers melt at temperatures of 52–65°C and possess melt viscosity in the range of 5600–19,400cP. This route represents an alternative method for producing aliphatic polyesters for possible use in the preparation of degradable disposable medical supplies.

Sokolsky-Papkov, Marina; Langer, Robert; Domb, Abraham J.

2014-01-01

50

Bifunctional Organic Polymeric Catalysts with a Tunable Acid-Base Distance and Framework Flexibility  

NASA Astrophysics Data System (ADS)

Acid-base bifunctional organic polymeric catalysts were synthesized with tunable structures. we demonstrated two synthesis approaches for structural fine-tune. In the first case, the framework flexibility was tuned by changing the ratio of rigid blocks to flexible blocks within the polymer framework. In the second case, we precisely adjusted the acid-base distance by distributing basic monomers to be adjacent to acidic monomers, and by changing the chain length of acidic monomers. In a standard test reaction for the aldol condensation of 4-nitrobenzaldehyde with acetone, the catalysts showed good reusability upon recycling and maintained relatively high conversion percentage.

Chen, Huanhui; Wang, Yanan; Wang, Qunlong; Li, Junhui; Yang, Shiqi; Zhu, Zhirong

2014-09-01

51

Surface properties of pillared acid-activated bentonite as catalyst for selective production of linear alkylbenzene  

NASA Astrophysics Data System (ADS)

Acid-activated and pillared montmorillonite were prepared as novel catalysts for alkylation of benzene with 1-decene for production of linear alkylbenzene. The catalysts were characterized by X-ray diffraction, FT-IR spectroscopy, N2 adsorption isotherms, temperature programmed desorption of NH3, scanning electron microscopy and elemental and thermal analysis techniques. It was found that acid-activation of clays prior to pillaring increased the porosity, total specific surface area, total pore volume and surface acidity of the catalysts. Optimization of the reaction conditions was performed by varying catalyst concentration (0.25-1.75 wt%), reactants ratio (benzene to 1-decene of 8.75, 12 and 15) and temperature (115-145 °C) in a batch slurry reactor. Under optimized conditions more than 98% conversion of 1-decene, and complete selectivity for monoalkylbenzenes were achieved.

Faghihian, Hossein; Mohammadi, Mohammad Hadi

2013-01-01

52

Production of biodiesel and lactic acid from rapeseed oil using sodium silicate as catalyst.  

PubMed

Biodiesel and lactic acid from rapeseed oil was produced using sodium silicate as catalyst. The transesterification in the presence of the catalyst proceeded with a maximum yield of 99.6% under optimized conditions [3% (w/w) sodium silicate, methanol/oil molar ratio 9/1, reaction time 60 min, reaction temperature 60°C, and stirring rate 250 rpm]. After six consecutive transesterification reactions, the catalyst was collected and used for catalysis of the conversion of glycerol to lactic acid. A maximum yield of 80.5% was achieved when the reaction was carried out at a temperature of 300°C for 90 min. Thus, sodium silicate is an effective catalyst for transesterification and lactic acid production from the biodiesel by-product, glycerol. PMID:21530245

Long, Yun-Duo; Guo, Feng; Fang, Zhen; Tian, Xiao-Fei; Jiang, Li-Qun; Zhang, Fan

2011-07-01

53

The outer-coordination sphere: incorporating amino acids and peptides as ligands for homogeneous catalysts to mimic enzyme function  

SciTech Connect

Great progress has been achieved in the field of homogeneous transition metal-based catalysis, however, as a general rule these solution based catalysts are still easily outperformed, both in terms of rates and selectivity, by their analogous enzyme counterparts, including structural mimics of the active site. This observation suggests that the features of the enzyme beyond the active site, i.e. the outer-coordination sphere, are important for their exceptional function. Directly mimicking the outer-coordination sphere requires the incorporation of amino acids and peptides as ligands for homogeneous catalysts. This effort has been attempted for many homogeneous catalysts which span the manifold of catalytic reactions and often require careful thought regarding solvent type, pH and characterization to avoid unwanted side reactions or catalyst decomposition. This article reviews the current capability of synthesizing and characterizing this often difficult category of metal-based catalysts. This work was funded by the DOE Office of Science Early Career Research Program through the Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Shaw, Wendy J.

2012-10-09

54

A highly active bagasse-derived solid acid catalyst with properties suitable for production of biodiesel.  

PubMed

A novel bagasse-based solid acid catalyst was successfully prepared through sulfonation of incompletely carbonized bagasse. A range of conditions for producing the catalyst were investigated, and the optimized catalyst, produced under carbonization at 648 K for 0.5 h and sulfonation at 423 K for 15 h, showed excellent catalytic activity and resulted in around 95 % yield of methyl oleate. Its activity was not only substantially greater than that of niobic acid and Amberlyst-15, but also comparable to or superior to that of catalysts made from pure starch or glucose, respectively. Additionally, the bagasse-derived catalyst could be repeatedly employed for at least eight cycles and still retained around 90 % of its original activity, exhibiting excellent operational stability. Furthermore, the catalyst efficiently converted waste cooking oils with 38.6 wt % free fatty acids into biodiesel and afforded a high yield of about 93.8 % within 12 h. These results clearly show that the bagasse-derived catalyst is economic, eco-friendly, and promising for biodiesel production from low-cost feedstocks and may find wide applications. PMID:22693163

Lou, Wen-Yong; Guo, Qiang; Chen, Wen-Jing; Zong, Min-Hua; Wu, Hong; Smith, Thomas J

2012-08-01

55

[Experimental and kinetic modeling of acid/base and redox reactions over oxide catalysts]. Technical progress report  

SciTech Connect

The research has involved the characterization of catalyst acidity, {sup 2}D NMR studies of Bronsted acid sites, and kinetic, calorimetric, and spectroscopic studies of methylamine synthesis and related reactions over acid catalysts. Approach of this work was to explore quantitative correlations between factors that control the generation, type, strength, and catalytic properties of acid sites on zeolite catalysts. Microcalorimetry, thermogravimetric analysis, IR spectroscopy, and NMR spectroscopy have provided information about the nature and strength of acid sites in zeolites. This was vital in understanding the catalytic cycles involved in methylamine synthesis and related reactions over zeolite catalysts.

Not Available

1993-07-01

56

Esterification of palmitic acid with methanol over tungsten oxide supported on zirconia solid acid catalysts: effect of method of preparation of the catalyst on its structural stability and reactivity  

Microsoft Academic Search

Esterification of palmitic acid with methanol was studied on zirconia supported tungsten oxide solid acid catalysts prepared by both impregnation and co-precipitation methods; the tungsten loading and calcination temperature were varied. These catalysts were characterized by X-ray diffraction for structural elucidation and by temperature-programmed desorption of ammonia for their surface acidity. Whereas the impregnated catalysts exhibited both tetragonal and monoclinic

Sridarala Ramu; N. Lingaiah; B. L. A. Prabhavathi Devi; R. B. N. Prasad; I. Suryanarayana; P. S. Sai Prasad

2004-01-01

57

Improved anode catalysts for coal gas-fueled phosphoric acid fuel cells  

NASA Astrophysics Data System (ADS)

The development, optimization and demonstration of contaminant-tolerant anode catalyst formulations for phosphoric acid fuel cells is the overall objective of this project. The goal is to develop supported catalyst systems that will not only be able to operate on feed gases containing high levels of CO, H2S, and COS, but will, in fact, encourage the shift reaction to convert the CO to additional H2 or anodically convert CO to CO2, boosting the power content of the fuel gas. Of CO conversion is not feasible, a secondary goal is to demonstrate CO- and H2S-tolerant catalysts so that gas cleanup requirements can be minimized. Upper limits for individual contaminant concentrations and mixtures of contaminant gases that can be tolerated by the advanced anode catalysts will be determined. This quarter, the two catalysts selected for testing were Pt-Ti-Ru and Pt-Ti-ZA, hydrogen/hydrogen cell testing continued.

Kackley, Nancy; Kosek, John A.

1989-09-01

58

Sulfamic acid as a cost-effective catalyst instead of metal-containing acids for acetolysis of cyclic ethers  

Microsoft Academic Search

Sulfamic acid has been used as an efficient catalyst and green alternative for metal-containing acidic materials to promote the acetolysis reaction of THF to produce 1,4-diacetoxybutane. This method is also applicable to the acetolysis of other cyclic ethers, such as methyl substituted THF and tetrahydropyran and 1,4-dioxane, which is less reactive.

Bo Wang; Yanlong Gu; Weizhong Gong; Yuru Kang; Liming Yang; Jishuan Suo

2004-01-01

59

Generalization of ACID Properties Brahim Medjahed  

E-print Network

University http://www.cs.purdue.edu/homes/mourad/ Ahmed K. Elmagarmid Cyber Center and Department of Computer-aided design, computer-aided manufacturing, office automation, network management, multidatabases, and mobile depends on the way #12;ACID properties are generalized. An extensive coverage of advanced transaction

Medjahed, Brahim

60

Direct asymmetric hydrogenation of ?-keto acids by using the highly efficient chiral spiro iridium catalysts.  

PubMed

A new efficient and highly enantioselective direct asymmetric hydrogenation of ?-keto acids employing the Ir/SpiroPAP catalyst under mild reaction conditions has been developed. This method might be feasible for the preparation of a series of chiral ?-hydroxy acids on a large scale. PMID:25384177

Yan, Pu-Cha; Xie, Jian-Hua; Zhang, Xiang-Dong; Chen, Kang; Li, Yuan-Qiang; Zhou, Qi-Lin; Che, Da-Qing

2014-11-20

61

Highly enantioselective electrophilic ?-bromination of enecarbamates: chiral phosphoric acid and calcium phosphate salt catalysts.  

PubMed

Metal-free chiral phosphoric acids and chiral calcium phosphates both catalyze highly enantio- and diastereoselective electrophilic ?-bromination of enecarbamates to provide an atom-economical synthesis of enantioenriched vicinal haloamines. Either enantiomer can be formed in good yield with excellent diastereo- and enantioselectivity simply by switching the catalyst from a phosphoric acid to its calcium salt. PMID:22686436

Alix, Aurélien; Lalli, Claudia; Retailleau, Pascal; Masson, Géraldine

2012-06-27

62

Cyclic amino acid salts as catalysts for the asymmetric Michael reaction  

Microsoft Academic Search

Different chiral cyclic amino acid alkali metal and ammonium salts were used as catalysts for the asymmetric Michael addition of aldehydes to nitrostyrene. The reaction yield and stereoselectivity depend slightly on the salt cation. The highest yield of the reaction (up to 100%) was obtained with (S)-morpholine-3-carboxylic acid salts, which gave moderate to good enantioselectivities (up to 72% ee) and

Marju Laars; Henri Raska; Margus Lopp; Tõnis Kanger

2010-01-01

63

Application of Supercritical Fluids to Solid Acid Catalyst Alkylation and Regeneration  

SciTech Connect

Supercritical fluid (SCF) regeneration is a promising alternative method for regenerating solid catalysts deactivated by carbonaceous deposits. The unique solvent and transport properties of SCFs such as solvent strength similar to liquids and transport properties similar to gases make them highly suitable for extraction of fouling materials from porous heterogeneous catalysts. A brief review of the research work performed at the Idaho National Laboratory (INL) on the application of supercritical fluids to both isobutane/butene alkylation reaction and solid acid catalyst regeneration is presented in this contribution.

Lucia M. Petkovic; Daniel M. Ginosar; David N. Thompson; Kyle C. Burch

2007-05-01

64

Bioleaching of spent refinery processing catalyst using Aspergillus niger with high-yield oxalic acid  

Microsoft Academic Search

A spent refinery processing catalyst was physically and chemically characterized, and subjected to one-step and two-step bioleaching processes using Aspergillus niger. During bioleaching of the spent catalysts of various particle sizes (“as received”, 100–150?m, <37?m, and x¯=2.97 (average) ?m) and pulp densities, the biomass dry weight and pH were determined. The corresponding leach liquor was analysed for excreted organic acids

Deenan Santhiya; Yen-Peng Ting

2005-01-01

65

Novel Solid Acid Catalyst, Bentonite-Supported Polytrifluoromethanesulfosiloxane for Friedel–Crafts Acylation of Ferrocene  

Microsoft Academic Search

Solid acid catalyst, bentonite-supported polytrifluoromethanesulfosiloxane (B-PTFMSS) has been for the first time prepared and used in the Friedel–Crafts acylation of ferrocene with various acyl chlorides. The catalytic activities were influenced by reaction time, reaction temperature, solvent and loaded amount of B-PTFMSS. It was found that the new catalyst B-PTFMSS possessed the advantages of high activities giving similar yield of aliphatic

Rui-Jue Hu; Bao-Guo Li

2004-01-01

66

Novel acidic ionic liquids mediated zinc chloride: Highly effective catalysts for the Beckmann rearrangement  

Microsoft Academic Search

A mild, efficient, and eco-friendly procedure for Beckmann rearrangement was catalyzed by a series of novel Brønsted acidic ionic liquids (ILs) consisiting double –SO3H cations mediated zinc chloride (ILs–ZnCl2) catalytic system. High yields of amides were achieved by using 5mol.% of ILs–ZnCl2 catalysts. In addition, the catalyst system could be recycled and reused for three times.

Xiaofei Liu; Linfei Xiao; Hugjiltu Wu; Zhen Li; Jing Chen; Chungu Xia

2009-01-01

67

Catalysis science of the solid acidity of model supported tungsten oxide catalysts  

Microsoft Academic Search

A series of supported WO3 catalysts were synthesized by incipient wetness impregnation of ammonium metatungstate aqueous solutions onto Al2O3, TiO2, Nb2O5, and ZrO2 supports as a function of tungsten oxide loading. The resulting solid acid catalysts were physically characterized with in situ Raman and UV–vis spectroscopy and chemically probed by methanol dehydration to dimethyl ether (CH3OH-TPSR and steady-state CH3OH dehydration).

Israel E. Wachs; Taejin Kim; Elizabeth I. Ross

2006-01-01

68

Process for the generation of .alpha., .beta.-unsaturated carboxylic acids and esters using niobium catalyst  

DOEpatents

A process using a niobium catalyst includes the step of reacting an ester or carboxylic acid with oxygen and an alcohol in the presence a niobium catalyst to respectively produce an .alpha.,.beta.-unsaturated ester or carboxylic acid. Methanol may be used as the alcohol, and the ester or carboxylic acid may be passed over the niobium catalyst in a vapor stream containing oxygen and methanol. Alternatively, the process using a niobium catalyst may involve the step of reacting an ester and oxygen in the presence the niobium catalyst to produce an .alpha.,.beta.-unsaturated carboxylic acid. In this case the ester may be a methyl ester. In either case, niobium oxide may be used as the niobium catalyst with the niobium oxide being present on a support. The support may be an oxide selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide and mixtures thereof. The catalyst may be formed by reacting niobium fluoride with the oxide serving as the support. The niobium catalyst may contain elemental niobium within the range of 1 wt % to 70 wt %, and more preferably within the range of 10 wt % to 30 wt %. The process may be operated at a temperature from 150 to 450.degree. C. and preferably from 250 to 350.degree. C. The process may be operated at a pressure from 0.1 to 15 atm. absolute and preferably from 0.5-5 atm. absolute. The flow rate of reactants may be from 10 to 10,000 L/kg.sub.(cat) /h, and preferably from 100 to 1,000 L/kg.sub.(cat) /h.

Gogate, Makarand Ratnakav (Durham, NC); Spivey, James Jerome (Cary, NC); Zoeller, Joseph Robert (Kingsport, TN)

1999-01-01

69

Reaction of dicyclopentadiene with formic acid and chloroacetic acid with and without cation-exchange resins as catalysts  

Microsoft Academic Search

The uncatalysed and catalysed (with cation-exchange resin) esterification of formic acid and chloroacetic acid, with dicyclopentadiene (DCPD), i.e. 4,7-methano-3a,4,7,7a-tetrahydroindene, was carried out. The effect of various parameters, e.g. speed of agitation, catalyst loading, mole ratio of the reactants, temperature, concentration of formic acid in aqueous solutions were studied to optimise the reaction conditions. DCPD cam be quantitatively converted to the

Basudeb Saha; Man Mohan Sharma

1997-01-01

70

Oxidation catalyst  

DOEpatents

The present invention generally relates to catalyst systems and methods for oxidation of carbon monoxide. The invention involves catalyst compositions which may be advantageously altered by, for example, modification of the catalyst surface to enhance catalyst performance. Catalyst systems of the present invention may be capable of performing the oxidation of carbon monoxide at relatively lower temperatures (e.g., 200 K and below) and at relatively higher reaction rates than known catalysts. Additionally, catalyst systems disclosed herein may be substantially lower in cost than current commercial catalysts. Such catalyst systems may be useful in, for example, catalytic converters, fuel cells, sensors, and the like.

Ceyer, Sylvia T. (Cambridge, MA); Lahr, David L. (Cambridge, MA)

2010-11-09

71

Vanadium phosphate catalysts for biodiesel production from acid industrial by-products.  

PubMed

Biodiesel production from high acidity industrial by-products was studied using heterogeneous acid catalysts. These by-products contain 26-39% of free fatty acids, 45-66% of fatty acids methyl esters and 0.6-1.1% of water and are consequently inadequate for direct basic catalyzed transesterification. Macroporous vanadyl phosphate catalysts with V/P=1 (atomic ratio) prepared via sol-gel like technique was used as catalyst and it was possible to produce in one reaction batch a biodiesel contain 87% and 94% of FAME, depending on the by-product used as raw material. The initial FAME content in the by-products had a beneficial effect on the reactions because they act as a co-solvent, thus improving the miscibility of the reaction mixture components. The water formed during esterification process seems to hinder the esters formation, possibly due to competitive adsorption with methanol and to the promotion of the FAME hydrolysis reaction.The observed catalyst deactivation seems to be related to the reduction of vanadium species. However, spent catalysts can be regenerated, even partially, by reoxidation of the reduced vanadium species with air. PMID:22902409

Domingues, Carina; Correia, M Joana Neiva; Carvalho, Renato; Henriques, Carlos; Bordado, João; Dias, Ana Paula Soares

2013-04-10

72

40 CFR 76.3 - General Acid Rain Program provisions.  

...2014-07-01 2014-07-01 false General Acid Rain Program provisions. 76.3 Section...CONTINUED) AIR PROGRAMS (CONTINUED) ACID RAIN NITROGEN OXIDES EMISSION REDUCTION PROGRAM § 76.3 General Acid Rain Program provisions. The...

2014-07-01

73

Ammonolysis of esters of hydroxybenzoic acids on a boron phosphate catalyst  

SciTech Connect

In this investigation boron phosphate catalyst was used for ammonolysis of methyl and ethyl esters of salicylic and 4-hydroxybenzoic acids. It was shown that ammonolysis of methyl and ethyl esters of salicylic and 4-hydroxybenzoic acids in presence of boron phosphate catalyst at a ratio of 3-7 moles of ammonia per mole of ester in a contact time of 1-5 sec at 380-400/sub 0/ can be used for obtaining o- and p- hydroxybenzonitriles in yields of over 90% of the theoretical.

Suvorov, B.V.; Bukeikhanov, N.R.; Li, L.V.; Zulkasheva, A.Z.

1987-09-10

74

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts M. Roussel1  

E-print Network

1 Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts M. Roussel1 , M. Bouchard1VNbO catalysts could be made up from (VNbMo)5O14-type microdomains embedded in MoO3 matrix seems still topical. Keywords MoVNbO catalysts; acetic acid; ethylene; mild oxidation of ethane; nanosized (VNbMo)5O14

Paris-Sud XI, Université de

75

Esterification by ZrO2 and Mo-ZrO2 ECO-Friendly Solid Acid Catalysts  

Microsoft Academic Search

Esterification of mono-and dicarboxylic acids catalysed by single (ZrO2) and mixed oxide (Mo-ZrO2) eco-friendly solid acid catalysts is described. The Mo-ZrO2 catalyst exhibits better catalytic performance than ZrO2.

Basude Manohar; Vangala R. Reddy; Benjaram M. Reddy

1998-01-01

76

Efficient conversion of triacylglycerols and fatty acids to biodiesel in a microwave reactor using metal triflate catalysts.  

PubMed

We report that catalytic quantities of the Lewis acidic metal catalysts scandium triflate and bismuth triflate promote conversion of oleic, linoleic, palmitic and myristic acids and their glyceryl triesters to the corresponding methyl esters (biodiesel) in greater than 90% yield upon microwave heating. Additionally, both catalysts could be recovered and reused in esterification reactions at least six times. PMID:20714659

Socha, Aaron M; Sello, Jason K

2010-10-21

77

Sulfamic acid: an efficient, cost-effective and recyclable solid acid catalyst for the Friedlander quinoline synthesis  

Microsoft Academic Search

o-Aminoaryl ketones undergo smooth condensation with ?-methylene ketones in the presence of sulfamic acid (NH2SO3H) (SA) under mild reaction conditions to afford the corresponding polysubstituted quinolines in excellent yields. The catalyst can be recovered by simple filtration and can be recycled in subsequent reactions. The method is simple, cost-effective and environmentally benign.

J. S. Yadav; P. Purushothama Rao; D. Sreenu; R. Srinivasa Rao; V. Naveen Kumar; K. Nagaiah; A. R. Prasad

2005-01-01

78

Enhanced Oxygen Reduction Activity In Acid By Tin-Oxide Supported Au Nanoparticle Catalysts  

SciTech Connect

Gold nanoparticles supported on hydrous tin-oxide (Au-SnO{sub x}) are active for the four-electron oxygen reduction reaction in an acid electrolyte. The unique electrocatalytic of the Au-SnO is confirmed by the low amount of peroxide detected with rotating ring-disk electrode voltammetry and Koutecky-Levich analysis. In comparison, 10 wt % Au supported on Vulcan carbon and SnO{sub x} catalysts both produce significant peroxide in the acid electrolyte, indicating only a two-electron reduction reaction. Characterization of the Au-SnO{sub x} catalyst reveals a high-surface area, amorphous support with 1.7 nm gold metal particles. The high catalytic activity of the Au-SnO is attributed to metal support interactions. The results demonstrate a possible path to non-Pt catalysts for proton exchange membrane fuel cell cathodes.

Baker,W.; Pietron, J.; Teliska, M.; Bouwman, P.; Ramaker, D.; Swider-Lyons, K.

2006-01-01

79

Catalytic wet air oxidation of carboxylic acids on TiO{sub 2}-supported ruthenium catalysts  

SciTech Connect

The total oxidation of aqueous solutions of carboxylic acids by air was studied in a slurry reactor over the temperature range 180--100 C and oxygen partial pressure of 0.3--1.8 MPa in the presence of a 2.8%Ru/TiO{sub 2} catalyst. The influence of various parameters is presented: the catalytic wet air oxidation of succinic acid is 0 order with respect to succinic acid; the order with respect to oxygen pressure is 0.4, and the activation energy is ca. 125 kJ/mol. It was found that acetic acid, which is one of the intermediates, and CO{sub 2} have no retarding effect on the total organic carbon abatement rate of succinic acid. Substitution of one hydrogen atom of the methyl group in acetic acid by Cl, OH, or NH{sub 2} gives an increase of the oxidation rate. However, it was proposed that the low activity of acetic acid oxidation is due not only to the difficulty to oxidize the methyl group, but also to the low adsorption coefficient of acetic acid on ruthenium surface. Inorganic salts, such as sodium chloride, only slightly decrease the oxidation rate of acetic acid. The absence of metal ions (Ru, Ti) in the effluents after reaction and the absence of particle sintering indicate also a high stability of the catalyst under the conditions employed. The catalyst can be recycled without loss of activity after the second run. The activity becomes stable after the attainment of a steady-state coverage of the Ru particles by oxygen. The study of the effect of reduction-oxidation treatments of the catalyst showed that the activity depends on the oxidation state of the surface.

Beziat, J.C.; Besson, M.; Gallezot, P. [CNRS, Villeurbanne (France). Inst. de Recherches sur la Catalyse] [CNRS, Villeurbanne (France). Inst. de Recherches sur la Catalyse; Durecu, S. [TREDI, Vandoeuvre-les-Nancy (France). Dept. Recherche] [TREDI, Vandoeuvre-les-Nancy (France). Dept. Recherche

1999-02-15

80

Platinum catalyst degradation in phosphoric acid fuel cells for stationary applications  

Microsoft Academic Search

A study is presented on the degradation of platinum alloy cathode catalysts operated in phosphoric acid fuel cells. The impact of time and temperature on the fundamental decay mechanism was studied with a surface area loss model and experimental electrochemical surface area measurements. It is suggested that platinum particle migration on the carbon support surface is the dominant mechanism for

T. T. Aindow; A. T. Haug; D. Jayne

2011-01-01

81

Alkene Isomerization Using a Solid Acid as Activator and Support for a Homogeneous Catalyst  

ERIC Educational Resources Information Center

An upper-level undergraduate experiment that, in addition to introducing students to catalysis using an air sensitive transition-metal complex, introduces the use of a solid acid as an activator and support for the catalyst is developed. The increased stability acquired in the course of the process affords the opportunity to characterize the…

Seen, Andrew J.

2004-01-01

82

SYNTHESIS OF COUMARINS CATALYZED BY ECO-FRIENDLY W\\/ZrO2 SOLID ACID CATALYST  

Microsoft Academic Search

Synthesis of substituted coumarins via reactions of resorcinol and substituted resorcinol with ethyl acetoacetate and ethyl ?-methylacetoacetate (Pechmann reaction) are reported, in which the production of environmentally harmful waste streams is minimized by the use of a novel solid acid catalyst.

Benjaram M. Reddy; Vangala R. Reddy; D. Giridhar

2001-01-01

83

Sulfamic acid: an efficient, cost-effective and recyclable solid acid catalyst for the three-component synthesis of ?-amino nitriles  

Microsoft Academic Search

?-Amino nitriles are synthesized by the three-component coupling reaction of aldehydes, amines and trimethylsilyl cyanide using sulfamic acid as a heterogeneous solid acid catalyst, under solvent-free conditions in excellent yields. The catalyst was recovered by simple filtration and was recycled in subsequent reactions.

Akbar Heydari; Samad Khaksar; Mehrdad Pourayoubi; Ali Reza Mahjoub

2007-01-01

84

An efficient green catalyst comprising 12-tungstophosphoric acid and MCM-41: synthesis characterization and diesterification of succinic acid, a potential bio-platform molecule  

Microsoft Academic Search

An efficient green catalyst comprising 12-tungstophosphoric acid (TPA) and MCM-41 was synthesized. The catalytic activity was evaluated for liquid phase solvent free diesterification of succinic acid. The support and the synthesized catalyst were characterized by various physico-chemical techniques. Fourier transform infrared, diffuse reflectance spectroscopy, and P NMR spectra indicate that the Keggin structure of TPA was not destroyed after anchoring

Varsha Brahmkhatri; Anjali Patel

2012-01-01

85

An efficient green catalyst comprising 12-tungstophosphoric acid and MCM-41: synthesis characterization and diesterification of succinic acid, a potential bio-platform molecule  

Microsoft Academic Search

An efficient green catalyst comprising 12-tungstophosphoric acid (TPA) and MCM-41 was synthesized. The catalytic activity was evaluated for liquid phase solvent free diesterification of succinic acid. The support and the synthesized catalyst were characterized by various physico-chemical techniques. Fourier transform infrared, diffuse reflectance spectroscopy, and P NMR spectra indicate that the Keggin structure of TPA was not destroyed after anchoring

Varsha Brahmkhatri; Anjali Patel

2011-01-01

86

Synergistic chiral ion pair catalysts for asymmetric catalytic synthesis of quaternary ?,?-diamino acids.  

PubMed

The combination of a chiral phosphate anion with a silver ion has been demonstrated as a powerful and synergistic ion pair catalyst for the aza-Mannich reaction. A series of valuable quaternary ?,?-diamino acid derivatives was obtained in high yield, and with excellent diastereo- (up to 25:1 dr) and enantioselectivity (up to 99% ee). The adducts can be smoothly transformed into the corresponding protected chiral quaternary ?,?-diamino acids by a one-pot hydrolysis reaction. PMID:22472066

Shi, Shi-Hui; Huang, Fu-Ping; Zhu, Ping; Dong, Zhen-Wen; Hui, Xin-Ping

2012-04-20

87

Carbon quantum dots with photo-generated proton property as efficient visible light controlled acid catalyst  

NASA Astrophysics Data System (ADS)

Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ?pH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ?pH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03996j

Li, Haitao; Liu, Ruihua; Kong, Weiqian; Liu, Juan; Liu, Yang; Zhou, Lei; Zhang, Xing; Lee, Shuit-Tong; Kang, Zhenhui

2013-12-01

88

31P chemical shift of adsorbed trialkylphosphine oxides for acidity characterization of solid acids catalysts.  

PubMed

A comprehensive study has been made to predict the adsorption structures and (31)P NMR chemical shifts of various trialkylphosphine oxides (R3PO) probe molecules, viz., trimethylphosphine oxide (TMPO), triethylphosphine oxide (TEPO), tributylphosphine oxide (TBPO), and trioctylphosphine oxide (TOPO), by density functional theory (DFT) calculations based on 8T zeolite cluster models with varied Si-H bond lengths. A linear correlation between the (31)P chemical shifts and proton affinity (PA) was observed for each of the homologous R3PO probe molecules examined. It is found that the differences in (31)P chemical shifts of the R3POH(+) adsorption complexes, when referring to the corresponding chemical shifts in their crystalline phase, may be used not only in identifying Brønsted acid sites with varied acid strengths but also in correlating the (31)P NMR data obtained from various R3PO probes. Such a chemical shift difference therefore can serve as a quantitative measure during acidity characterization of solid acid catalysts when utilizing (31)P NMR of various adsorbed R3PO, as proposed in our earlier report (Zhao; et al. J. Phys. Chem. B 2002, 106, 4462) and also illustrated herein by using a mesoporous H-MCM-41 aluminosilicate (Si/Al = 25) test adsorbent. It is indicative that, with the exception of (TMPO), variations in the alkyl chain length of the R3PO (R = C(n)H(2n+1); n > or = 2) probe molecules have only negligible effect on the (31)P chemical shifts (within experimental error of ca. 1-2 ppm) either in their crystalline bulk or in their corresponding R3POH(+) adsorption complexes. Consequently, an average offset of 8 +/- 2 ppm was observed for (31)P chemical shifts of adsorbed R3PO with n > or = 2 relative to TMPO (n = 1). Moreover, by taking the value of 86 ppm predicted for TMPO adsorbed on 8T cluster models as a threshold for superacidity (Zheng; et al. J. Phys. Chem. B 2008, 112, 4496), a similar threshold (31)P chemical shift of ca. 92-94 ppm was deduced for TEPO, TBPO, and TOPO. PMID:18646739

Zheng, Anmin; Huang, Shing-Jong; Chen, Wen-Hua; Wu, Pei-Hao; Zhang, Hailu; Lee, Huang-Kuei; de Ménorval, Louis-Charles; Deng, Feng; Liu, Shang-Bin

2008-08-14

89

Hydrogenation of biofuels with formic acid over a palladium-based ternary catalyst with two types of active sites.  

PubMed

A composite catalyst including palladium nanoparticles on titania (TiO2) and on nitrogen-modified porous carbon (Pd/TiO2@N-C) is synthesized from palladium salts, tetrabutyl titanate, and chitosan. N2 sorption isotherms show that the catalyst has a high BET surface area (229?m(2) ?g(-1)) and large porosity. XPS and TEM characterization of the catalyst shows that palladium species with different chemical states are well dispersed across the TiO2 and nitrogen-modified porous carbon, respectively. The Pd/TiO2@N-C catalyst is very active and shows excellent stability towards hydrogenation of vanillin to 2-methoxy-4-methylphenol using formic acid as hydrogen source. This activity can be attributed to a synergistic effect between the Pd/TiO2 (a catalyst for dehydrogenation of formic acid) and Pd/N-C (a catalyst for hydrogenation of vanillin) sites. PMID:24861954

Wang, Liang; Zhang, Bingsen; Meng, Xiangju; Su, Dang Sheng; Xiao, Feng-Shou

2014-06-01

90

Elucidating the nature of the cobalt centres in CoAPO-18 acid catalysts  

SciTech Connect

A combined UV-Vis and FTIR spectroscopic approach, supplemented by the use of probe molecules (N{sub 2}, CO, C{sub 2}H{sub 4} and H{sub 2}O) as selective adsorbates, has clarified the atomic environment of cobalt centres in CoAPO-18 solid acid catalysts. These catalysts have both framework Co(II) ions in tetrahedral coordination and coordinatively-unsaturated Co(II) Lewis acid centres. But, only approximately half of the tetrahedral ions generate Bronsted OH groups (bridged between Co and P) and are oxidizable to framework Co(III). These bridged OHs, which are the active catalytic centres in acid-catalysis, are strongly influenced by the adsorbates in that the Co(H) ions of the [O{sub 3}CoO(H)] units undergo significant changes in the coordination sphere: the stronger is the ligand (adsorbate), the larger is the number of catalytic centres that are modified.

Marchese, L.; Martra, G.; Damilano, N.; Coluccia, S. [Universita di Torino (Italy); Thomas, J.M. [Royal Institution of Great Britain, London (United Kingdom)

1996-12-31

91

The effect of oleic acid stabilizer on the surface properties of bimetallic PtNi catalysts.  

PubMed

A detailed study on the surface properties of oleic acid-stabilized PtNi nanoparticles supported on silica is reported. The oleic acid-stabilized PtNi nanoparticles were synthesized using NaBH4 as the reducing agent at various temperatures and oleic acid concentrations, prior to incorporation onto the silica support. X-ray diffraction studies of the unsupported oleic acid-stabilized PtNi particles revealed that the PtNi existed as alloys. Upon incorporation onto silica support, surface properties of the catalysts were investigated using H2-temperature reduction (H2-TPR), H2-temperature desorption (H2-TPD) and H2-chemisorption techniques. It was found that for the bimetallic catalysts, no oxides or very little oxidation occurred. Furthermore, these catalysts exhibited both Pt and Ni active sites on its surface though the availability of Ni active sites was dominant. A comparison of the surface properties of these materials with those prepared without oleic acid in our previous work [N. H. H. Abu Bakar et al., J. Catal. 265, 63 (2009)] and how they affect the hydrogenation of benzene is also discussed. PMID:23901527

Abu Bakar, N H H; Abu Bakar, M; Bettahar, M M; Ismail, J; Monteverdi, S

2013-07-01

92

Synthesis of highly dispersed and active palladium/carbon nanofiber catalyst for formic acid electrooxidation  

NASA Astrophysics Data System (ADS)

Highly dispersed and active palladium/carbon nanofiber (Pd/CNF) catalyst is synthesized by NaBH4 reduction with trisodium citrate as the stabilizing agent. The obtained Pd/CNF catalyst is characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The results show that the Pd nanoparticles with an average particle size of ca. 3.8 nm are highly dispersed on the CNF support even with a small ratio of citrate to Pd precursor, which is believed to be due to the pH adjustment of citrate stabilized colloidal Pd nanoparticles. The cyclic voltammetry and chronoamperometry techniques show that the obtained Pd/CNF catalyst exhibits good catalytic activity and stability for the electrooxidation of formic acid.

Qin, Yuan-Hang; Yue-Jiang; Yang, Hou-Hua; Zhang, Xin-Sheng; Zhou, Xing-Gui; Niu, Li; Yuan, Wei-Kang

2011-05-01

93

Production of biodiesel from mixed waste vegetable oil using an aluminium hydrogen sulphate as a heterogeneous acid catalyst  

Microsoft Academic Search

Al(HSO4)3 heterogeneous acid catalyst was prepared by the sulfonation of anhydrous AlCl3. This catalyst was employed to catalyze transesterification reaction to synthesis methyl ester when a mixed waste vegetable oil was used as feedstock. The physical and chemical properties of aluminum hydrogen sulphate catalyst were characterized by scanning electron microscopy (SEM) measurements, energy dispersive X-ray (EDAX) analysis and titration method.

Kasirajan Ramachandran; Pandian Sivakumar; Tamilarasan Suganya; Sahadevan Renganathan

2011-01-01

94

Acidity and Catalytic Activity of a Nafion-H\\/Silica Nanocomposite Catalyst Compared with a Silica-Supported Nafion Sample  

Microsoft Academic Search

The characterization of acid sites in the recently developed Nafion-H\\/silica nanocomposite catalyst was carried out through pyridine adsorption using the surface FT-IR technique. For comparison, an impregnated Nafion-H\\/SiO2 catalyst was also studied. A large number of free surface SO3H groups was detected on the surface of the Nafion-H\\/silica nanocomposite, in contrast to the impregnated catalyst. Pyridine adsorption demonstrates that Brønsted

Béla Török; Imre Kiricsi; Árpád Molnár; George A. Olah

2000-01-01

95

Catalytic wet air oxidation of acetic acid on carbon-supported ruthenium catalysts  

SciTech Connect

Ruthenium catalysts prepared by ion exchange of active carbons and high-surface-area graphites are active for the wet air oxidation of aqueous solutions of acetic acid (5-20 g/liter). A total conversion into CO{sub 2} can be achieved between 448 and 473 K using air as oxidizing agent. No leaching of ruthenium can be detected which indicates that the reaction proceeds on the heterogeneous catalysts. For the same particle size (1 nm), graphite-supported ruthenium catalysts are much more active (up to 0.4 mol h{sup -1} g{sub RU}{sup -1} at 473 K in a stirred batch reactor pressurized with air at 10 MPa) than active carbon-supported catalysts. The lower activities of the latters could be due to internal diffusion limitation since the 1-nm Ru particles are located inside the micropores. However, graphite-supported catalysts might be intrinsically more active because of an electron transfer from graphite to metal particles which would increase the resistance of ruthenium to oxygen poisoning. It was also shown that the activity of ruthenium is particle size dependent: the smaller the sizes, the lower the activities. This effect could be interpreted by the higher adsorption energy of oxygen on the small particles which produces a poisoning of the metal surface. From measurements of the reaction rates on the Ru/HSAG graphite catalyst at different temperatures, pressures, and acetic acid concentrations, it was established that the reaction orders were zero and 0.65 with respect to the concentration and oxygen pressure, respectively; the activation energy of the reaction was 100.5 kJ mol{sup -1}. An equation describing the reaction kinetics was proposed. 23 refs., 4 figs., 2 tabs.

Gallezot, P.; Chaumet, S.; Perrard, A. [Institut de Recherches sur la Catalyse, Villeurbanne (France)] [and others] [Institut de Recherches sur la Catalyse, Villeurbanne (France); and others

1997-05-01

96

Efficient production of biodiesel from high free fatty acid-containing waste oils using various carbohydrate-derived solid acid catalysts.  

PubMed

In the present study, such carbohydrate-derived catalysts have been prepared from various carbohydrates such as d-glucose, sucrose, cellulose and starch. The catalytic and textural properties of the prepared catalysts have been investigated in detail and it was found that the starch-derived catalyst had the best catalytic performance. The carbohydrate-derived catalysts exhibited substantially higher catalytic activities for both esterification and transesterification compared to the two typical solid acid catalysts (sulphated zirconia and Niobic acid), and gave markedly enhanced yield of methyl esters in converting waste cooking oils containing 27.8wt% high free fatty acids (FFAs) to biodiesel. In addition, under the optimized reaction conditions, the starch-derived catalyst retained a remarkably high proportion (about 93%) of its original catalytic activity even after 50 cycles of successive re-use and thus displayed very excellent operational stability. Our results clearly indicate that the carbohydrate-derived catalysts, especially the starch-derived catalyst, are highly effective, recyclable, eco-friendly and promising solid acid catalysts that are highly suited to the production of biodiesel from waste oils containing high FFAs. PMID:18504123

Lou, Wen-Yong; Zong, Min-Hua; Duan, Zhang-Qun

2008-12-01

97

Carbon-supported PtAu alloy nanoparticle catalysts for enhanced electrocatalytic oxidation of formic acid  

NASA Astrophysics Data System (ADS)

The understanding of the electrocatalytic activity of bimetallic nanoparticle catalysts requires the ability to precisely control the composition and phase properties. In this report, we describe a new strategy in the preparation of a series of carbon supported platinum-gold bimetallic nanoparticles with various bimetallic compositions which were loaded onto a carbon black support and subjected subsequently by thermal treatment (Pt100-mAum/C). The Pt100-mAum/C catalysts are characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), and induced coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for the bimetallic nanoparticles shows single-phase alloy character. This ability enabled us to establish the correlation between the bimetallic composition and the electrocatalytic activity for formic acid (FA) electrooxidation. The electrocatalytic activities of the catalysts toward FA oxidation reaction are shown to strongly depend on the bimetallic PtAu composition. Within a wide range of bimetallic composition, the Pt50Au50/C catalyst shows the highest electrocatalytic activity for the FA oxidation, with a mass activity eight times higher than that of Pt/C. The high performance of the PtAu/C catalyst can be ascribed to the increased selectivity toward the FA dehydrogenation at the decreased availability of adjacent Pt atoms.

Chen, Guoqin; Li, Yunhua; Wang, Dong; Zheng, Li; You, Guirong; Zhong, Chuan-Jian; Yang, Lefu; Cai, Fan; Cai, Junxiu; Chen, Bing H.

2011-10-01

98

Reducing Pt use in the catalysts for formic acid electrooxidation via nanoengineered surface structure  

NASA Astrophysics Data System (ADS)

The design of active and durable catalysts for formic acid (FA) electrooxidation requires controlling the amount of three neighboring platinum atoms in the surface of Pt-based catalysts. Such requirement is studied by preparing Pt decorated Pd/C (donated as Pt-Pd/C) with various Pt:Pd molar ratios via galvanic displacement making the amount of three neighboring Pt atoms in the surface of Pt-Pd/C tunable. The decorated nanostructures are confirmed by XPS, HS-LEIS, cyclic voltammetry and chronoamperometric measurements, demonstrating that Pt-Pd/C (the optimal molar ratio, Pt:Pd = 1:250) exhibits superior activity and durability than Pd/C and commercial Pt/C (J-M, 20%) catalysts for FA electrooxidation. The mass activity of Pt-Pd/C (Pt:Pd = 1:250) (3.91 A mg-1) is about 98 and 6 times higher than that of commercial Pt/C (0.04 A mg-1) and Pd/C (0.63 A mg-1) at a given potential of 0.1 V vs SCE, respectively. The controlled synthesis of Pt-Pd/C lead to the formation of largely discontinuous Pd and Pt sites and inhibition of CO formation, exhibiting unprecedented electrocatalytic performance toward FA electrooxidation while the cost of the catalyst almost the same as Pd/C. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for FA electrooxidation.

Liao, Mengyin; Wang, Yulu; Chen, Guoqin; Zhou, Hua; Li, Yunhua; Zhong, Chuan-Jian; Chen, Bing H.

2014-07-01

99

Synthesis of biodiesel from a model waste oil feedstock using a carbon-based solid acid catalyst: reaction and separation.  

PubMed

A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt. The structure of these catalysts was characterized by a variety of techniques. A new process that used the coupling of the reaction and separation was employed, which greatly improved the conversion of cottonseed oil (triglyceride) and free fatty acids (FFA) when a model waste oil feedstock was used. The vegetable oil asphalt-based catalyst showed the highest catalytic activity. This was due to the high density and stability of its acid sites, its loose irregular network, its hydrophobicity that prevented the hydration of -OH species, and large pores that provided more acid sites for the reactants. PMID:20219353

Shu, Qing; Nawaz, Zeeshan; Gao, Jixian; Liao, Yuhui; Zhang, Qiang; Wang, Dezheng; Wang, Jinfu

2010-07-01

100

Methanol Production By Reduction Of Formic Acid Over Cu Catalyst Under Hydrothermal Conditions  

NASA Astrophysics Data System (ADS)

In this paper, a two-step process for converting carbon dioxide into methanol was established, consisting of conversion of carbon dioxide into formic acid and formic acid into methanol by hydrothermal treatment. For our previous studies has investigated the reduction of carbon dioxide to formic acid under hydrothermal conditions, the focus of this paper was set on the reduction of formic acid into methanol. The synthesis of methanol was examined by varying the following parameters: amount of Cu as catalyst, pH of the reagent, amount of Zn as reductant, reaction time and so on. The highest yield of 27.8% was achieved. The results indicated that Zn or Al was able to reduce formic acid to methanol more efficiently than other metal reductants. It was also found out that the addition of acid or alkali was not favorable for the synthesis of methanol.

Cheng, Min; Wu, Bing; Jin, Fangming; Duan, Xiaokun; Wang, Yuanqing

2010-11-01

101

Fructose dehydration to 5-hydroxymethylfurfural over solid acid catalysts in a biphasic system.  

PubMed

Different acidic heterogeneous catalysts like alumina, aluminosilicate, zirconium phosphate, niobic acid, ion-exchange resin Amberlyst-15, and zeolite MOR have been studied in fructose dehydration to 5-hydroxymethylfurfural (HMF). The acidity of these materials was characterized using temperature-programmed desorption of NH? and IR spectroscopy of adsorbed pyridine. The nature and strength of acid sites was shown to play a crucial role in the selectivity towards HMF. Brønsted acid sites in the case of zeolites and ion-exchange resin led to high selectivities in the dehydration of fructose with an increase in selectivity with the addition of an organic phase. Lewis acidity in the case of phosphate and oxides resulted in the intensive production of humins from fructose at the initial stages of the process, whereas organic phase addition did not affect selectivity. PMID:22777706

Ordomsky, Vitaly V; van der Schaaf, John; Schouten, Jaap C; Nijhuis, T Alexander

2012-09-01

102

Enhancement of Biodiesel Production from Marine Alga, Scenedesmus sp. through In Situ Transesterification Process Associated with Acidic Catalyst  

PubMed Central

The aim of this study was to increase the yield of biodiesel produced by Scenedesmus sp. through in situ transesterification by optimizing various process parameters. Based on the orthogonal matrix analysis for the acidic catalyst, the effects of the factors decreased in the order of reaction temperature (47.5%) > solvent quantity (26.7%) > reaction time (17.5%) > catalyst amount (8.3%). Based on a Taguchi analysis, the effects of the factors decreased in the order of solvent ratio (34.36%) > catalyst (28.62%) > time (19.72%) > temperature (17.32%). The overall biodiesel production appeared to be better using NaOH as an alkaline catalyst rather than using H2SO4 in an acidic process, at 55.07 ± 2.18% (based on lipid weight) versus 48.41 ± 0.21%. However, in considering the purified biodiesel, it was found that the acidic catalyst was approximately 2.5 times more efficient than the alkaline catalyst under the following optimal conditions: temperature of 70°C (level 2), reaction time of 10?hrs (level 2), catalyst amount of 5% (level 3), and biomass to solvent ratio of 1?:?15 (level 2), respectively. These results clearly demonstrated that the acidic solvent, which combined oil extraction with in situ transesterification, was an effective catalyst for the production of high-quantity, high-quality biodiesel from a Scenedesmus sp. PMID:24689039

Kim, Ga Vin; Choi, WoonYong; Kang, DoHyung; Lee, ShinYoung; Lee, HyeonYong

2014-01-01

103

Pd/C Synthesized with Citric Acid: An Efficient Catalyst for Hydrogen Generation from Formic Acid/Sodium Formate  

PubMed Central

A highly efficient hydrogen generation from formic acid/sodium formate aqueous solution catalyzed by in situ synthesized Pd/C with citric acid has been successfully achieved at room temperature. Interestingly, the presence of citric acid during the formation and growth of the Pd nanoparticles on carbon can drastically enhance the catalytic property of the resulted Pd/C, on which the conversion and turnover frequency for decomposition of formic acid/sodium formate system can reach the highest values ever reported of 85% within 160?min and 64?mol H2 mol?1 catalyst h?1, respectively, at room temperature. The present simple, low cost, but highly efficient CO-free hydrogen generation system at room temperature is believed to greatly promote the practical application of formic acid system on fuel cells. PMID:22953041

Wang, Zhi-Li; Yan, Jun-Min; Wang, Hong-Li; Ping, Yun; Jiang, Qing

2012-01-01

104

Geminal Br?nsted Acid Ionic Liquids as Catalysts for the Mannich Reaction in Water  

PubMed Central

Quaternary ammonium geminal Brønsted acid ionic liquids (GBAILs) based on zwitterionic 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (where the carbon number of the alkyl chain is 4, 8, 10, 12, 14, 16, or 18) and p-toluenesulfonic acid monohydrate were synthesized. The catalytic ionic liquids were applied in three-component Mannich reactions with an aldehyde, ketone, and amine at 25 °C in water. The effects of the type and amount of catalyst and reaction time as well as the scope of the reaction were investigated. Results showed that GBAIL-C14 has excellent catalytic activity and fair reusability. The catalytic procedure was simple, and the catalyst could be recycled seven times via a simple separation process without noticeable decreases in catalytic activity. PMID:24837832

He, Leqin; Qin, Shenjun; Chang, Tao; Sun, Yuzhuang; Zhao, Jiquan

2014-01-01

105

Studies on structure and properties of CNSL novolac resins prepared with succinic acid catalyst  

Microsoft Academic Search

Cashew nut shell liquid (CNSL) was used to prepare a glass fabric laminate. Two fast curing model resins were prepared using\\u000a cardanol and formaldehyde in the presence of succinic acid catalyst. The resins possess ortho-ortho and ortho-para linkages.\\u000a The curing kinetics of the resins showed that the resin prepared with mole ratio 0·8 possesses good curing characteristics.\\u000a The IR spectra

K Sathiyalekshmi

1993-01-01

106

Ionic Liquids as Catalysts for Sulfuric Acid Production and Cleaning of Flue Gases  

Microsoft Academic Search

\\u000a The present paper is concerned with catalytic pollution abatement of sulfur and nitrogen oxides in flue gases from industrial\\u000a sources. Especially fundamental and applied research on industrial catalysts and their model systems is presented with regards\\u000a to cleaning of flue gases from fossil fuel based power plants and plants producing sulfuric acid. Combined DeSOx and DeNOx processes are very common

Rasmus Fehrmann; K. M. Eriksen; S. B. Rasmussen; J. Winnick

107

Catalytic cracking of a polyolefin mixture over different acid solid catalysts  

Microsoft Academic Search

Catalytic cracking of a polyolefin mixture consisting of polypropylene and both low- and high-density polyethylene has been studied at 400 C over a variety of acid solids as catalysts. The highest activities were obtained over HMCM-41, n-HZSM-5 zeolite, with nanometer crystal size, and HBeta zeolite. The high surface area and large pores present in HMCM-41 are responsible for the high

David P. Serrano; José Aguado; José M. Escola

2000-01-01

108

Highly efficient Brønsted acidic ionic liquid-based catalysts for biodiesel synthesis from vegetable oils  

Microsoft Academic Search

Biodiesel has been produced by transesterification of canola oil with methanol in the presence of highly Brønsted acidic ionic liquids based on 1-benzyl-1H-benzimidazole, and the effect of reaction temperature, type and amount of catalyst, molar ratio and reaction time investigated. The results show that the 4B ionic liquid has the highest catalytic activity and best recyclability under the optimised reaction

M. Ghiaci; B. Aghabarari; S. Habibollahi; A. Gil

2011-01-01

109

Synthesis of a nano-crystalline solid acid catalyst from fly ash and its catalytic performance  

Microsoft Academic Search

The synthesis of nano-crystalline activated fly ash catalyst (AFAC) with crystallite size of 12nm was carried out by chemical and thermal treatment of fly ash, a waste material generated from coal-burning power plants. Fly ash was chemically activated using sulfuric acid followed by thermal activation at 600°C. The variation of surface and Physico-chemical properties of the fly ash by activation

Chitralekha Khatri; Ashu Rani

2008-01-01

110

COMPARISON OF CATALYSTS FOR DIRECT TRANSESTERIFICATION OF FATTY ACIDS IN FREEZE DRIED FORAGE SAMPLES  

Microsoft Academic Search

Our objective was to compare 1.09 M methanolic HCl to 14% BF3 in methanol as catalysts for direct transesterification of fatty acids in freeze-dried forage samples. Samples included blue grama (Bouteloua gracilis), fringed sage (Artemisia frigida), western wheatgrass (Pascopyrum smithii), needle-and-thread (Stipa comata), dalmation toadflax (Linaria dalmatica), needleleaf sedge (Carex eleocharis), and scarlet globemallow (Sphaelercea coccinea). Thin layer chromatographic evaluation

T. R. Weston; J. D. Derner; C. M. Murrieta; B. W. Hess

2006-01-01

111

MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid. Influence of niobium and/or palladium on physicochemical  

E-print Network

1 MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid. Influence to acetic acid and ethylene is examined. Catalysts without molybdenum (VNb031Pd3e-4Ox) are also studied for comparison. The structural properties of the precursors and of the catalysts obtained by calcination

Paris-Sud XI, Université de

112

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst  

Microsoft Academic Search

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)2O using sulfamic acid as catalyst (5mol%) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter

Dharita J. Upadhyaya; Alessandro Barge; Rachele Stefania; Giancarlo Cravotto

2007-01-01

113

Activity and stability of non-precious metal catalysts for oxygen reduction in acid and alkaline electrolytes  

Microsoft Academic Search

The activity and stability of non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in both acid and alkaline electrolytes were studied by the rotating disk electrode technique. The NPMCs were prepared through the pyrolysis of cobalt–iron–nitrogen chelate followed by combination of pyrolysis, acid leaching, and re-pyrolysis. In both environments, the catalysts heat-treated at 800–900°C exhibited relatively high activity.

Xuguang Li; Gang Liu; Branko N. Popov

2010-01-01

114

40 CFR 75.3 - General Acid Rain Program provisions.  

Code of Federal Regulations, 2013 CFR

...17 2013-07-01 2013-07-01 false General Acid Rain Program provisions. 75.3 Section 75.3 Protection...CONTINUOUS EMISSION MONITORING General § 75.3 General Acid Rain Program provisions. The provisions of part 72,...

2013-07-01

115

40 CFR 75.3 - General Acid Rain Program provisions.  

...17 2014-07-01 2014-07-01 false General Acid Rain Program provisions. 75.3 Section 75.3 Protection...CONTINUOUS EMISSION MONITORING General § 75.3 General Acid Rain Program provisions. The provisions of part 72,...

2014-07-01

116

40 CFR 75.3 - General Acid Rain Program provisions.  

Code of Federal Regulations, 2012 CFR

...17 2012-07-01 2012-07-01 false General Acid Rain Program provisions. 75.3 Section 75.3 Protection...CONTINUOUS EMISSION MONITORING General § 75.3 General Acid Rain Program provisions. The provisions of part 72,...

2012-07-01

117

Catalytic cracking of a polyolefin mixture over different acid solid catalysts  

SciTech Connect

Catalytic cracking of a polyolefin mixture consisting of polypropylene and both low- and high-density polyethylene has been studied at 400 C over a variety of acid solids as catalysts. The highest activities were obtained over HMCM-41, n-HZSM-5 zeolite, with nanometer crystal size, and HBeta zeolite. The high surface area and large pores present in HMCM-41 are responsible for the high conversions obtained with this catalyst. Likewise, in the case of n-HZSM-5, the presence of a high external surface area enhances its cracking activity, because the zeolite external acid sites are not sterically hindered for the conversion of the bulky polyolefin molecules. Significant differences are observed in the product distribution: n-HZSM-5 shows the highest selectivity toward C{sub 1}--C{sub 4} gaseous hydrocarbons (50 wt %), HBeta leads mainly to liquid hydrocarbons in the range C{sub 5}--C{sub 12} (60 wt %), whereas HMCM-41 yields both C{sub 5}--C{sub 12} (54 wt %) and C{sub 13}--C{sub 30} (32 wt %) fractions. A certain loss of activity of these catalysts has been observed after one cycle of regeneration. For HMCM-41, this phenomenon is caused by both dealumination and particle aggregation that take place during the regeneration treatment.

Serrano, D.P.; Aguado, J.; Escola, J.M.

2000-05-01

118

Highly efficient Brønsted acidic ionic liquid-based catalysts for biodiesel synthesis from vegetable oils.  

PubMed

Biodiesel has been produced by transesterification of canola oil with methanol in the presence of highly Brønsted acidic ionic liquids based on 1-benzyl-1H-benzimidazole, and the effect of reaction temperature, type and amount of catalyst, molar ratio and reaction time investigated. The results show that the 4B ionic liquid has the highest catalytic activity and best recyclability under the optimised reaction conditions. Thus, this ionic liquid is able to catalyze the transesterification of canola oil to its methyl esters in 5 h with yields of more than 95%. Density functional calculations (B3LYP), using the 6-311G basis set, have been performed to have a better understanding on the reactivity of these catalysts. The catalytic activity of 4B for the transesterification of other vegetable oils and alcohols has also been studied. PMID:20970994

Ghiaci, M; Aghabarari, B; Habibollahi, S; Gil, A

2011-01-01

119

Catalytic hydrothermal pretreatment of corncob into xylose and furfural via solid acid catalyst.  

PubMed

Selectively catalytic hydrothermal pretreatment of corncob into xylose and furfural has been developed in this work using solid acid catalyst (SO4(2-)/TiO2-ZrO2/La(3+)). The effects of corncob-to-water ratio, reaction temperature and residence time on the performance of catalytic hydrothermal pretreatment were investigated. Results showed that the solid residues contained mainly lignin and cellulose, which was indicative of the efficient removal of hemicelluloses from corncob by hydrothermal method. The prepared catalyst with high thermal stability and strong acid sites originated from the acid functional groups was confirmed to contribute to the hydrolysis of polysaccharides into monosaccharides followed by dehydration into furfural. Highest furfural yield (6.18 g/100g) could be obtained at 180°C for 120 min with 6.80 g/100g xylose yield when the corncob/water ratio of was 10:100. Therefore, selectively catalytic hydrothermal pretreatment of lignocellulosic biomass into important platform chemicals by solid acids is considered to be a potential treatment for biodiesel and chemical production. PMID:24632409

Li, Huiling; Deng, Aojie; Ren, Junli; Liu, Changyu; Lu, Qi; Zhong, Linjie; Peng, Feng; Sun, Runcang

2014-04-01

120

A general formula for reactant conversion over a single catalyst particle in TAP pulse experiments  

E-print Network

catalysis" [Zheng et al., 2008]). For example, heterogeneous CO oxidation over plat- inum catalyst deposited on its sur- face. Since all experiments use the same basic unit, namely, the catalyst particle

Feres, Renato

121

Oil palm trunk and sugarcane bagasse derived solid acid catalysts for rapid esterification of fatty acids and moisture-assisted transesterification of oils under pseudo-infinite methanol.  

PubMed

The use of pseudo-infinite methanol in increasing the rate of esterification and transesterification reactions was studied using oil palm trunk (OPT) and sugarcane bagasse (SCB) derived solid acid catalysts. The catalysts were prepared by incomplete carbonisation at 400°C for 8h, followed by sulfonation at 150°C for 15h and characterised using TGA/DTA, XRD, FT-IR, SEM-EDS, EA and titrimetric determinations of acid sites. Under optimal reaction conditions, the process demonstrated rapid esterification of palmitic acid, with FAME yields of 93% and 94% in 45min for OPT and SCB catalysts, respectively. With the process, moisture levels up to 16.7% accelerated the conversion of low FFA oils by sulfonated carbon catalysts, through moisture-induced violent bumping. Moisture assisted transesterification of palm olein containing 1.78% FFA and 8.33% added water gave FAME yield of 90% in 10h, which was two folds over neat oil. PMID:24561631

Ezebor, Francis; Khairuddean, Melati; Abdullah, Ahmad Zuhairi; Boey, Peng Lim

2014-04-01

122

Acid zeolites as alcohol racemization catalysts: screening and application in biphasic dynamic kinetic resolution.  

PubMed

Acid zeolites were screened as heterogeneous catalysts for racemization of benzylic alcohols. The most promising zeolites appeared to be H-Beta zeolites, for which the optimal reaction conditions were studied in further detail. The zeolite performance was compared to that of homogeneous acids and acid resins under similar reaction conditions. In a second part of the research, H-Beta zeolites were applied in dynamic kinetic resolution (DKR) of 1-phenylethanol, which was conducted by means of a two-phase approach and which resulted in yields smoothly crossing the 50% border up to 90%, with an enantiomeric excess of >99%. To explore the applicability of this biphasic methodology, several other substrates were examined in the standard racemization reaction and in the biphasic dynamic kinetic resolution. PMID:15565578

Wuyts, S; De Temmerman, K; De Vos, D E; Jacobs, P A

2004-12-17

123

Lactic acid conversion to 2,3-pentanedione and acrylic acid over silica-supported sodium nitrate: Reaction optimization and identification of sodium lactate as the active catalyst  

SciTech Connect

Lactic acid is converted to 2,3-pentanedione, acrylic acid, and other products in vapor-phase reactions over silica-supported sodium lactate formed from sodium nitrate. Multiparameter optimization of reaction conditions using a Box-Benkhen experimental design shows that the highest yield and selectivity to 2,3-pentanedione are achieved at low temperature, elevated pressure, and long contact time, while yield and selectivity to acrylic acid are most favorable at high temperature, low pressure, and short contact time. Post-reaction Fourier transform infrared spectroscopic analyses of the catalyst indicate that sodium nitrate as the initial catalyst material is transformed to sodium lactate at the onset of reaction via proton transfer from lactic acid to nitrate. The resultant nitric acid vaporizes as it is formed, leaving sodium lactate as the sole sodium-bearing species on the catalyst during reaction. 19 refs., 8 figs., 5 tabs.

Wadley, D.C.; Tam, M.S.; Miller, D.J. [Michigan State Univ., East Lansing, MI (United States)] [and others] [Michigan State Univ., East Lansing, MI (United States); and others

1997-01-15

124

Isoselenazolones as catalysts for the activation of bromine: bromolactonization of alkenoic acids and oxidation of alcohols.  

PubMed

Isoselenazolones were synthesized by a copper-catalyzed Se-N bond forming reaction between 2-halobenzamides and selenium powder. The catalytic activity of the various isoselenazolones was studied in the bromolactonization of pent-4-enoic acid. Isoselenazolone 9 was studied as a catalyst in several reactions: the bromolactonization of a series of alkenoic acids with bromine or N-bromosuccinimide (NBS) in the presence of potassium carbonate as base, the bromoesterification of a series of alkenes using NBS and a variety of carboxylic acids, and the oxidation of secondary alcohols to ketones using bromine as an oxidizing reagent. Mechanistic details of the isoselenazolone-catalyzed bromination reaction were revealed by (77)Se NMR spectroscopic and ES-MS studies. The oxidative addition of bromine to the isoselenazolone gives the isoselenazolone(IV) dibromide, which could be responsible for the activation of bromine under the reaction conditions. Steric effects from an N-phenylethyl group on the amide of the isoselenazolone and electron-withdrawing fluoro substituents on the benzo fused-ring of the isoselenazolone appear to enhance the stability of the isoselenazolone as a catalyst for the bromination reaction. PMID:23046286

Balkrishna, Shah Jaimin; Prasad, Ch Durga; Panini, Piyush; Detty, Michael R; Chopra, Deepak; Kumar, Sangit

2012-11-01

125

Photodegradation of nalidixic acid assisted by TiO(2) nanorods/Ag nanoparticles based catalyst.  

PubMed

Two different nanosized TiO2-based catalysts supported onto glass with tailored photocatalytic properties upon irradiation by UV light were successfully employed for the degradation of nalidixid acid, a widely diffused antibacterial agent of environmental relevance known to be non-biodegradable. Anatase rod-like TiO2 nanocrystals (TiO2NRs) and a semiconductor oxide-noble metal nanocomposite TiO2 NRs/Ag nanoparticles (NPs), synthesized by colloidal chemistry routes, were cast onto glass slide and employed as photocatalysts. A commercially available catalyst (TiO2 P25), also immobilized onto a glass slide, was used as a reference material. It was found that both TiO2 NRs/Ag NPs composite and TiO2 NRs demonstrated a photocatalytic efficiency significantly higher than the reference TiO2 P25. Specifically, TiO2 NRs/Ag NPs showed a photoactivity in nalidixic acid degradation 14 times higher than TiO2 P25 and 4 times higher than bare TiO2 NRs in the first 60min of reaction. Several by-products were identified by HPLC-MS along the nalidixic acid degradation, thus getting useful insight on the degradation pathway. All the identified by-products resulted completely removed after 6h of reaction. PMID:23466278

Petronella, F; Diomede, S; Fanizza, E; Mascolo, G; Sibillano, T; Agostiano, A; Curri, M L; Comparelli, R

2013-05-01

126

Enhanced catalytic performance of Pd catalyst for formic acid electrooxidation in ionic liquid aqueous solution  

NASA Astrophysics Data System (ADS)

A protic ionic liquid (IL), n-butylammonium nitrate (N4NO3), is prepared and employed as the electrolyte for formic acid electrooxidation reaction (FAOR) on Pd catalysts. The oxidation peak potential of FAOR in the IL solution shows about a 200 mV negative shift as compared with those in traditional H2SO4/HClO4 electrolytes, suggesting that FAOR can be more easily carried out on Pd catalysts in IL media. The catalytic properties of Pd toward FAOR are not only dependent on the concentration of IL, as a consequence of the varied electronic conductivity of the IL solution, but also on the high potential limit of the cyclic voltammograms. When the Pd catalyst is cycled up to 1.0 V (vs. SCE), which induces a significant oxidation of Pd, it shows ca. 4.0 times higher activity than that not subjected to the Pd oxidation (up to 0.6 V). The Pd oxides, which are more easily formed in IL solution than in traditional H2SO4/HClO4 electrolytes, may play a crucial role in increasing the catalytic activities of Pd toward FAOR. Our work would shed new light on the mechanism of FAOR and highlight the potential applications of IL as green and environment-friendly electrolytes in fuel cells and other technologies.

Feng, Yuan-Yuan; Yin, Qian-Ying; Lu, Guo-Ping; Yang, Hai-Fang; Zhu, Xiao; Kong, De-Sheng; You, Jin-Mao

2014-12-01

127

Catalytic Friedel-Crafts acylation of benzene, chlorobenzene, and fluorobenzene using a novel catalyst system, hafnium triflate and trifluoromethanesulfonic acid  

Microsoft Academic Search

Catalytic Friedel-Crafts acylation of benzene and unactivated benzenes such as chlorobenzene and fluorobenzene has been successfully carried out using hafnium (IV) triflate and trifluoromethanesulfonic acid as catalysts. Both aromatic and aliphatic carboxylic acid chlorides reacted smoothly under the conditions to afford the corresponding aromatic ketones in good yields.

Sh? Kobayashi; Shunsuke Iwamoto

1998-01-01

128

Indium metal-organic frameworks as high-performance heterogeneous catalysts for the synthesis of amino Acid derivatives.  

PubMed

Indium metal-organic frameworks (MOFs) were first used as recyclable heterogeneous Lewis acid catalysts for the synthesis of amino acid derivatives with excellent conversion yields. Moreover, exposed ether groups (Lewis basic sites) on the pore walls of In-MOF 2 could activate trimethylsilyl cyanide, forming hypervalent silicate intermediates, as proven by (29)Si NMR. PMID:25244398

Xia, Jing; Xu, Jianing; Fan, Yong; Song, Tianyou; Wang, Li; Zheng, Jifu

2014-10-01

129

A facile approach for the preparation of tunable acid nano-catalysts with a hierarchically mesoporous structure.  

PubMed

A facile and efficient approach to prepare hierarchically and radially mesoporous nano-catalysts with tunable acidic properties has been successfully developed. The nanospheres show excellent catalytic performance for the acid catalysed reactions, i.e. cracking of 1,3,5-triisopropylbenzene and hydrolysis of sucrose. PMID:24898618

Choi, Youngbo; Yun, Yang Sik; Park, Hongseok; Park, Dae Sung; Yun, Danim; Yi, Jongheop

2014-07-21

130

UBC Social Ecological Economic Development Studies (SEEDS) Student Report Investigation of Solid Acid Catalyst Functionalization for the Production of Biodiesel  

E-print Network

, waste vegetable oils can be used as a feedstock for biodiesel production. However, waste vegetable oils on the development of the acid density of the catalyst; and analyze the effect of functionalization steps phase contact (BC-A-VS), or ozonating the biochar (BC-A-O). These procedures increase the acid density

131

SYNTHESIS AND CHARACTERIZATION OF A NOVEL SOLID ACID CATALYST FOR IMPROVED USE OF WASTE OIL FEEDSTOCK FOR BIODIESEL PRODUCTION  

EPA Science Inventory

Carbon Catalyst Synthesis - Sucrose was treated directly with excess sulfuric acid sulfuric acid (9:1 mol/mol, 25°C). A carbon foam (nearly 20 fold increase in bulk volume) was immediately formed. The foam was then washed until no sulfate was dete...

132

Transesterification of soybean oil over WO3 supported on AlPO4 as a solid acid catalyst.  

PubMed

WO(3)/AlPO(4) catalysts were prepared by impregnation of AlPO(4) with ammonium metatungstate. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric and differential thermal analysis (TG-DTA) demonstrated that the tungsten compound was incorporated into AlPO(4) forming the catalyst with an enhanced acidity. When transesterification of soybean oil over the catalysts was performed, the catalyst with 30 wt.% WO(3) loading and calcined at 1073 K, exhibited the best catalytic activity with a conversion of 72.5%. The transesterification was optimal at 453 K for 5h with a methanol/oil ratio of 30:1 and catalyst dosage of 5 wt.%. Free fatty acid (FFA) and water did not affect the catalytic activity. The catalyst proved to be stable over four transesterification cycles as it lost only 4% of its activity after being reused four times. The catalyst could be used for the transesterification of low-cost oils for biodiesel production. PMID:22728183

Xie, Wenlei; Yang, Dong

2012-09-01

133

On the nature of the deactivation of supported palladium nanoparticle catalysts in the decarboxylation of fatty acids.  

SciTech Connect

Supported palladium catalysts are effective catalysts for the hydrogen-free decarboxylation of fatty acids. However, the catalysts deactivate severely after one use. Here, the recyclability of a well-defined, mesoporous silica-supported palladium nanoparticle catalyst is evaluated in the batch decarboxylation of stearic acid at 300 C under inert atmosphere, producing n-heptadecane. The nature of the catalyst deactivation is examined in detail via an array of characterization techniques. X-ray photoelectron spectroscopy (XPS) demonstrates that little palladium surface oxidation occurs over the course of the reaction, and a combination of X-ray absorption spectroscopy and transmission electron microscopy (TEM) suggests negligible particle sintering or agglomeration. Physisorption and chemisorption measurements demonstrate substantial loss in total surface area and porosity as well as accessible palladium surface area with these losses attributed to significant organic deposition on the catalyst, as verified via thermogravimetric analysis. High temperature calcination is applied to combust and remove these residues, but resultant nanoparticle agglomeration is significant. Solid state nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and solid dissolution followed by organic extraction methodologies demonstrate that the carbonaceous deposits are not coke but rather strongly adsorbed reactants and products. Detrimental coke formation, as suggested by prior literature, is verified to be absent, as extraction of the surface-deposited organic species yields nearly complete recovery of the total surface area, pore volume, and active palladium surface area. Furthermore, the regenerated catalyst exhibits a corresponding significant recovery of decarboxylation activity.

Ping, E. W.; Pierson, J.; Wallace, R.; Miller, J. T.; Fuller, T. F.; Jones, C. W. (Chemical Sciences and Engineering Division); (Georgia Institute of Technology)

2011-04-15

134

A novel catalyst of Fe-octacarboxylic acid phthalocyanine supported by attapulgite for degradation of Rhodamine B  

SciTech Connect

A novel nano-composite catalyst was prepared from immobilization of Fe-octacarboxylic acid phthalocyanine onto the supporting material attapulgite. The morphology and structure of the catalyst were analyzed by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and ultraviolet-visible spectroscopy. The catalyst activity was examined through comparative experiments, and results showed that it exhibited high activity for degradation of Rhodamine B in the presence of hydrogen peroxide. The recycling test was also carried out to prove its reusability in catalytic application.

Fang, Ying [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Shanghai 201620 (China) [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Shanghai 201620 (China); College of Materials Science and Engineering, Donghua University, Shanghai 201620 (China); Chen, Dajun, E-mail: cdj@dhu.edu.cn [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Shanghai 201620 (China) [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Shanghai 201620 (China); College of Materials Science and Engineering, Donghua University, Shanghai 201620 (China)

2010-11-15

135

Thermal stability, acidity, catalytic properties, and deactivation behaviour of SAPO-5 catalysts: Effect of silicon content, acid treatment, and Na exchange  

SciTech Connect

Crystalline microporous SAPO-5 molecular sieves with different silicon content, acid-treated SAPO-5 and Na-exchanged SAPO-5 were investigated for their thermal stability, and acidic and catalytic properties. SAPO-5 materials with increasing SI framework content exhibited lower thermal stability. The effects of the thermal treatment and Na exchange on the N{sub 2}-sorption capacity (at 78 K) of these materials were studied. In situ IR spectroscopic investigations of pyridine chemisorbed on the aluminophosphate catalysts revealed that the concentration of Broensted and Lewis acid sites are strongly affected by the Si content in the AlPO{sub 4} framework, acid treatment, and Na exchange. The results of temperature programmed desorption (TPD) and stepwise thermal desorption of pyridine suggest that there exists a broad site energy distribution over the aluminophosphate catalysts increases with the increasing Si content in the AlPO{sub 4} framework. The acid treatment and Na exchange showed a decrease in the number of strong acid sites on SAPO-5. The TPD of pyridine over SAPO-5, acid-treated SAPO-5, and Na-exchanged SAPO-5 indicated the presence of two types of acid sites. Correlation between the number of strong acid sites (measured in terms of the chemisorption of pyridine at 673 K) and framework charge on the aluminophosphate catalysts has also been obtained. The catalytic activities of SAPO-5 catalysts in the ethanol, n-hexane, isooctane, toluene, and o-xylene conversion reactions were studied. 22 refs., 11 figs., 5 tabs.

Akolekar, D.B. [Univ. of New South Wales, Kensington (Australia)] [Univ. of New South Wales, Kensington (Australia)

1994-09-01

136

The Origin of Regioselectivity in 2-butanol Dehydration on Solid Acid Catalysts  

SciTech Connect

The origin in the variations of trans-/cis-2-butene product selectivity ratios in 2-butanol dehydration over solid acid catalysts were investigated using a combined experimental-theory approach. Reactivity measurements over ?-Al2O3, AlOx/SBA-15, and H-form zeolites with widely varying Si/Al ratios and pore structures showed over two orders of magnitude change in the trans-/cis-2-butene product ratio. Activation energy barriers calculated for the concerted C-O and ?-C-H bond breakings of adsorbed butoxy intermediates by dispersion-corrected DFT calculations correctly predicted the trans-/cis-2-butene product ratio observed on ?-Al2O3. The very low trans-2-butene selectivity on ?-Al2O3 can now be understood by the formation of a late transition state with high energy barrier caused by the strong van der Waals interaction between the ?-H atoms and the flat catalyst surface. Decreasing the dispersive attractive force between the adsorbed butoxide and the surface (e.g., by moving it further away from the support surface in AlOx/SBA-15) leads to almost equimolar formation of the trans- and cis-2-butene isomers. Trans-/cis-2-butene selectivity ratios much higher than that dictated by thermodynamic equilibrium can be achieved by introducing additional geometric constraints around the active catalytic site (e.g., varying the 3D environment around the active center in zeolites). We propose a model to explain the widely varying trans-/cis-2-butene selectivity in 2-butanol dehydration over solid acid catalysts that is consistent with the experimental results in this study. A key outcome of the study is the realization that van der Waals interactions between the reactant and the active catalyst surface must be included in the theoretic models in order to be able to accurately predict product selectivities. This information, in turn, significantly advances our ability to develop catalyst materials with designed active centers in order to achieve desired regioselectivities.

Kwak, Ja Hun; Rousseau, Roger J.; Mei, Donghai; Peden, Charles HF; Szanyi, Janos

2011-10-17

137

Sulfonated mesoporous silica-carbon composites and their use as solid acid catalysts  

NASA Astrophysics Data System (ADS)

The synthesis of highly functionalized porous silica-carbon composites made up of sulfonic groups attached to a carbon layer coating the pores of three types of mesostructured silica (i.e. SBA-15, KIT-6 and mesocellular silica) is presented. The synthesis procedure involves the following steps: (a) removal of the surfactant, (b) impregnation of the silica pores with a carbon precursor, (c) carbonization and (d) sulfonation. The resulting silica-carbon composites contain ˜30 wt % of carbonaceous matter with a high density of acidic groups attached to the deposited carbon (i.e.sbnd SO3H, sbnd COOH and sbnd OH). The structural characteristics of the parent silica are retained in the composite materials, which exhibit a high surface area, a large pore volume and a well-ordered porosity made up uniform mesopores. The high density of the sulfonic groups in combination with the mesoporous structure of the composites ensures that a large number of active sites are easily accessible to reactants. These sulfonated silica-carbon composites behave as eco-friendly, active, selective, water tolerant and recyclable solid acids. In this study we demonstrate the usefulness of these composites as solid acid catalysts for the esterification of maleic anhydride, succinic acid and oleic acid with ethanol. These composites exhibit a superior intrinsic catalytic activity to other commercial solid acids such as Amberlyst-15.

Valle-Vigón, Patricia; Sevilla, Marta; Fuertes, Antonio B.

2012-11-01

138

Effects of metal and acidic sites on the reaction by-products of butyl acetate oxidation over palladium-based catalysts.  

PubMed

Catalytic oxidation is widely used in pollution control technology to remove volatile organic compounds. In this study, Pd/ZSM-5 catalysts with different Pd contents and acidic sites were prepared via the impregnation method. All the catalysts were characterized by means of N2 adsorption-desorption, X-ray fluorescence (XRF), H2 temperature programmed reduction (H2-TPR), and NH3 temperature programmed desorption (NH3-TPD). Their catalytic performance was investigated in the oxidation of butyl acetate experiments. The by-products of the reaction were collected in thermal desorption tubes and identified by gas chromatography/mass spectrometry. It was found that the increase of Pd content slightly changed the catalytic activity of butyl acetate oxidation according to the yield of CO2 achieved at 90%, but decreased the cracking by-products, whereas the enhancement of strong acidity over Pd-based catalysts enriched the by-product species. The butyl acetate oxidation process involves a series of reaction steps including protolysis, dehydrogenation, dehydration, cracking, and isomerization. Generally, butyl acetate was cracked to acetic acid and 2-methylpropene and the latter was an intermediate of the other by-products, and the oxidation routes of typical by-products were proposed. Trace amounts of 3-methylpentane, hexane, 2-methylpentane, pentane, and 2-methylbutane originated from isomerization and protolysis reactions. PMID:25079284

Yue, Lin; He, Chi; Hao, Zhengping; Wang, Shunbing; Wang, Hailin

2014-03-01

139

Insights into the interplay of Lewis and Brønsted acid catalysts in glucose and fructose conversion to 5-(hydroxymethyl)furfural and levulinic acid in aqueous media.  

PubMed

5-(Hydroxymethyl)furfural (HMF) and levulinic acid production from glucose in a cascade of reactions using a Lewis acid (CrCl3) catalyst together with a Brønsted acid (HCl) catalyst in aqueous media is investigated. It is shown that CrCl3 is an active Lewis acid catalyst in glucose isomerization to fructose, and the combined Lewis and Brønsted acid catalysts perform the isomerization and dehydration/rehydration reactions. A CrCl3 speciation model in conjunction with kinetics results indicates that the hydrolyzed Cr(III) complex [Cr(H2O)5OH](2+) is the most active Cr species in glucose isomerization and probably acts as a Lewis acid-Brønsted base bifunctional site. Extended X-ray absorption fine structure spectroscopy and Car-Parrinello molecular dynamics simulations indicate a strong interaction between the Cr cation and the glucose molecule whereby some water molecules are displaced from the first coordination sphere of Cr by the glucose to enable ring-opening and isomerization of glucose. Additionally, complex interactions between the two catalysts are revealed: Brønsted acidity retards aldose-to-ketose isomerization by decreasing the equilibrium concentration of [Cr(H2O)5OH](2+). In contrast, Lewis acidity increases the overall rate of consumption of fructose and HMF compared to Brønsted acid catalysis by promoting side reactions. Even in the absence of HCl, hydrolysis of Cr(III) decreases the solution pH, and this intrinsic Brønsted acidity drives the dehydration and rehydration reactions. Yields of 46% levulinic acid in a single phase and 59% HMF in a biphasic system have been achieved at moderate temperatures by combining CrCl3 and HCl. PMID:23432136

Choudhary, Vinit; Mushrif, Samir H; Ho, Christopher; Anderko, Andrzej; Nikolakis, Vladimiros; Marinkovic, Nebojsa S; Frenkel, Anatoly I; Sandler, Stanley I; Vlachos, Dionisios G

2013-03-13

140

Thermal decomposition of lignocellulosic biomass in the presence of acid catalysts.  

PubMed

Transformation of lignocellulosic biomass to biofuels involves multiple processes, in which thermal decomposition, hydrotreatment are the most central steps. Current work focuses on the impact of several solid acids and Keggin-type heteropolyacids on the decomposition temperature (Td) of pine wood and the characterization of the resulted products. It has been observed that a mechanical mixture of solid acids with pine wood has no influence on Td, while the use of heteropolyacids lower the Td by 100°C. Moreover, the treatment of biomass with a catalytic amount of H3PW12O40 leads to formation of three fractions: solid, liquid and gas, which have been investigated by elemental analysis, TGA, FTIR, GC-MS and NMR. The use of heteropolyacid leads, at 300°C, to a selective transformation of more than 50 wt.% of the holocellulose part of the lignocellulosic biomass. Moreover, 60 wt.% of the catalyst H3PW12O40 are recovered. PMID:24055967

Larabi, Cherif; al Maksoud, Walid; Szeto, Kai C; Roubaud, Anne; Castelli, Pierre; Santini, Catherine C; Walter, Jean J

2013-11-01

141

Continuous esterification of free Fatty acids in crude biodiesel by an integrated process of supercritical methanol and sodium methoxide catalyst.  

PubMed

An integrated process of supercritical methanol (SCM) and sodium methoxide catalyst was developed to produce fatty acid methyl esters (FAMEs) via continuous esterification from crude biodiesel. The crude biodiesel with high free fatty acid (FFA) content must be refined to reduce the acid value (AV) for meeting the quality standards. The process parameters were studied by Box-Behnken design (BBD) of response surface methodology (RSM). The experimental results revealed that the AV of crude biodiesel decreased from 18.66 to 0.55 mg KOH g(-1) at the reaction conditions of 350 °C, 0.5 % amount of sodium methoxide catalyst, and 10 MPa. Temperature shows the most significant effect on the esterification, followed by pressure and amount of sodium methoxide catalyst. This integrated process proved to be a potential route to refine the crude biodiesel because of its continuity, high efficiency, and less energy consumption with relatively moderate reaction conditions compared with conventional methods. PMID:25119550

Zeng, Dan; Li, Ruosong; Feng, Mingjun; Fang, Tao

2014-10-01

142

Porosity and surface area of monolithic carbon aerogels prepared using alkaline carbonates and organic acids as polymerization catalysts  

Microsoft Academic Search

Carbon aerogels were prepared by polymerization of a resorcinol–formaldehyde mixture using different polymerization catalysts such as: sodium or potassium carbonates, oxalic acid or para-toluenesulfonic acid. The carbon aerogel obtained with this last acid was further CO2-activated to 8.5% and 22% burn-off. All samples were characterized by N2 and CO2 adsorption at ?196 and 0°C, respectively, and by mercury porosimetry, scanning

D. Fairén-Jiménez; F. Carrasco-Marín; C. Moreno-Castilla

2006-01-01

143

Catalytic pyrolysis of oil fractions separated from food waste leachate over nanoporous acid catalysts.  

PubMed

Oil fractions, separated from food waste leachate, can be used as an energy source. Especially, high quality oil can be obtained by catalytic cracking. In this study, nanoporous catalysts such as Al-MCM-41 and mesoporous MFI type zeolite were applied to the catalytic cracking of oil fractions using the pyrolysis gas chromatography/mass spectrometry. Mesoporous MFI type zeolite showed better textural porosity than Al-MCM-41. In addition, mesoporous MFI type zeolite had strong Brönsted acidity while Al-MCM-41 had weak acidity. Significant amount of acid components in the food waste oil fractions were converted to mainly oxygenates and aromatics. As a result of its well-defined nanopores and strong acidity, the use of a mesoporous MFI type zeolite produced large amounts of gaseous and aromatic compounds. High yields of hydrocarbons within the gasoline range were also obtained in the case of mesoporous MFI type zeolite, whereas the use of Al-MCM-41, which exhibits relatively weak acidity, resulted in high yields of oxygenates and diesel range hydrocarbons. PMID:22121679

Kim, Seung-Soo; Heo, Hyeon Su; Kim, Sang Guk; Ryoo, Ryong; Kim, Jeongnam; Jeon, Jong-Ki; Park, Sung Hoon; Park, Young-Kwon

2011-07-01

144

Electrowinning of Nickel from Spent Nickel Catalyst Leachate with Sulphoric Acid  

Microsoft Academic Search

Large amount of Nickel catalysts are used by different industries resulting in the production of large amount of solid waste containing nickel which is the spent or deactivated catalysts. These catalysts contain from 14-24% nickel based on the production company and the process. Nickel electro-winning from spent catalyst leachate solutions is studied to determine the best operative conditions such as

R. Ghanem; H. Farag; Y. Eltaweel; Mona E. Ossman

145

Mesoporous siliconiobium phosphate as a pure Brønsted acid catalyst with excellent performance for the dehydration of glycerol to acrolein.  

PubMed

The development of solid acid catalysts that contain a high density of Brønsted acid sites with suitable acidity, as well as a long lifetime, is one of great challenges for the efficient dehydration of glycerol to acrolein. Herein, we report on a mesoporous siliconiobium phosphate (NbPSi-0.5) composite, which is a promising solid Brønsted acid that is a potential candidate for such a high-performance catalyst. A variety of characterization results confirm that NbPSi-0.5 contains nearly pure Brønsted acid sites and has well-defined large mesopores. In addition, NbPSi-0.5 contains a similar amount of acid sites and exhibits weaker acidity than that of the highly acidic niobium phosphate and HZSM-5 zeolite. NbPSi-0.5 is quite stable and has a high activity for the dehydration of glycerol. The stability of NbPSi-0.5 is about three times higher than that of the reported catalyst. The significantly enhanced catalytic performance of NbPSi-0.5 can be attributed to 1) nearly pure Brønsted acidity, which suppresses side reactions that lead to coke formation; 2) a significant reduction of pore blocking due to the mesopores; and 3) a decrease in the amount and oxidation temperature of coke. PMID:23132784

Choi, Youngbo; Park, Dae Sung; Yun, Hyeong Jin; Baek, Jayeon; Yun, Danim; Yi, Jongheop

2012-12-01

146

Activity and Evolution of Vapor Deposited Pt-Pd Oxygen Reduction Catalysts for Solid Acid Fuel Cells  

SciTech Connect

The performance of hydrogen fuel cells based on the crystalline solid proton conductor CsH2PO4 is circumscribed by the mass activity of platinum oxygen reduction catalysts in the cathode. Here we report on the first application of an alloy catalyst in a solid acid fuel cell, and demonstrate an activity 4.5 times greater than Pt at 0.8 V. These activity enhancements were obtained with platinum-palladium alloys that were vapor-deposited directly on CsH2PO4 at 210 C. Catalyst mass activity peaks at a composition of 84 at% Pd, though smaller activity enhancements are observed for catalyst compositions exceeding 50 at% Pd. Prior to fuel cell testing, Pd-rich catalysts display lattice parameter expansions of up to 2% due to the presence of interstitial carbon. After fuel cell testing, a Pt-Pd solid solution absent of lattice dilatation and depleted in carbon is recovered. The structural evolution of the catalysts is correlated with catalyst de-activation.

Papandrew, Alexander B [ORNL; Chisholm, Calum R [ORNL; Zecevic, strahinja [LiOx, Inc., Pasadena, California 91106, United States; Veith, Gabriel M [ORNL; Zawodzinski, Thomas A [ORNL

2013-01-01

147

A Brønsted acidic ionic liquid as an efficient and environmentally benign catalyst for biodiesel synthesis from free fatty acids and alcohols.  

PubMed

Biodiesel could be synthesized using Brønsted acidic ionic liquid N-methyl-2-pyrrolidonium methyl sulfonate ([NMP][CH(3)SO(3)]) as a catalyst, specially with free long-chain fatty acids or their mixtures, as well as with low-molecular weight alcohols as substrates. This catalyst showed good catalytic and reusable performance under mild conditions and without any additional organic solvent. The ionic liquid could be reused eight times after the water in the ionic liquid was removed. The yields of fatty acid alkyl esters could reach between 93.6% and 95.3% after the esterifications were carried out at 70 degrees C for 8h. Therefore, an efficient and environmentally friendly catalyst was provided for the synthesis of biodiesel from low-cost feedstocks such as waste oils. PMID:19427782

Zhang, Lei; Xian, Mo; He, Yucai; Li, Liangzhi; Yang, Jianming; Yu, Shitao; Xu, Xin

2009-10-01

148

Sulfuric acid functional zirconium (or aluminum) incorporated mesoporous MCM-48 solid acid catalysts for alkylation of phenol with tert-butyl alcohol  

NASA Astrophysics Data System (ADS)

Several zirconium (or aluminum) incorporated mesoporous MCM-48 solid acid catalysts (SO42-/Zr-MCM-48 and SO42-/Al-MCM-48) were prepared by the impregnation method and their physicochemical properties were characterized by means of XRD, FT-IR, TEM, NH3-TPD and N2 physical adsorption. Also, the catalytic activities of these solid acid catalysts were evaluated by the alkylation of phenol with tert-butyl alcohol. The effect of weight hour space velocity (WHSV), reaction time and reaction temperature on catalytic properties was also studied. The results show that the SO42-/Zr-MCM-48 and SO42-/Al-MCM-48 still have good mesoporous structure and long range ordering. Compared with the Zr (or Al)-MCM-48 samples, SO42-/Zr-MCM-48 and SO42-/Al-MCM-48 solid acid catalysts have strong acidity and exhibit high activities in alkylation reaction of phenol with tert-butyl alcohol. The SO42-/Zr-MCM-48-25 (molar ratio of Si/Zr=0.04) catalyst was found to be the most promising and gave the highest phenol conversion among all catalysts. A maximum phenol conversion of 91.6% with 4-tert-butyl phenol (4-TBP) selectivity of 81.8% was achieved when the molar ratio of tert-butyl alcohol:phenol is 2:1, reaction time is 2 h, the WHSV is 2 h-1 and the reaction temperature is 140 °C.

Jiang, Tingshun; Cheng, Jinlian; Liu, Wangping; Fu, Lie; Zhou, Xuping; Zhao, Qian; Yin, Hengbo

2014-10-01

149

Production of biodiesel from mixed waste vegetable oil using an aluminium hydrogen sulphate as a heterogeneous acid catalyst.  

PubMed

Al(HSO(4))(3) heterogeneous acid catalyst was prepared by the sulfonation of anhydrous AlCl(3). This catalyst was employed to catalyze transesterification reaction to synthesis methyl ester when a mixed waste vegetable oil was used as feedstock. The physical and chemical properties of aluminum hydrogen sulphate catalyst were characterized by scanning electron microscopy (SEM) measurements, energy dispersive X-ray (EDAX) analysis and titration method. The maximum conversion of triglyceride was achieved as 81 wt.% with 50 min reaction time at 220°C, 16:1 molar ratio of methanol to oil and 0.5 wt.% of catalyst. The high catalytic activity and stability of this catalyst was related to its high acid site density (-OH, Brönsted acid sites), hydrophobicity that prevented the hydration of -OH group, hydrophilic functional groups (-SO(3)H) that gave improved accessibility of methanol to the triglyceride. The fuel properties of methyl ester were analyzed. The fuel properties were found to be observed within the limits of ASTM D6751. PMID:21621409

Ramachandran, Kasirajan; Sivakumar, Pandian; Suganya, Tamilarasan; Renganathan, Sahadevan

2011-08-01

150

Catalyst Activity and Post-operation Analyses of Pt/TiO2 (Rutile) Catalysts Used in the Sulfuric Acid Decomposition Reaction  

SciTech Connect

Production of hydrogen by splitting of water at lower temperatures than by direct thermal decomposition can be achieved by a series of particular chemical reactions that establish a thermochemical cycle [1]. Among the high number of thermochemical water-splitting cycles proposed in the literature [2], the sulfur-based group is of considerable interest. All the sulfur-based cycles employ the catalytic decomposition of sulfuric acid into SO2 and O2. The produced O2 corresponds to the O2 generated from water in the overall cycle. Research performed at the Idaho National Laboratory [3] has found that even one of the most stables catalysts, Pt supported on low surface area titania, deactivates with time on stream (TOS). To develop an understanding of the factors that cause catalyst deactivation, samples of 1% Pt supported on titania (rutile) catalyst were submitted to flowing concentrated sulfuric acid at 1123 K and atmospheric pressure for different TOSs between 0 and 548 h and a number of chemical and spectroscopic analyses applied to the spent samples.

Lucia M. Petkovic; Daniel M. Ginosar; Harry W. Rollins; Kyle C. Burch; Patrick J. Pinhero; Helen H. Farrell

2007-06-01

151

A general route to hollow mesoporous rare-earth silicate nanospheres as a catalyst support.  

PubMed

Hollow mesoporous structures have recently aroused intense research interest owing to their unique structural features. Herein, an effective and precisely controlled synthesis of hollow rare-earth silicate spheres with mesoporous shells is reported for the first time, produced by a simple hydrothermal method, using silica spheres as the silica precursors. The as-prepared hollow rare-earth silicate spheres have large specific surface area, high pore volume, and controllable structure parameters. The results demonstrate that the selection of the chelating reagent plays critical roles in forming the hollow mesoporous structures. In addition, a simple and low-energy-consuming approach to synthesize highly stable and dispersive gold nanoparticle-yttrium silicate (AuNPs/YSiO) hollow nanocomposites has also been developed. The reduction of 4-nitrophenol with AuNPs/YSiO hollow nanocomposites as the catalyst has clearly demonstrated that the hollow rare-earth silicate spheres are good carriers for Au nanoparticles. This strategy can be extended as a general approach to prepare multifunctional yolk-shell structures with diverse compositions and morphologies simply by replacing silica spheres with silica-coated nanocomposites. PMID:24449457

Jin, Renxi; Yang, Yang; Zou, Yongcun; Liu, Xianchun; Xing, Yan

2014-02-17

152

Silica-bonded N-propyl sulfamic acid used as a heterogeneous catalyst for transesterification of soybean oil with methanol.  

PubMed

The transesterification of soybean oil with methanol was carried out, to produce biodiesel, over silica-bonded N-propyl sulfamic acid in a heterogeneous manner. Results showed that a maximum conversion of 90.5% was achieved using a 1:20 M ratio of soybean oil to methanol and a catalyst amount of 7.5 wt.% at 423 K for 60 h. It was found that the free fatty acid (FFA) and water present in the feedstock had no significant influence on the catalytic activity to the transesterification reaction. Besides, the catalyst also showed activities towards the esterification reaction of FFAs, in terms of the FFA conversion of 95.6% at 423 K for 30 h. Furthermore, the catalyst could be recovered with a better reusability. PMID:21871795

Xie, Wenlei; Yang, Dong

2011-10-01

153

Cyclization of alkynoic acids in water in the presence of a vesicular self-assembled amphiphilic pincer palladium complex catalyst.  

PubMed

Alkynoic acids were cyclized in the presence of a vesicular palladium-based catalyst and a catalytic amount of triethylamine in water to give the corresponding lactones in moderate-to-good yields. The formation of a vesicular structure was shown to be essential for the promotion of the reaction. PMID:25303771

Hamasaka, Go; Uozumi, Yasuhiro

2014-12-01

154

Polyvalent-metal salts of heteropolyacid as efficient heterogeneous catalysts for Friedel–Crafts acylation of arenes with carboxylic acids  

Microsoft Academic Search

Polyvalent-metal (Ti4+, Fe3+, Sn4+, Bi3+, Ru3+) salts of dodecatungstophosphate act as effective heterogeneous catalysts for Friedel–Crafts acylation of aromatics with carboxylic acids. The Fe3+ salt shows high yields and the highest turnover number (2500) reported to date and can be reused without loss of activity, providing one of the greenest route to aromatic ketones.

Ken-ichi Shimizu; Kenjiro Niimi; Atsushi Satsuma

2008-01-01

155

Comparative analysis of different whole cell immobilized aspergillus niger catalysts for gluconic acid fermentation using pretreated cane molasses  

Microsoft Academic Search

To compare the efficiency of various whole cell immobilization techniques for the production of gluconic acid by Aspergillus niger were investigated using potassium ferrocyanide-treated cane molasses as the substrate. The techniques followed were:(1)Calcium alginate entrapment,(2)cross-linking with glutaraldehyde after cell permeabilization with (a) acetone, (b) toluene and (c) isopropanol and(3)development of granular catalyst.

D. Subba Rao; T. Panda

1994-01-01

156

Green and Efficient Procedure for the Trimethylsilylation of Hydroxy Groups and Their Regeneration Using Sulfamic Acid as Recyclable Catalyst  

Microsoft Academic Search

Structurally diverse alcohols and phenols were efficiently transformed into their corresponding trimethylsilyl ethers with hexamethyldisilazane (HMDS) in the presence of catalytic amounts of sulfamic acid (SA) at room temperature under both acetonitrile and solvent-free conditions. Deprotection of these trimethylsilyl ethers to their parent alcohols and phenols was also achieved using this catalyst in water at room temperature.

Amin Rostami; Firoz Ahmad-Jangi; Mohammad Rezgar Zarebin; Jamal Akradi

2010-01-01

157

A novel direct and one-pot Mannich synthesis of fluorinated ?-aminobutanones with sulfamic acid as a green catalyst  

Microsoft Academic Search

A variety of fluorinated ?-aminobutanones could be obtained in good to excellent yields at room temperature through the direct and three-component Mannich reactions of unmodified acetone with aldehydes and fluorinated anilines in one-pot procedure. Among the catalysts screened, sulfamic acid was tested to the best in aspect of outstanding stability, inexpensive cost, ready recovery and excellently catalytic activity. All the

Min Xia; Yue-Dong Lu

2006-01-01

158

Kinetics and Mechanism of Ethane Oxidation to Acetic Acid on Catalysts Based on Mo-V-Nb Oxides  

E-print Network

Kinetics and Mechanism of Ethane Oxidation to Acetic Acid on Catalysts Based on Mo-V-Nb Oxides and isotopic studies showed that C-H bond activation in ethane by surfaces essentially saturated with lattice oxygens is the sole kinetically relevant step in ethane oxidation on Mo-V-NbOx mixed oxides

Iglesia, Enrique

159

Structural Synergism in Functionalized Polymers: New Catalysts for Transacylation Reactions of Derivatives of Carboxylic and Phosphoric Acids.  

National Technical Information Service (NTIS)

This project has focused on the development of new highly-efficient, selective catalysts for widely-used commercial and biological reactions of carboxylic and phosphoric acids and their derivatives. The first phase of the project included the design and s...

M. Zeldin, W. K. Fife

1991-01-01

160

Chlorine-free Friedel–Crafts acylation of benzene with benzoic anhydride on insoluble heteropoly acid catalyst  

Microsoft Academic Search

Friedel–Crafts acylation of benzene (BEN) with benzoic anhydride (BAN) to produce benzophenone (BPH) was studied over various ion-exchanged heteropoly acids (HPA). No metal chloride such as AlCl3 was used as a catalyst. No acid chloride was used as an acylating agent. Therefore, this reaction could be a model of chlorine-free fine chemical synthesis process. As the activity of benzene was

Tomohiko Tagawa; Junichi Amemiya; Shigeo Goto

2004-01-01

161

One-pot synthesis of 3,4-dihydropyrimidin-2(1 H)-ones using boric acid as catalyst  

Microsoft Academic Search

A simple effective synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives, using boric acid as catalyst, from aromatic aldehydes, 1,3-dicarbonyl compounds and urea in glacial acetic acid is described. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (86–97%) and short reaction time (0.5–2 h).

Shujang Tu; Fang Fang; Chunbao Miao; Hong Jiang; Youjian Feng; Daqing Shi; Xiangshan Wang

2003-01-01

162

Catalysts based in cerium oxide for wet oxidation of acrylic acid in the prevention of environmental risks  

Microsoft Academic Search

Acrylic acid is a refractory compound for the non-catalytic wet oxidation (WO) process and can seriously damage the environment when released in industrial effluents. Oxidation of acrylic acid by catalytic wet oxidation (CWO) was studied in slurry conditions in a high-pressure batch reactor at 200°C and 15bar of oxygen partial pressure. Several solid cerium-based catalysts prepared in our laboratory were

Adrián M. T Silva; Rita R. N Marques; Rosa M Quinta-Ferreira

2004-01-01

163

On the Acid-Base Mechanism for Ruthenium Water Oxidation Catalysts  

E-print Network

We present a detailed theoretical study of the pathway for water oxidation in synthetic ruthenium-based catalysts. As a first step, we consider a recently discovered single center catalyst, where experimental observations ...

Wang, Lee-Ping

164

Direct Hydrogenation of Biomass-Derived Butyric Acid to n-Butanol over a Ruthenium-Tin Bimetallic Catalyst.  

PubMed

Catalytic hydrogenation of organic carboxylic acids and their esters, for example, cellulosic ethanol from fermentation of acetic acid and hydrogenation of ethyl acetate is a promising possibility for future biorefinery concepts. A hybrid conversion process based on selective hydrogenation of butyric acid combined with fermentation of glucose has been developed for producing biobutanol. ZnO-supported Ru-Sn bimetallic catalysts exhibits unprecedentedly superior performance in the vapor-phase hydrogenation of biomass-derived butyric acid to n-butanol (>98?% yield) for 3500?h without deactivation. PMID:25123894

Lee, Jong-Min; Upare, Pravin P; Chang, Jong-San; Hwang, Young Kyu; Lee, Jeong Ho; Hwang, Dong Won; Hong, Do-Young; Lee, Seung Hwan; Jeong, Myung-Geun; Kim, Young Dok; Kwon, Young-Uk

2014-11-01

165

Sulfamic Acid: An Efficient, Cost-Effective, and Reusable Solid Acid Catalyst for the Synthesis of 1,8-Naphthyridines Under Solvent-Free Heating and Microwave Irradiation  

Microsoft Academic Search

An efficient and convenient method is described for the synthesis of 1,8-naphthyridines in excellent yields by condensation of 2-aminonicotinaldehyde with various active methylene compounds in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

Y. Thirupathi Reddy; P. Raghotham Reddy; M. Nikhil Reddy; B. Rajitha; Peter A. Crooks

2008-01-01

166

Asymmetric synthesis of protected ?-amino boronic acid derivatives with an air- and moisture-stable Cu(II) catalyst.  

PubMed

The asymmetric borylation of N-tert-butanesulfinyl imines with bis(pinacolato)diboron is achieved using a Cu(II) catalyst and provides access to synthetically useful and pharmaceutically relevant ?-amino boronic acid derivatives. The Cu(II)-catalyzed reaction is performed on the benchtop in air at room temperature using commercially available, inexpensive reagents at low catalyst loadings. A variety of N-tert-butanesulfinyl imines, including ketimines, react readily to provide ?-sulfinamido boronate esters in good yields and with high stereoselectivity. In addition, this transformation is applied to the straightforward, telescoped synthesis of ?-sulfinamido trifluoroborates. PMID:24684495

Buesking, Andrew W; Bacauanu, Vlad; Cai, Irene; Ellman, Jonathan A

2014-04-18

167

The influence of metal and carrier natures on the effectiveness of catalysts of the deoxygenation of fatty acids into hydrocarbons  

NASA Astrophysics Data System (ADS)

The activity and selectivity of palladium, copper, platinum, and nickel catalysts in the decarbonylation of stearic acid into hydrocarbons were studied at a 14 atm hydrogen pressure and temperatures of 300-350°C. If ?-alumina was used as a carrier, the catalysts formed the series Pd > Cu > Pt > Ni according to desired product yields. Quantum-chemical simulation was performed to show that the free energy of activation increased in the same series. The same metals deposited on mixed tungsten and zirconium oxides catalyzed decarbonylation with a low yield of C17 hydrocarbons, likely because such a superacidic carrier could catalyse cracking of olefins or their oligomers formed.

Berenblyum, A. S.; Shamsiev, R. S.; Podoplelova, T. A.; Danyushevsky, V. Ya.

2012-08-01

168

Tuning the acid/metal balance of carbon nanofiber-supported nickel catalysts for hydrolytic hydrogenation of cellulose.  

PubMed

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/?-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other. PMID:22730195

Van de Vyver, Stijn; Geboers, Jan; Schutyser, Wouter; Dusselier, Michiel; Eloy, Pierre; Dornez, Emmie; Seo, Jin Won; Courtin, Christophe M; Gaigneaux, Eric M; Jacobs, Pierre A; Sels, Bert F

2012-08-01

169

Degradation of salicylic acid by photo-assisted Fenton reaction using Fe ions on strongly acidic ion exchange resin as catalyst  

Microsoft Academic Search

The photo-assisted Fenton degradation of salicylic acid (SA) was studied by using strongly acidic ion exchange resin (SAIER) exchanged with Fe ions as catalyst in the presence of UV light (254nm) and H2O2. The X-ray photoelectron spectroscopy (XPS) results revealed that the Fe ions are indeed anchored by the sulfonate groups on the surface of the SAIER and are Fe3+.

Jiyun Feng; Xijun Hu; Po Lock Yue

2004-01-01

170

A highly efficient magnetic solid acid catalyst for synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation.  

PubMed

Fe(3)O(4) nanoparticles were prepared by chemical coprecipitation method and subsequently coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. Grafting of chlorosulfuric acid on the amino-functionalized Fe(3)O(4) nanoparticles afforded sulfamic acid-functionalized magnetic nanoparticles (SA-MNPs). SA-MNPs was found to be a mild and effective solid acid catalyst for the efficient, one-pot, three-component synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation. This protocol afforded corresponding imidazoles in shorter reaction durations, and in high yields. This green procedure has many obvious advantages compared to those reported in the previous literatures, including avoiding the use of harmful catalysts, easy and quick isolation of the products, excellent yields, short routine, and simplicity of the methodology. PMID:23137656

Safari, Javad; Zarnegar, Zohre

2013-03-01

171

Study on the structure, acidic properties of V-Zr nanocrystal catalysts in oxidative dehydrogenation of propane  

NASA Astrophysics Data System (ADS)

A series of V-doped zirconia nanocrystal (the molar ratio of V/Zr varying from 0.001 to 0.15) were prepared via hydrothermal method and performed in oxidative dehydrogenation of propane. It was found that vanadium was highly dispersed on the surface and in the bulk of ZrO2. The distribution of the vanadium species, the valence states and the aggregation state of V species on the surface, as well as the acid properties of the catalysts including kinds, number and strength were detected by the various characteristic methods. The correlation between the V content and the surroundings of the different V species has been studied. The function of acid properties, especially Brønsted acid in the catalytic performance has been discussed. Oxidative dehydrogenation reactions were carried out in a continuous flow fixed bed reactor and ZrV0.01 catalyst showed good conversion and selectivity with a yield of propylene of 21.3%.

Chen, Shu; Ma, Fei; Xu, Aixin; Wang, Lina; Chen, Fang; Lu, Weimin

2014-01-01

172

Model reaction for the in situ characterization of the hydrogenating and acid properties of industrial hydrocracking catalysts  

SciTech Connect

A kinetic study of o-xylene transformation was carried out on a sulfided NiMo on Y zeolite catalyst during the hydrocracking of a model compound (n-heptane) under the following conditions of the process: high hydrogen pressure (5.7 MPa), presence of nitrogen and sulfur-containing compounds. o-Xylene inhibits n-heptane transformation, which can be explained by a competition for the adsorption on the acid sites between o-xylene and the olefinic intermediates of hydrocracking. The products of o-xylene transformation are the following: p- and m-xylenes (isomerization), toluene and trimethylbenzenes (disproportionation), and saturated C{sub 8} naphthenes (dimethylcyclohexane and trimethylcyclopentanes). It is shown that 1,3- and 1,4-dimethylcyclohexanes (and trimethylcyclopentanes) result from the isomerization of m- and p-xylenes. Therefore, the hydrogenating activity of hydrocracking catalysts can be characterized by the formation of dimethylyclohexanes and trimethylcyclopentanes. Furthermore, the isomerization of xylenes, which occurs through an acid mechanism, can be used for characterizing the acid activity of hydrocracking catalysts. This is not the case for disproportion whose rate depends on hydrogen pressure. The validity of o-xylene transformation for characterizing the acid and hydrogenating activities of bifunctional hydrocracking catalysts was confirmed by the use of a series of catalysts having either the same content of NiMo and different contents of zeolite or the same content of zeolite and different contents of NiMo. While the isomerization activity is strictly proportional to the zeolite content and independent of the NiMo content, and the hydrogenating activity is proportional to the NiMo content and independent of the zeolite content. 27 refs., 17 figs., 3 tabs.

Guisnet, M.; Thomazeau, C.; Lemberton, J.L. [Laboratoire de Catalyse en Chimie Organique, Poitiers (France)] [Laboratoire de Catalyse en Chimie Organique, Poitiers (France); Mignard, S. [Institut Francais du Petrole, Rueil-Malmaison (France)] [Institut Francais du Petrole, Rueil-Malmaison (France)

1995-01-01

173

Stepwise engineering of a Pichia pastoris D-amino acid oxidase whole cell catalyst  

PubMed Central

Background Trigonopsis variabilis D-amino acid oxidase (TvDAO) is a well characterized enzyme used for cephalosporin C conversion on industrial scale. However, the demands on the enzyme with respect to activity, operational stability and costs also vary with the field of application. Processes that use the soluble enzyme suffer from fast inactivation of TvDAO while immobilized oxidase preparations raise issues related to expensive carriers and catalyst efficiency. Therefore, oxidase preparations that are more robust and active than those currently available would enable a much broader range of economically viable applications of this enzyme in fine chemical syntheses. A multi-step engineering approach was chosen here to develop a robust and highly active Pichia pastoris TvDAO whole-cell biocatalyst. Results As compared to the native T. variabilis host, a more than seven-fold enhancement of the intracellular level of oxidase activity was achieved in P. pastoris through expression optimization by codon redesign as well as efficient subcellular targeting of the enzyme to peroxisomes. Multi copy integration further doubled expression and the specific activity of the whole cell catalyst. From a multicopy production strain, about 1.3 × 103 U/g wet cell weight (wcw) were derived by standard induction conditions feeding pure methanol. A fed-batch cultivation protocol using a mixture of methanol and glycerol in the induction phase attenuated the apparent toxicity of the recombinant oxidase to yield final biomass concentrations in the bioreactor of ? 200 g/L compared to only 117 g/L using the standard methanol feed. Permeabilization of P. pastoris using 10% isopropanol yielded a whole-cell enzyme preparation that showed 49% of the total available intracellular oxidase activity and was notably stabilized (by three times compared to a widely used TvDAO expressing Escherichia coli strain) under conditions of D-methionine conversion using vigorous aeration. Conclusions Stepwise optimization using a multi-level engineering approach has delivered a new P. pastoris whole cell TvDAO biocatalyst showing substantially enhanced specific activity and stability under operational conditions as compared to previously reported preparations of the enzyme. The production of the oxidase through fed-batch bioreactor culture and subsequent cell permeabilization is high-yielding and efficient. Therefore this P. pastoris catalyst has been evaluated for industrial purposes. PMID:20420682

2010-01-01

174

Efficient hydroalkoxylation of alkenes to generate octane-boosting ethers using recyclable metal triflates and highly active metal triflate\\/Brønsted acid-assisted catalysts  

Microsoft Academic Search

gem-Disubstituted alkenes are directly and readily etherified with alcohols using Al(OTf)3 and Zr(OTf)4 as recyclable Lewis acid catalysts. In contrast, primary or secondary alkene analogues were inert under these conditions, enabling excellent chemoselectivity. Lanthanide triflates are inactive as catalysts for such reactions, as is phosphoric acid. But a combination of these two otherwise inactive entities led to an ‘assisted acidity

D. Bradley G. Williams; Mike S. Sibiya; Pieter S. van Heerden

175

Catalyst-free fatty acid methyl ester production from wet activated sludge under subcritical water and methanol condition.  

PubMed

Wet activated sludge was converted directly into biodiesel using water as hydrolysis reagent to enhance the extraction of lipid in activated sludge, and as catalyst for the conversion of neutral lipids into biodiesel under subcritical conditions. At 175°C, 3.5MPa, a methanol to sludge ratio of 30 (mL/g) and a sludge water content of 84wt.%, about 90% conversion to fatty acid methyl esters was achieved within 24h without the need for conventional catalysts such as KOH and H(2)SO(4). Since water is employed as a catalyst, its removal is not required; therefore, the processing costs for producing biodiesel from activated sludge are reduced. The method has the potential for applications to other feedstock with high water contents such as micro-algae. PMID:22940307

Huynh, Lien Huong; Tran Nguyen, Phuong Lan; Ho, Quoc Phong; Ju, Yi-Hsu

2012-11-01

176

Reactions of aqueous glucose solution over solid-acid Y-zeolite catalyst at 110-160 C  

SciTech Connect

Reactions of glucose with solid-acid Y-zeolite catalyst were studied to see if this heterogeneous system could produce oxygenated hydrocarbons by shape-selective, acid-catalyzed processes at fairly low temperatures. Experimentally, aqueous solutions of glucose (12 wt %) were reacted with HY-zeolite powder in a well-mixed batch reactor at temperatures ranging from 110 to 160 C and catalyst concentrations ranging from 2 to 20 g/150 ml. Unreacted glucose and oxygenated hydrocarbon products were measured by HPLC as a function of reaction time (0-24 h) and process conditions. Glucose conversions of 100% were obtained at 160 C after an 8-h reaction time. The apparent activation energy based on glucose conversion was 23.25 [plus minus] 0.40 kcal/mol. Several acid-catalyzed reactions were identified, including isomerization of glucose to fructose, partial dehydration of glucose to 5-(hydroxymethyl)furfural (HMF), rehydration and cleavage of HMF to formic acid and 4-oxo-pentanoic acid, and carbonization . Polymers of HMF and seven minor additional products in the lower molecular weight organic acids/aldehydes/ketones elution range were also isolated by HPLC. High yields of organic acids relative to HMF and lowered selectivity of HMF in the bulk phase relative to the homogeneous acid-catalyzed reaction suggests the possibility of molecular sieving reactions within the Y-zeolite in addition to reactions on the outer surface of the Y-zeolite particle.

Lourvanij, K.; Rorrer, G.L. (Oregon State Univ., Corvallis (United States))

1993-01-01

177

A novel method for synthesis of phosphomolybdic acid-modified Pd/C catalysts for oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

This manuscript reports a convenient method for immobilizing phosphomolybdic acid (HPMo) on polyaniline (PAN-) functionalized carbon supports. The obtained HPMo-PAN-C sample is used as the support to prepare a Pd/HPMo-PAN-C catalyst. The samples are characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and X-ray diffraction analysis. The results suggest that HPMo retains its Keggin structure and that the presence of HPMo reduces the average particle size of the Pd nano-particles in the obtained Pd/HPMo-PAN-C catalyst. Electro-chemical measurements in 0.5 M HClO4 solution reveal that the Pd/HPMo-PAN-C catalyst has higher catalytic activity for oxygen reduction reactions than does a Pd/C catalyst prepared using a similar procedure. The stability of the Pd/HPMo-PAN-C catalyst is evaluated by multiple-cycle voltammetry techniques; the mass catalytic activity decreases by only 10% after 100 scanning cycles.

Zhu, Mingyuan; Gao, Xiaoling; Luo, Guangqin; Dai, Bin

2013-03-01

178

Multifunctional pd/ni-co catalyst for hydrogen production by chemical looping coupled with steam reforming of acetic Acid.  

PubMed

High yield of high-purity H2 from acetic acid, a model compound of bio-oil obtained from the fast pyrolysis of biomass, was produced by sorption-enhanced steam reforming (SESR). An oxygen carrier was introduced into a chemical loop (CL) coupled to the cyclical SESR process to supply heat in?situ for the endothermic sorbent regeneration to increase the energy efficiency of the process. A new multifunctional 1?%Pd/20?%Ni-20?%Co catalyst was developed for use both as oxygen carrier in the CL and as reforming catalyst in the SESR whereas a CaO-based material was used as CO2 sorbent. In the sorbent-air regeneration step, the Ni-Co atoms in the catalyst undergo strong exothermic oxidation reactions that provide heat for the CaO decarbonation. The addition of Pd to the Ni-Co catalyst makes the catalyst active throughout the whole SESR-CL cycle. Pd significantly promotes the reduction of Ni-Co oxides to metallic Ni-Co during the reforming stage, which avoids the need for a reduction step after regeneration. H2 yield above 90?% and H2 purity above 99.2?vol?% were obtained. PMID:25209388

Fermoso, Javier; Gil, María V; Rubiera, Fernando; Chen, De

2014-11-01

179

MIL-101-SO3 H: A Highly Efficient Brønsted Acid Catalyst for Heterogeneous Alcoholysis of Epoxides under Ambient Conditions.  

PubMed

For the first time, a ?100?% sulfonic acid functionalized metal-organic framework (MOF), MIL-101-SO3 H, with giant pores has been prepared by a hydrothermal process followed by a facile postsynthetic HCl treatment strategy. The replete readily accessible Lewis acidic and especially Brønsted acidic sites distributed throughout the framework as well as high stability endow the resultant MOF exceptionally high efficiency and recyclability, which surpass all other MOF-based catalysts, for the ring opening of epoxides with alcohols (especially, methanol) as nucleophiles under ambient conditions. PMID:25291973

Zhou, Yu-Xiao; Chen, Yu-Zhen; Hu, Yingli; Huang, Gang; Yu, Shu-Hong; Jiang, Hai-Long

2014-11-10

180

Surfactants from biomass: a two-step cascade reaction for the synthesis of sorbitol fatty acid esters using solid acid catalysts.  

PubMed

Sorbitol fatty esters have been prepared through a two-step catalytic process which involves the protection of the polyalcohol by ketalization followed by esterification with the fatty acid. Inorganic molecular sieves with different pore topologies as well as heteropolyacids (HPA) were used as acid catalysts to perform both the ketalization and the esterification step. These catalysts are found to hydrolyze the ketal function and promote the esterification between the free hydroxy groups and oleic acid in a cascade process. The results show a positive shape-selectivity effect when the process is carried out using tridirectional, and especially monodirectional (mordenite), zeolites, such that the ratio of mono- to higher esters and the hydroxy number of the final product are increased as compared to those obtained for the homogeneous-catalyzed process. PMID:18605669

Corma, Avelino; Hamid, Sharifah B A; Iborra, Sara; Velty, Alexandra

2008-01-01

181

Atmospheric Secondary Aerosol Formation by Heterogeneous Reactions of Aldehydes in the Presence of a Sulfuric Acid Aerosol Catalyst  

NASA Astrophysics Data System (ADS)

Particle growth by the heterogeneous reaction of aldehydes was observed in 0.5 m3 indoor Teflon bags in the presence of background seed aerosols. The aldehydes used were: glyoxal, butanal, hexanal, octanal, and decanal. To study acid catalyst effects on aldehyde heterogeneous reactions, one of the Teflon bags was initially filled with seed aerosols composed of ammonium sulfate-aerosol acidified with sulfuric acid. This result was compared to particle growth reactions that contained only ammonium sulfate as a background seed aerosol. The gas phase aldehydes were then added to the Teflon bags. In selected experiments, 1-decanol was also added to the Teflon bags with aldehydes to clarify particle growth via a heterogeneous hemiacetal/acetal formation in the presence/absence of an acid catalyst. The particle size distribution and growth were measured using a differential mobility analyzer (DMA), and the results were applied to predicting aerosol growth and size distribution changes by condensation and heterogeneous reactions. Aerosols created from the heterogeneous reactions of aldehydes were collected directly on an ungreased zinc selenide (ZnSe) FTIR disk (25 mm in diameter) by impaction. The ZnSe disks were directly analyzed for product functional groups in the aerosol phase using a Fourier transform infrared (FTIR) spectrometer with a deuterated triglycine sulfate (DTGS) detector. Aerosol growth by heterogeneous aldehyde reactions proceeds via a hydration, polymerization process, hemiacetal/acetal formation from the reaction of aldehydes with alcohols. These aldehyde heterogeneous reactions were accelerated in the presence of an acid catalyst, H2SO4, and led to higher aerosol yields than when H2SO4 was not present in the seed aerosol. The FTIR spectra obtained from the growing aerosol, also illustrated aldehyde group transformation in the particle phase as a function of the heterogeneous reaction. It was concluded that aldehydes, which can be produced by atmospheric photochemical reactions, can significantly contribute on secondary aerosol formation through heterogeneous reactions in the presence of an acid catalyst.

Jang, M.; Kamens, R. M.

2001-12-01

182

Development of biomimetic catalytic oxidation methods and non-salt methods using transition metal-based acid and base ambiphilic catalysts  

PubMed Central

This review focuses on the development of ruthenium and flavin catalysts for environmentally benign oxidation reactions based on mimicking the functions of cytochrome P-450 and flavoenzymes, and low valent transition-metal catalysts that replace conventional acids and bases. Several new concepts and new types of catalytic reactions based on these concepts are described. PMID:21558760

MURAHASHI, Shun-Ichi

2011-01-01

183

Oxyhydrochlorination catalyst  

DOEpatents

An improved catalyst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HCl and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

Taylor, Charles E. (Pittsburgh, PA); Noceti, Richard P. (Pittsburgh, PA)

1992-01-01

184

Facile and Promising Method for Michael Addition of Indole and Pyrrole to Electron-Deficient trans-?-Nitroolefins Catalyzed by a Hydrogen Bond Donor Catalyst Feist's Acid and Preliminary Study of Antimicrobial Activity  

PubMed Central

The importance of cooperative hydrogen-bonding effects has been demonstrated using novel 3-methylenecyclopropane-1,2-dicarboxylic acid (Feist's acid (FA)) as hydrogen bond donor catalysts for the addition of indole and pyrrole to trans-?-nitrostyrene derivatives. Because of the hydrogen bond donor (HBD) ability, Feist's acid (FA) has been introduced as a new class of hydrogen bond donor catalysts for the activation of nitroolefin towards nucleophilic substitution reaction. It has effectively catalyzed the Michael addition of indoles and pyrrole to ?-nitroolefins under optimum reaction condition to furnish the corresponding Michael adducts in good to excellent yields (up to 98%). The method is general, atom-economical, convenient, and eco-friendly and could provide excellent yields and regioselectivities. Some newly synthesized compounds were for examined in vitro antimicrobial activity and their preliminary results are reported. PMID:24574906

Al Majid, Abdullah M. A.; Islam, Mohammad Shahidul; Barakat, Assem; Al-Agamy, Mohamed H. M.; Naushad, Mu.

2014-01-01

185

One-pot three-component Mannich-type reactions using Sulfamic acid catalyst under ultrasound irradiation  

Microsoft Academic Search

Sulfamic acid (NH2SO3H, SA) was used as an efficient, inexpensive, non-toxic and recyclable green catalyst for the ultrasound-assisted one-pot Mannich reaction of aldehydes with ketones and amines. This ultrasound protocol has advantages of high yield, mild condition, no environmental pollution, and simple work-up procedures. Most importantly, ?-aminocarbonyl compounds with ortho-substituted aromatic amines are obtained in acceptable to good yields by

Hongyao Zeng; Hua Li; Huawu Shao

2009-01-01

186

CuO\\/NiO monolithic catalysts for NO x removal from nitric acid plant flue gas  

Microsoft Academic Search

The performance of copper\\/nickel oxide catalysts supported on ceramic monoliths of ?-alumina\\/silicate, for the selective catalytic reduction (SCR) of nitrogen oxides in flue gas from nitric acid plants ([NO]\\/[NOx]=0.7) has been studied. The monoliths prepared were characterised by thermogravimetry, nitrogen adsorption–desorption, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), electron probe microanalysis wavelength dispersion spectroscopy (EPMA-WDS) and their mechanical strengths were

Jesús Blanco; Pedro Avila; Silvia Suárez; Malcolm Yates; Juan Antonio Martin; Luis Marzo; Carlos Knapp

2004-01-01

187

Chiral rare earth organophosphates as homogeneous Lewis acid catalysts for the highly enantioselective hetero-Diels–Alder reactions  

Microsoft Academic Search

Various trivalent rare earth-chiral phosphate complexes [(R)-1-RE, (R)-3-RE, and (R)-4-Ce] were prepared and evaluated as a Lewis acid catalyst for the asymmetric hetero-Diels–Alder reaction of aldehydes with the Danishefsky's diene. Some of them effectively promoted the reaction at room temperature in the presence or absence of achiral additives under homogeneous conditions to afford the corresponding cycloadducts with high ee's (up

Hiroshi Furuno; Tetsuji Hayano; Takeshi Kambara; Yuichi Sugimoto; Takeshi Hanamoto; Yumiko Tanaka; Yong Zhi Jin; Takumi Kagawa; Junji Inanaga

2003-01-01

188

Effects of Lewis acid-surfactant-combined catalysts on aldol and Diels-Alder reactions in water  

Microsoft Academic Search

Aldol and Diels-Alder reactions in water in the presence of various dodecyl sulfate and dodecanesulfonate salts as Lewis acid-surfactant-combined catalysts have been studied. In the aldol reactions, these salts differed from each other with respect to their catalytic ability at the initial stage of the reaction and to the final yields of the aldol product, while these salts did not

Kei Manabe; Yuichiro Mori; Sh? Kobayashi

1999-01-01

189

Recovery of molybdenum and vanadium from synthetic sulphuric acid leach solutions of spent hydrodesulphurisation catalysts using solvent extraction  

Microsoft Academic Search

A commercially available extractant, LIX®63 was used to investigate the extraction of molybdenum(VI) and vanadium(V) from a synthetic sulphuric acid leach solution of spent hydrodesulphurisation catalysts. The molybdenum(VI) and vanadium(V) were extracted and separated completely from other metals at pH 1.5. The loaded organic solution was easily stripped by NaOH solution with excellent phase separation. After the precipitation of most

Li Zeng; Chu Yong Cheng

2010-01-01

190

Synthesis and characterization of sulfonated single-walled carbon nanotubes and their performance as solid acid catalyst  

SciTech Connect

Single-walled carbon nanotubes (SWCNTs) were treated with sulfuric acid at 300 deg. C to synthesize sulfonated SWCNTs (s-SWCNTs), which were characterized by electron microscopy, infrared, Raman and X-ray photoelectron spectroscopy, and thermo analysis. Compared with activated carbon, more sulfonic acid groups can be introduced onto the surfaces of SWCNTs. The high degree ({approx}20 wt%) of surface sulfonation led to hydrophilic sidewalls that allows the SWCNTs to be uniformly dispersed in water and organic solvents. The high surface acidity of s-SWCNTs was demonstrated by NH{sub 3} temperature-programmed desorption technique and tested by an acetic acid esterification reaction catalyzed by s-SWCNTs. The results show that the water-dispersive s-SWCNTs are an excellent solid acid catalyst and demonstrate the potential of SWCNTs in catalysis applications. - Graphical abstract: Sulfonated SWCNTs with 20 wt% -SO{sub 2}OH groups were prepared by a high-temperature H{sub 2}SO{sub 4} process, which transformed the hydrophobic surface of pristine SWCNTs to a hydrophilic surface and provided an excellent performance as solid acid catalyst.

Yu Hao [School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510641 (China)], E-mail: yuhao@scut.edu.cn; Jin Yuguang; Li Zhili [School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510641 (China); Peng Feng [School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510641 (China)], E-mail: cefpeng@scut.edu.cn; Wang Hongjuan [School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510641 (China)

2008-03-15

191

Tosic Acid-on-Silica Gel: A Cheap and Eco-friendly Catalyst for a Convenient One-pot Synthesis of Substituted Benzimidazoles  

Microsoft Academic Search

Summary.  2-Substituted and 1,2-disubstited benzimidazoles were prepared efficiently from o-phenylenediamines and aryl aldehydes using p-toluenesulphonic acid (5?mol%)-on-silica gel as a cheap and environmentally benign catalyst.

Manas Chakrabarty; Ratna Mukherjee; Sulakshana Karmakar; Yoshihiro Harigaya

2007-01-01

192

Solvent-Free Tetrahydropyranylation of Alcohols with Sulfamic Acid as Reusable Catalyst  

Microsoft Academic Search

An efficient H2NSO3H-catalyzed solvent-free tetrahydropyranylation of various alcohols at room temperature was investigated. The features of mild conditions, cost-efficient catalyst, simple work-up, and the recyclability of the catalyst were displayed in this article.

Bo Wang; Li-Ming Yang; Ji-Shuan Suo

2003-01-01

193

Solvent free synthesis of quinoxalines, dipyridophenazines and chalcones under microwave irradiation with sulfated Degussa titania as a novel solid acid catalyst  

Microsoft Academic Search

Sulfated TiO2–P25 (Degussa titania) has been prepared by sol–gel method using H2SO4 and characterized by FT-IR, XRD, FE-SEM, EDS, HR-TEM, XPS, DRS and BET surface area measurements. Sulfate loading by H2SO4 increases the Lewis acidity of Degussa tiatania. This catalyst gives an excellent yield with less reaction time and is an inexpensive and easily recyclable solid acid catalyst for the

B. Krishnakumar; M. Swaminathan

194

Catalytic Upgrading of bio-oil using 1-octene and 1-butanol over sulfonic acid resin catalysts  

SciTech Connect

Raw bio-oil from fast pyrolysis of biomass must be refined before it can be used as a transporation fuel, a petroleum refinery feed or for many other fuel uses. Raw bio-oil was upgraded with the neat model olefin, 1-octene, and with 1-octene/1-butanol mixtures over sulfonic acid resin catalysts frin 80 to 150 degrees celisus in order to simultaneously lower water content and acidity and to increase hydrophobicity and heating value. Phase separation and coke formation were key factors limiting the reaction rate during upgrading with neat 1-octene although octanols were formed by 1-octene hydration along with small amounts of octyl acetates and ethers. GC-MS analysis confirmed that olefin hydration, carboxylic acid esterification, acetal formation from aldehydes and ketones and O- and C-alkylations of phenolic compounds occurred simultaneously during upgrading with 1-octene/1-butanol mixtures. Addition of 1-butanol increased olefin conversion dramatically be reducing mass transfer restraints and serving as a cosolvent or emulsifying agent. It also reacted with carboxylic acids and aldehydes/ketones to form esters, and acetals, respectively, while also serving to stabilize bio-oil during heating. 1-Butanol addition also protected the catalysts, increasing catalyst lifetime and reducing or eliminationg coking. Upgrading sharply increased ester content and decreased the amounts of levoglucosan, polyhydric alcohols and organic acids. Upgrading lowered acidity (pH value rise from 2.5 to >3.0), removed the uppleasant ordor and increased hydrocarbon solubility. Water content decreased from 37.2% to < 7.5% dramatically and calorific value increased from 12.6 MJ kg to about 30.0 MJ kg.

Zhang, Zhijun; Wang, Qingwen; Tripathi, Prabhat; Pittman, Charles U.

2011-02-04

195

40 CFR 72.71 - Acceptance of State Acid Rain programs-general.  

...2014-07-01 false Acceptance of State Acid Rain programs-general. 72.71 Section...PROGRAMS (CONTINUED) PERMITS REGULATION Acid Rain Phase II Implementation § 72.71 Acceptance of State Acid Rain programs—general. (a)...

2014-07-01

196

Aerobic oxidation of trimethylbenzenes catalyzed by N, N?, N?-trihydroxyisocyanuric acid (THICA) as a key catalyst  

Microsoft Academic Search

The oxidation of trimethylbenzenes was examined with air or O2 using N,N?,N?-trihydroxyisocyanuric acid (THICA) as a key catalyst. Thus, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzenes under air (20atm) in the presence of THICA (5mol%), Co(OAc)2 (0.5mol%), Mn(OAc)2, and ZrO(OAc)2 at 150°C were oxidized to the corresponding benzenetricarboxylic acids in good yields (81–97%). In the aerobic oxidation of 1,2,4-trimethylbenzene by the THICA\\/Co(II)\\/Mn(II) system,

Naruhisa Hirai; Yoshinobu Tatsukawa; Michiko Kameda; Satoshi Sakaguchi; Yasutaka Ishii

2006-01-01

197

Sulfonic Acid Functionalized Nano-?-Al2O3: A New, Efficient, and Reusable Catalyst for Synthesis of 3-Substituted-2H-1,4-Benzothiazines  

PubMed Central

A simple and efficient synthetic protocol has been developed for the synthesis of 3-substituted-2H-1,4-benzothiazines by using a novel sulfonic acid functionalized nano-?-Al2O3 catalyst, devoid of corrosive acidic, and basic reagents. The developed method has the advantages of good to excellent yields, short reaction times, operational simplicity, and a recyclable catalyst. The catalyst can be prepared by a simple procedure from inexpensive and readily available nano-?-Al2O3 and has been shown to be recoverable and reusable up to six cycles without any loss of activity. PMID:23935435

Li, Wei Lin; Tian, Shuan Bao; Zhu, Feng

2013-01-01

198

Improved performance of Mo-V-Te-Nb-O x catalysts prepared from a solution containing drying control chemical additives in propane oxidation to acrylic acid  

Microsoft Academic Search

Mo1.0V0.4Te0.25Nb0.24O\\u000a x\\u000a catalyst was prepared by hydrothermal synthesis in a solution containing a drying control chemical additive (DCCA) such as\\u000a propionic acid (PA) or formamide (FA). The performance of the prepared catalysts in propane oxidation for producing acrylic\\u000a acid (AA) was improved because the catalyst showed an increase in both the activity and AA selectivity. The activity was increased\\u000a due

Sang Seop Kum; Yoon Sik Park; Sang Heup Moon

2011-01-01

199

Ti-MCM-41 supported phosphotungstic acid: An effective and environmentally benign catalyst for epoxidation of styrene  

NASA Astrophysics Data System (ADS)

Mesoporous Ti-MCM-41 molecular sieve was synthesized under hydrothermal conditions. 5, 10, 20, 30 and 50 wt.% phosphotungstic acid (H 3PW 12O 40) (PW) were supported on Ti-MCM-41 and the resulting catalysts were characterized by powder X-ray diffraction (XRD), N 2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H 2O 2 (30%) as an oxidizing agent under liquid-phase reaction conditions over PW/Ti-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H 2O 2 mmol ratios and acetonitrile (MeCN) to N, N-dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Ti-MCM-41 was more active than other catalysts. The PW/Ti-MCM-41, moreover, was found to be reusable and effective for the epoxidation of styrene.

Wang, GuangJian; Liu, GuangQing; Xu, MingXia; Yang, ZhenXing; Liu, ZhengWang; Liu, YiWu; Chen, ShiFu; Wang, Lei

2008-12-01

200

Zirconium(IV) tungstate nanoparticles prepared through chemical co-precipitation method and its function as solid acid catalyst  

NASA Astrophysics Data System (ADS)

In this paper, we report the synthesis of zirconium(IV) tungstate nanoparticles, a new and efficient catalyst for the oxidation of benzyl alcohol and esterification of acetic acid with various alcohols. The nanoparticle catalyst was prepared using the room temperature chemical co-precipitation method. The catalyst was characterized with thermogravimetric and differential thermal analysis, elemental analysis, X-ray diffraction analysis (XRD), fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and the Brunauer-Emmett-Teller (BET) surface area. The crystallite size was found to be ~20 nm as revealed by XRD, HRTEM and AFM. The Na+ exchange capacity was found to be 2.76 meq g-1 and the surface area of the compound measured using BET method was found to be 250-265 m2 g-1. The high value of ion exchange capacity indicates the presence of surface hydroxyl groups. The prepared nanoparticles have proven to be excellent catalysts for both oxidation and ester synthesis under mild reaction conditions. The mechanism of the catalytic reaction was studied as well.

Sadanandan, Manoj; Bhaskaran, Beena

2014-08-01

201

An unprecedented (3,4,24)-connected heteropolyoxozincate organic framework as heterogeneous crystalline Lewis acid catalyst for biodiesel production  

PubMed Central

A novel 3D hexadecanuclear heteropolyoxozincate organic framework, IFMC-200, has been successfully synthesized based on a late transition metal-oxygen cluster. IFMC-200 not only represents the first example of (3,4,24)-connected framework but also contains the first 24-connected single metal cluster in a crystal structure. It exhibits superior thermal stability, good water-stability, and even insensitivity to the existence of acid and base within a certain range of pH values. Furthermore, it performs as a heterogeneous crystalline Lewis acid catalyst with good activity for the conversion of long-chain fatty acids rather than short-chain ones, and high recycling efficiency for esterification reaction of fatty acids with alcohols to produce biodiesel. PMID:24019078

Du, Dong-Ying; Qin, Jun-Sheng; Sun, Zhong; Yan, Li-Kai; O'Keeffe, Michael; Su, Zhong-Min; Li, Shun-Li; Wang, Xiao-Hong; Wang, Xin-Long; Lan, Ya-Qian

2013-01-01

202

Nanoporous TiO 2-supported bimetallic catalysts for methanol oxidation in acidic media  

Microsoft Academic Search

New dynamic aspects of the catalysis of methanol oxidation reaction have been studied. The submonolayer films of bi-functional catalysts (PtRu) were deposited on novel nanostructured supporting materials, designed with the goal of achieving high variability of their electronic and chemical properties to influence the catalytic activity of sub-monolayer catalyst. The mesoscopic TiO2 supporting film formation was investigated using EQCN, voltammetric,

Maria Hepel; Indee Kumarihamy; C. J. Zhong

2006-01-01

203

Hydrocracking catalyst  

Microsoft Academic Search

The invention relates to a particular method for the preparation of a hydrocracking catalyst, using a high iron content bauxite as a basis. This bauxite is ground and screened to a specific size and mixed with three types of additives: a promoter additive of the P, Mo, Co, Ni, W type. A hardener additive of the phosphoric acid type, ammonium

B. Arias; R. Galiasso; H. Kum

1985-01-01

204

TiO 2–SO 4 2? as a novel solid acid catalyst for highly efficient, solvent free and easy synthesis of chalcones under microwave irradiation  

Microsoft Academic Search

TiO2–SO42? has been prepared by the sol–gel method using H2SO4 and used for the synthesis of chalcones under microwave irradiation. Sulfate loading by H2SO4 increases the Lewis acidity of TiO2. This catalyst gives an excellent yield with less reaction time and is an inexpensive, easily recyclable catalyst for this reaction.

B. Krishnakumar; R. Velmurugan; M. Swaminathan

2011-01-01

205

Copper-exchanged mordenites as active catalysts for NO selective catalytic reduction by propene under oxidising conditions: Effect of Si\\/Al ratio, copper content and Brönsted acidity  

Microsoft Academic Search

CuMOR catalysts with different Si\\/Al ratios and copper contents, prepared from the acid and sodium forms, were studied in NO reduction with propene in the presence of excess oxygen. It was observed that the influence of zeolite Si\\/Al ratio on CuMOR catalytic activity for NO SCR by propene depends on the catalyst copper content, the reverse being also true. For

C. Torre-Abreu; M. F. Ribeiro; C. Henriques; F. R. Ribeiro

1997-01-01

206

Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported N-heterocyclic carbene–palladium complex catalyst  

PubMed Central

Summary The Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported Pd–NHC complex catalyst has been realized for the first time. The polymer-supported catalyst can be re-used several times still retaining high activity for this transformation. Various aryltriazenes were investigated as electrophilic substrates at room temperature to give biaryls in good to excellent yields and showed good chemoselectivity over aryl halides in the reactions. PMID:20703375

Nan, Guangming; Ren, Fang

2010-01-01

207

Removal of salicylic acid on perovskite-type oxide LaFeO3 catalyst in catalytic wet air oxidation process.  

PubMed

It has been found that salicylic acid can be removal effectively at the lower temperature of 140 degrees C on perovskite-type oxide LaFeO3 catalyst in the catalytic wet air oxidation (CWAO) process. Under the same condition, the activities for the CWAO of phenol, benzoic acid and sulfonic salicylic acid have been also investigated. The results indicated that, with compared to the very poor activities for phenol and benzoic acid, the activities for salicylic acid and sulfonic salicylic acid were very high, which are attributed to their same intramolecular H-bonding structures. With the role of hard acidity of intramolecular H-bonding, salicylic acid and sulfonic salicylic acid can be adsorbed effectively on the basic center of LaFeO3 catalyst and are easy to take place the total oxidation reaction. However, at temperatures higher than 140 degrees C, the intramolecular H-bonding structure of salicylic acid was destroyed and the activities at 160 and 180 degrees C decreased greatly, which confirms further the key role of intramolecular H-bonding in the CWAO. Moreover, the LaFeO3 catalyst also indicated a superior stability of activity and structure in CWAO of salicylic acid. PMID:16870333

Yang, Min; Xu, Aihua; Du, Hongzhang; Sun, Chenglin; Li, Can

2007-01-01

208

Preparation and characterizations of highly dispersed carbon supported PdxPty/C catalysts by a modified citrate reduction method for formic acid electrooxidation  

NASA Astrophysics Data System (ADS)

Carbon supported PdxPty/C (atomic ratio x:y from 1:1 to 6:1) have been prepared by a modified citrate reduction method assisted by inorganic stabilizers. Without using high molecular capping agents as stabilizers, the PdxPty/C catalysts are highly dispersed on the carbon support and no particle aggregations are found for the PdxPty/C catalysts. X-ray photoelectron spectroscopy reveals either Pt or Pd segregation for the PdxPty/C catalysts depending on Pd/Pt atomic ratio. CO stripping in 0.5 M H2SO4 and repeated formic acid oxidation cyclic voltammetry in 0.5 M HCHO + 0.5 M H2SO4 have been conducted to test out the CO tolerance and stability of the catalysts, respectively. It has been found that, with the increase of Pd/Pt atomic ratio, the CO stripping peak potential increases (less CO tolerant), whereas the catalyst stability towards formic acid oxidation decreases. The as-prepared catalysts reveal excellent mass-normalized formic acid oxidation activity as compared with published results possibly due to high dispersion and the absence of high molecular capping agents.

Li, Zuopeng; Li, Muwu; Han, Mingjia; Zeng, Jianhuang; Li, Yuexia; Guo, Yanqin; Liao, Shijun

2014-05-01

209

Transport activity-dependent intracellular sorting of the yeast general amino acid permease  

E-print Network

Intracellular trafficking of the general amino acid permease, Gap1p, of Saccharomyces cerevisiae is regulated by amino acid abundance. When amino acids are scarce Gap1p is sorted to the plasma membrane, whereas when amino ...

Cain, Natalie Elaine

210

The Catalytic Cracking of Hydrocarbons in a Riser Simulator: The Effect of Catalyst Accessibility and Acidity  

E-print Network

1 The Catalytic Cracking of Hydrocarbons in a Riser Simulator: The Effect of Catalyst Accessibility-zeolites as main component and on ZSM-5 as additive. These zeolites are bounded individually in a spray-dried the catalytic cracking of 1,3,5-TIPB was #12;3 carried out in other study using the riser

Al-Khattaf, Sulaiman

211

An evaluation of Pt sulfite acid (PSA) as precursor for supported Pt catalysts  

E-print Network

upon impregnation, calcination, and reduction. While all catalysts show retention of some S, reasonably (niobia and silica) display some storage of S even while only Pt-O bands are observed after calcination or reoxidation. More sulfur was eliminated by high temperature calcinations followed by reduction in hydrogen

Regalbuto, John R.

212

Activity enhancement by acetic acid in cyclohexane oxidation using Ti-containing zeolite catalyst  

Microsoft Academic Search

Titanium silicalite (TS-1) was hydrothermally crystallised from a titanosilicate gel. The solid material was characterised by XRD, IR, and SEM, and then used as a catalyst in the liquid phase oxidation of cyclohexane with hydrogen peroxide. The reaction was carried out for 6h, at the temperature between 40 and 80°C. It was found that a marked increase in the catalytic

Tawan Sooknoi; Jumras Limtrakul

2002-01-01

213

Hydrometallurgical route to recover molybdenum, nickel, cobalt and aluminum from spent hydrotreating catalysts in sulphuric acid medium.  

PubMed

This work describes a hydrometallurgical route for processing spent commercial catalysts (CoMo and NiMo/Al2O3), for recovering the active phase and support components. They were initially pre-oxidized (500 degrees C, 5h) in order to eliminate coke and other volatile species present. Pre-oxidized catalysts were dissolved in H2SO4 (9molL-1) at approximately 90 degrees C, and the remaining residues separated from the solution. Molybdenum was recovered by solvent extraction using tertiary amines. Alamine 304 presented the best performance at pH around 1.8. After this step, cobalt (or nickel) was separated by adding aqueous ammonium oxalate in the above pH. Before aluminum recovery, by adding NaOH to the acid solution, phosphorus (H2PO4-) was removed by passing the liquid through a strong anion exchange column. Final wastes occur as neutral and colorless sodium sulphate solutions and the insoluble solid in the acid leachant. The hydrometallurgical route presented in this work generates less final aqueous wastes, as it is not necessary to use alkaline medium during the metal recovery steps. The metals were isolated in very high yields (>98wt.%). PMID:18400377

Valverde, Ivam Macedo; Paulino, Jéssica Frontino; Afonso, Julio Carlos

2008-12-30

214

One-Pot Synthesis of Graphene-Supported Monodisperse Pd Nanoparticles as Catalyst for Formic Acid Electro-oxidation  

NASA Astrophysics Data System (ADS)

To synthesize monodisperse palladium nanoparticles dispersed on reduced graphene oxide (RGO) sheets, we have developed an easy and scalable solvothermal reduction method from an organic solution system. The RGO-supported palladium nanoparticles with a diameter of 3.8 nm are synthesized in N-methyl-2-pyrrolidone (NMP) and in the presence of oleylamine and trioctylphosphine, which facilitates simultaneous reduction of graphene oxide and formation of Pd nanocrystals. So-produced Pd/RGO was tested for potential use as electrocatalyst for the electro-oxidation of formic acid. Pd/RGO catalyzes formic acid oxidation very well compared to Pd/Vulcan XC-72 catalyst. This synthesis method is a new way to prepare excellent electrocatalysts, which is of great significance in energy-related catalysis.

Yang, Sudong; Dong, Jing; Yao, Zhaohui; Shen, Chengmin; Shi, Xuezhao; Tian, Yuan; Lin, Shaoxiong; Zhang, Xiaogang

2014-03-01

215

One-pot synthesis of graphene-supported monodisperse Pd nanoparticles as catalyst for formic acid electro-oxidation.  

PubMed

To synthesize monodisperse palladium nanoparticles dispersed on reduced graphene oxide (RGO) sheets, we have developed an easy and scalable solvothermal reduction method from an organic solution system. The RGO-supported palladium nanoparticles with a diameter of 3.8?nm are synthesized in N-methyl-2-pyrrolidone (NMP) and in the presence of oleylamine and trioctylphosphine, which facilitates simultaneous reduction of graphene oxide and formation of Pd nanocrystals. So-produced Pd/RGO was tested for potential use as electrocatalyst for the electro-oxidation of formic acid. Pd/RGO catalyzes formic acid oxidation very well compared to Pd/Vulcan XC-72 catalyst. This synthesis method is a new way to prepare excellent electrocatalysts, which is of great significance in energy-related catalysis. PMID:24675779

Yang, Sudong; Dong, Jing; Yao, Zhaohui; Shen, Chengmin; Shi, Xuezhao; Tian, Yuan; Lin, Shaoxiong; Zhang, Xiaogang

2014-01-01

216

One-Pot Synthesis of Graphene-Supported Monodisperse Pd Nanoparticles as Catalyst for Formic Acid Electro-oxidation  

PubMed Central

To synthesize monodisperse palladium nanoparticles dispersed on reduced graphene oxide (RGO) sheets, we have developed an easy and scalable solvothermal reduction method from an organic solution system. The RGO-supported palladium nanoparticles with a diameter of 3.8?nm are synthesized in N-methyl-2-pyrrolidone (NMP) and in the presence of oleylamine and trioctylphosphine, which facilitates simultaneous reduction of graphene oxide and formation of Pd nanocrystals. So-produced Pd/RGO was tested for potential use as electrocatalyst for the electro-oxidation of formic acid. Pd/RGO catalyzes formic acid oxidation very well compared to Pd/Vulcan XC-72 catalyst. This synthesis method is a new way to prepare excellent electrocatalysts, which is of great significance in energy-related catalysis. PMID:24675779

Yang, Sudong; Dong, Jing; Yao, Zhaohui; Shen, Chengmin; Shi, Xuezhao; Tian, Yuan; Lin, Shaoxiong; Zhang, Xiaogang

2014-01-01

217

H-Gallosilicate (MFI) Propane Aromatization Catalyst: Influence of Si\\/Ga Ratio on Acidity, Activity and Deactivation Due to Coking  

Microsoft Academic Search

Influence of bulk Si\\/Ga ratio of H-gallosilicate (MFI) on its degalliation (during calcination for removal of template and deammoniation of NH4form), acidity\\/acid strength distribution (measured by stepwise thermal desorption and chemisorption of pyridine at 50–400°C using GC techniques and also by acid catalyzed model reactions viz. iso-octane cracking and toluene disproportionation) and initial activity\\/product selectivity and catalyst deactivation in propane

V. R. Choudhary; A. K. Kinage; C. Sivadinarayana; P. Devadas; S. D. Sansare; M. Guisnet

1996-01-01

218

Silica-bonded N-propyl sulfamic acid as an efficient catalyst for the formylation and acetylation of alcohols and amines under heterogeneous conditions  

Microsoft Academic Search

A simple and efficient procedure for the preparation of silica-bonded N-propyl sulfamic acid (SBNPSA) by the reaction of 3-aminopropylsilica (1) and chlorosulfonic acid in chloroform is described. This solid acid is employed as a new catalyst for the formylation of alcohols and amines with ethyl formate under mild and heterogeneous conditions at room temperature with good to excellent yields. Also,

Khodabakhsh Niknam; Dariush Saberi

2009-01-01

219

Reaction of carboxylic acids with vinyl ethers under solvent-free conditions using molecular iodine as a catalyst.  

PubMed

The reaction of vinyl ethers with carboxylic acids using iodine as a catalyst under solvent-free conditions was investigated. The reaction of saturated carboxylic acids with vinyl ethers gave the corresponding esters. Mechanistic studies revealed the production of the adduct of the vinyl ether with the carboxylic acid, which then rearranged to form the ester. At low temperatures, the reaction of 2-(1-hydroxycyclohexyl)acetic acid (1) and butyl vinyl ether yielded a butyl ester. However, at a reaction temperature of 80°C, both the esterification and the elimination of a water molecule occurred, yielding the unsaturated butyl ester butyl 2-cyclohexenylacetate. The reaction of 2-((1S,2S,4R)-2-hydroxy-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl)acetic acid (12) with butyl vinyl ether at low temperatures resulted in a mixture of four compounds. However, similar to the high-temperature (>60°C) reaction of 1, the esterification was accompanied by the elimination of a water molecule to give the unsaturated butyl ester (E)-butyl 2-((1S,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)acetate. While a ?-hydrogen was abstracted to form the endo-type double bond in the reaction of 1, an ?-hydrogen was abstracted to form the exo-type double bond in the reaction of 12. PMID:23357815

Hanzawa, Yohko; Kasashima, Yoshio; Hashimoto, Kahoko; Sasaki, Tatsuhiro; Tomisaki, Keita; Mino, Takashi; Sakamoto, Masami; Fujita, Tsutomu

2013-01-01

220

Activated carbons treated with sulphuric acid: Catalysts for catalytic wet peroxide oxidation  

Microsoft Academic Search

Different liquid phase thermal treatments were applied to a commercial activated carbon (Norit ROX 0.8) in order to produce modified activated carbons with varying surface chemistry and increased acidic character. Chemical characterization of the prepared materials includes determination of the point of zero charge and evaluation of the concentration and nature of acidic and basic surface functionalities by acid\\/base titrations

Helder T. Gomes; Sandra M. Miranda; Maria J. Sampaio; Adrián M. T. Silva; Joaquim L. Faria

2010-01-01

221

Tungsten oxide catalysts supported on activated carbons: effect of tungsten precursor and pretreatment on dispersion, distribution, and surface acidity of catalysts  

Microsoft Academic Search

Tungsten catalysts supported on activated carbon were prepared using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide. The catalysts were pretreated in He, dry air, or wet air at 623 K for 6 h before being characterized by N2 adsorption at 77 K, temperature-programmed desorption, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, and by testing their behavior in

A. F. Pérez-Cadenas; C. Moreno-Castilla; F. J. Maldonado-Hódar; J. L. G. Fierro

2003-01-01

222

Salicylato titanocene complexes as cooperative organometallic Lewis acid and Brønsted acid catalysts for three-component mannich reactions.  

PubMed

A binary acid system has been developed that features an air-stable organometallic precursor, titanocene dichloride, and simple organic cooperative Brønsted acids, which allowed for mild and highly efficient Mannich reactions of both aryl and alkyl ketones with excellent yields and satisfactory diastereoselectivity. Mechanistic studies, including (1) H?NMR titration, X-ray structure analyses as well as isolation of catalytically active species, elucidated the dramatic synergistic effects of this new binary acid system. PMID:24954651

Wu, Ya; Chen, Chun; Jia, Gai; Zhu, Xuyang; Sun, Huaming; Zhang, Guofang; Zhang, Weiqiang; Gao, Ziwei

2014-07-01

223

General Method for Determination of the Surface Composition in Bimetallic Nanoparticle Catalysts from the L Edge X-ray Absorption Near-Edge Spectra  

SciTech Connect

Bimetallic PtPd on silica nano-particle catalysts have been synthesized and their average structure determined by Pt L3 and Pd K-edge extended X-ray absorption finestructure (EXAFS) spectroscopy. The bimetallic structure is confirmed from elemental line scans by STEM for the individual 1-2 nm sized particles. A general method is described to determine the surface composition in bimetallic nanoparticles even when both metals adsorb, for example, CO. By measuring the change in the L3 X-ray absorption near-edge structure (XANES) spectra with and without CO in bimetallic particles and comparing these changes to those in monometallic particles of known size the fraction of surface atoms can be determined. The turnover rates (TOR) and neopentane hydrogenolysis and isomerization selectivities based on the surface composition suggest that the catalytic and spectroscopic properties are different from those in monometallic nano-particle catalysts. At the same neo-pentane conversion, the isomerization selectivity is higher for the PtPd catalyst while the TOR is lower than that of both Pt and Pd. As with the catalytic performance, the infrared spectra of adsorbed CO are not a linear combination of the spectra on monometallic catalysts. Density functional theory calculations indicate that the Pt-CO adsorption enthalpy increases while the Pd-CO bond energy decreases. The ability to determine the surface composition allows for a better understanding of the spectroscopic and catalytic properties of bimetallic nanoparticle catalysts.

Wu, Tiapin; Childers, David; Gomez, Carolina; Karim, Ayman M.; Schweitzer, Neil; Kropf, Arthur; Wang, Hui; Bolin, Trudy B.; Hu, Yongfeng; Kovarik, Libor; Meyer, Randall; Miller, Jeffrey T.

2012-10-31

224

Sulfamic acid: An efficient and cost-effective solid acid catalyst for the synthesis of ?-aminophosphonates at ambient temperature  

Microsoft Academic Search

Sulfamic acid catalyzed solvent-free protocol has been developed for the synthesis of ?-aminophosphonates by three component condensation between aldehydes, amines and diethyl phosphite at ambient temperature.

S. D. Mitragotri; D. M. Pore; U. V. Desai; P. P. Wadgaonkar

2008-01-01

225

Molecular\\/electronic structure–surface acidity relationships of model-supported tungsten oxide catalysts  

Microsoft Academic Search

A series of model-supported WO3 catalysts were synthesized on preformed Al2O3, Nb2O5, TiO2, and ZrO2 supports by impregnation of aqueous ammonium metatungstate, (NH4)10W12O41?5H2O. The molecular and electronic structures of the supported tungsten oxide phases were determined with in situ Raman and UV–vis spectroscopy, respectively. The supported tungsten oxide structures are the same on all oxide supports as a function of

Taejin Kim; Andrew Burrows; Christopher J. Kiely; Israel E. Wachs

2007-01-01

226

Non-platinum group metal oxgyen reduction catalysts and their mechanism in both acid and alkaline media: The effect of the catalyst precursor and the ionomer on oxygen reduction  

NASA Astrophysics Data System (ADS)

Non-platinum catalysts are an attractive strategy for lowering the cost of fuel cells, but much more development is needed in order to replace platinum, especially at the cathode where oxygen is reduced. Research groups worldwide have donated material for a study in which precursor structure to catalyst activity correlations are made. The donated samples have been divided into three classes based on their precursor; macrocyclic chelates, small molecule, and polymeric precursors. The precursor is one activity-dictating factor among many, but it is one of the most influential. It was found that macrocyclic chelates on average produced the most active catalysts, having the highest limiting, diffusion-limited, kinetic, and exchange current densities, as well as the lowest overpotentials and H2O2 production. This suggests that the M-N4 atomic structure of the precursor remains largely static throughout heat treatment, as the M-Nx motif is the accepted active site conformation. The other classes were somewhat less active, but the breadth of precursor materials that range in structure and functionality, as well as low associated costs, make them attractive precursor materials. Careful precursor selection based on this analysis was applied to a new generation of catalyst derived from iron salt and 4-aminoantipyrine. An extensive investigation of the reduction of oxygen on the material performed in both acid and alkaline media, and it was found that reduction follows a two-step pathway. While the peroxide reducing step is also very fast, the first step is so rapid that, even at low active site density, the material is almost as active as platinum if all diffusion limitations are removed. In addition to bottom-up catalyst design, the catalyst:ionomer complex, by which catalyst is incorporated into the membrane electrode assembly, also affects reductive kinetics. A series of novel anionically conductive ionomers have been evaluated using a well-described cyanamide derived catalyst, and the ionomeric influence on activity was mechanistically evaluated. It was found that the water-uptake percentage of the ionomer and the ion exchange capacity has a major role in catalyzing the reaction. The ionomer content of the complex must balance ionic and electrical charge transfer, as well as manage a certain degree of hydration at the active site. In order for a catalyst to perform optimally in an operational fuel cell, design considerations must be addressed at the precursor, support, synthesis, morphological, and ionomer-complexing levels. If any level of design is neglected, catalytic performance will be sacrificed.

Robson, Michael H.

227

Scandium trifluoromethanesulfonate as an extremely active Lewis acid catalyst in acylation of alcohols with acid anhydrides and mixed anhydrides  

SciTech Connect

Scandium triflate catalyzes the acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The catalytic activity of the scandium triflates is found to be quite high allowing the acylation of secondary and tertiary alcohols.

Ishihara, K.; Kubota, M.; Kurihara, H.; Yamamoto, H. [Nagoya Univ. (Japan)] [Nagoya Univ. (Japan)

1996-07-12

228

Sulfamic acid: a novel and efficient catalyst for the synthesis of aryl-14 H-dibenzo[ a. j]xanthenes under conventional heating and microwave irradiation  

Microsoft Academic Search

A simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a.j]xanthenes is described through a one-pot condensation of ?-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

B. Rajitha; B. Sunil Kumar; Y. Thirupathi Reddy; P. Narsimha Reddy; N. Sreenivasulu

2005-01-01

229

Sulfamic acid as a cost-effective and recyclable catalyst for liquid Beckmann rearrangement, a green process to produce amides from ketoximes without waste  

Microsoft Academic Search

Sulfamic acid (H2NSO3H) has been proved to be an efficient and green catalyst for liquid Beckmann rearrangement of ketoxime in dried acetonitrile. The use of basic neutralization agent has been avoided in this system due to its intrinsic zwitterionic property. Thus it is a green process for preparation of amide from ketoxime without producing any waste.

Bo Wang; Yanlong Gu; Cheng Luo; Tao Yang; Liming Yang; Jishuan Suo

2004-01-01

230

Vanadium Recovery by Leaching in Spent Catalysts for Sulfuric Acid Production Recuperação do Vanádio Contido em Catalisadores Gastos na Produção de Ácido Sulfúrico  

Microsoft Academic Search

Sulfuric acid plants often need catalyst replacement in order to cope with process improvements, removal of broken pellets, dust and moisture damaged particles. This removed material can not be discarded because has high amounts of vanadium. According to the Brazilian Environmental Authority this material must be stored under specified conditions. This situation requires large storing areas potentially useful for other

JOSÉ LUÍS MAGNANI; GEORGE CURY KACHAN; NEWTON LIBANIO FERREIRA

231

Silica sulfuric acid: an efficient and reusable catalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2(1 H)-ones  

Microsoft Academic Search

Silica sulfuric acid efficiently catalyzes the three-component Biginelli reaction between an aldehyde, a ?-dicarbonyl compound and urea or thiourea in refluxing ethanol to afford the corresponding dihydropyrimidinones in high yields. The catalyst is reusable and can be applied several times without any decrease in the yield of the reactions.

Peyman Salehi; Minoo Dabiri; Mohammad Ali Zolfigol; Mohammad Ali Bodaghi Fard

2003-01-01

232

A sulfated ZrO2 hollow nanostructure as an acid catalyst in the dehydration of fructose to 5-hydroxymethylfurfural.  

PubMed

Mesoporous hollow colloidal particles with well-defined characteristics have potential use in many applications. In liquid-phase catalysis, in particular, they can provide a large active surface area, reduced diffusion resistance, improved accessibility to reactants, and excellent dispersity in reaction media. Herein, we report the tailored synthesis of sulfated ZrO2 hollow nanostructures and their catalytic applications in the dehydration of fructose. ZrO2 hollow nanoshells with controllable thickness were first synthesized through a robust sol-gel process. Acidic functional groups were further introduced to the surface of hollow ZrO2 shells by sulfuric acid treatment followed by calcination. The resulting sulfated ZrO2 hollow particles showed advantageous properties for liquid-phase catalysis, such as well-maintained structural integrity, good dispersity, favorable mesoporosity, and a strongly acidic surface. By controlling the synthesis and calcination conditions and optimizing the properties of sulfated ZrO2 hollow shells, we have been able to design superacid catalysts with superior performance in the dehydration of fructose to 5-hydroxymethyfurfural than the solid sulfated ZrO2 nanocatalyst. PMID:24023048

Joo, Ji Bong; Vu, Austin; Zhang, Qiao; Dahl, Michael; Gu, Minfen; Zaera, Francisco; Yin, Yadong

2013-10-01

233

A kinetic study of plutonium dioxide dissolution in hydrochloric acid using iron (II) as an electron transfer catalyst  

SciTech Connect

Effective dissolution of plutonium dioxide has traditionally been accomplished by contact with strong nitric acid containing a small amount of fluoride at temperatures of {approximately} 100 C. In spite of these aggressive conditions, PuO{sub 2} dissolution is sometimes incomplete requiring additional contact with the solvent. This work focused on an alternative to conventional dissolution in nitric acid where an electron transfer catalyst, Fe(II), was used in hydrochloric acid. Cyclic voltammetry was employed as an in-situ analytical technique for monitoring the dissolution reaction rate. The plutonium oxide selected for this study was decomposed plutonium oxalate with > 95% of the material having a particle diameter (< 70 {micro}m) as determined by a scanning laser microscopy technique. Attempts to dry sieve the oxide into narrow size fractions prior to dissolution in the HCl-Fe(II) solvent system failed, apparently due to significant interparticle attractive forces. Although sieve splits were obtained, subsequent scanning laser microscopy analysis of the sieve fractions indicated that particle segregation was not accomplished and the individual sieve fractions retained a particle size distribution very similar to the original powder assemblage. This phenomena was confirmed through subsequent dissolution experiments on the various screen fractions which illustrated no difference in kinetic behavior between the original oxide assemblage and the sieve fractions.

Fife, K.W.

1996-09-01

234

Regiocontrolled intramolecular cyclizations of carboxylic acids to carbon-carbon triple bonds promoted by acid or base catalyst.  

PubMed

We systematically investigated, for the first time, the relationship between regioselectivity and acid/base effects in the cyclization reactions between carboxylic acids and carbon-carbon triple bonds. We found novel acid- and base-promoted cyclizations to selectively give isocoumarin or pyran-2(2H)-one and phthalide or furan-2(5H)-one skeletons, respectively, and established a catalytic version of regioselective heterocyclic ring synthesis. Density functional theory calculations and application to a short route to thunberginol A were also described. [reaction: see text]. PMID:17107061

Uchiyama, Masanobu; Ozawa, Hiroki; Takuma, Kazuya; Matsumoto, Yotaro; Yonehara, Mitsuhiro; Hiroya, Kou; Sakamoto, Takao

2006-11-23

235

Surface characteristics and electrochemical capacitances of carbon aerogels obtained from resorcinol and pyrocatechol using boric and oxalic acids as polymerization catalysts  

Microsoft Academic Search

Carbon aerogels were prepared by carbonizing (at 500–1500°C) organic aerogels obtained from the polymerization reaction of resorcinol and\\/or pyrocatechol with formaldehyde using boric and oxalic acids as polymerization catalysts. Prepared samples were characterized by different techniques to ascertain their composition, surface chemistry, morphology, and surface physics, determining their electrochemical capacitances in acidic medium. The use of pyrocatechol yielded carbon aerogels

Carlos Moreno-Castilla; Marta B. Dawidziuk; Francisco Carrasco-Marín; Zulamita Zapata-Benabithe

2011-01-01

236

Oxide acid-base reaction relating to the inhibition of vandium attack on REY zeolite catalysts. [Rare earth-exchanged yttrium  

Microsoft Academic Search

Certain materials, especially Sn, passivate the rare earth-exchanged Y zeolite (REY) used in petrochemical fluid-cracking catalysts against vanadium degradation caused by V impurities in the feed oil. The mechanism of passivation was investigated here from the standpoint of high-temperature oxide acid-base reaction; i.e., where the controlling factors were considered to be Lewis acid-base reactions between VâOâ, the RE oxides, SnOâ,

1991-01-01

237

Cu nanoclusters supported on nanocrystalline SiO?-MnO?: a bifunctional catalyst for the one-step conversion of glycerol to acrylic acid.  

PubMed

A material consisting of highly dispersed Cu nanoclusters anchored on nanocrystalline SiO2-MnO2 has been prepared, and was found to act as a bifunctional catalyst for the one-step conversion of glycerol to acrylic acid using H2O2. Under optimized conditions a glycerol conversion of 77.1%, with 74.7% selectivity for acrylic acid, was achieved after 30 h reaction time. PMID:25017454

Sarkar, Bipul; Pendem, Chandrashekar; Sivakumar Konathala, L N; Tiwari, Ritesh; Sasaki, Takehiko; Bal, Rajaram

2014-09-01

238

Transport activity dependent regulation of the yeast general amino acid permease  

E-print Network

The general amino acid permease Gap1p of Saccharomyces cerevisiae scavenges amino acids from the extracellular medium for use as nitrogen sources in starvation conditions. Because unlimited uptake of both naturally occurring ...

Cain, Natalie E. (Natalie Elaine)

2011-01-01

239

An efficient solid acid catalyst: Poly p-styrenesulfonic acid supported on SBA15 via surface-initiated ATRP  

Microsoft Academic Search

The sulfonic acid-functionalized mesoporous organic–inorganic hybrid materials were synthesized via atom transfer radical polymerization (ATRP) method. SBA-15 material was first grafted with 4-(chloromethyl)phenyltrimethoxysilane. The surface-initiated polymerization of sodium p-styrenesulfonate inside the pore wall of functionalized SBA-15 results in p-styrenesulfonic acid functionalized SBA-15 (PSS-SBA-15). The results of FT-IR, nitrogen sorption isotherm, XRD, TEM and thermal gravimetric analyses (TGA) confirm that the

Congming Li; Jie Yang; Peiyuan Wang; Jian Liu; Qihua Yang

2009-01-01

240

Polycationic ligands in gold catalysis: synthesis and applications of extremely ?-acidic catalysts.  

PubMed

Very often ligands are anionic or neutral species. Cationic ones are rare, and, when used, the positively charged groups are normally appended to the periphery of the ligand. Here, we describe a dicationic phosphine with no spacer between the phosphorus atom and the two positively charged groups. This structural feature makes its donor ability poorer than that of phosphites and only comparable to extremely toxic or pyrophoric compounds such as PF3 or P(CF3)3. By exploiting these properties, a new Au catalyst has been developed displaying a dramatically enhanced capacity to activate ?-systems. This has been used to synthesize very sterically hindered and naturally occurring 4,5-disubstituted phenanthrenes. The present approach is expected to be applicable to the development and improvement of many other transition metal catalyzed transformations that benefit from extremely strong ?-acceptor ligands. The mechanism of selected catalytic transformations has been explored by density functional calculations. PMID:24308636

Carreras, Javier; Gopakumar, Gopinadhanpillai; Gu, Lianghu; Gu, Liangu; Gimeno, Ana; Linowski, Pawel; Petuškova, Jekaterina; Thiel, Walter; Alcarazo, Manuel

2013-12-18

241

A well-defined monomeric aluminum complex as an efficient and general catalyst in the meerwein-ponndorf-verley reduction.  

PubMed

The metal-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction allows for the mild and sustainable reduction of aldehydes and ketones but has not found widespread application in organic synthesis due to the high catalyst loading often required to obtain satisfactory yields of the reduced product. We report here on the synthesis and structure of a sterically extremely overloaded siloxide-supported aluminum isopropoxide capable of catalytically reducing a wide range of aldehydes and ketones (52 examples) in excellent yields under mild conditions and with low catalyst loadings. The unseen activity of the developed catalyst system in MPV reductions is due to its unique monomeric nature and the neutral donor isopropanol weakly coordinating to the aluminum center. The present work implies that monomeric aluminum alkoxide catalysts may be attractive alternatives to transition-metal-based systems for the selective reduction of aldehydes and ketones to primary and secondary alcohols. PMID:25284749

McNerney, Brian; Whittlesey, Bruce; Cordes, David B; Krempner, Clemens

2014-11-10

242

Activation of ZSM-5 catalysts  

SciTech Connect

Greatly increased yields of aromatics were obtainied in the reaction of ethanol over ZSM-5 zeolites if the protonated catalyst was pretreated in aqueous mineral acids or if hydrogen choloride or dichloroethane was added to the feed. The treated catalysts apparently contained less sodium than the ammonium-exchanged catalysts, and in some cases, some alumimum was removed. The product distributions at > 95% conversion were, e.g., 2% by wt benzene, 12% toluene, 24% xylenes, 34% trimethylbenzene, and 11% C/sub 10/+ aromatics from a catalyst treated in 0.6 M nitric acid, and 3% xylenes and 92% C/sub 10/+ aromatics from a catalyst treated in hydrofluoric acid.

Rajadhyaksha, R.A.; Anderson, J.R.

1980-06-01

243

Preparation and Evaluation of Advanced Catalysts for Phosphoric Acid Fuel Cells.  

National Technical Information Service (NTIS)

The platinum electrocatalysts were characterized for their crystallite sizes and the degree of dispersion on the carbon supports. One application of these electrocatalysts was for anodic oxidation of hydrogen in hot phosphoric acid fuel cells, coupled wit...

P. Stonehart, J. Baris, J. Hockmuth, P. Pagliaro

1984-01-01

244

Elucidation of the catalytic cracking pathway for unsaturated mono-, di-, and triacylglycerides on solid acid catalysts  

Microsoft Academic Search

Heterogeneous catalytic transformation of lipids to transportation fuels offers a unique opportunity to provide sustainable energy while utilizing the current petroleum refining infrastructure. The reaction chemistry for the heterogeneous catalytic cracking of unsaturated acylglycerides was studied. Mono-, di-, and triolein, which are acylglycerides with oleic acid as the fatty acid constituent, were reacted at 400°C over H+ZSM-5, faujasite, and silica–alumina

Tracy J. Benson; Rafael Hernandez; W. Todd French; Earl G. Alley; William E. Holmes

2009-01-01

245

Zymomonas mobilis As Catalyst for the Biotechnological Production of Sorbitol and Gluconic Acid  

Microsoft Academic Search

The conversion of glucose and fructose into gluconic acid (GA) and sorbitol (SOR) was conducted in a batch reactor with free\\u000a (CTAB-treated or not) or immobilized cells of Zymomonas mobilis. High yields (more than 90%) of gluconic acid and sorbitol were attained at initial substrate concentration of 600 g\\/L (glucose\\u000a plus fructose at 1:1 ratio), using cells with glucose-fructose-oxidoreductase activity

Gilmar Sidney Erzinger; Michele Vitolo

246

Zymomonas mobilis as catalyst for the biotechnological production of sorbitol and gluconic acid  

Microsoft Academic Search

The conversion of glucose and fructose into gluconic acid (GA) and sorbitol (SOR) was conducted in a batch reactor with free\\u000a (CTAB-treated or not) or immobilized cells of Zymomonas mobilis. High yields (more than 90%) of gluconic acid and sorbitol were attained at initial substrate concentration of 600 g\\/L (glucose\\u000a plus fructose at 1:1 ratio), using cells with glucose-fructose-oxidoreductase activity

Gilmar Sidney Erzinger; Michele Vitolo

2006-01-01

247

Eco-friendly heterogeneous solid acids as novel and recyclable catalysts in ionic medium for tetrahydropyranols  

Microsoft Academic Search

A variety of aldehydes and homoallylic alcohols undergo smoothly Prins-cyclization on the surface of solid acids such as H-ZSM-5 zeolite or Amberlyst-15® ion-exchange resin in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid to afford the corresponding tetrahydropyranols in high yields with cis-diastereoselectivity. The recovered ionic liquid containing solid acid was recycled in subsequent runs without loss of activity.

J. S Yadav; B. V. S Reddy; M. Sridhar Reddy; N Niranjan

2004-01-01

248

Zn(1.2)H(0.6)PW(12)O(40) Nanotubes with double acid sites as heterogeneous catalysts for the production of biodiesel from waste cooking oil.  

PubMed

Out of the frying pan: A ZnPW nanotube catalyst containing Brønsted and Lewis double acid sites promotes the conversion of waste cooking oil into biodiesel. The catalytic activity of the ZnPW nanotubes is stable to the presence of free fatty acids or water in the feedstock. The high catalytic activity of the ZnPW nanotubes is attributed to the synergistic effect of Lewis acid sites and Brønsted acid sites.Zinc dodecatungstophosphate (Zn(1.2)H(0.6)PW(12)O(40); ZnPW) nanotubes, which feature Lewis acid and Brønsted acid sites, were prepared using cellulose fibers as templates. The structure, acid properties, and catalytic activity of the nanotubes as heterogeneous catalysts for biodiesel production were then studied in detail. The ZnPW nanocatalyst exhibited higher catalytic activities for the simultaneous esterification and transesterification of palmitic acid than the parent acid catalyst 12-tungstophosphoric acid (H(3)PW(12)O(40)). Moreover, the doubly acidic nanotubes led to markedly enhanced yields of methyl esters in the conversion of waste cooking oil (containing 26.89 wt % free fatty acids and 1 % moisture) to biodiesel. The catalyst could be recycled and reused with negligible loss in activity over five cycles. The ZnPW nanocatalyst is acid- and water-tolerant and is an environmentally benign heterogeneous catalyst for the production of biodiesel from low-quality feedstocks. PMID:19191363

Li, Jing; Wang, Xiaohong; Zhu, Weimin; Cao, Fenghua

2009-01-01

249

3D-nanoarchitectured Pd/Ni catalysts prepared by atomic layer deposition for the electrooxidation of formic acid.  

PubMed

Three-dimensionally (3D) nanoarchitectured palladium/nickel (Pd/Ni) catalysts, which were prepared by atomic layer deposition (ALD) on high-aspect-ratio nanoporous alumina templates are investigated with regard to the electrooxidation of formic acid in an acidic medium (0.5 M H2SO4). Both deposition processes, Ni and Pd, with various mass content ratios have been continuously monitored by using a quartz crystal microbalance. The morphology of the Pd/Ni systems has been studied by electron microscopy and shows a homogeneous deposition of granularly structured Pd onto the Ni substrate. X-ray diffraction analysis performed on Ni and NiO substrates revealed an amorphous structure, while the Pd coating crystallized into a fcc lattice with a preferential orientation along the [220]-direction. Surface chemistry analysis by X-ray photoelectron spectroscopy showed both metallic and oxide contributions for the Ni and Pd deposits. Cyclic voltammetry of the Pd/Ni nanocatalysts revealed that the electrooxidation of HCOOH proceeds through the direct dehydrogenation mechanism with the formation of active intermediates. High catalytic activities are measured for low masses of Pd coatings that were generated by a low number of ALD cycles, probably because of the cluster size effect, electronic interactions between Pd and Ni, or diffusion effects. PMID:24605281

Assaud, Loïc; Monyoncho, Evans; Pitzschel, Kristina; Allagui, Anis; Petit, Matthieu; Hanbücken, Margrit; Baranova, Elena A; Santinacci, Lionel

2014-01-01

250

Structural and electrochemical characterization of carbon supported Pt-Pr catalysts for direct ethanol fuel cells prepared using a modified formic acid method in a CO atmosphere.  

PubMed

Pt-Pr/C electrocatalysts were prepared using a modified formic acid method, and their activity for carbon monoxide and ethanol oxidation was compared to Pt/C. No appreciable alloy formation was detected by XRD analysis. By TEM measurements it was found that Pt particle size increases with an increasing Pr content in the catalysts and with decreasing metal precursor addition time. XPS measurements indicated Pt segregation on the catalyst surface and the presence of Pr2O3 and PrO2 oxides. The addition of Pr increased the electro-catalytic activity of Pt for both CO and CH3CH2OH oxidation. The enhanced activity of Pt-Pr/C catalysts was ascribed to both an electronic effect, caused by the presence of Pr2O3, and the bi-functional mechanism, caused by the presence of PrO2. PMID:23752757

Corradini, Patricia Gon; Antolini, Ermete; Perez, Joelma

2013-07-28

251

Graphene-based nanomaterials as heterogeneous acid catalysts: a comprehensive perspective.  

PubMed

Acid catalysis is quite prevalent and probably one of the most routine operations in both industrial processes and research laboratories worldwide. Recently, "graphene", a two dimensional single-layer carbon sheet with hexagonal packed lattice structure, imitative of nanomaterials, has shown great potential as alternative and eco-friendly solid carbocatalyst for a variety of acid-catalyzed reactions. Owing to their exceptional physical, chemical, and mechanical properties, graphene-based nanomaterials (G-NMs) offer highly stable Brønsted acidic sites, high mass transfer, relatively large surface areas, water tolerant character, and convenient recoverability as well as recyclability, whilst retaining high activity in acid-catalyzed chemical reactions. This comprehensive review focuses on the chemistry of G-NMs, including their synthesis, characterization, properties, functionalization, and up-to-date applications in heterogeneous acid catalysis. In line with this, in certain instances readers may find herein some criticisms that should be taken as constructive and would be of value in understanding the scope and limitations of current approaches utilizing graphene and its derivatives for the same. PMID:25225721

Garg, Bhaskar; Bisht, Tanuja; Ling, Yong-Chien

2014-01-01

252

One-pot bio-synthesis: N-acetyl-d-neuraminic acid production by a powerful engineered whole-cell catalyst  

PubMed Central

Whole cell biocatalysis is an important tool for pharmaceutical intermediates synthesis, although it is hindered by some shortcomings, such as high cost and toxicity of inducer, mass transfer resistance caused by cell membrane and side reactions. Whole-cell catalysis using N-acetyl-d-glucosamine 2-epimerase (EC 5.1.3.8) and N-acetyl-d-neuraminic acid (Neu5Ac) aldolase (EC 4.1.3.3) is a promising approach for the production of Neu5Ac, a potential precursor of many anti-viral drugs. A powerful catalyst was developed by packaging the enzymes in an engineered bacterium and using a safe temperature-induced vector. Since the mass transfer resistance and the side reactions were substantially reduced, a high Neu5Ac amount (191?mM) was achieved. An efficient method was also presented, which allows one-pot synthesis of Neu5Ac with a safe and economic manner. The results highlight the promise of large-scale Neu5Ac synthesis and point at a potential of our approach as a general strategy to improve whole-cell biocatalysis. PMID:22355659

Tao, Fei; Zhang, Yinan; Ma, Cuiqing; Xu, Ping

2011-01-01

253

CO2-free power generation on an iron group nanoalloy catalyst via selective oxidation of ethylene glycol to oxalic acid in alkaline media.  

PubMed

An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO2-free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO2, produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4 V vs. the reversible hydrogen electrode (RHE), without CO2 generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system. PMID:25004118

Matsumoto, Takeshi; Sadakiyo, Masaaki; Ooi, Mei Lee; Kitano, Sho; Yamamoto, Tomokazu; Matsumura, Syo; Kato, Kenichi; Takeguchi, Tatsuya; Yamauchi, Miho

2014-01-01

254

CO2-Free Power Generation on an Iron Group Nanoalloy Catalyst via Selective Oxidation of Ethylene Glycol to Oxalic Acid in Alkaline Media  

PubMed Central

An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO2-free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO2, produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4?V vs. the reversible hydrogen electrode (RHE), without CO2 generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system. PMID:25004118

Matsumoto, Takeshi; Sadakiyo, Masaaki; Ooi, Mei Lee; Kitano, Sho; Yamamoto, Tomokazu; Matsumura, Syo; Kato, Kenichi; Takeguchi, Tatsuya; Yamauchi, Miho

2014-01-01

255

Ionic liquid-regulated sulfamic acid: chemoselective catalyst for the transesterification of ?-ketoesters  

Microsoft Academic Search

1-Propyl-3-methylimidazolium chloride ([C3MIm]Cl) ionic liquid and sulfamic acid (NH2SO3H), as a synergetic catalytic medium, were used for the transesterification of acetoacetate with alcohols of different structures. It shows the good ability for the chemoselective transesterificatin of ?-ketoesters and maintains its catalytic activity in the reuse.

Wang Bo; Yang Li Ming; Suo Ji Shuan

2003-01-01

256

Ascorbic Acid as a Standard for Iodometric Titrations. An Analytical Experiment for General Chemistry  

Microsoft Academic Search

Ascorbic acid is suggested as the weighable compound for the standardization of iodine solutions in an analytical experiment in general chemistry. The experiment involves an iodometric titration in which iodine reacts with ascorbic acid, oxidizing it to dehydroascorbic acid. The redox titration endpoint is determined by the first iodine excess that is complexed with starch, giving a deep blue-violet color.

Cesar R. Silva; Jose A. Simoni; Carol H. Collins; Pedro L. O. Volpe

1999-01-01

257

H-gallosilicate (MFI) propane aromatization catalyst: Influence of Si/Ga ratio on acidity, activity and deactivation due to coking  

SciTech Connect

Influence of bulk Si/Ga ratio of H-gallosilicate (MFI) on its degalliation (during calcination for removal of template and deammoniation of NH{sub 4} form), acidity/acid strength distribution (measured by stepwise thermal desorption and chemisorption of pyridine at 50-400{degrees}C using GC techniques and also by acid catalyzed model reactions viz. iso-octane cracking and toluene disproportionation) and initial activity/product selectivity and catalyst deactivation in propane aromatization (at 550{degrees}C) has been investigated. Framework Si/Ga ratio was measured by {sup 29}Si MAS NMR. Information on the external acid sites is obtained by isooctane cracking. The influence of poisoning of strong acid sites (by pyridine) on acid catalyzed model reactions and the effect of deactivation on the product distribution in the propane aromatization have also been studied. 21 refs., 19 figs., 3 tabs.

Choudhary, V.R.; Kinage, A.K.; Sivadinarayana, C. [National Chemical Lab., Pune (India)] [and others] [National Chemical Lab., Pune (India); and others

1996-01-01

258

Lysergic Acid Diethylamide and Stimulus Generalization: Rate-Dependent Effects  

Microsoft Academic Search

A stimulus generalization procedure was used to investigate the effects of LSD on sensitivity to auditory stimuli in rats. The shape of the generalization gradient was changed after administration of the drug only with a dose which produced decreases in relatively high rates of responding.

Linda A. Dykstra; James B. Appel

1972-01-01

259

ZnO/carbon nano composite: Effective catalyst for the photo degradation of Acid Blue 113  

NASA Astrophysics Data System (ADS)

Zinc oxide carbon composite (ZnO/C) was synthesized by self - propagating solution combustion method. This method enabled the addition of carbon insitu to the metal oxide. The composite synthesized were characterised by XRD, SEM and BET analysis. This composite was used for the removal of organic pollutants such as the dye Acid blue 113 by UV irradiation performed in a batch reactor. The influence of various experimental parameters such as the initial concentration of the dye, Concentration of the photocatalyst and the pH on the photo catalytic degradation under UV irradiation was studied. It has been observed that the degradation of the dye to be more pronounced in neutral medium. The degradation of acid blue 113 was found to increase with ZnO/C composites loading and decreases with decrease in concentration of the composite.

Sunitha, S.; Rao, A. Nageswara; Karthikeyan, J.; Krithiga, T.

2013-06-01

260

Silanized nucleic acids: a general platform for DNA immobilization.  

PubMed

We have developed a method for simultaneous deposition and covalent cross-linking of oligonucleotide or PCR products on unmodified glass surfaces. By covalently conjugating an active silyl moiety onto oligonucleotides or cDNA in solutions we have generated a new class of modified nucleic acids, namely silanized nucleic acids. Such silanized molecules can be immobilized instantly onto glass surfaces after manual or automated deposition. This method provides a simple and rapid, yet very efficient, solution to the immobilization of prefabricated oligonucleotides and DNA for chip production. PMID:10908345

Kumar, A; Larsson, O; Parodi, D; Liang, Z

2000-07-15

261

Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid using nanocrystalline cryptomelane composite catalysts  

Microsoft Academic Search

2,4-Dichlorophenoxyacetic acid is a common systemic herbicide used in the control of broadleaf weeds. It is the third-most widely used herbicide in the world. 2,4-D heterogeneous photocatalysis has emerged as a useful process to aid remediation of wastewater contamination. Manganese oxide with 2×2 tunnel structure, cryptomelane show good results in the photodegradation of 2,4-D and excellent performance in the photodegradation

M. Alvarez Lemus; T. López; S. Recillas; D. M. Frías; M. Montes; J. J. Delgado; M. A. Centeno; J. A. Odriozola

2008-01-01

262

Catalyst Alloys Processing  

NASA Astrophysics Data System (ADS)

Catalysts are one of the key materials used for diamond formation at high pressures. Several such catalyst products have been developed and applied in China and around the world. The catalyst alloy most widely used in China is Ni70Mn25Co5 developed at Changsha Research Institute of Mining and Metallurgy. In this article, detailed techniques for manufacturing such a typical catalyst alloy will be reviewed. The characteristics of the alloy will be described. Detailed processing of the alloy will be presented, including remelting and casting, hot rolling, annealing, surface treatment, cold rolling, blanking, finishing, packaging, and waste treatment. An example use of the catalyst alloy will also be given. Industrial experience shows that for the catalyst alloy products, a vacuum induction remelt furnace can be used for remelting, a metal mold can be used for casting, hot and cold rolling can be used for forming, and acid pickling can be used for metal surface cleaning.

Tan, Xincai

2014-10-01

263

General and selective C-3 alkylation of indoles with primary alcohols by a reusable Pt nanocluster catalyst.  

PubMed

The platinum rule: Heterogeneous, additive-free C-3 selective alkylation of indoles by aliphatic and aromatic alcohols proceeded under transfer hydrogenation conditions with the reusable Pt/?-Al2 O3 catalyst (see scheme; TON=turnover number). PMID:24127322

Siddiki, S M A Hakim; Kon, Kenichi; Shimizu, Ken-Ichi

2013-10-18

264

Photocatalytic oxidation of salicylic acid and 4-chlorophenol in aqueous solutions mediated by modified AlFe 2O 3 catalyst under sunlight  

Microsoft Academic Search

The visible light photochemical and photocatalytic oxidation of salicylic acid and 4-chlorophenol in a photoelectrocatalytic degradation reactor, at room temperature, under sunlight illumination, coated with anatase TiO2-based Fe2O3 and AlFe2O3 photocatalysts were investigated. The solar radiation can effectively be applied to accelerate the process using suitable catalyst for economically cleaning the major fresh water sources. The profile of the oxidation

S. S. Shinde; C. H. Bhosale; K. Y. Rajpure

2011-01-01

265

Silica supported perchloric acid (HClO 4SiO 2): A highly efficient and reusable catalyst for geminal diacylation of aldehydes under solvent-free conditions  

Microsoft Academic Search

Perchloric acid immobilized on silica gel has been found to be an efficient and expedient catalyst for geminal diacylation of aldehydes. A wide variety of aromatic and aliphatic aldehydes can be easily transformed into the corresponding acylals using 0.5mol% HClO4-SiO2 within 2–10min under solvent-free conditions at room temperature. The notable advantages of this protocol are: the reaction requires less reaction

Abu T. Khan; Lokman H. Choudhury; Subrata Ghosh

2006-01-01

266

Mesoporous silica iron-doped as stable and efficient heterogeneous catalyst for the degradation of C.I. Acid Orange 7 using sono–photo-Fenton process  

Microsoft Academic Search

Iron-containing mesostructured silica (Fe2O3\\/SBA-15) was prepared and used as heterogeneous catalyst in the integrated sono–photo-Fenton process. The effect of hydrogen peroxide concentration, initial pH, Fe2O3\\/SBA-15 loading, ultrasonic power, and initial solution concentration on the decolorization of C.I. Acid Orange 7 (AO7) by the integrated heterogeneous sono–photo-Fenton process was investigated in order to optimize process efficiency. The results showed that the

Xin Zhong; Sebastien Royer; Hui Zhang; Qianqian Huang; Luojing Xiang; Sabine Valange; Joel Barrault

2011-01-01

267

[BPy]HSO4 Acidic Ionic Liquid as a Novel, Efficient, and Environmentally Benign Catalyst for Synthesis of 1,5?Benzodiazepines under Mild Conditions  

Microsoft Academic Search

A novel and simple ionic liquid methodology for the synthesis of 1,5?benzodiazepines is described. 1?Butylpyridinium hydrogen sulphate ([BPy]HSO4), an acidic room?temperature ionic liquid, as a novel and efficient catalyst, was synthesized and used in the preparation of a series of 1,5?benzodiazepine derivatives by the reaction of o?phenylenediamine with chalcones under mild conditions. This method is easy, efficient, environmentally friendly, economical,

Yuying Du; Fuli Tian; Wenzhi Zhao

2006-01-01

268

Platinum-nickel catalyst: The effect of promoters in cis-oleic acid adsorption  

NASA Astrophysics Data System (ADS)

The study of the cis-oleic acid adsorption, on clean and promoted (K, Mg, Co, B or Pd) PtNi(1 1 1) surface was performed by quatum chemical calculations. The oleic acid adsorption on PtNi(1 1 1) surface shows a weak molecule-surface interaction. No preferential site for Cdbnd C adsorption is computed and only the Cdbnd O adsorption is favored on the clean PtNi(1 1 1) surface. The adsorption properties of the PtNi(1 1 1) are improved by promoters. The stability of the system is increased and the Cdbnd C/surface distances are reduced when promoters are present. Among the considered promoters, Co has the best performance in terms of system stability. The lowest C p orbital substantially interacts with Pt and Co s, p and d orbitals. The change electron density of metal centers, enhance the Cdbnd C adsorption being the Pt-C interaction the more favored. After adsorption, the strength of the Cdbnd C, Ptsbnd Pt and Ptsbnd Co bonds decrease while a molecule-surface bond is formed.

Simonetti, S.; Martirena, M.; Ulacco, S.; Brizuela, G.

2013-01-01

269

Oxidative degradation of dinitro butyl phenol (DNBP) utilizing hydrogen peroxide and solar light over a Al2O3-supported Fe(III)-5-sulfosalicylic acid (ssal) catalyst.  

PubMed

A novel and efficient photo-Fenton catalyst of Fe(III)-5-sulfosalicylic acid (ssal) supported on Al(2)O(3) was prepared and characterized by FT-IR and TEM-EDX technique. A detailed investigation of photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using this catalyst and H(2)O(2) under solar light irradiation was carried out. The effects of reaction parameters on photodegradation performance were investigated by examining H(2)O(2) dosage, catalyst loading, solution pH, initial DNBP concentration and temperature. The optimal conditions were an initial DNBP concentration of 40 mg L(-1) at pH 2.5 and temperature 30 degrees C with catalyst loading of 1.0 g L(-1) and H(2)O(2) concentration of 5 mmol L(-1) under solar light irradiation for 100 min. Almost complete degradation of DNBP was observed with [Fe(III)-ssal]-Al(2)O(3)/H(2)O(2) process under the optimal conditions. The degradation of DNBP by photo-Fenton-type process can be divided into the initiation phase and the fast phase. The kinetics of Fenton oxidation is complex and the degradation of DNBP in the two phases both can be described by a pseudo-first-order kinetic model. No obvious decline in efficiency of the [Fe(III)-ssal]-Al(2)O(3) catalyst was observed after 5 repeated cycles indicating this catalyst is stable and reusable. A possible reaction mechanism was proposed on the basis of all the information obtained under various experimental conditions. PMID:20034737

Zhang, Qian; Jiang, Wen-Feng; Wang, Hui-Long; Chen, Mao-Du

2010-04-15

270

A metal-free aerobic oxidation of nitrotoluenes catalyzed by N,N',N?-trihydroxyisocyanuric acid (THICA) and a novel approach to the catalyst.  

PubMed

A metal-free catalytic system with N,N',N?-trihydroxyisocyanuric acid (THICA) as the catalyst for the oxidation of nitrotoluenes is introduced, and a novel Pd-free approach for the synthesis of THICA was developed. In a solution of acetic acid, THICA and concentrated nitric acid, nitrotoluenes especially polynitrotoluenes such as 2,4,6-trinitrotoluene (TNT), were converted into the desired carboxylic acids under 0.2 MPa of O(2) at 100°C with yields up to 99%. THICA was synthesized from N-hydroxyphtalimide through a four-step synthesis in a total yield of 46%. A possible mechanism of this catalytic process was proposed where NO(2) and nitric acid first induced a radical of THICA, which then abstracts a hydrogen atom from the methyl on the aromatic ring to form a benzyl radical. This radical then initiates subsequent reactions. The production of the benzyl radical was supported by ESR measurements. PMID:20869170

Wang, Kai; Zhou, Zhiming; Song, Jinhong; Bi, Lixue; Shen, Ning; Wu, Yukai; Chen, Fuxue; Wen, Hongliang

2010-12-15

271

Solvent-free direct preparation of dichloropropanol from glycerol and hydrochloric acid gas in the presence of H 3PMo 12? X W X O 40 catalyst and\\/or water absorbent  

Microsoft Academic Search

Solvent-free direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas was carried out in the presence of H3PMo12?XWXO40 (X=0, 3, 6, 9, and 12) heteropolyacid (HPA) catalyst and\\/or water absorbent. Acid strength of the HPA catalyst played an important role in determining the catalytic performance in the solvent-free direct preparation of DCP. Water formed during the reaction retarded

Sang Hee Lee; Sun Ho Song; Dong Ryul Park; Ji Chul Jung; Ji Hwan Song; Sung Yul Woo; Won Seob Song; Myong Suk Kwon; In Kyu Song

2008-01-01

272

Amino acids regulate the transcription, internal sorting, and intrinsic activity of the general amino acid permease (GAP1) in S. cerevisiae  

E-print Network

The high capacity general amino acid permease in Saccharomyces cerevisiae (GAP1) is regulated such that it actively imports amino acids into the cell from the extracellular medium only when internal amino acid levels are ...

Risinger, April L. (April Lynn)

2007-01-01

273

Green chemistry: biodiesel made with sugar catalyst.  

PubMed

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for 'biodiesel' production. PMID:16281026

Toda, Masakazu; Takagaki, Atsushi; Okamura, Mai; Kondo, Junko N; Hayashi, Shigenobu; Domen, Kazunari; Hara, Michikazu

2005-11-10

274

Green chemistry: Biodiesel made with sugar catalyst  

NASA Astrophysics Data System (ADS)

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for `biodiesel' production.

Toda, Masakazu; Takagaki, Atsushi; Okamura, Mai; Kondo, Junko N.; Hayashi, Shigenobu; Domen, Kazunari; Hara, Michikazu

2005-11-01

275

Development of ternary alloy cathode catalysts for phosphoric acid fuel cells: Final report  

SciTech Connect

The overall objective of the program was the identification development and incorporation of high activity platinum ternary alloys on corrosion resistant supports, for use in advanced phosphoric acid fuel cells. Two high activity ternary alloys, Pr-Cr-Ce and Pt-Ni-Co, both supported on Vulcan XC-72, were identified during the course of the program. The Pr-Ni-Co system was selected for optimization, including preparation and evaluation on corrosion resistant supports such as 2700/degree/C heat-treated Vulcan XC-72 and 2700/degree/ heat-treated Black Pearls 2000. A series of tests identified optimum metal ratios, heat-treatment temperatures and heat-treatment atmospheres for the Pr-Ni-Co system. During characterization testing, it was discovered that approximately 50% of the nickel and cobalt present in the starting material could be removed, subsequent to alloy formation, without degrading performance. Extremely stable full cell performance was observed for the Pt-Ni-Co system during a 10,000 hour atmosphere pressure life test. Several theories are proposed to explain the enhancement in activity due to alloy formation. Recommendations are made for future research in this area. 62 refs., 23 figs., 27 tabs.

Not Available

1988-11-01

276

Formic Acid Dehydrogenation on Au-Based Catalysts at Near-Ambient Temperatures  

SciTech Connect

Formic acid (HCOOH) is a convenient hydrogen carrier in fuel cells designed for portable use. Recent studies have shown that HCOOH decomposition is catalyzed with Ru-based complexes in the aqueous phase at near-ambient temperatures. HCOOH decomposition reactions are used frequently to probe the effects of alloying and cluster size and of geometric and electronic factors in catalysis. These studies have concluded that Pt is the most active metal for HCOOH decomposition, at least as large crystallites and extended surfaces. The identity and oxidation state of surface metal atoms influence the relative rates of dehydrogenation (HCOOH {yields} H{sub 2} + CO{sub 2}) and dehydration (HCOOH {yields} H{sub 2}O + CO) routes, a selectivity requirement for the synthesis of CO-free H{sub 2} streams for low-temperature fuel cells. Group Ib and Group VIII noble metals catalyze dehydrogenation selectively, while base metals and metal oxides catalyze both routes, either directly or indirectly via subsequent water-gas shift (WGS) reactions.

Ojeda, Manuel; Iglesia, Enrique

2008-11-24

277

Activation of carboxylic acids in asymmetric organocatalysis.  

PubMed

Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles. PMID:24888674

Monaco, Mattia Riccardo; Poladura, Belén; Diaz de Los Bernardos, Miriam; Leutzsch, Markus; Goddard, Richard; List, Benjamin

2014-07-01

278

Efficient synthesis of spironaphthopyrano [2,3-d]pyrimidine-5,3'-indolines under solvent-free conditions catalyzed by SBA-Pr-SO3H as a nanoporous acid catalyst.  

PubMed

A green, simple one-pot synthesis of spironaphthopyrano[2,3-d]pyrimidine-5,3'-indoline derivatives by a three-component reaction of isatins, 2-naphthol, and barbituric acids under solvent-free conditions in the presence of SBA-Pr-SO(3)H has been accomplished. Sulfonic acid functionalized SBA-15 (SBA-Pr-SO(3)H) as a heterogeneous nanoporous solid acid catalyst was found to be an efficient and recyclable acid catalyst in this synthesis. PMID:25286212

Ziarani, Ghodsi Mohammadi; Lashgari, Negar; Faramarzi, Sakineh; Badiei, Alireza

2014-01-01

279

Esterification of bio-oil from mallee (Eucalyptus loxophleba ssp. gratiae) leaves with a solid acid catalyst: Conversion of the cyclic ether and terpenoids into hydrocarbons.  

PubMed

Bio-oil from pyrolysis of mallee (Eucalyptus loxophleba ssp. gratiae) leaves differs from that obtained with wood by its content of cyclic ethers, terpenoids and N-containing organic compounds. Upgrading of the leaf bio-oil in methanol with a solid acid catalyst was investigated and it was found that the N-containing organics in the bio-oil lead to deactivation of the catalyst in the initial stage of exposure and have to be removed via employing high catalyst loading to allow the occurrence of other acid-catalysed reactions. Eucalyptol, the main cyclic ether in the bio-oil, could be converted into the aromatic hydrocarbon, p-cymene, through a series of intermediates including ?-terpineol, terpinolene, and ?-terpinene. Various steps such as ring-opening, dehydration, isomerisation, and aromatization were involved in the conversion of eucalyptol. The terpenoids in bio-oil could also be converted into aromatic hydrocarbons that can serve as starting materials for the synthesis of fine chemicals, via the similar processes. PMID:22940326

Hu, Xun; Gunawan, Richard; Mourant, Daniel; Wang, Yi; Lievens, Caroline; Chaiwat, Weerawut; Wu, Liping; Li, Chun-Zhu

2012-11-01

280

The effect of metal–acid balance in Pt-loading dealuminated Y zeolite catalysts on the hydrogenation of benzene  

Microsoft Academic Search

The performances of various Pt-loading dealuminated Y zeolite catalysts for the hydrogenation of benzene were investigated in detail. The load of platinum was from 0.05% to 2% and the Si\\/Al ratio of the dealuminated Y zeolite was 17 or 2.6. It is found that the reaction condition and catalyst composition can influence the benzene conversion and the product selectivity substantially.

Jun Wang; Quanzhi Li; Jiandong Yao

1999-01-01

281

Convenient synthesis of unsymmetrical organochalcogenides using organoboronic acids with dichalcogenides via cleavage of the S-S, Se-Se, or Te-Te bond by a copper catalyst.  

PubMed

This article describes the methodology for a copper-catalyzed preparation of numerous monochalcogenides from dichalcogenides with organoboronic acids. Unsymmetrical diorgano-monosulfides, selenides, and tellurides can be synthesized by the coupling of dichalcogenides with aryl- or alkylboronic acids using a copper catalyst in air. The present reaction can take advantage of both organochalcogenide groups on dichalcogenide. PMID:17288374

Taniguchi, Nobukazu

2007-02-16

282

Sulfamic acid as an efficient and recyclable catalyst for the ring opening of epoxides with amines and anilines: An easy synthesis of ?-amino alcohols under solvent-free conditions  

Microsoft Academic Search

Application of sulfamic acid as an efficient and green catalyst for the ring opening of epoxides by aliphatic and aromatic amines under solvent-free conditions is described. In this process the use of basic neutralization agent was not required due to the intrinsic zwitterionic property of sulfamic acid. The salient features of this methodology are cheaper process, easy availability of the

Ahmed Kamal; B. Rajendra Prasad; A. Malla Reddy; M. Naseer A. Khan

2007-01-01

283

Tungstophosphoric acid supported on silica gel (H 3PW 12O 40\\/SiO 2) as an eco-friendly, reusable and heterogeneous catalyst for chemoselective oxathioacetalization of carbonyl compounds in solution or under solvent-free conditions  

Microsoft Academic Search

Solid heteropoly acid supported on silica gel (H3PW12O40\\/SiO2) is easily used as a heterogonous, reusable and efficient catalyst for conversion of aromatic and aliphatic aldehydes and ketones to their corresponding 1,3-oxathiolanes at room temperature in solution or under solvent-free conditions. The catalyst can be easily recovered and reused for several times without loss of its activity.

Habib Firouzabadi; Nasser Iranpoor; Abbas Ali Jafari; Mohammad Reza Jafari

2006-01-01

284

pKa Modulation of the Acid/Base Catalyst within GH32 and GH68: A Role in Substrate/Inhibitor Specificity?  

PubMed Central

Glycoside hydrolases of families 32 (GH32) and 68 (GH68) belong to clan GH-J, containing hydrolytic enzymes (sucrose/fructans as donor substrates) and fructosyltransferases (sucrose/fructans as donor and acceptor substrates). In GH32 members, some of the sugar substrates can also function as inhibitors, this regulatory aspect further adding to the complexity in enzyme functionalities within this family. Although 3D structural information becomes increasingly available within this clan and huge progress has been made on structure-function relationships, it is not clear why some sugars bind as inhibitors without being catalyzed. Conserved aspartate and glutamate residues are well known to act as nucleophile and acid/bases within this clan. Based on the available 3D structures of enzymes and enzyme-ligand complexes as well as docking simulations, we calculated the pKa of the acid-base before and after substrate binding. The obtained results strongly suggest that most GH-J members show an acid-base catalyst that is not sufficiently protonated before ligand entrance, while the acid-base can be fully protonated when a substrate, but not an inhibitor, enters the catalytic pocket. This provides a new mechanistic insight aiming at understanding the complex substrate and inhibitor specificities observed within the GH-J clan. Moreover, besides the effect of substrate entrance on its own, we strongly suggest that a highly conserved arginine residue (in the RDP motif) rather than the previously proposed Tyr motif (not conserved) provides the proton to increase the pKa of the acid-base catalyst. PMID:22662155

Yuan, Shuguang; Le Roy, Katrien; Venken, Tom; Lammens, Willem; Van den Ende, Wim; De Maeyer, Marc

2012-01-01

285

pKa modulation of the acid/base catalyst within GH32 and GH68: a role in substrate/inhibitor specificity?  

PubMed

Glycoside hydrolases of families 32 (GH32) and 68 (GH68) belong to clan GH-J, containing hydrolytic enzymes (sucrose/fructans as donor substrates) and fructosyltransferases (sucrose/fructans as donor and acceptor substrates). In GH32 members, some of the sugar substrates can also function as inhibitors, this regulatory aspect further adding to the complexity in enzyme functionalities within this family. Although 3D structural information becomes increasingly available within this clan and huge progress has been made on structure-function relationships, it is not clear why some sugars bind as inhibitors without being catalyzed. Conserved aspartate and glutamate residues are well known to act as nucleophile and acid/bases within this clan. Based on the available 3D structures of enzymes and enzyme-ligand complexes as well as docking simulations, we calculated the pKa of the acid-base before and after substrate binding. The obtained results strongly suggest that most GH-J members show an acid-base catalyst that is not sufficiently protonated before ligand entrance, while the acid-base can be fully protonated when a substrate, but not an inhibitor, enters the catalytic pocket. This provides a new mechanistic insight aiming at understanding the complex substrate and inhibitor specificities observed within the GH-J clan. Moreover, besides the effect of substrate entrance on its own, we strongly suggest that a highly conserved arginine residue (in the RDP motif) rather than the previously proposed Tyr motif (not conserved) provides the proton to increase the pKa of the acid-base catalyst. PMID:22662155

Yuan, Shuguang; Le Roy, Katrien; Venken, Tom; Lammens, Willem; Van den Ende, Wim; De Maeyer, Marc

2012-01-01

286

Kinetics, energetics and specificity of a general amino acid transporter from the ectomycorrhizal fungus Paxillus involutus  

Microsoft Academic Search

~~ ~~ ~ The kinetics, energetics and specificity of a general amino acid transporter were studied in the ectomycorrhizal fungus Paxillus involutus (Batsch) Fr. The uptake of amino acids showed features characteristic of active transport. After correction for a non-mediated transport component, the kinetics of glutamate, glutamine, alanine and aspartate uptake measured over a wide concentration range followed the simple

Michel Chalot; A. Brun; B. Botton; B. Soderstrom

1996-01-01

287

Ascorbic Acid as a Standard for Iodometric Titrations. An Analytical Experiment for General Chemistry  

NASA Astrophysics Data System (ADS)

Ascorbic acid is suggested as the weighable compound for the standardization of iodine solutions in an analytical experiment in general chemistry. The experiment involves an iodometric titration in which iodine reacts with ascorbic acid, oxidizing it to dehydroascorbic acid. The redox titration endpoint is determined by the first iodine excess that is complexed with starch, giving a deep blue-violet color. The results of the titration of iodine solution using ascorbic acid as a calibration standard were compared with the results acquired by the classic method using a standardized solution of sodium thiosulfate. The standardization of the iodine solution using ascorbic acid was accurate and precise, with the advantages of saving time and avoiding mistakes due to solution preparation. The colorless ascorbic acid solution gives a very clear and sharp titration end point with starch. It was shown by thermogravimetric analysis that ascorbic acid can be dried at 393 K for 2 h without decomposition. This experiment allows general chemistry students to perform an iodometric titration during a single laboratory period, determining with precision the content of vitamin C in pharmaceutical formulations.

Silva, Cesar R.; Simoni, Jose A.; Collins, Carol H.; Volpe, Pedro L. O.

1999-10-01

288

Reuse of sewage sludge as a catalyst in ozonation--efficiency for the removal of oxalic acid and the control of bromate formation.  

PubMed

Sewage derived sludge is produced with an annual amount increase of 2% all over the world and it is an urgent issue to be addressed by human being. In the present study, sludge was converted into sludge-based catalyst (SBC) with ZnCl2 as activation agent and characterized by several methods (e.g., scanning electron microscope, X-ray photoelectron spectroscope and Fourier transform infrared spectroscope). Then it was used as a catalyst to enhance the removal of refractory organic matter, oxalic acid, and to control the formation of bromate (BrO3-) in bench semi-continuous ozonation experiments. The effects of various operating parameters on the control of BrO3- formation were investigated. Furthermore, the mechanism for the enhancement of organic matter removal and the control of BrO3- formation was discussed as well. Results indicate that the combination of SBC with ozone shows a strong synergistic effect, resulting in a notable improvement on oxalic acid removal. A crucial surface reaction mechanism for the enhancement of organic matter removal is proposed on the basis of negative effect of higher pH and no inhibition effect of tert-butanol. The control for BrO3- formation was demonstrated and the reason for its control in the process of O3/SBC is the combined effect of SBC reductive properties, ozone exposure decrease and hydrogen peroxide concentration increase. PMID:23021317

Wen, Gang; Pan, Zhi-Hui; Ma, Jun; Liu, Zheng-Qian; Zhao, Lei; Li, Jun-Jing

2012-11-15

289

Deactivation mechanism of potassium on the V?O?/CeO? catalysts for SCR reaction: acidity, reducibility and adsorbed-NOx.  

PubMed

A series of V2O5/CeO2 catalysts with different potassium loadings were prepared to investigate alkali deactivations for selective catalytic reduction of NOx with NH3. An alkali poisoning mechanism could be attributed to surface acidity, reducibility, and NOx adsorption/desorption behaviors. The detailed factors are as follows: (1) decrease of surface acidity suppresses NH3 adsorption by strong bonding of alkali to vanadia (major factor); (2) low reducibility prohibits NH3 activation and NO oxidation by formation bonding of alkali to vanadia and ceria (important factor); (3) active NOx(-) species at low temperature diminish because of coverage of alkali on the surfaces (minor factor); and (4) stable, inactive nitrate species at high temperature increase by generating new basic sites (important factor). PMID:24634979

Peng, Yue; Li, Junhua; Huang, Xu; Li, Xiang; Su, Wenkang; Sun, Xiaoxu; Wang, Dezhi; Hao, Jiming

2014-04-15

290

Isolable gold(I) complexes having one low-coordinating ligand as catalysts for the selective hydration of substituted alkynes at room temperature without acidic promoters.  

PubMed

Hydration of a wide range of alkynes to the corresponding ketones has been afforded in high yields at room temperature by using gold(I)-phosphine complexes as catalyst, with no acidic cocatalysts required. Suitable substrates covering alkyl and aryl terminal alkynes, enynes, internal alkynes, and propargylic alcohols, including enantiopure forms, are cleanly transformed to the corresponding ketones in nearly quantitative yields. Acid-labile groups present in the substrates are preserved. The catalytic activity strongly depends on both the nature of the phosphine coordinated to the gold (I) center and the softness of the counteranion, the complex AuSPhosNTf(2) showing the better activity. A plausible mechanism for the hydration of alkynes through ketal intermediates is proposed on the basis of kinetic studies. The described catalytic system should provide an efficient alternative to mercury-based methodologies and be useful in synthetic programs. PMID:19170603

Leyva, Antonio; Corma, Avelino

2009-03-01

291

Catalysts and method  

DOEpatents

An improved catlayst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HC1 and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

Taylor, Charles E. (Pittsburgh, PA); Noceti, Richard P. (Pittsburgh, PA)

1991-01-01

292

Heterogeneous base catalysts for edible palm and non-edible Jatropha-based biodiesel production  

PubMed Central

Background Transesterification catalyzed by solid base catalyst is a brilliant technology for the noble process featuring the fast reaction under mild reacting condition in biodiesel production. Heterogeneous base catalysts are generally more reactive than solid acid catalysts which require extreme operating condition for high conversion and biodiesel yield. In the present study, synthesis of biodiesel was studied by using edible (palm) or non-edible (Jatropha) feedstock catalyzed by heterogeneous base catalysts such as supported alkali metal (NaOH/Al2O3), alkaline-earth metal oxide (MgO, CaO and SrO) and mixed metal oxides catalysts (CaMgO and CaZnO). Results The chemical characteristic, textural properties, basicity profile and leaching test of synthesized catalysts were studied by using X-ray diffraction, BET measurement, TPD-CO2 and ICP-AES analysis, respectively. Transesterification activity of solid base catalysts showed that?>?90% of palm biodiesel and?>?80% of Jatropha biodiesel yield under 3 wt.% of catalyst, 3 h reaction time, methanol to oil ratio of 15:1 under 65°C. This indicated that other than physicochemical characteristic of catalysts; different types of natural oil greatly influence the catalytic reaction due to the presence of free fatty acids (FFAs). Conclusions Among the solid base catalysts, calcium based mixed metal oxides catalysts with binary metal system (CaMgO and CaZnO) showed capability to maintain the transesterification activity for 3 continuous runs at?~?80% yield. These catalysts render high durability characteristic in transesterification with low active metal leaching for several cycles. PMID:24812574

2014-01-01

293

Generalization of morphine and lysergic acid diethylamide (LSD) stimulus properties to narcotic analgesics  

Microsoft Academic Search

The present investigation sought to determine whether the stimulus properties of morphine and lysergic acid diethylamide (LSD) would generalize to several narcotic analgesics which vary in their subjective effects. Morphine and saline served as discriminative stimuli for one group of rats in a 2-lever discrimination task. LSD and saline were discriminative stimuli for a second group. Depression of one lever

I. D. Hirschhorn; J. A. Rosecrans

1976-01-01

294

Gallium(III) Trifluormethanesulfonate: A Water-Tolerant, Reusable Lewis Acid Catalyst for Friedel-Crafts Reactions  

Microsoft Academic Search

The application of gallium(III) trifluoromethanesulfonate (triflate, OTf) in Friedel-Crafts alkylation and acylation reactions is described. Gallium triflate was found to be an excellent catalyst for the adamantylation of toluene with 1-bromoadamantane, where its activity was compared to that of well-known rare earth metal triflates. As Ga(OTf)3 does not decompose in the presence of water the isopropylation of aromatics can be

G. K. Surya Prakash; Ping Yan; Béla Török; Imre Bucsi; Mutsuo Tanaka; George A. Olah

2003-01-01

295

Incorporating Amino Acid Esters into Catalysts for Hydrogen Oxidation: Steric and Electronic Effects and the Role of Water as a Base  

SciTech Connect

Four derivatives of a hydrogen oxidation catalyst, [Ni(PCy2NBn-R2)]2+ (Cy=cyclohexyl, Bn=benzyl, R= OMe, COOMe, CO-Alanine-methyl ester or CO-Phenylalanine-methyl ester), have been prepared to investigate steric and electronic effects on catalysis. Each complex was characterized spectroscopically and electrochemically, and thermodynamic data were determined. Crystal structures are also reported for the -OMe and -COOMe derivatives. All four catalysts were found to be active for H2 oxidation. The methyl ester (R = COOMe) and amino acid ester containing complexes (R = CO-Alanine-methyl ester or CO-Phenylalanine-methyl ester) had slower rates (4 s-1) than that of the parent complex (10 s-1), in which R = H, consistent with the lower amine pKa’s and less favorable ?GH2’s found for these electron-withdrawing substituents. Dynamic processes for the amino acid ester containing complexes were also investigated and found not to hinder catalysis. The electron-donating methoxy ether derivative (R = OMe) was prepared to compare electronic effects and has a similar catalytic rate as the parent complex. In the course of these studies, it was found that water could act as a weak base for H2 oxidation, although catalytic turnover requires a significantly higher potential and utilizes a different sequence of catalytic steps than when using a base with a higher pKa. Importantly, these catalysts provide a foundation upon which larger peptides can be attached to [Ni(PCy2NBn2)2]2+ hydrogen oxidation catalysts in order to more fully investigate and implement the effects of the outer-coordination sphere. This work was funded by the DOE Office of Science Early Career Research Program through the Office of Basic Energy Sciences (SL and WJS), by the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (JR), and by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (AMA, AJ). Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Lense, Sheri; Ho, Ming-Hsun; Chen, Shentan; Jain, Avijita; Raugei, Simone; Linehan, John C.; Roberts, John A.; Appel, Aaron M.; Shaw, Wendy J.

2012-10-08

296

Use of Pyrolyzed Iron Ethylenediaminetetraacetic Acid Modified Activated Carbon as Air-Cathode Catalyst in Microbial Fuel Cells  

E-print Network

Use of Pyrolyzed Iron Ethylenediaminetetraacetic Acid Modified Activated Carbon as Air activity of AC cathodes, AC powders were pyrolyzed with iron ethylenediaminetetraacetic acid (Fe MFCs was 50% lower than MFCs with the AC cathodes. Pyridinic nitrogen, quaternary nitrogen and iron

297

Engelhard acquires German catalyst maker  

SciTech Connect

Engelhard will acquire the precious- and base-metal catalyst businesses of Doduco GmbH & Co. (Pforzheim, Germany), a privately held supplier of catalysts to the chemical and pharmaceutical industries. {open_quotes}This is an excellent product expansion for us, one that we believe can be leveraged throughout Europe and, later, globally,{close_quotes} says James A. Martin, group v.p., president, and general manager of Engelhard`s chemical catalysts group.

NONE

1996-10-16

298

Bioleaching of spent fluid catalytic cracking catalyst using Aspergillus niger  

Microsoft Academic Search

The use of the fungus Aspergillus niger for the bioleaching of heavy metals from spent catalyst was investigated, with fluid catalytic cracking (FCC) catalyst as a model. Bioleaching was examined in batch cultures with the spent catalysts at various pulp densities (1–12%). Chemical leaching was also performed using mineral acids (sulphuric and nitric acids) and organic acids (citric, oxalic and

Khin Moh Moh Aung; Yen-Peng Ting

2005-01-01

299

Transalkylation of toluene with trimethylbenzenes catalyzed by various AFI catalysts  

Microsoft Academic Search

Substitution of transition metals in the AlPO4-5 framework was found to afford novel heterogeneous catalysts for the transalkylation of toluene (T) with trimethylbenzenes (TMBs). The activity of MeAPO-5 catalysts follows the order of SiAPO>MgAPO>MnAPO>ZnAPO>CoAPO which can be correlated with the acid properties of catalysts. The same correlation was found for MeAPSO-5 catalysts. The strength of acid sites of the catalyst

E Dumitriu; C Guimon; V Hulea; D Lutic; I Fechete

2002-01-01

300

Laser-induced removal of a dye C.I. Acid Red 87 using n-type WO3 semiconductor catalyst.  

PubMed

Water contamination by organic substances such as dyes is of great concern worldwide due to their utilization in many industrial processes and environmental concerns. To cater the needs for waste water treatment polluted with organic dyes, laser-induced photocatalytic process was investigated for removal of a dye derivative namely Acid Red 87 using n-type WO3 semiconductor catalyst. The degradation was investigated in aqueous suspensions of tungsten oxide under different experimental conditions using laser instead of conventional UV lamp as an irradiation source. The degradation process was monitored by measuring the change in dye concentration as a function of laser irradiation time by employing UV spectroscopic analysis. The degradation of dye was studied by varying different parameters such as laser energy, reaction pH, substrate concentration, catalyst concentration, and in the presence of electron acceptors such as hydrogen peroxide (H2O2), and potassium bromate (KBrO3). The degradation rates were found to be strongly dependent on all the above-mentioned parameters. Our experimental results revealed that the dye degradation process was very fast (within few minutes) under laser irradiation as compared to conventional setups using broad spectral lamps (hours or days) and this laser-induced photocatalytic degradation method could be an effective means to eliminate the pollutants present in liquid phase. The experience gained through this study could be beneficial for treatment of waste water contaminated with organic dyes and other organic pollutants. PMID:19540669

Qamar, M; Gondal, M A; Hayat, K; Yamani, Z H; Al-Hooshani, K

2009-10-30

301

Covalent protein crosslinks: general detection, quantitation, and characterization via modification with diphenylborinic acid.  

PubMed

Progressive crosslinking of proteins appears to be a general phenomenon in aging cells and tissues. Crosslinked proteins can form insoluble aggregates which become increasingly resistant to proteolysis as more crosslinks form. However, most evidence for progressive crosslinking with age is indirect, and little is known about the chemical mechanisms involved. We have therefore developed a method for detection and isolation of any type of stable covalent crosslink from protein hydrolysates which requires no prior knowledge of the molecular structure of whatever crosslink(s) may be present. It utilizes the specificity of the diphenylborinic acid reagent for alpha-amino acid groups and the chromatographic properties and uv absorbance of the crosslink derivatives. The method is demonstrated using eight different crosslinks from collagen and fibrin, and a general procedure is given for detection of any type of crosslink in a protein hydrolysate. PMID:8203759

Graham, L; Gallop, P M

1994-03-01

302

Aluminum dodecatungstophosphate (AlPW 12O 40) as a non-hygroscopic Lewis acid catalyst for the efficient Friedel–Crafts acylation of aromatic compounds under solvent-less conditions  

Microsoft Academic Search

Stable and non-hygroscopic aluminum dodecatungstophosphate (AlPW12O40), which is prepared easily from cheap and commercially available compounds was found to be an effective catalyst for Friedel–Crafts acylation reactions using carboxylic acids, acetic anhydride and benzoyl chloride in the absence of solvent under mild reaction conditions.

Habib Firouzabadi; Nasser Iranpoor; Farhad Nowrouzi

2004-01-01

303

A convenient synthesis of chiral succinic acid-d 2 by catalytic asymmetric reduction using a ruthenium BINAP catalyst  

Microsoft Academic Search

The synthesis of (2R,3R) and (2S,3S) dideuteriosuccinic acid in 63 ± 10% enantiomeric excess by reduction of the half acid ester of ethyl fumarate from (R) and (S) BINAP ruthenium (II) diacetate complex, respectively, is reported. (2R,3R) and (2S,3S)-Dideuteriosuccinic acid has also been prepared from (R)-BINAP ruthenium (II) dicarboxylate complex directly in similar optical purity by reversing the sequence of

Cheok N. Tam; Timothy A. Keiderling

1995-01-01

304

General aspect of catalytic hydrogenation and isomerization reactions on oxide catalyst. Characteristics of the reactions via ionic and nonionic intermediates  

SciTech Connect

An analysis of new and available data, mostly published by Tanaka and Okuhara, on the hydrogenation of alkenes and conjugated dienes and the hydrogen-deuterium exchange on the oxides of cadmium, magnesium, zinc, cobalt, chromium, thorium, zirconium, and lanthanum, and on molybdenum disulfide suggested that the partial hydrogenation of conjugated dienes catalyzed by cadmium and magnesium oxide proceeds by a mechanism which is similar to that of diene hydrogenation on supported alkali metals or on alkali metal hydride and involves allyl carbanion intermediates. The same ionic mechanism apparently also occurs in the double-bond migration of n-alkenes on cadmium oxide, and the isomerization catalyzed by molybdenum disulfide. The nonionic reaction mechanism via o-alkyl and o- or m-allyl intermediates apparently proceeds on active sites of a definite structure, i.e., a specific degree of coordination, but the ionic mechanism seems to depend only on the acidity or basicity of the sites. The nonspecific nature of the site for the ionic mechanism may result in high resistance to poisoning.

Tanaka, K.; Okuhara, T.

1980-09-01

305

General Roles of Abscisic and Jasmonic Acids in Gene Activation as a Result of Mechanical Wounding  

Microsoft Academic Search

Exogenous application of abscisic acid (ABA) has been shown to induce a systemic pattern of proteinase inhibitor II (pin2) mRNA accumulation identical to that induced by mechanical wounding. Evidence is presented that the ABA-specific response is not restricted to pin2 genes but appears to,be part of a general reaction to wound stress. Four other wound- induced, ABAresponsive genes that encode

Thomas Hildmann; Marcus Ebneth; Hugo Peiia-Cortth; Jose J. Sánchez-Serrano; Lothar Willmitzer; Salomti Prat

1992-01-01

306

Oxide acid-base reaction relating to the inhibition of vandium attack on REY zeolite catalysts. [Rare earth-exchanged yttrium  

SciTech Connect

Certain materials, especially Sn, passivate the rare earth-exchanged Y zeolite (REY) used in petrochemical fluid-cracking catalysts against vanadium degradation caused by V impurities in the feed oil. The mechanism of passivation was investigated here from the standpoint of high-temperature oxide acid-base reaction; i.e., where the controlling factors were considered to be Lewis acid-base reactions between V{sub 2}O{sub 5}, the RE oxides, SnO{sub 2}, etc. Molten salt tests at 680{degree}C showed SnO{sub 2}, presumably because of its acidic nature, to be essentially nonreactive with V{sub 2}O{sub 5} or Na{sub 2}O-V{sub 2}O{sub 5} compounds. A hypothesis was developed to explain how the passivation effect by Sn might result from the unique resistivity of SnO{sub 2} to reaction with V{sub 2}O{sub 5}.

Jones, R.L. (Naval Research Lab., Washington, D.C. (USA))

1991-05-01

307

Bimetallic Catalysts.  

ERIC Educational Resources Information Center

Chemical reaction rates can be controlled by varying composition of miniscule clusters of metal atoms. These bimetallic catalysts have had major impact on petroleum refining, where work has involved heterogeneous catalysis (reacting molecules in a phase separate from catalyst.) Experimentation involving hydrocarbon reactions, catalytic…

Sinfelt, John H.

1985-01-01

308

Boron Stress Activates the General Amino Acid Control Mechanism and Inhibits Protein Synthesis  

PubMed Central

Boron is an essential micronutrient for plants, and it is beneficial for animals. However, at high concentrations boron is toxic to cells although the mechanism of this toxicity is not known. Atr1 has recently been identified as a boron efflux pump whose expression is upregulated in response to boron treatment. Here, we found that the expression of ATR1 is associated with expression of genes involved in amino acid biosynthesis. These mechanisms are strictly controlled by the transcription factor Gcn4 in response to boron treatment. Further analyses have shown that boron impaired protein synthesis by promoting phosphorylation of eIF2? in a Gcn2 kinase dependent manner. The uncharged tRNA binding domain (HisRS) of Gcn2 is necessary for the phosphorylation of eIF2? in the presence of boron. We postulate that boron exerts its toxic effect through activation of the general amino acid control system and inhibition of protein synthesis. Since the general amino acid control pathway is conserved among eukaryotes, this mechanism of boron toxicity may be of general importance. PMID:22114689

Uluisik, Irem; Kaya, Alaattin; Fomenko, Dmitri E.; Karakaya, Huseyin C.; Carlson, Bradley A.; Gladyshev, Vadim N.; Koc, Ahmet

2011-01-01

309

Mechanistic characterization of the HDV genomic ribozyme: solvent isotope effects and proton inventories in the absence of divalent metal ions support C75 as the general acid.  

PubMed

The hepatitis delta virus (HDV) ribozyme uses the nucleobase C75 and a hydrated Mg(2+) ion as the general acid-base catalysts in phosphodiester bond cleavage at physiological salt. A mechanistic framework has been advanced that involves one Mg(2+)-independent and two Mg(2+)-dependent channels. The rate-pH profile for wild-type (WT) ribozyme in the Mg(2+)-free channel is inverted relative to the fully Mg(2+)-dependent channel, with each having a near-neutral pKa. Inversion of the rate-pH profile was used as the crux of a mechanistic argument that C75 serves as general acid both in the presence and absence of Mg(2+). However, subsequent studies on a double mutant (DM) ribozyme suggested that the pKa observed for WT in the absence of Mg(2+) arises from ionization of C41, a structural nucleobase. To investigate this further, we acquired rate-pH/pD profiles and proton inventories for WT and DM in the absence of Mg(2+). Corrections were made for effects of ionic strength on hydrogen ion activity and pH meter readings. Results are accommodated by a model wherein the Mg(2+)-free pKa observed for WT arises from ionization of C75, and DM reactivity is compromised by protonation of C41. The Brønsted base appears to be water or hydroxide ion depending on pH. The observed pKa's are related to salt-dependent pH titrations of a model oligonucleotide, as well as electrostatic calculations, which support the local environment for C75 in the absence of Mg(2+) being similar to that in the presence of Mg(2+) and impervious to bulk ions. Accordingly, the catalytic role of C75 as the general acid does not appear to depend on divalent ions or the identity of the Brønsted base. PMID:18842044

Cerrone-Szakal, Andrea L; Siegfried, Nathan A; Bevilacqua, Philip C

2008-11-01

310

Cooperative activation with chiral nucleophilic catalysts and N-haloimides: enantioselective iodolactonization of 4-arylmethyl-4-pentenoic acids.  

PubMed

Chiral triaryl phosphates promote the enantioselective iodolactonization of 4-substituted 4-pentenoic acids to give the corresponding iodolactones in high yields with high enantioselectivity. N-Chlorophthalimide (NCP) is employed as a Lewis acidic activator and oxidant of I2 for the present iodolactonization. In combination with 1.5?equivalents of NCP, only 0.5?equivalents of I2 are sufficient to generate the iodinating reagent. PMID:24840957

Nakatsuji, Hidefumi; Sawamura, Yasuhiro; Sakakura, Akira; Ishihara, Kazuaki

2014-07-01

311

Method of performing sugar dehydration and catalyst treatment  

SciTech Connect

The invention includes a method of treating a solid acid catalyst. After exposing the catalyst to a mixture containing a sugar alcohol, the catalyst is washed with an organic solvent and is then exposed to a second reaction mixture. The invention includes a process for production of anhydrosugar alcohol. A solid acid catalyst is provided to convert sugar alcohol in a first sample to an anhydrosugar alcohol. The catalyst is then washed with an organic solvent and is subsequently utilized to expose a second sample. The invention includes a method for selective production of an anhydrosugar. A solid acid catalyst is provided within a reactor and anhydrosugar alcohol is formed by flowing a starting sugar alcohol into the reactor. The acid catalyst is then exposed to an organic solvent which allows a greater amount of additional anhydrosugar to be produced than would occur without exposing the acid catalyst to the organic solvent.

Hu, Jianli [Kennewick, WA; Holladay, Johnathan E [Kennewick, WA; Zhang, Xinjie [Burlington, MA; Wang, Yong [Richland, WA

2010-06-01

312

No catalyst addition and highly efficient dissociation of H2O for the reduction of CO2 to formic acid with Mn.  

PubMed

The "greenhouse effect" caused by the increasing atmospheric CO2 level is becoming extremely serious, and thus, the reduction of CO2 emissions has become an extensive, urgent, and long-term task. The dissociation of water for CO2 reduction with solar energy is regarded as one of the most promising methods for the sustainable development of the environment and energy. However, a high solar-to-fuel efficiency keeps a great challenge. In this work, the first observation of a highly effective, highly selective, and robust system of dissociating water for the reduction of carbon dioxide (CO2) into formic acid with metallic manganese (Mn) is reported. A considerably high formic acid yield of more than 75% on a carbon basis from NaHCO3 was achieved with 98% selectivity in the presence of simple commercially available Mn powder without the addition of any catalyst, and the proposed process is exothermic. Thus, this study may provide a promising method for the highly efficient dissociation of water for CO2 reduction by combining solar-driven thermochemistry with the reduction of MnO into Mn. PMID:24787746

Lyu, Lingyun; Zeng, Xu; Yun, Jun; Wei, Feng; Jin, Fangming

2014-05-20

313

An efficient procedure for protection of carbonyls catalyzed by sulfamic acid  

Microsoft Academic Search

Sulfamic acid (H2NSO3H) has been used as an efficient and recyclable catalyst for acetalization and ketalization between carbonyl compounds and diols. This system is reasonably general and can be applied to converting several carbonyl compounds to the corresponding acetals and ketals using neopentyl glycol and other diols as protection reagents. The use of an inexpensive, green and stable catalyst, convenient

Bo Wang; Yanlong Gu; Guoyong Song; Tao Yang; Liming Yang; Jishuan Suo

2005-01-01

314

Synthesis and characterization of ternary Pt-Ni-M/C (M=Cu, Fe, Ce, Mo, W) nano-catalysts for low temperature fuel cells  

NASA Astrophysics Data System (ADS)

Ternary metal catalysts were synthesized by impregnation method. The mixture of metal solutions was reduced slowly under inert atmosphere and the reduced metals were deposited on the Vulcan Carbon(VC). Tungsten, molybdenum, cerium, iron and copper were added to specified amounts of platinum and nickel. Addition of nickel generally improves catalytic activity of platinum. The XRD of the catalysts was done and the crystallite size and other parameters were calculated. Crystallite sizes were in the range of 5 to 16 nm. Electrochemical surface areas of the catalysts were determined by cyclic voltammetry (CV) in acidic media and are compared. Electro oxidation of methanol on the catalysts was done and peak potential, peak current, mass activity of the catalysts were calculated and are compared. These parameters were determined in acidic and basic media. It was found that mass activity increased significantly in basic media. Rate constants for the electro oxidation of methanol were also calculated in acidic and basic media and are compared and discussed. Rate constants were generally higher in basic media. Ternary catalysts showed improved catalytic activity than the binary catalyst. Nano alloying improved the catalytic activity and stability of the ternary catalysts.

Ahmed, Riaz; Jamil, Rabia; Shahid Ansari, Muhammad

2014-06-01

315

Generalized chemical route to develop fatty acid capped highly dispersed semiconducting metal sulphide nanocrystals  

SciTech Connect

Highlights: ? Chemical route for the synthesis of OA-capped CdS, ZnS and PbS at low temperature. ? Synthesized nanocrystals via thermolysis of their metal–oleate complexes. ? Size quantized nanocrystals were highly dispersed and stable at room temperature. -- Abstract: This work deals with the synthesis of highly dispersed semiconducting nanocrystals (NCs) of cadmium sulphide (CdS), zinc sulphide (ZnS) and lead sulphide (PbS) through a simple and generalized process using oleic acid (OA) as surfactant. To synthesize these NCs, metal–oleate (M–O) complexes were obtained from the reaction at 140 °C between metal acetates and OA in hexanes media. Subsequently, M–O complexes were sulphurized using thioacetamide at the same temperature. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations show that the synthesized products are of nanoscale-size with highly crystalline cubic phase. The optical absorption of OA-capped metal sulphide NCs confirms that their size quantization induced a large shift towards visible region. Photoluminescence (PL) spectrum of CdS NCs shows a broad band-edge emission with shallow and deep-trap emissions, while PL spectrum of ZnS NCs reveals a broad emission due to defects states on the surface. The thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy indicate that fatty acid monolayers were bound strongly on the nanocrystal surface as a carboxylate and the two oxygen atoms of the carboxylate were coordinated symmetrically to the surface of the NCs. The strong binding between the fatty acid and the NCs surface enhances the stability of NCs colloids. In general, this generalized route has a great potential in developing nanoscale metal sulphides for opto-electronic devices.

Patel, Jayesh D. [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada) [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada); Chemical Engineering Department, University of Laval, Quebec, QC, G1K 7P4 (Canada); Mighri, Frej, E-mail: Frej.Mighri@gch.ulaval.ca [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada) [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada); Chemical Engineering Department, University of Laval, Quebec, QC, G1K 7P4 (Canada); Ajji, Abdellah [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada) [Center for Applied Research on Polymers and Composites, CREPEC, Quebec (Canada); Chemical Engineering Department, Ecole Polytechnique, C.P. 6079, Succ. Centre-Ville Montreal, QC, H3C 3A7 (Canada)

2012-08-15

316

Base-free direct oxidation of 1-octanol to octanoic acid and its octyl ester over supported gold catalysts.  

PubMed

The choice of a suitable support for gold nanoparticles (Au NPs) enabled the direct oxidation of unreactive aliphatic alcohol, 1-octanol, to octanoic acid and octyl octanoate in the absence of a base. Under optimized conditions, Au NPs supported on NiO (Au/NiO) exhibited remarkably high catalytic activities and excellent selectivities to octanoic acid (e.g., 97?%) at full conversion. In contrast to Au/NiO, Au/CeO? selectively produced octyl octanoate as a major product in a base-free aqueous solution with a maximum selectivity of 82?% under optimized conditions. PMID:23065901

Ishida, Tamao; Ogihara, Yuichiro; Ohashi, Hironori; Akita, Tomoki; Honma, Tetsuo; Oji, Hiroshi; Haruta, Masatake

2012-11-01

317

Transcriptional and posttranslational regulation of the general amino acid permease of Saccharomyces cerevisiae.  

PubMed Central

The cellular level and activity of the general amino acid permease, the product of the GAP1 gene of Saccharomyces cerevisiae, are regulated at the level of transcription by two systems, the products of URE2/GLN3 and NIL1 in response to the nitrogen sources of the growth medium and inactivation in response to the presence of glutamine or glutamate. Active permease is phosphorylated. The addition of glutamine causes rapid dephosphorylation and inactivation of the permease with the same kinetics, which is followed by slower disappearance of the protein. These results suggest that inactivation of the permease results from its dephosphorylation. PMID:7798155

Stanbrough, M; Magasanik, B

1995-01-01

318

Amino acid modified Ni catalyst exhibits reversible H2 oxidation/production over a broad pH range at elevated temperatures.  

PubMed

Hydrogenases interconvert H2 and protons at high rates and with high energy efficiencies, providing inspiration for the development of molecular catalysts. Studies designed to determine how the protein scaffold can influence a catalytically active site have led to the synthesis of amino acid derivatives of [Formula: see text] complexes, [Formula: see text] (CyAA). It is shown that these CyAA derivatives can catalyze fully reversible H2 production/oxidation at rates approaching those of hydrogenase enzymes. The reversibility is achieved in acidic aqueous solutions (pH = 0-6), 1 atm 25% H2/Ar, and elevated temperatures (tested from 298 to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the catalytic activity is dependent upon H2 and proton concentrations. CyArg is significantly faster in both directions (?300 s(-1) H2 production and 20 s(-1) H2 oxidation; pH = 1, 348 K, 1 atm 25% H2/Ar) than the other two derivatives. The slower turnover frequencies for CyArgOMe (35 s(-1) production and 7 s(-1) oxidation under the same conditions) compared with CyArg suggests an important role for the COOH group during catalysis. That CyArg is faster than CyGly (3 s(-1) production and 4 s(-1) oxidation) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H2 addition/release. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site and can play an important role for synthetic molecular electrocatalysts, as has been observed for the protein scaffold of redox active enzymes. PMID:25368196

Dutta, Arnab; DuBois, Daniel L; Roberts, John A S; Shaw, Wendy J

2014-11-18

319

DNA-directed growth of ultrafine CoAuPd nanoparticles on graphene as efficient catalysts for formic acid dehydrogenation.  

PubMed

Ultrafine and well dispersed CoAuPd nanoparticles grown on a DNA-reduced-graphene-oxide (DNA-rGO) composite have been successfully synthesized using a DNA-directed method. The resultant CoAuPd/DNA-rGO composite exhibits high activity and 100% H2 selectivity toward the dehydrogenation of formic acid without any additive at 298 K. PMID:24473636

Wang, Zhi-Li; Wang, Hong-Li; Yan, Jun-Min; Ping, Yun; O, Song-Il; Li, Si-Jia; Jiang, Qing

2014-03-14

320

Design, synthesis, and application of tartaric acid derived N-spiro quaternary ammonium salts as chiral phase-transfer catalysts†‡  

PubMed Central

A novel class of tartaric acid-derived N-spiro quaternary ammonium salts was synthesised starting from known TADDOLs. These compounds were found to catalyse the asymmetric ?-alkylation of glycine Schiff bases with high enantioselectivities and in good yields. PMID:22038391

Waser, Mario; Gratzer, Katharina; Herchl, Richard; Muller, Norbert

2014-01-01

321

Generation of ricinoleic acid from castor oil using the lipase from ground oat ( Avena sativa L.) seeds as a catalyst  

Microsoft Academic Search

Summary The lipase found in oat seeds acts upon castor oil in organic solvent, yielding approximately 90% ricinoleic acid. Initial velocity is a poor predictor of the time required for complete lipolysis except at low oil concentrations. Equations were developed to estimate kinetic parameters necessary to accurately predict the degree of lipolysis.

George J. Piazza; Harold M. Farrell

1991-01-01

322

Polymer-Supported Rare Earth Catalysts Used in Organic Synthesis  

Microsoft Academic Search

Three types of polymer-supported rare earth catalysts, Nafion-based rare earth catalysts, polyacrylonitrile-based rare earth\\u000a catalysts, and microencapsulated Lewis acids, are discussed. Use of polymer-supported catalysts offers several advantages\\u000a in preparative procedures such as simplification of product work-up, separation, and isolation, as well as the reuse of the\\u000a catalyst including flow reaction systems leading to economical automation processes. Although the use

Sh? Kobayashi

323

pKa cycling of the general acid/base in glycoside hydrolase families 33 and 34.  

PubMed

Glycoside hydrolase families 33 and 34 catalyse the hydrolysis of terminal sialic acid residues from sialyl oligosaccharides and glycoconjugates with a net retention of the stereochemistry at the anomeric centre. It is generally believed that the conserved aspartic acid in the active site functions as a general acid to protonate the hydroxyl group of the departing aglycone during glycosylation, and then as a general base to facilitate the nucleophilic attack of the water molecule on the intermediate state during the deglycosylation reaction. The dual role of the general acid/base places specific demands upon its protonation state, and thus pKa values. However, it is not fully understood how this catalytic residue can achieve such pKa cycling during catalysis. We present both MM and combined QM/MM simulations to characterise the pKa values of the proposed catalytic general acid/base in the glycoside hydrolase families 33 and 34. Collectively, our study suggests that the binding of anionic substrates and the local solvation properties along with the neutralisation of the nearby glutamic acid upon glycosylation modulate the electrostatic environment around the general acid/base to achieve its proper protonation states. PMID:24535426

Yu, Haibo; Griffiths, Thomas M

2014-03-28

324

Oxidative degradation of 2,6-dibromophenol using anion-exchange resin supported supramolecular catalysts of iron(III)-5,10,15,20-tetrakis (p-hydroxyphenyl)porphyrin bound to humic acid prepared via formaldehyde and urea-formaldehyde polycondensation.  

PubMed

An iron(III)-porphyrin catalyst, iron(III)-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP), was introduced into a humic acid via a formaldehyde or urea-formaldehyde polycondensation reaction to stabilize the catalyst. The prepared supramolecular catalysts were then attached to Dowex-22, an anion-exchange resin. The oxidation of 2,6-dibromophenol (2,6-DBP) was then used, to evaluate the catalytic activities of the supported catalysts. The supported catalyst prepared via the urea-formaldehyde polycondensation reaction showed the highest catalytic activity of all catalysts tested. However, no debromination was observed under any conditions. To examine the reusability of the supported catalysts, they were evaluated on the basis of the decrease in the percent degradation of 2,6-DBP for the number times that they could be used. To determine why the catalytic activities decreased with increasing use, the surface of the supported catalysts were observed by scanning electron microscopy and energy dispersive X-ray spectrometry (SME-EDS) after each use. The poor reusability of the supported catalysts can be attributed to the fact that 2,6-DBP and/or brominated byproducts are tightly absorbed to the catalyst in the vicinity of the active site, which leads to inactivation of the supported catalysts. PMID:20721797

Shigetatsu, Satoko; Fukushima, Masami; Nagao, Seiya

2010-10-01

325

Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining  

NASA Astrophysics Data System (ADS)

Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

Buurmans, Inge L. C.; Ruiz-Martínez, Javier; Knowles, William V.; van der Beek, David; Bergwerff, Jaap A.; Vogt, Eelco T. C.; Weckhuysen, Bert M.

2011-11-01

326

Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining.  

PubMed

Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials. PMID:22024882

Buurmans, Inge L C; Ruiz-Martínez, Javier; Knowles, William V; van der Beek, David; Bergwerff, Jaap A; Vogt, Eelco T C; Weckhuysen, Bert M

2011-11-01

327

FRETmatrix: a general methodology for the simulation and analysis of FRET in nucleic acids  

PubMed Central

Förster resonance energy transfer (FRET) is a technique commonly used to unravel the structure and conformational changes of biomolecules being vital for all living organisms. Typically, FRET is performed using dyes attached externally to nucleic acids through a linker that complicates quantitative interpretation of experiments because of dye diffusion and reorientation. Here, we report a versatile, general methodology for the simulation and analysis of FRET in nucleic acids, and demonstrate its particular power for modelling FRET between probes possessing limited diffusional and rotational freedom, such as our recently developed nucleobase analogue FRET pairs (base–base FRET). These probes are positioned inside the DNA/RNA structures as a replacement for one of the natural bases, thus, providing unique control of their position and orientation and the advantage of reporting from inside sites of interest. In demonstration studies, not requiring molecular dynamics modelling, we obtain previously inaccessible insight into the orientation and nanosecond dynamics of the bases inside double-stranded DNA, and we reconstruct high resolution 3D structures of kinked DNA. The reported methodology is accompanied by a freely available software package, FRETmatrix, for the design and analysis of FRET in nucleic acid containing systems. PMID:22977181

Preus, S?ren; Kilsa, Kristine; Miannay, Francois-Alexandre; Albinsson, Bo; Wilhelmsson, L. Marcus

2013-01-01

328

Results of catalyst testing using iron-based catalysts  

SciTech Connect

As coal liquefaction catalysts, iron-based products are generally inferior to the more expensive molybdenum, cobalt, or nickel-based materials. However, the lower costs of production and recovery (or in the case of some iron catalysts, non-recovery) give the iron-based materials a potential economic advantage over the more efficient precious and semi-precious metal catalysts for this application. Recent research has shown that a number of different iron-containing materials can be successfully utilized as coal liquefaction catalysts or as catalyst. Pyrrhotite (Fe[sub 1-x]S) or a similar iron-sulfide phase is commonly believed to be the active catalyst in coal liquefaction and model compound pyrolysis reactions, although no specific phase has been yet been isolated as the actual catalyst species. The active iron-containing catalyst is usually generated in situ from an iron-oxide precursor and an elemental sulfur source under reducing conditions in the reactor vessel. Most research has concentrated on the use of common iron-oxide phases such as hematite or goethite (and their derivatives) as the iron-bearing precursor, or on non-specific iron materials produced by the reaction of various iron salts and compounds in the coal or liquefaction reactor. To our knowledge there has been no systematic effort to determine the optimum iron-containing precursor phase for producing active coal liquefaction catalysts, despite the fact that there are over ten iron-(hydroxy)oxide phases which can be easily synthesized in the laboratory. We have undertaken a systematic study to identify the most active iron-oxide catalyst precursor phases, the co-catalysts, and the coal pretreatments which will provide optimum yields in coal liquefaction processes.

Linehan, J.C.; Darab, J.G.; Matson, D.W.

1993-03-01

329

Results of catalyst testing using iron-based catalysts  

SciTech Connect

As coal liquefaction catalysts, iron-based products are generally inferior to the more expensive molybdenum, cobalt, or nickel-based materials. However, the lower costs of production and recovery (or in the case of some iron catalysts, non-recovery) give the iron-based materials a potential economic advantage over the more efficient precious and semi-precious metal catalysts for this application. Recent research has shown that a number of different iron-containing materials can be successfully utilized as coal liquefaction catalysts or as catalyst. Pyrrhotite (Fe{sub 1-x}S) or a similar iron-sulfide phase is commonly believed to be the active catalyst in coal liquefaction and model compound pyrolysis reactions, although no specific phase has been yet been isolated as the actual catalyst species. The active iron-containing catalyst is usually generated in situ from an iron-oxide precursor and an elemental sulfur source under reducing conditions in the reactor vessel. Most research has concentrated on the use of common iron-oxide phases such as hematite or goethite (and their derivatives) as the iron-bearing precursor, or on non-specific iron materials produced by the reaction of various iron salts and compounds in the coal or liquefaction reactor. To our knowledge there has been no systematic effort to determine the optimum iron-containing precursor phase for producing active coal liquefaction catalysts, despite the fact that there are over ten iron-(hydroxy)oxide phases which can be easily synthesized in the laboratory. We have undertaken a systematic study to identify the most active iron-oxide catalyst precursor phases, the co-catalysts, and the coal pretreatments which will provide optimum yields in coal liquefaction processes.

Linehan, J.C.; Darab, J.G.; Matson, D.W.

1993-03-01

330

PseAAC-General: Fast Building Various Modes of General Form of Chou's Pseudo-Amino Acid Composition for Large-Scale Protein Datasets  

PubMed Central

The general form pseudo-amino acid composition (PseAAC) has been widely used to represent protein sequences in predicting protein structural and functional attributes. We developed the program PseAAC-General to generate various different modes of Chou’s general PseAAC, such as the gene ontology mode, the functional domain mode, and the sequential evolution mode. This program allows the users to define their own desired modes. In every mode, 544 physicochemical properties of the amino acids are available for choosing. The computing efficiency is at least 100 times that of existing programs, which makes it able to facilitate the extensive studies on proteins and peptides. The PseAAC-General is freely available via SourceForge. It runs on both Linux and Windows. PMID:24577312

Du, Pufeng; Gu, Shuwang; Jiao, Yasen

2014-01-01

331

Sulfamic Acid as a Novel, Efficient, Cost?Effective, and Reusable Solid Acid Catalyst for the Synthesis of Pyrroles under Solvent?Free Conditions  

Microsoft Academic Search

Paal–Knorr condensation of 2,5?hexadione with primary amines in the presence of a catalytic amount of sulfamic acid under solvent?free conditions has been accomplished with an excellent yield. This is a very easy, rapid, and high?yielding reaction for the synthesis N?substituted pyrrole derivatives.

Surya K. De

2008-01-01

332

Ultrasound assisted production of fatty acid methyl esters from transesterification of triglycerides with methanol in the presence of KOH catalyst: optimization, mechanism and kinetics.  

PubMed

Ultrasound assisted transesterification of triglycerides (TG) with methanol in the presence of KOH catalyst was investigated, where the changes in the reactants and products (diglycerides (DG), monoglycerides (MG), fatty acid methyl esters (FAME) and glycerin (GL)) concentrations were discussed to understand the reaction mechanism and kinetics under ultrasound irradiation. The optimum reaction condition for the FAME production was the concentration of KOH 1.0 wt.%, molar ratio of TG to methanol of 1:6, and irradiation time of 25 min. The rate constants during the TG transesterification with methanol into GL and FAME were estimated by a curve fitting method with simulated curves to the obtained experimental results. The rate constants of [Formula: see text] were estimated to be 0.21, 0.008, 0.23, 0.005, 0.14 and 0.001 L mol(-1)min(-1), respectively. The rate determining step for the TG transesterification with methanol into GL and FAME was the reaction of MG with methanol into GL and FAME. PMID:24161255

Thanh, Le Tu; Okitsu, Kenji; Maeda, Yasuaki; Bandow, Hiroshi

2014-03-01

333

Pillared laponite clay-based Fe nanocomposites as heterogeneous catalysts for photo-Fenton degradation of acid black 1  

Microsoft Academic Search

A series of pillared laponite clay-based Fe nanocomposites (denoted as Fe-Lap-RD) were synthesized by the so-called pillaring technique under different conditions. N2 adsorption\\/desorption, X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) were used to characterize the Fe-Lap-RD nanocomposites. The photo-catalytic activity of the Fe-Lap-RD nanocomposites was evaluated in the photo-Fenton mineralization of 0.1mM azo-dye acid

Oliver Sze Nga Sum; Jiyun Feng; Xijun Hu; Po Lock Yue

2004-01-01

334

Chiral transition-metal complexes as Brønsted-acid catalysts for the asymmetric Friedel-Crafts hydroxyalkylation of indoles.  

PubMed

The Friedel-Crafts reaction between 3,3,3-trifluoropyruvates and indoles is efficiently catalysed by the iridium complex [(?(5)-C5Me5)Ir{(R)-Prophos}(H2O)][SbF6]2 (1) with up to 84% ee. Experimental data and theoretical calculations support a mechanism involving the Brønsted-acid activation of the pyruvate carbonyl by the protons of the coordinated water molecule in 1. Water is not dissociated during the process and, therefore, the catalytic reaction occurs with no direct interaction between the substrates and the metal. PMID:24902782

Carmona, Daniel; Lamata, M Pilar; Sánchez, Antonio; Viguri, Fernando; Rodríguez, Ricardo; Oro, Luis A; Liu, Chunhui; Díez-González, Silvia; Maseras, Feliu

2014-08-01

335

Oxyiodination catalyst  

SciTech Connect

This patent describes a process for preparation of mono and diiodo benzene, naphthalene or diphenyl by iodinating a fluoro, chloro, bromo, iodo, hydroxy, or cyclo substituted benzene, naphthalene or diphenyl, which comprises reacting, at a temperature in the range of 100/sup 0/ to 500/sup 0/C, a source of iodine with the substituted benzene, naphthalene or diphenyl in the presence of molecular oxygen over a zeolite catalyst with a pore size of 6 angstroms or greater and greater than ten percent of the exchangeable cations being alkali, alkaline earth or rare earth metal cations, wherein the catalyst contains an amount of a modifier effective to substantially prevent deactivation of the catalyst by alkyl substituted aromatic compounds, the modifier being selected from the group consisting of hydrogen, copper, zinc, cadmium, silver, and mercury ions or salts thereof.

Kingsport, M.R.

1988-11-29

336

Tangstophosphoric acid (H 3PW 12O 40): An efficient and eco-friendly catalyst for the one-pot synthesis of dihydropyrimidin-2(1 H)-ones  

Microsoft Academic Search

Tangstophosphoric acid both in bulk form or supported on silica gel efficiently catalyzed the three-component condensation reaction of aldehyde, 1,3-dicarbonyl compound and urea or thiourea to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones in high yields under solvent-free conditions at 80°C. This catalyst is efficient not only for open chained ?-dicarbonyl compounds, but for the cyclic ?-diketones, ?-diester or ?-diamide derivatives such as

Mostafa Mohammadpour Amini; Ahmad Shaabani; Ayoob Bazgir

2006-01-01

337

Selective staining of Brønsted acidity in zeolite ZSM-5-based catalyst extrudates using thiophene as a probe.  

PubMed

Optical absorption and confocal fluorescence micro-spectroscopy were applied to investigate Brønsted acidity in millimetre-sized extrudates of Na(H)-ZSM-5 and SiO2 with varying ZSM-5 content. Partially (residual Na present) and fully proton-exchanged extrudates were employed, using thiophene oligomerization as a probe reaction. Time-resolved in situ optical absorption spectra and time dependent DFT calculations revealed several initial reaction pathways during the oligomerization reaction. In particular, it was found that protonated thiophene monomers reacted by either oligomerization (via reaction with un-reacted thiophene monomers) or ring-opening, depending on the Brønsted acid site density in each sample. Moreover, fully-exchanged extrudates not only have significantly higher reactivity than partially-exchanged samples, but they also favour the formation of ring-opening products, that are not formed on the partially-exchanged samples. Confocal fluorescence microscopy was employed to visualise non-invasively in 3D, the heterogeneity and homogeneity of thiophene oligomers on partially- and fully-exchanged extrudates, respectively. Furthermore, it was observed that extrudates with high binder content produce a higher relative amount of conjugated species, related with a higher quantity of available monomer in the binder, which is able to react further with intermediates adsorbed on active sites. Moreover, these conjugated species appear to form near the external surface of ZSM-5 crystals/agglomerates. PMID:25188580

Whiting, Gareth T; Meirer, Florian; Valencia, Diego; Mertens, Machteld M; Bons, Anton-Jan; Weiss, Brian M; Stevens, Paul A; de Smit, Emiel; Weckhuysen, Bert M

2014-10-21

338

Synthesis, Structure, and Properties of a Mixed-Valent Triiron Complex of Tetramethyl Reductic Acid, an Ascorbic Acid Analog, and its Relationship to a Functional Non-Heme Iron Oxidation Catalyst System  

PubMed Central

The purple triiron(II,III,III) complex, [Fe3Cl2(TMRASQ)4(HTMRA)2]·C5H12 (1·C5H12), where H2(TMRA) is tetramethyl reductic acid, 4,4,5,5-tetramethyl-2,3-dihydroxy-2-cyclopenten-1-one, and H(TMRASQ) is the semiquinone form of this ligand, was prepared from (Et4N)2[Fe2OCl6] and H2(TMRA) and characterized by X-ray crystallography, Mössbauer spectroscopy, and redox titrations. The physical properties of the complex in solution are consistent with its mixed-valent character, as delineated by a solid-state structure analysis. Assignments of the iron and ligand oxidation states in the crystal were made on the basis of a valence bond sum analysis and the internal ligand geometry. As the first well-characterized iron complex of an ascorbic acid H2(AA) analog, 1 provides insight into the possible coordination geometry of the family of complexes containing H2AA and its analogues. In the presence of air and H2TMRA, 1 is able to catalyze the oxidation of cyclohexane to cyclohexanol with remarkable selectivity, but the nature of the true catalyst remains unknown. PMID:17579400

Kim, YooJin; Feng, Xudong; Lippard, Stephen J.

2011-01-01

339

Plasma and erythrocyte membrane phospholipids and fatty acids in Italian general population and hemodialysis patients  

PubMed Central

Background Dyslipidemia and abnormal phospholipid metabolism are frequent in uremic patients and increase their risk of cardiovascular disease (CVD): ?-3 polyunsaturated fatty acids (PUFAs) may reduce this risk in the general population. In this study we compared the plasma and erythrocyte cell membrane composition of PUFAs in a group of Caucasian hemodialysis (HD) patients and in a control group of healthy subjects and evaluated the erythrocyte/cell membrane fatty acid ratio as a marker of the dietary intake of phospholipids. The relationship between ?-3 and ?-6 fatty acids and the possible differences in PUFAs concentrations were also investigated. Methods and results After obtaining a fully informed consent, a total of ninety-nine HD patients and 160 non uremic control subjects from “Tor Vergata” University Hospital were enrolled into the study. None of them took antioxidant drugs or dietary supplements for at least 90 days prior to the observation. Blood samples were analysed by gas-chromatographic coupled to a mass spectrometric detector. The daily intake of total calories, proteins, lipids and carbohydrates is significantly lower in HD patients than in controls (p?

2014-01-01

340

Multiphasic control of hepatic protein degradation by regulatory amino acids. General features and hormonal modulation.  

PubMed

Previous studies with livers from fed rats perfused in the single-pass mode have shown that regulatory amino acids (Leu, Tyr, Gln, Pro, Met, His, and Trp) as a group as well as leucine alone inhibit deprivation-induced protein degradation optimally at 0.5 and 4 times (X) normal plasma amino acid concentrations. However, they lose inhibitory effectiveness almost completely within a narrow zone centered at normal (1 X) levels (Pösö, A. R., Wert, J. J., Jr., and Mortimore, G.E. (1982) J. Biol. Chem. 257, 12114-12120; Pösö, A. R., and Mortimore, G. E. (1984) Proc. Natl. Acad. Sci. U. S. A. 81, 4270-4274). We now report similar effects for tyrosine and glutamine and suggest that this multiphasic dose response is a general feature of the regulatory group. Insulin (2.4 micrograms h-1) selectively modulated the response by abolishing the zonal loss, whereas glucagon (10 micrograms h-1) blocked the initial inhibition (0.5 X); proteolytic suppression was restored at 4 X normal plasma levels. Although the zonal loss of inhibition at 1 X was associated with a near maximal increase in the volume density of macroautophagy, the vacuoles differed from those induced by stringent amino acid deprivation in containing 4.5-fold more smooth than rough endoplasmic reticulum and thus represented a separate population. Surprisingly, the leucine analog, L-alpha-hydroxyisocaproate, elicited multiphasic responses identical to those of L-leucine, including inhibition at 0.1 mM (equivalent to 0.5 X Leu). Inasmuch as alpha-ketoisocaproate is not effective at this concentration, the initial suppression of protein degradation could be mediated from a site that recognizes structural features common to leucine and its hydroxyl analog. PMID:3316218

Mortimore, G E; Pösö, A R; Kadowaki, M; Wert, J J

1987-12-01

341

Therapeutic effects of docosahexaenoic acid ethyl ester in patients with generalized peroxisomal disorders.  

PubMed

Generalized peroxisomal disorders are severe congenital diseases that involve the central nervous system, leading to severe psychomotor retardation, retinopathy, liver disease, and early death. In these disorders, peroxisomes are not normally formed and their enzymes are deficient. Characteristically, plasmalogen synthesis and beta-oxidation of very-long-chain fatty acids (VLCFAs) are affected. We found that patients with generalized peroxisomal disorders have a profound brain deficiency of docosahexaenoic acid (DHA; 22:6n-3) and low DHA concentrations in all tissues and the blood. Given the fundamental role of DHA in neuronal and retinal membranes, a DHA deficiency of this magnitude might be pathogenic. Thus, we studied the possible therapeutic effect of normalizing DHA concentrations in patients with peroxisomal disorders. We chose the DHA ethyl ester (DHA-EE) because of its high degree of purity at daily oral doses of 100-500 mg. This article summarizes the results of treatment of 13 patients with DHA-EE, with some follow-up evidence of clinical improvement. Supplementation with DHA-EE normalized blood DHA values within a few weeks. Plasmalogen concentrations increased in erythrocytes in most patients and after DHA concentrations were normalized, amounts of VLCFAs decreased in plasma. Liver enzymes returned almost to normal in most cases. From a clinical viewpoint, most patients showed improvement in vision, liver function, muscle tone, and social contact. In 3 patients, normalization of brain myelin was detected by magnetic resonance imaging. In 3 others, myelination improved. In a seventh patient, myelination is progressing at a normal rate. These results suggest a fundamental role of DHA in the pathogenesis of Zellweger syndrome. DHA therapy is thus strongly recommended, not only to alleviate symptoms in patients with life-threatening diseases, but also to clarify remaining questions regarding the role of DHA in health and disease. PMID:10618001

Martínez, M; Vázquez, E; García-Silva, M T; Manzanares, J; Bertran, J M; Castelló, F; Mougan, I

2000-01-01

342

Catalysts for a cleaner environment  

SciTech Connect

Pollution-abatement catalysts remain a challenging area for process development. That`s because the pollutants themselves often poison the catalysts, and the new catalytic processes are now required to capture pollutants from very dilute waste streams. A case in point in the US is how severely low-level emissions of halogenated hydrocarbons are regulated through Title III regulations on toxic compounds. While common oxidation catalysts may be quite effective at eliminating most VOC [volatile organic compound] emissions, the presence of halogenated hydrocarbons can adversely affect catalyst performance. Only recently have catalysts become available that will be effective at oxidizing the halogenated hydrocarbons. The items described below illustrate the variety and scope of recently introduced catalysts that have proved themselves by increasing yields and reducing emissions. The offerings include catalysts for: improving yield in the production of acrylic acid, ammonia, styrene, phthalic anhydride and alcohol; reducing the sulfur and aromatic content of fuels; curtailing byproduct production in fluid-catalytic cracking units; oxidizing emissions of chlorinated hydrocarbons; and reducing NOx in combustion gas using hydrogen or carbon monoxide.

NONE

1995-09-01

343

Fundamental studies of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry  

SciTech Connect

Highly dispersed transition metal catalysts are used in numerous commercial processes such as hydrocarbon conversions. For example, the use of Pt supported on acidic alumina or silica-alumina for reforming of naphtha in the production of gasoline is well known. Another use of supported catalysts is in automobile emission control where supported Pt-Rh bimetallic catalysts are used. Supported Ru can be used in Fischer-Tropsch synthesis for the production of higher hydrocarbons from synthesis gas. While many of these catalyst systems have been in commercial operation for several decades there is still a lack of consensus regarding the exact role of the catalyst on a molecular level. In particular, little is known about the mechanisms operating on the catalyst surface at the high pressure and high temperature conditions typically used in commercial operations. This report contains the general introduction and conclusions and an appendix containing the operating instructions for a microcalorimeter. Three chapters have been processed separately. They are: the effect of K on the kinetics and thermodynamics of hydrogen adsorption on Ru/SiO{sub 2}; hydrogen adsorption states on silica supported Ru-Ag and Ru-Cu bimetallic catalysts investigated via microcalorimetry; a comparative study of hydrogen chemisorption on silica supported Ru, Rh, and Pt.

Narayan, R.L.

1997-06-24

344

Lipoic Acid Synthesis: A New Family of Octanoyltransferases Generally Annotated as Lipoate Protein Ligases†  

PubMed Central

Bacillus subtilis lacks a recognizable homologue of the LipB octanoyltransferase, an enzyme essential for lipoic acid synthesis in Escherichia coli. LipB transfers the octanoyl moiety from octanoyl-acyl carrier protein to the lipoyl domains of the 2-oxoacid dehydrogenases via a thioester-linked octanoyl-LipB intermediate. The octanoylated dehydrogenase is then converted to the enzymatically active lipoylated species by insertion of two sulfur atoms into the octanoyl moiety by the S-adenosyl-L-methionine radical enzyme, LipA (lipoate synthase). Bacillus subtilis synthesizes lipoic acid and contains a LipA homologue that is fully functional in E. coli. Therefore, the lack of a LipB homologue presented the puzzle of how B. subtilis synthesizes the LipA substrate. We report that B. subtilis encodes an octanoyltransferase that has virtually no sequence resemblance to E. coli LipB, but instead has a sequence that resembles that of the E. coli lipoate ligase, LplA. Based on this resemblance these genes have generally been annotated as encoding a lipoate ligase, an enzyme that in E. coli scavenges lipoic acid from the environment, but which plays no role in de novo synthesis. We have named the B. subtilis octanoyltransferase LipM and find that, like LipB, the LipM reaction proceeds through a thioester-linked acyl enzyme intermediate. The LipM active site nucleophile was identified as C150 by the finding that this thiol becomes modified when LipM is expressed in E. coli. The level of the octanoyl-LipM intermediate can be significantly decreased by blocking fatty acid synthesis during LipM expression and C150 was confirmed as an essential active site residue by site-directed mutagenesis. LipM homologues seem the sole type of octanoyltransferase present in the Firmicutes and are also present in the Cyanobacteria. LipM type octanoyltransferases represent a new clade of the PF03099 protein family suggesting that octanoyltransfer activity has evolved at least twice within this superfamily. PMID:20882995

Christensen, Quin H.; Cronan, John E.

2010-01-01

345

Clays as selective catalysts in organic synthesis  

Microsoft Academic Search

Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity,

John M. Adams; Keith Martin; Richard W. McCabe

1987-01-01

346

A facile and general approach for the direct fabrication of 3D, vertically aligned carbon nanotube array/transition metal oxide composites as non-Pt catalysts for oxygen reduction reactions.  

PubMed

A simple and effective strategy involving nebulized ethanol assisted infiltration for the general synthesis of 3D structure-based vertically aligned carbon nanotube arrays (VACNTs) uniformly and deeply decorated with various transition-metal oxide (MOs) has been developed. Furthermore, it is demonstrated that the 3D structure-based VACNTs with decorated MnO2 can exhibit superior electrocatalytic oxygen reduction reaction activity, long-term stability, and an excellent resistance to crossover effects compared to the commercial Pt/C catalyst. PMID:24616041

Yang, Zhi; Zhou, Xuemei; Jin, Zhiping; Liu, Zheng; Nie, Huagui; Chen, Xi'an; Huang, Shaoming

2014-05-21

347

Rhizobium leguminosarum Has a Second General Amino Acid Permease with Unusually Broad Substrate Specificity and High Similarity to BranchedChain Amino Acid Transporters (Bra\\/LIV) of the ABC Family  

Microsoft Academic Search

Amino acid uptake by Rhizobium leguminosarum is dominated by two ABC transporters, the general amino acid permease (Aap) and the branched-chain amino acid permease (BraRl). Characterization of the solute specificity of BraRl shows it to be the second general amino acid permease of R. leguminosarum. Although BraRl has high sequence identity to members of the family of hydrophobic amino acid

A. H. F. Hosie; D. Allaway; C. S. Galloway; H. A. Dunsby; P. S. Poole

2002-01-01

348

The Existence of Quantum Entanglement Catalysts  

E-print Network

Without additional resources, it is often impossible to transform one entangled quantum state into another with local quantum operations and classical communication. Jonathan and Plenio [Phys. Rev. Lett. 83, 3566(1999)] presented an interesting example showing that the presence of another state, called a catalyst, enables such a transformation without changing the catalyst. They also pointed out that in general it is very hard to find an analytical condition under which a catalyst exists. In this paper we study the existence of catalysts for two incomparable quantum states. For the simplest case of $2\\times 2$ catalysts for transformations from one $4\\times 4$ state to another, a necessary and sufficient condition for existence is found. For the general case, we give an efficient polynomial time algorithm to decide whether a $k\\times k$ catalyst exists for two $n\\times n$ incomparable states, where $k$ is treated as a constant.

Xiaoming Sun; Runyao Duan; Mingsheng Ying

2003-11-19

349

Effect of catalyst concentration and simulation of precipitation processes on liquid-phase catalytic oxidation of p-xylene to terephthalic acid  

Microsoft Academic Search

The influence of catalyst concentration, i.e. cobalt naphthenate, on product distribution and kinetic constants of the lumped kinetic scheme of liquid-phase p-xylene oxidation proposed in previous works (cf. Cao et al., 1994a, b) is investigated. The experiments involving various levels of catalyst concentrations (from 1.67 to 33.3 × 10?4 mol\\/kgl) are conducted in an isothermal semi-batch oxidation reactor where both

A. Cincotti; R. Orrù; A. Broi; G. Cao

1997-01-01

350

Significant Role of Ru-Oxide Present in the Pt-Ru Alloy Catalyst for Ethanol ElectroOxidation in Acid Medium  

Microsoft Academic Search

This work relates to the search for optimum Pt-Ru catalyst composition for electro-oxidation of ethanol. The structure, morphology, and composition of the synthesized Pt-Ru catalysts were investigated through techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) while cyclic-voltammetry, polarization, chronoamperometry, impedance spectroscopy were employed to study the electrocatalytic behavior of

J. Datta; S. Sen Gupta; S. Singh; S. Mukherjee; M. Mukherjee

2011-01-01

351

Lewis acid organocatalysts.  

PubMed

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 degrees C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of their cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. PMID:21494948

Sereda, Oksana; Tabassum, Sobia; Wilhelm, René

2010-01-01

352

Lewis Acid Organocatalysts  

NASA Astrophysics Data System (ADS)

The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of their cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis.

Sereda, Oksana; Tabassum, Sobia; Wilhelm, René

353

Resin catalysts and method of preparation  

DOEpatents

Heat stabilized catalyst compositions are prepared from nuclear sulfonic acid, for example, macroporous crosslinked polyvinyl aromatic compounds containing sulfonic acid groups are neutralized with a metal of Al, Fe, Zn, Cu, Ni, ions or mixtures and alkali, alkaline earth metals or ammonium ions by contacting the resin containing the sulfonic acid with aqueous solutions of the metals salts and alkali, alkaline earth metal or ammonium salts. The catalysts have at least 50% of the sulfonic acid groups neutralized with metal ions and the balance of the sulfonic acid groups neutralized with alkali, alkaline earth ions or ammonium ions.

Smith, L.A. Jr.

1986-12-16

354

Resin catalysts and method of preparation  

DOEpatents

Heat stabilized catalyst compositions are prepared from nuclear sulfonic acid, for example, macroporous crosslinked polyvinyl aromatic compounds containing sulfonic acid groups are neutralized with a metal of Al, Fe, Zn, Cu, Ni, ions or mixtures and alkali, alkaline earth metals or ammonium ions by contacting the resin containing the sulfonic acid with aqueous solutions of the metals salts and alkali, alkaline earth metal or ammonium salts. The catalysts have at least 50% of the sulfonic acid groups neutralized with metal ions and the balance of the sulfonic acid groups neutralized with alkali, alkaline earth ions or ammonium ions.

Smith, Jr., Lawrence A. (P.O. Box 34687, Houston, TX 77243)

1986-01-01

355

Cationic Ruthenium Catalysts for Olefin Hydrovinylation  

E-print Network

Stereoselective carbon?carbon bond formation is one of the most important types of bond construction in organic chemistry. A mild and acid free catalyst system for the hydrovinylation reaction utilizing a cationic, ruthenium center is described. A...

Sanchez, Richard P., Jr

2010-01-14

356

Preparation of monolithic catalysts  

Microsoft Academic Search

Monolithic catalysts can be attractive replacements for conventional catalysts in randomly packed beds or slurry reactors. The conventional procedures for preparing catalysts, however, cannot simply be applied to monolithic catalysts. Different procedures are discussed on how to put a coat layer of a catalyst support material like alumina, silica, or carbon on a monolith body by either filling the pores

T. Alexander Nijhuis; Annemarie E. W. Beers; Theo Vergunst; Ingrid Hoek; Freek Kapteijn; Jacob A. Moulijn

2001-01-01

357

Organic acids tunably catalyze carbonic acid decomposition.  

PubMed

Density functional theory calculations predict that the gas-phase decomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transfer reaction, can be catalyzed by a monocarboxylic acid or a dicarboxylic acid, including carbonic acid itself. Carboxylic acids are found to be more effective catalysts than water. Among the carboxylic acids, the monocarboxylic acids outperform the dicarboxylic ones wherein the presence of an intramolecular hydrogen bond hampers the hydrogen transfer. Further, the calculations reveal a direct correlation between the catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzed hydrogen-transfer reactions. The catalytic efficacy of a dicarboxylic acid, on the other hand, is significantly affected by the strength of an intramolecular hydrogen bond. Transition-state theory estimates indicate that effective rate constants for the acid-catalyzed decomposition are four orders-of-magnitude larger than those for the water-catalyzed reaction. These results offer new insights into the determinants of general acid catalysis with potentially broad implications. PMID:24933150

Kumar, Manoj; Busch, Daryle H; Subramaniam, Bala; Thompson, Ward H

2014-07-10

358

Supported phosphate and carbonate salts for heterogeneous catalysis of triglycerides to fatty acid methyl esters  

NASA Astrophysics Data System (ADS)

Fatty acid methyl esters made from vegetable oil, or biodiesel, have been identified as a substitute for diesel derived from crude oil. Biodiesel is currently made using a homogeneous base catalyst to perform the transesterification of triglycerides with methanol to generate fatty acid methyl esters (FAME). The use of a homogeneous catalyst necessitates additional purification of the product and byproducts before sale, and the catalyst is consumed and discarded. The development of a heterogeneous basic catalyst for the production of FAME is desirable. Tribasic phosphate salts and dibasic carbonate salts are active for the production of FAME but generally operate as homogeneous catalysts. Supporting these phosphate and carbonate salts on mesoporous MCM-41, microporous silica gel, and nonporous a-alumina proved successful to greater or lesser degrees depending on the identity of the support and pretreatment of the support. Although these salts were supported and were active for the production of FAME from canola oil, they proved to be operating as homogeneous catalysts due to leaching of the active species off the surface of the support. Further investigation of the active species present in the tribasic phosphate catalysts identified the active support as orthophosphate, and NMR studies revealed the phosphorus to be present as orthophosphate and diphosphate in varying proportions in each catalyst. Evaluation of the acid-washing support pretreatment process revealed that the exposure of the support to acid plays a large role in the development of activity on the surface of the catalyst, but manipulation of these parameters did not prevent leaching of the active site off the surface of the catalyst. Alternate methods of support pretreatment were no more effective in preventing leaching. Tribasic phosphate supported on silica gel is not effective as a heterogeneous catalyst for FAME production from triglycerides because of the lack of stability of the phosphate on the support. The support is not stable under the reaction conditions, and alternatives should be explored to develop a heterogeneous base catalyst for the production of FAME.

Britton, Stephanie Lynne

359

Reversible in situ catalyst formation.  

PubMed

Acid catalysts play a vital role in the industrial synthesis and production of a plethora of organic chemicals. But, their subsequent neutralization and disposal is also a giant source of waste. For example, for a Friedel-Crafts acylation with AlCl 3, a kilogram of product yields up to 20 kg of (contaminated) waste salt. Other processes are even worse, and this waste is both an environmental and economic shortcoming. Here we address this issue by showing a series of acid catalysts where the neutralization is "built in" to the system and thus eliminates waste. Clearly these will not replace all organic and mineral acid catalysts, but they can replace many. Further, we show how these self-neutralizing catalysts can often eliminate unwanted byproducts, improve selectivity, or elimination of mass transfer limitations by changing from heterogeneous to homogeneous systems. They readily facilitate separations and promote recycling, to promote both green chemistry and good economics. First is near-critical water, or liquid water under pressure, where the K W for dissociation goes up 3-4 decades between 0 degrees C and 250 degrees C, thus facilitating both acid and base catalysis. Moreover, as the exothermic hydrogen bonding diminishes, the dielectric constant goes down to the point at which both salts and organics are soluble in this very hot water. For example, toluene and water are completely miscible at 305 degrees C. This eliminates mass transfer limitations for the reactions, and postreaction cooling not only lowers the K W to neutralize the ions without waste but also results in facile separations from simple liquid-liquid immiscibility. Further, we show the formation of catalysts with alkylcarbonic acids from alcohols and CO2, analogous to carbonic acid from water and CO2. We show a number of applications for these self-neutralizing catalysts, including the formation of ketals, the formation of diazonium intermediates to couple with electron-rich aromatics to produce dye molecules, and the hydration of beta-pinene. Here also these systems often enhance phase behavior to cut mass transfer resistance. In an analogous application we show that peroxide and CO2 gives peroxycarbonic acid, also reversible upon the removal of the CO2, and we show application to epoxidation reactions. The bottom line is that these catalysts afford profound advantages for both green chemistry and improved economics. The methods outlined here have potential for abundant applications, and we hope that this work will motivate such opportunities. PMID:18251512

Hallett, Jason P; Pollet, Pamela; Liotta, Charles L; Eckert, Charles A

2008-03-01

360

[Catalyst research]. Final Report  

SciTech Connect

Research results are the areas of catalyst precursor synthesis, catalyst fluxionality, catalyst stability, polymerization of {alpha}-olefins as well as the chemistry of Group IV and Group V metal centers with aryloxide and arylsulfide ligands.

Ian P Rothwell (deceased); David R McMillin (in his place)

2005-03-14

361

Catalyst Manufacturing Science and  

E-print Network

mixing, extrusion, calcination, etc. This is integrated with a number of educational activities including, catalyst preparation), William Borghard (calcination, catalyst preparation), Silvina Tomassone sampling, Calcination, Slurry Mixing, Pellet compaction, Roller Compaction, Powder segregation, Catalyst

362

Cr(III)-containing Fe3O4/mercaptopropanoic acid-poly(2-hydroxyethyl acrylate) nanocomposite: a highly active magnetic catalyst in solvent-free aerobic oxidation of alcohols.  

PubMed

In this study, polymer-grafted magnetic nanoparticles containing chromium(iii) ions incorporated onto Fe3O4/mercaptopropanoic acid-poly(2-hydroxyethyl acrylate) (Fe3O4/MPA-PHEA-Cr) was prepared via a simple and in situ method. The obtained magnetic nanocomposite exhibited a high catalytic activity and excellent selectivity in the aerobic oxidation of alcohols under solvent-free conditions. The magnetic catalyst could also be separated by an external magnet and reused seven times without any significant loss of activity/selectivity. PMID:24413435

Zamani, Farzad; Hosseini, Seyed Mohsen; Kianpour, Sahar

2014-03-01

363

Highly Active and Selective Nickel–Platinum Catalyst for the Low Temperature Hydrogenation of Maleic Anhydride to Succinic Anhydride and Synthesis of Succinic Acid at 40 °C  

Microsoft Academic Search

\\u000a Abstract  PtNi bimetallic and Ni monometallic catalysts supported on HY–Al2O3, HX–Al2O3, ZSM-5–Al2O3, USY–Al2O3, Beta–Al2O3 and Al2O3 were prepared and evaluated for the hydrogenation of maleic anhydride in the temperature range of 40–150 °C. Results from\\u000a flow reactor studies showed that supports strongly affected the catalytic properties of different bimetallic and monometallic\\u000a catalysts. The results showed that the HY–Al2O3 support exhibited the highest

Jie LiWei-Ping; Wei-Ping Tian; Li Shi

2011-01-01

364

A Mössbauer study of iron-containing phases in a vanadium oxide catalyst for the oxidation of sulphur dioxide in sulphuric acid production  

Microsoft Academic Search

The iron-containing phases in fresh and partly deactivated vanadium oxide catalyst are identified by Mssbauer spectroscopy.\\u000a As a result of exploitation of the catalyst the new phases of Fe3O4, FeSO4 and Fe2(SO4)3 alongwith presence of ?-Fe2O3 are formed. The Mssbauer spectroscopy presents new possibilities for studying the composition changes in iron-containing\\u000a phases, and provides a tool to reveal the reasons

D. Klissurski; L. Makedonski; I. Mitov; V. Bluskov

1990-01-01

365

Waste catalysts for waste polymer.  

PubMed

Catalytic cracking of high-density polyethylene (HDPE) over fluid catalytic cracking (FCC) catalysts (1:6 ratio) was carried out using a laboratory fluidized bed reactor operating at 450 degrees C. Two fresh and two steam deactivated commercial FCC catalysts with different levels of rare earth oxide (REO) were compared as well as two used FCC catalysts (E-Cats) with different levels of metal poisoning. Also, inert microspheres (MS3) were used as a fluidizing agent to compare with thermal cracking process at BP pilot plant at Grangemouth, Scotland, which used sand as its fluidizing agent. The results of HDPE degradation in terms of yield of volatile hydrocarbon product are fresh FCC catalysts>steamed FCC catalysts approximately used FCC catalysts. The thermal cracking process using MS3 showed that at 450 degrees C, the product distribution gave 46 wt% wax, 14% hydrocarbon gases, 8% gasoline, 0.1% coke and 32% nonvolatile product. In general, the product yields from HDPE cracking showed that the level of metal contamination (nickel and vanadium) did not affect the product stream generated from polymer cracking. This study gives promising results as an alternative technique for the cracking and recycling of polymer waste. PMID:17084608

Salmiaton, A; Garforth, A

2007-01-01

366

Catalyst regeneration process including metal contaminants removal  

DOEpatents

Spent catalysts removed from a catalytic hydrogenation process for hydrocarbon feedstocks, and containing undesired metals contaminants deposits, are regenerated. Following solvent washing to remove process oils, the catalyst is treated either with chemicals which form sulfate or oxysulfate compounds with the metals contaminants, or with acids which remove the metal contaminants, such as 5-50 W % sulfuric acid in aqueous solution and 0-10 W % ammonium ion solutions to substantially remove the metals deposits. The acid treating occurs within the temperature range of 60.degree.-250.degree. F. for 5-120 minutes at substantially atmospheric pressure. Carbon deposits are removed from the treated catalyst by carbon burnoff at 800.degree.-900.degree. F. temperature, using 1-6 V % oxygen in an inert gas mixture, after which the regenerated catalyst can be effectively reused in the catalytic process.

Ganguli, Partha S. (Lawrenceville, NJ)

1984-01-01

367

Catalyst inventory control in an ebullated bed process  

SciTech Connect

This patent describes an improved method of maintaining a selected weight of catalyst in a reactor in a continuous process for treating a fluent hydrocarbon feedstock with a hydrogen-containing gas at elevated catalytic reaction temperatures and pressures in the presence of a bed of particulate solid catalyst. The process comprises introducing the hydrogen-containing gas and feedstock into the lower end of a generally vertical catalyst containing reaction vessel at sufficient velocity whereby the catalyst is placed in random motion within the fluent hydrocarbon. The catalyst bed is expanded to a volume greater than its static volume. The mixture of feedstock, gas and catalyst constitutes a turbulent zone from which zone aged catalyst is removed and fresh catalyst is added. The upper portion of the turbulent zone is defined by an interface with a substantially catalyst depleted zone from which zone hydrocarbon is removed.

Chan, T.Y.; Strickland, J.C.

1990-02-20

368

Feature Synthesis and Extraction for the Construction of Generalized Properties of Amino Acids  

Microsoft Academic Search

Amino acid similarity matrices are used for protein sequence com- parison. It has been shown previously that they can be reconstructed from equivalence classes between amino acids. The goal of the current study is to propose an algorithm for identification of the properties that generate these equivalence classes. An approximate reasoning method for feature extraction and synthesis is developed to

Witold R. Rudnicki; Henryk Jan Komorowski

2004-01-01

369

Economic effects of catalyst deactivation during VOC oxidation  

Microsoft Academic Search

Catalytic oxidation of volatile organic compounds (VOCs) is widely used for air pollution control. While catalytic oxidation offers several advantages over alternative processes, the catalyst can deactivate over time, resulting in changes in activity and selectivity with time-on-stream. To maintain constant catalyst activity, required for environmental regulations, the temperature is generally increased gradually to compensate for catalyst deactivation. This results

Sanjay K. Agarwal; James J. Spivey

1993-01-01

370

Activity of vanadium catalysts for sulfuric acid production, promoted with Na, K, Rb, Cs, and Mg compounds, at various pressures of sulfur oxides  

Microsoft Academic Search

The activities of vanadium catalysts promoted with Na, K, Rb, Cs, and Mg sulfates (ratio Me:V = 4) were studied in conditions of low (up to 1 kPa) and high (up to 70 kPa) partial pressures of sulfur oxides at 693 and 758 K. The authors report results of reaction kinetic studies.

S. V. Ivanenko; R. R. Dzhoraev

1995-01-01

371

General and Facile Surface Functionalization of Hydrophobic Nanocrystals with Poly(amino acid) for Cell Luminescence Imaging  

NASA Astrophysics Data System (ADS)

Hydrophobic nanocrystals with various shape, size, and chemical composition were successfully functionalized by poly(amino acid) with one particle per micelle without aggregation or precipitation via a facile, general, and low-cost strategy. Via simply tuning the pH value, multifunctional nanocomposites consisting of different nanocrystals were also fabricated. Due to the poly(amino acid) coating, these nanocrystals are highly water-stable, biocompatible, and bioconjugatable with chemical and biological moieties. Meanwhile, their shape, size, optical/magnetic properties are well retained, which is highly desirable for bioapplications. This developed strategy presents a novel opportunity to apply hydrophobic nanocrystals to various biomedical fields.

Huang, Sheng; Bai, Min; Wang, Leyu

2013-06-01

372

Functional Identification of the General Acid and Base in the Dehydration Step of Indole-3-glycerol Phosphate Synthase Catalysis*  

PubMed Central

The tryptophan biosynthetic enzyme indole-3-glycerol phosphate synthase is a proposed target for new antimicrobials and is a favored starting framework in enzyme engineering studies. Forty years ago, Parry proposed that the enzyme mechanism proceeds through two intermediates in a series of condensation, decarboxylation, and dehydration steps. X-ray crystal structures have suggested that Lys-110 (numbering according to the Sulfolobus solfataricus enzyme) behaves as a general acid both in the condensation and dehydration steps, but did not reveal an efficient pathway for the reprotonation of this critical residue. Our mutagenesis and kinetic experiments suggest an alternative mechanism whereby Lys-110 acts as a general acid in the condensation step, but another invariant residue, Lys-53, acts as the general acid in the dehydration step. These studies also indicate that the conserved residue Glu-51 acts as the general base in the dehydration step. The revised mechanism effectively divides the active site into discrete regions where the catalytic surfaces containing Lys-110 and Lys-53/Glu-51 catalyze the ring closure (i.e. condensation and decarboxylation) and dehydration steps, respectively. These results can be leveraged toward the development of novel inhibitors against this validated antimicrobial target and toward the rational engineering of the enzyme to produce indole derivatives that are highly prized by the pharmaceutical and agricultural industries. PMID:23900843

Zaccardi, Margot J.; Yezdimer, Eric M.; Boehr, David D.

2013-01-01

373

Biodiesel production from waste cooking oil using a heterogeneous catalyst from pyrolyzed rice husk.  

PubMed

A solid acid catalyst was prepared by sulfonating pyrolyzed rice husk with concentrated sulfuric acid, and the physical and chemical properties of the catalyst were characterized in detail. The catalyst was then used to simultaneously catalyze esterification and transesterification to produce biodiesel from waste cooking oil (WCO). In the presence of the as-prepared catalyst, the free fatty acid (FFA) conversion reached 98.17% after 3h, and the fatty acid methyl ester (FAME) yield reached 87.57% after 15 h. By contrast, the typical solid acid catalyst Amberlyst-15 obtained only 95.25% and 45.17% FFA conversion and FAME yield, respectively. Thus, the prepared catalyst had a high catalytic activity for simultaneous esterification and transesterification. In addition, the catalyst had excellent stability, thereby having potential use as a heterogeneous catalyst for biodiesel production from WCO with a high FFA content. PMID:24405650

Li, Ming; Zheng, Yan; Chen, Yixin; Zhu, Xifeng

2014-02-01

374

Laser-synthesized catalysts  

SciTech Connect

A solid catalyst material is evaporated from a coating on a transparent solid substrate and is condensed onto a solid polymeric organic catalyst carrier or into a liquid, by passing a laser beam through said solid transparent substrate and onto the back of said coating and contacting said catalyst carrier or liquid with the evaporated catalyst material. Suitably, the laser source is a ruby or a rhodamine dye laser; a suitable catalyst material is rhodium metal; and a suitable solid polymeric organic catalyst carrier is polystyrene crosslinked by divinyl benzene and a suitable liquid is aqueous polyvinyl alcohol. The process minimizes the exposure to heat of the catalyst carrier or suspending liquid.

Menger-Hammond, E.L.; Novotny, M.

1984-09-18

375

Acute generalized exanthematous pustulosis: A rare side effect of a common over-the-counter drug, Acetylsalicylic acid.  

PubMed

Acute generalized exanthematous pustulosis is an uncommon cutaneous reaction characterized by sudden onset of generalized non-follicular aseptic pustules. It is most often secondary to drugs but causes as varied from viral infection to insect bites are reported. A case report of a 48-year-old male who developed pustular eruptions after taking acetylsalicylic acid is reported here. Clinicians need to be aware of this entity when dealing with pustular rash as this rare side effect of a very common drug is both, easy to miss and easy to manage. PMID:23984244

Bahuguna, Amit

2013-07-01

376

Long-Life Catalyst  

NASA Technical Reports Server (NTRS)

STC Catalysts, Inc. (SCi) manufactures a noble metal reducible oxide catalyst consisting primarily of platinum and tin dioxide deposited on a ceramic substrate. It is an ambient temperature oxidation catalyst that was developed primarily for Carbon Dioxide Lasers.The catalyst was developed by the NASA Langley Research Center for the Laser Atmospheric Wind Sounder Program (LAWS) which was intended to measure wind velocity on a global basis. There are a number of NASA owned patents covering various aspects of the catalyst.

1999-01-01

377

Cellular responses to L-serine in Saccharomyces cerevisiae: roles of general amino acid control, compartmentalization, and aspartate synthesis.  

PubMed

In addition to its other roles, L-serine functions in one-carbon metabolism and is interconvertable with glycine via serine hydroxymethyltransferases. However, the transcriptional response by Saccharomyces cerevisiae to L-serine addition is markedly different from that to glycine, with L-serine acting as a nutrient source rather than one-carbon units. Following addition of excess L-serine, 743 genes showed significant expression changes. Induced functions included amino acid synthesis, some stress responses, and FeS metabolism, while ribosomal RNA processing, ribosome biogenesis and hexose transport were repressed. A co-regulated network of ten transcription factors could together control more than 90% of the induced and repressed genes forming a general response to changes induced by other amino acids or stresses and including the general amino acid control system usually activated in response to starvation for amino acids. A specific response to L-serine was induction of CHA1 encoding serine (threonine) dehydratase. L-serine addition resulted in a substantial transient increase in L-aspartate, which is, rather than L-glutamate, the major metabolite for short-term storage of ammonia derived from degradation of L-serine. L-aspartate synthesis was exclusively through mitochondrial metabolism of L-serine to pyruvate and ammonia, involving Cha1p, cytoplasmic pyruvate carboxylases Pyc1p and Pyc2p, and the cytoplasmic aspartate aminotransferase Aat2p. PMID:23837815

Lee, Johnny C-Y; Tsoi, Abraham; Kornfeld, Geoffrey D; Dawes, Ian W

2013-11-01

378

Selective N 2 O Removal from the Process Gas of Nitric Acid Plants Over Ceramic 12CaO · 7Al 2 O 3 Catalyst  

Microsoft Academic Search

Catalytic high temperature decomposition (secondary abatement) of nitrous oxide over calcium aluminate 12CaO · 7Al2O3 (mayenite) was studied in the model laboratory tests (TPSR) and pilot units (steady-state) using the real feed. X-ray diffraction\\u000a (XRD), scanning electron microscopy (SEM), N2-sorption (BET), electron paramagnetic resonance (EPR) and Raman spectroscopies were used to characterize the synthesized\\u000a material. The catalyst exhibited high efficiency and selectivity

Monika Ruszak; Marek Inger; Stefan Witkowski; Marcin Wilk; Andrzej Kotarba; Zbigniew Sojka

2008-01-01

379

Sand consolidation methods using adsorbable catalysts  

SciTech Connect

Methods are provided for selectively consolidating sand grains within a subterranean formation. First an acidic zirconium salt catalyst, such as ZrOCl/sub 2/, Zr(SO/sub 4/)/sub 2/, or ZrCl/sub 4/, is injected into the subterranean formation, wherein the acidic salt catalyst is adsorbed to the surface of the sand grains. Next a polymerizable resin composition such as furfuryl alcohol oligomer is introduced into the well formation. Polymerization of the resin occurs upon exposure to the elevated well temperatures and contact with the acid salt catalyst adsorbed to the sand grains. The polymerized resin serves to consolidate the surfaces of the sand grains while retaining permeability through the pore spaces. An ester of a weak organic acid is included with the resin compositions to control the extent of a polymerization by consuming the water by-product formed during the polymerization reaction.

Friedman, R. H.

1985-04-23

380

Fusidic acid cream in the treatment of impetigo in general practice: double blind randomised placebo controlled trial  

PubMed Central

Objective To test the hypothesis that fusidic acid would not increase the treatment effect of disinfecting with povidone-iodine alone in children with impetigo. Design Randomised placebo controlled trial. Setting General practices in Greater Rotterdam. Participants 184 children aged 0-12 years with impetigo. Main outcome measures Clinical cure and bacterial cure after one week. Results After one week of treatment 55% of the patients in the fusidic acid group were clinically cured compared with 13% in the placebo group (odds ratio 12.6, 95% confidence interval 5.0 to 31.5, number needed to treat 2.3). After two weeks and four weeks the differences in cure rates between the two groups had become smaller. More children in the placebo group were non-compliant (12 v 5) and received extra antibiotic treatment (11 v 3), and more children in the placebo group reported adverse effects (19 v 7). Staphylococcus aureus was found in 96% of the positive cultures; no strains were resistant to fusidic acid. Conclusions Fusidic acid is much more effective than placebo (when both are given in combination with povidone-iodine shampoo) in the treatment of impetigo. Because of the low rate of cure and high rate of adverse events in the placebo group, the value of povidone-iodine in impetigo can be questioned. What is already known on this topicImpetigo is the most common skin infection in childrenFusidic acid, which is advocated as topical treatment in several countries, has never been investigated in a placebo controlled studyWhat this study addsIn combination with povidone-iodine, treatment with fusidic acid is much more effective than placeboNone of the strains of Staphylococcus aureus isolated at baseline showed resistance to fusidic acidThe value of treatment with povidone-iodine alone can be questioned PMID:11809642

Koning, Sander; van Suijlekom-Smit, Lisette W A; Nouwen, Jan L; Verduin, Cees M; Bernsen, Roos M D; Oranje, Arnold P; Thomas, Siep; van der Wouden, Johannes C

2002-01-01

381

ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. II. ACID AND GENERAL BASE CATALYZED HYDROLYSIS  

EPA Science Inventory

SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to calculate acid and neutral hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition states of a ...

382

The first general method for alpha-trifluoromethylation of carboxylic acids using BrF3.  

PubMed

2-Carbomethoxy-1,1-bis(methylsulfide)-1-alkenes, easily made from carboxylic acids, CS(2) and MeI, were treated with BrF(3) producing eventually the desired alpha-trifluoromethyl carboxylate derivatives--RCH(CF(3))COOR'--in good yields. PMID:14973624

Hagooly, Aviv; Rozen, Shlomo

2004-03-01

383

BIOINSPIRED CATALYSTS: SYNTHESIS, CHARACTERISATION AND SOME APPLICATIONS  

Microsoft Academic Search

Our recent work concerning the synthesis, characterisation and some applications of bioinspired electron-transfer catalysts is reviewed in this contribution. The catalysts were various mono- or heterobimetallic complexes having either Cu(II) or Cu(II) and Zn(II) as central ions and amino acids, their derivatives or various N- containing organic molecules as ligands. Emphasis was based upon the solid support immobilised versions of

István Pálinkó

384

Versatile reactivity of Pd-catalysts: mechanistic features of the mono-N-protected amino acid ligand and cesium-halide base in Pd-catalyzed C-H bond functionalization.  

PubMed

The widely used C-H functionalization strategies and some complexities in the Pd-catalyzed chemical transformations were analyzed. It was emphasized that in the course of catalysis various Pd-intermediates (including nano-scale Pd-clusters) could act as active catalysts. However, both identification of these catalytically active species and determination of factors controlling the overall catalytic process require more comprehensive and multi-disciplinary approaches. Recent joint computational and experimental approaches were instrumental in: (1) demonstrating that the addition of Pd(OAc)2 as a catalyst precursor to RSeH and RSH reagents forms the [Pd(SeR)2]n and [Pd(SR)2]n clusters, respectively, which show an unprecedented ability for selective synthesis of Markovnikov-type products starting with a mixture of reagents RSH/RSeH and acetylenic hydrocarbons; (2) predicting a valid mechanism of the amino acid ligand-assisted Pd(II)-catalyzed C-H activation that is shown to proceed via the formation of the catalytically active Pd(II) intermediate with a bidentately coordinated dianionic amino acid ligand; (3) demonstrating that the amino acid ligand plays crucial roles in the ligand-assisted Pd(II)-catalyzed C-H activation by acting as: (a) a weakly coordinating ligand to stabilize the desirable Pd(II)-precatalyst, (b) a soft proton donor and a bidentately coordinated dianionic ligand in the catalytically active Pd(II) intermediate, and (c) a proton acceptor accelerating the C-H deprotonation via the CMD mechanism; and (4) revealing the roles of the CsF base (and "cesium effect") in the Pd(0)/PCy3-catalyzed intermolecular arylation of the terminal ?-C(sp(3))-H bond of aryl amide and predicting the unprecedented "Cs2-I-F cluster" assisted mechanism for this reaction. PMID:24626313

Musaev, Djamaladdin G; Figg, Travis M; Kaledin, Alexey L

2014-07-21

385

Delta-Aminolevulinic Acid Dehydratase Activity in the General Population of Southern Minas Gerais, Brazil  

Microsoft Academic Search

Blood samples were collected from 113 subjects (56 males and 57 females) living in the district of Alfenas, in southern Minas Gerais state, Brazil, to establish reference values for delta- aminolevulinic acid dehydratase activity (ALA-D, EC 4.2.1.24). The state of health of the population was confirmed by hematological and biochemical parameters analyzed in blood and urine samples. ALA-D determination was

Maria Elisa; Pereira Bastos de SIQUEIRA; Patricia Penido; Danielle Palma de OLIVEIRA; Denise Moura; Leite LUENGO

386

The generalized lewis acid-base titration of palladium and niobium  

Microsoft Academic Search

The high thermodynamic stability of alloys composed of platinum group metals and group IVB and VB metals has been explained\\u000a by an electronic interaction analogous to the Lewis acid-base concept for nontransition elements. The analogy is further demonstrated\\u000a by the titration of palladium by addition of niobium. The activity of niobium in solid palladium was measured as a function\\u000a of

M. Cima; L. Brewer

1988-01-01

387

New synthesis of pyrrole-2-carboxylic and pyrrole-2,5-dicarboxylic acid esters in the presence of iron-containing catalysts  

Microsoft Academic Search

Alkyl 1H-pyrrole-2-carboxylates and dialkyl 1H-pyrrole-2,5-dicarboxylates were synthesized in quantitative yield by reactions of 1H-pyrrole, 2-acetyl-1H-pyrrole, and 1-methyl-1H-pyrrole with carbon tetrachloride and aliphatic alcohols in the presence of iron-containing catalysts. A probable reaction\\u000a mechanism was proposed, and the rate constants and energies of activation of particular steps were determined on the basis\\u000a of experimental data.

R. I. Khusnutdinov; A. R. Baiguzina; R. R. Mukminov; I. V. Akhmetov; I. M. Gubaidullin; S. I. Spivak; U. M. Dzhemilev

2010-01-01

388

Catalyst deactivation in hydrodemetallisation  

SciTech Connect

The present work is focused on hydrodemetallization reaction kinetics of model porphyrin compounds, the characterization of metal deposits on the catalyst surface, and state of the art catalysts deactivation modeling.

Janssens, J.P.; Langeveld, A.D. van; Sie, S.T.; Moulijn, J.A. [Delft Univ. of Technology (Netherlands)

1995-12-31

389

Fusidic acid cream in the treatment of impetigo in general practice: double blind randomised placebo controlled trial  

Microsoft Academic Search

OBJECTIVE: To test the hypothesis that fusidic acid would not increase the\\u000a treatment effect of disinfecting with povidone-iodine alone in children\\u000a with impetigo. DESIGN: Randomised placebo controlled trial. SETTING:\\u000a General practices in Greater Rotterdam. PARTICIPANTS: 184 children aged\\u000a 0-12 years with impetigo. MAIN OUTCOME MEASURES: Clinical cure and\\u000a bacterial cure after one week. RESULTS: After one week of treatment 55%

Sander Koning; Suijlekom-Smit van L. W. A; J. L. Nouwen; C. M. Verduin; R. M. D. Bernsen; A. P. Oranje; Siep Thomas; Wouden van der J. C

2002-01-01

390

Process and catalyst for carbonylating olefins  

DOEpatents

Disclosed is an improved catalyst system and process for preparing aliphatic carbonyl compounds such as aliphatic carboxylic acids, alkyl esters of aliphatic carboxylic acids and anhydrides of aliphatic carboxylic acids by carbonylating olefins in the presence of a catalyst system comprising (1) a first component selected from at least one Group 6 metal, i.e., chromium, molybdenum, and/or tungsten and (2) a second component selected from at least one of certain halides and tertiary and quaternary compounds of a Group 15 element, i.e., nitrogen, phosphorus and/or arsenic, and (3) as a third component, a polar, aprotic solvent. The process employing the improved catalyst system is carried out under carbonylating conditions of pressure and temperature discussed herein. The process constitutes and improvement over known processes since it can be carried out at moderate carbonylation conditions without the necessity of using an expensive noble metal catalyst, volatile, toxic materials such as nickel tetracarbonyl, formic acid or a formate ester. Further, the addition of a polar, aprotic solvent to the catalyst system significantly increases, or accelerates, the rate at which the carbonylation takes place.

Zoeller, Joseph Robert (Kingsport, TN)

1998-06-02

391

Newest hydrogenation catalysts  

SciTech Connect

A new generation of hydrogenation catalysts, bimetallic palladium catalysts, is now available. They meet the very stringent requirements of new refining and petrochemical industry that has to face a difficult economic period in which the highest performance becomes standard. Therefore the demand for these new very efficient catalysts and for the associated technologies is rapidly growing.

Boitaux, J.-P.; Cosyns, J.; Derrien, M.; Leger, G.

1985-03-01

392

Promotion of silver catalysts for selective oxidation of methanol  

SciTech Connect

The catalytic and physicochemical properties of supported silver catalysts modified by oxides of rare and rare-earth metals have been studied. The effects of modifiers on electronic structure, degree of dispersion and surface diffusion of the supported metal, on Broensted`s acidity, and coking degree of the catalyst surface have been determined. The promotion effect of cerium and zirconium oxides on the catalyst have been found also.

Pestryakov, A.N.; Roznina, M.I.; Belousova, V.N.

1994-04-10

393

Hydrodechlorination of tetrachloroethylene over sulfided catalysts: kinetic study  

Microsoft Academic Search

In this work, a commercial sulfided hydrotreatment catalyst (2.8% NiO, 13.5% MoO3, supported on ?-alumina, supplied by Shell) is compared with different iron sulfide based catalysts. These catalysts were prepared from a by-product (called red mud (RM)) of the bauxite leaching in the Bayer process. Two different activation procedures were tested, both based in dissolving the RM in an acid

S. Ordóñez; F. V. D??ez; H. Sastre

2002-01-01

394

Hydrodesulfurization catalyst by Chevrel phase compounds  

DOEpatents

A process is disclosed for the hydrodesulfurization of sulfur-containing hydrocarbon fuel with reduced ternary molybdenum sulfides, known as Chevrel phase compounds. Chevrel phase compounds of the general composition M/sub x/Mo/sub 6/S/sub 8/, with M being Ho, Pb, Sn, Ag, In, Cu, Fe, Ni, or Co, were found to have hydrodesulfurization activities comparable to model unpromoted and cobalt-promoted MoS/sub 2/ catalysts. The most active catalysts were the ''large'' cation compounds (Ho, Pb, Sn), and the least active catalysts were the ''small'' cation compounds (Cu, Fe, Ni, Co.).

McCarty, K.F.; Schrader, G.L.

1985-05-20

395

Catalyst system comprising a first catalyst system tethered to a supported catalyst  

Microsoft Academic Search

The present invention provides new catalyst formats which comprise a supported catalyst tethered to a second and different catalyst by a suitable tethering ligand. A preferred system comprises a heterogeneous supported metal catalyst tethered to a homogeneous catalyst. This combination of homogeneous and heterogeneous catalysts has a sufficient lifetime and unusually high catalytic activity in arene hydrogenations, and potentially many

R. J. Angelici; H. Gao

1998-01-01

396

General route for preparing ?-nitrocarbonyl compounds using copper thermal redox catalysis.  

PubMed

Using a simple copper catalyst, the alkylation of nitroalkanes with ?-bromocarbonyls is now possible. This method provides a general, functional group tolerant route to ?-nitrocarbonyl compounds, including nitro amides, esters, ketones, and aldehydes. The highly sterically dense, functional group rich products from these reactions can be readily elaborated into a range of complex nitrogen-containing molecules, including highly substituted ?-amino acids. PMID:24870052

Gietter, Amber A S; Gildner, Peter G; Cinderella, Andrew P; Watson, Donald A

2014-06-01

397

Insights into the Interplay of Lewis and Brnsted Acid Catalysts in Glucose and Fructose Conversion to 5(Hydroxymethyl)furfural and  

E-print Network

York 10016, United States *S Supporting Information ABSTRACT: 5-(Hydroxymethyl)furfural (HMF]2+ . In contrast, Lewis acidity increases the overall rate of consumption of fructose and HMF and rehydration reactions. Yields of 46% levulinic acid in a single phase and 59% HMF in a biphasic system have

Frenkel, Anatoly

398

Novel multimetallic hydroisomerization catalysts  

SciTech Connect

Recent work in this laboratory with supported multimetallic catalysts has resulted in the discovery of a class of catalysts with unique selectivity and activity for the hydroisomerization of 1-butene, as well as the hydrogenation of butadiene. Specifically, it was found that catalysts particles are composed of three metallic components, one from the third row of the periodic table, one from the first row of rare earths, and a platinum group metal, have higher activity and are far more selective for 1-butene isomerization than any single metal catalyst, including commercial catalysts widely used for selective hydrogenation. 19 refs., 3 figs., 2 tabs.

Not Available

1994-04-01

399

Inhibition by phase transfer catalysts  

Microsoft Academic Search

While phase transfer catalysts have generally a positive effect on substitution of halides by rhodanide ion in two-phase reaction systems changing the structure of alkyl halide from primary to tert.-alkyl groups, catalysis reverses into inhibition. The assumption that this is due to the change in reaction mechanism from SN2 to SN1 was proved on hydrolysis of triphenylmethyl chloride in a

J. Šilhánek; J. Bartl; R. Mat?ju; M. Zbirovský

1982-01-01

400

System for reactivating catalysts  

DOEpatents

A method of reactivating a catalyst, such as a solid catalyst or a liquid catalyst is provided. The method comprises providing a catalyst that is at least partially deactivated by fouling agents. The catalyst is contacted with a fluid reactivating agent that is at or above a critical point of the fluid reactivating agent and is of sufficient density to dissolve impurities. The fluid reactivating agent reacts with at least one fouling agent, releasing the at least one fouling agent from the catalyst. The at least one fouling agent becomes dissolved in the fluid reactivating agent and is subsequently separated or removed from the fluid reactivating agent so that the fluid reactivating agent may be reused. A system for reactivating a catalyst is also disclosed.

Ginosar, Daniel M. (Idaho Falls, ID); Thompson, David N. (Idaho Falls, ID); Anderson, Raymond P. (Idaho Falls, ID)

2010-03-02

401

Solid acid (superacid) catalyzed regioselective adamantylation of substituted benzenes  

Microsoft Academic Search

Adamantylation of substituted benzenes with 1-bromo-adamantane was catalyzed by solid acids including acidic ion exchange and ionomer resins, HY zeolite, sulfated zirconia and supported superacids on HY zeolite and SiO2. Adamantylation generally takes place in excellent yield giving predominantly para products without formation of byproducts. The reactions did not require the usual workup of Friedel-Crafts reactions as catalysts were simply

George A. Olah; Béla Török; Tatyana Shamma; Marianna Török; G. K. Surya Prakash

1996-01-01

402

Engineering catalyst microenvironments for metal-catalyzed hydrogenation of biologically derived platform chemicals.  

PubMed

It is shown that microenvironments formed around catalytically active sites mitigate catalyst deactivation by biogenic impurities that are present during the production of biorenewable chemicals from biologically derived species. Palladium and ruthenium catalysts are inhibited by the presence of sulfur-containing amino acids; however, these supported metal catalysts are stabilized by overcoating with poly(vinyl alcohol) (PVA), which creates a microenvironment unfavorable for biogenic impurities. Moreover, deactivation of Pd catalysts by carbon deposition from the decomposition of highly reactive species is suppressed by the formation of bimetallic PdAu nanoparticles. Thus, a PVA-overcoated PdAu catalyst was an order of magnitude more stable than a simple Pd catalyst in the hydrogenation of triacetic acid lactone, which is the first step in the production of biobased sorbic acid. A PVA-overcoated Ru catalyst showed a similar improvement in stability during lactic acid hydrogenation to propylene glycol in the presence of methionine. PMID:25196504

Schwartz, Thomas J; Johnson, Robert L; Cardenas, Javier; Okerlund, Adam; Da Silva, Nancy A; Schmidt-Rohr, Klaus; Dumesic, James A

2014-11-17

403

Lanthanide(III) nosylates as new nitration catalysts  

Microsoft Academic Search

Lanthanide(III) nosylates are novel, recyclable catalysts prepared from the noncorrosive and inexpensive p-nitrotoluenesulfonic acid and the corresponding lanthanide(III) oxide. With 5–10% catalyst loading, atom economic nitration of simple aromatic compounds was achieved in good to high yields.

Tatjana N. Parac-Vogt; Koen Binnemans

2004-01-01

404

Rapeseed oil methyl esters preparation using heterogeneous catalysts  

Microsoft Academic Search

The classical method of fatty acids methyl esters (FAME) production is based on triglyceride transesterification to methyl esters. Sodium hydroxide dissolved in methanol is used as a catalyst. The purpose of this work was to examine a heterogeneous catalyst, in particular calcium compounds, to produce methyl esters of rapeseed oil. This research showed that the transesterification of rapeseed oil by

S. Gryglewicz

1999-01-01

405

Cerium-containing catalysts for converting ethanol into ethylene  

NASA Astrophysics Data System (ADS)

Ce/?-Al2O3 and CeLa/?-Al2O3 catalysts are studied via electron microscopy and temperature-programmed desorption of ammonia. Their activity in the dehydration of ethanol is investigated. Doping Ce/?-Al2O3 catalyst with lanthanum is shown to increase its dispersion and the number of active acid sites, thereby improving its activity.

Dosumov, K.; Ergazieva, G. E.; Churina, D. Kh.; Tel'baeva, M. M.

2014-10-01

406

Microgel-supported Oxazaborolidines: Novel Catalysts for Enantioselective Reductions  

Microsoft Academic Search

Microgel-bound oxazaborolidines have been prepared and used as catalysts in the enantioselective reduction of prochiral ketones. The preparation of these soluble, crosslinked polymer molecules was accomplished by solution polymerisation. The approach involved the preparation of microgels bearing free boronic acid functionalities and their subsequent conversion to oxazaborolidines. The selectivities of these supported catalysts are in most cases comparable to those

C. Schunicht; A. Biffis; G. Wulff

2000-01-01

407

Catalyst patterning for nanowire devices  

NASA Technical Reports Server (NTRS)

Nanowire devices may be provided that are based on carbon nanotubes or single-crystal semiconductor nanowires. The nanowire devices may be formed on a substrate. Catalyst sites may be formed on the substrate. The catalyst sites may be formed using lithography, thin metal layers that form individual catalyst sites when heated, collapsible porous catalyst-filled microscopic spheres, microscopic spheres that serve as masks for catalyst deposition, electrochemical deposition techniques, and catalyst inks. Nanowires may be grown from the catalyst sites.

Li, Jun (Inventor); Cassell, Alan M. (Inventor); Han, Jie (Inventor)

2004-01-01

408

Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to TiO 2  

Microsoft Academic Search

The degradation of acid red 14 (AR14), commonly used as a textile dye, can be photocatalysed by ZnO. Using advanced oxidation processes (AOPs), zinc oxide appears to be a suitable alternative to TiO2 for water treatment. In this study, a detailed investigation of photocatalytic degradation of acid red 14 is presented. Photodegradation efficiency was small when the photolysis was carried

N Daneshvar; D Salari; A. R Khataee

2004-01-01

409

Reducing fischer-tropsch catalyst attrition losses in high agitation reaction systems  

DOEpatents

A method for reducing catalyst attrition losses in hydrocarbon synthesis processes conducted in high agitation reaction systems; a method of producing an attrition-resistant catalyst; a catalyst produced by such method; a method of producing an attrition-resistant catalyst support; and a catalyst support produced by such method. The inventive method of reducing catalyst attrition losses comprises the step of reacting a synthesis gas in a high agitation reaction system in the presence of a catalyst. In one aspect, the catalyst preferably comprises a .gamma.-alumina support including an amount of titanium effective for increasing the attrition resistance of the catalyst. In another aspect, the catalyst preferably comprises a .gamma.-alumina support which has been treated, after calcination, with an acidic, aqueous solution. The acidic aqueous solution preferably has a pH of not more than about 5. In another aspect, the catalyst preferably comprises cobalt on a .gamma.-alumina support wherein the cobalt has been applied to the .gamma.-alumina support by totally aqueous, incipient wetness-type impregnation. In another aspect, the catalyst preferably comprises cobalt on a .gamma.-alumina support with an amount of a lanthana promoter effective for increasing the attrition resistance of the catalyst. In another aspect, the catalyst preferably comprises a .gamma.-alumina support produced from boehmite having a crystallite size, in the 021 plane, in the range of from about 30 to about 55 .ANG.ngstrons. In another aspect, the inventive method of producing an attrition-resistant catalyst comprises the step of treating a .gamma.-alumina support, after calcination of and before adding catalytic material to the support, with an acidic solution effective for increasing the attrition resistance of the catalyst. In another aspect, the inventive method of producing an attrition-resistant catalyst support comprises the step of treating calcined .gamma.-alumina with an acidic, aqueous solution effective for increasing the attrition resistance of the .gamma.-alumina.

Singleton, Alan H. (Baden, PA); Oukaci, Rachid (Gibsonia, PA); Goodwin, James G. (Cranberry Township, PA)

2001-01-01

410

A change in the internal aldimine lysine (K42) in O-acetylserine sulfhydrylase to alanine indicates its importance in transimination and as a general base catalyst.  

PubMed

O-Acetylserine sulfhydrylase (OASS) is a pyridoxal 5'-phosphate dependent enzyme that catalyzes a beta-replacement reaction forming L-cysteine and acetate from O-acetyl-L-serine (OAS) and sulfide. The pyridoxal 5'-phosphate (PLP) is bound at the active site in Schiff base linkage with a lysine. In the present study, the Schiff base lysine was identified as lysine 42, and its role in the OASS reaction was determined by changing it to alanine using site-directed mutagenesis. K42A-OASS is isolated as an external aldimine with methionine or leucine and shows no reaction with the natural substrates. Apo-K42A-OASS can be reconstituted with PLP, suggesting that K42 is not necessary for cofactor binding and formation of the external Schiff base. The apo-K42A-OASS, reconstituted with PLP, shows slow formation of the external aldimine but does not form the alpha-aminoacrylate intermediate on addition of OAS, suggesting that K42 is involved in the abstraction of the alpha-proton in the beta-elimination reaction. The external aldimines formed upon addition of L-Ala or L-Ser are stable and represent a tautomer that absorbs maximally at 420 nm, while L-Cys gives a tautomeric form of the external aldimine that absorbs at 330 nm, and is also seen in the overall reaction after addition of primary amines to the assay system. The use of a small primary amine such as ethylamine or bromoethylamine in the assay system leads to the initial formation of an internal (gamma-thialysine) or external (ethylamine) aldimine followed by the slow formation of the alpha-aminoacrylate intermediate on addition of OAS. Activity could not be fully recovered, and only a single turnover is observed. Data suggest a significant rate enhancement resulting from the presence of K42 for transimination and general base catalysis. PMID:8873618

Rege, V D; Kredich, N M; Tai, C H; Karsten, W E; Schnackerz, K D; Cook, P F

1996-10-15

411

Textured catalysts and methods of making textured catalysts  

DOEpatents

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

Werpy, Todd (West Richland, WA); Frye, Jr., John G. (Richland, WA); Wang, Yong (Richland, WA); Zacher, Alan H. (Kennewick, WA)

2007-03-06

412

Development of Novel Supported Gold Catalysts: A Materials Perspective  

SciTech Connect

Since Haruta et al. discovered that small gold nanoparticles finely dispersed on certain metal oxide supports can exhibit surprisingly high activity in CO oxidation below room temperature, heterogeneous catalysis by supported gold nanoparticles has attracted tremendous attention. The majority of publications deal with the preparation and characterization of conventional gold catalysts (e.g., Au/TiO{sub 2}), the use of gold catalysts in various catalytic reactions, as well as elucidation of the nature of the active sites and reaction mechanisms. In this overview, we highlight the development of novel supported gold catalysts from a materials perspective. Examples, mostly from those reported by our group, are given concerning the development of simple gold catalysts with single metal-support interfaces and heterostructured gold catalysts with complicated interfacial structures. Catalysts in the first category include active Au/SiO{sub 2} and Au/metal phosphate catalysts, and those in the second category include catalysts prepared by pre-modification of supports before loading gold, by post-modification of supported gold catalysts, or by simultaneous dispersion of gold and an inorganic component onto a support. CO oxidation has generally been employed as a probe reaction to screen the activities of these catalysts. These novel gold catalysts not only provide possibilities for applied catalysis, but also furnish grounds for fundamental research.

Dai, Sheng [ORNL; Ma, Zhen [ORNL

2011-01-01

413

Modeling preparation condition and composition-activity relationship of perovskite-type LaxSr1-xFeyCo1-yO3 nano catalyst.  

PubMed

In this paper, an artificial neural network (ANN) is first applied to perovskite catalyst design. A series of perovskite-type oxides with the LaxSr1-xFeyCo1-yO3 general formula were prepared with a sol-gel autocombustion method under different preparation conditions. A three-layer perceptron neural network was used for modeling and optimization of the catalytic combustion of toluene. A high R2 value was obtained for training and test sets of data: 0.99 and 0.976, respectively. Due to the presence of full active catalysts, there was no necessity to use an optimizer algorithm. The optimum catalysts were La0.9Sr0.1Fe0.5Co0.5O3 (Tc=700 and 800 °C and [citric acid/nitrate]=0.750), La0.9Sr0.1Fe0.82Co0.18O3 (Tc=700 °C, [citric acid/nitrate]=0.750), and La0.8Sr0.2Fe0.66Co0.34O3 (Tc=650 °C, [citric acid/nitrate]=0.525) exhibiting 100% conversion for toluene. More evaluation of the obtained model revealed the relative importance and criticality of preparation parameters of optimum catalysts. The structure, morphology, reducibility, and specific surface area of catalysts were investigated with XRD, SEM, TPR, and BET, respectively. PMID:24102474

Oskoui, Samira Arefi; Niaei, Aligholi; Tseng, Hui-Hsin; Salari, Dariush; Izadkhah, Behrang; Hosseini, Seyed Ali

2013-12-01

414

Synthesis of 3- and 6-sulfonylindoles from ortho-alkynyl-N-sulfonylanilines by the use of Lewis acidic transition-metal catalysts.  

PubMed

Gold-catalyzed reactions of ortho-alkynyl-N-sulfonylanilines produced the corresponding 3-sulfonylindoles in good to high yields. For example, the reaction of N-mesyl-N-methyl-2-(1-pentynyl)aniline, N-mesyl-N-methyl-2-(phenylethynyl)-aniline, and 2-ethynyl-N-mesyl-N-methylaniline in the presence of 10 mol % of AuBr3 in toluene at 80 degrees C gave 3-mesyl-1-methyl-2-propylindole, 3-mesyl-1-methyl-2-phenylindole, and 3-mesyl-1-methylindole in 95, 92, and 71% yield, respectively. Furthermore, we found that the reactions of 2-alkynyl-6-methoxy-N-sulfonyl-anilines in the presence of indium catalyst (InBr3) afforded the corresponding 6-sulfonylindoles as the major product in good yields. For example, the reaction of 6-methoxy-N-methyl-2-(1-pentynyl)-N-tosylaniline in the presence of 5 mol % of InBr3 in toluene at 80 degrees C gave an 87:13 mixture of 7-methoxy-1-methyl-2-propyl-6-tosylindole and 7-methoxy-1-methyl-2-propyl-3-tosylindole in 95% yield. Most probably, the gold-catalyzed reactions of ortho-alkynyl-N-sulfonylanilines proceed through a [1,3] sulfonyl migration, whereas the indium-catalyzed cyclizations of 2-alkynyl-6-methoxy-N-sulfonylanilines, which produce 6-sulfonylindoles, proceed by an unprecedented [1,7] sulfonyl migration. PMID:18046686

Nakamura, Itaru; Yamagishi, Uichiro; Song, Dschun; Konta, Sayaka; Yamamoto, Yoshinori

2008-02-01

415

Stacking of molybdenum disulfide layers in hydrotreating catalysts  

Microsoft Academic Search

Over the past several years there has been an intensive effort addressing the nature of the active site(s) in supported hydro-processing catalysts. Generally, these catalysts are either nickel or cobalt-promoted molybdenum disulfide supported on an alumina carrier. The authors have recently prepared a number of alumina-based Ni\\/Mo and Co\\/Mo catalysts designed to aid us in understanding the roles played by

R. G. Ryan; R. A. Kemp; J. A. Smegal; D. R. Denley

1988-01-01

416

Methods of making textured catalysts  

DOEpatents

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

Werpy, Todd (West Richland, WA); Frye, Jr., John G. (Richland, WA); Wang, Yong (Richland, WA); Zacher, Alan H. (Kennewick, WA)

2010-08-17

417

Passivation of FCC catalysts  

SciTech Connect

This patent describes improvement in a method for cracking a hydrocarbon which comprises: contacting a hydrocarbon feedstock with a fluidized zeolite-containing cracking catalyst in a cracking zone under cracking condition; recovering the cracked products; passing the cracked catalyst from the cracking zone to a regeneration zone; regenerating the cracking catalyst in the regeneration zone by contact by oxygen-containing gas under regeneration conditions to produce a regenerated catalyst; and introducing the regenerated catalyst to the cracking zone for contact with the hydrocarbon feedstock; wherein the catalyst during the cracking process is contaminated with nickel contained in a feedstock, wherein nickel increases hydrogen and coke yield at the cracking temperatures and conditions in the cracking zone. The improvement comprises treating the feedstock containing the nickel contamination with cerium in an amount being from 0.005 to 8,000 ppm based on the concentration of the nickel in the feedstock.

Forester, D.R.

1991-11-12

418

The role of catalyst support in carbon nanotube synthesis  

NASA Astrophysics Data System (ADS)

Acetylene decomposition over supported cobalt (or iron) catalysts proved to be an effective method for the preparation of well-graphitized carbon nanotubes. Compared to other techniques, catalytic synthesis is operated under relatively mild reaction conditions (700 °C, atmospheric pressure) and experimental apparatus is very simple. In order to improve catalyst performance, we try to understand the reaction mechanism. Catalysts were prepared by the impregnation method using different materials as catalyst support. Physico-chemical characterization of the samples were carried out by XRD, IR, etc. Surface acidity was measured by pyridine adsorption technique. Catalyst samples were tested in the decomposition of acetylene in a fixed bed flow reactor at 722 °C. The quantity of carbon deposit was weighted (catalyst activity). The quality of carbon nanotubes produced was characterized by means of transmission electron microscopy.

Siska, Andrea; Hernadi, Klara; Kiricsi, Imre; Rojik, Imre; Nagy, Janos B.

1998-08-01

419

Method for regeneration and activity improvement of syngas conversion catalyst  

DOEpatents

A method is disclosed for the treatment of single particle iron-containing syngas (synthes.s gas) conversion catalysts comprising iron, a crystalline acidic aluminosilicate zeolite having a silica to alumina ratio of at least 12, a pore size greater than about 5 Angstrom units and a constraint index of about 1-12 and a matrix. The catalyst does not contain promoters and the treatment is applicable to either the regeneration of said spent single particle iron-containing catalyst or for the initial activation of fresh catalyst. The treatment involves air oxidation, hydrogen reduction, followed by a second air oxidation and contact of the iron-containing single particle catalyst with syngas prior to its use for the catalytic conversion of said syngas. The single particle iron-containing catalysts are prepared from a water insoluble organic iron compound.

Lucki, Stanley J. (Runnemede, NJ); Brennan, James A. (Cherry Hill, NJ)

1980-01-01

420

Use of aluminum phosphate as the dehydration catalyst in single step dimethyl ether process  

DOEpatents

The present invention pertains to a process for the coproduction of methanol and dimethyl ether (DME) directly from a synthesis gas in a single step (hereafter, the "single step DME process"). In this process, the synthesis gas comprising hydrogen and carbon oxides is contacted with a dual catalyst system comprising a physical mixture of a methanol synthesis catalyst and a methanol dehydration catalyst. The present invention is an improvement to this process for providing an active and stable catalyst system. The improvement comprises the use of an aluminum phosphate based catalyst as the methanol dehydration catalyst. Due to its moderate acidity, such a catalyst avoids the coke formation and catalyst interaction problems associated with the conventional dual catalyst systems taught for the single step DME process.

Peng, Xiang-Dong (Allentown, PA); Parris, Gene E. (Coopersburg, PA); Toseland, Bernard A. (Allentown, PA); Battavio, Paula J. (Allentown, PA)

1998-01-01

421

Hydrous oxide ion-exchange compound catalysts  

DOEpatents

A catalytic material of improved activity which comprises a hydrous, alkali metal or alkaline earth metal or quaternary ammonium titanate, zirconate, niobate, or tantalate, in which the metal or ammonium cations have been exchange with a catalytically effective quantity of a catalyst metal, and which has been subsequently treated with a solution of a Bronsted acid.

Dosch, Robert G. (Albuquerque, NM); Stephens, Howard P. (Albuquerque, NM)

1990-01-01

422

Treatment of spent catalyst from the nitrogenous fertilizer industry--a review of the available methods of regeneration, recovery and disposal.  

PubMed

Disposal of spent catalyst is a problem as it falls under the category of hazardous industrial waste. The recovery of metals from these catalysts is an important economic aspect as most of these catalysts are supported, usually on alumina/silica with varying percent of metal; metal concentration could vary from 2.5 to 20%. Metals like Ni, Mo, Co, Rh, Pt, Pd, etc., are widely used as a catalyst in chemical and petrochemical industries and fertilizer industries. They are generally supported on porous materials like alumina and silica through precipitation or impregnation processes. Many workers have adapted pyrometallurgy and Hydrometallurgy process for recovery of precious metals. Many workers have studied the recovery of nickel from a spent catalyst in an ammonia plant by leaching it in sulphuric acid solution (Hydrometallurgy). Ninety-nine percent of the nickel was recovered as nickel sulphate when the catalyst, having a particle size of 0.09 mm was dissolved in an 80% sulphuric acid solution for 50 min in at 70 degrees C. Many researcher have studied the extraction of metals from spent catalyst by roasting-extraction method (Pyrometallurgy). Chelating agents are the most effective extractants, which can be introduced in the soil washing fluid to enhance heavy metal extraction from contaminated soils. The advantages of chelating agents in soil cleanup include high efficiency of metal extraction, high thermodynamic stabilities of the metal complexes formed, good solubilities of the metal complexes, and low adsorption of the chelating agents on soils, But very few workers have attempted chelating agent to extract metals from spent catalyst. PMID:19286315

Singh, Bina

2009-08-15

423

Liquefaction with microencapsulated catalysts  

DOEpatents

A method of dispersing a liquefaction catalyst within coal or other carbonaceous solids involves providing a suspension in oil of microcapsules containing the catalyst. An aqueous solution of a catalytic metal salt is emulsified in the water-immiscible oil and the resulting minute droplets microencapsulated in polymeric shells by interfacial polycondensation. The catalyst is subsequently blended and dispersed throughout the powdered carbonaceous material to be liquefied. At liquefaction temperatures the polymeric microcapsules are destroyed and the catalyst converted to minute crystallites in intimate contact with the carbonaceous material.

Weller, Sol W. (Williamsville, NY)

1985-01-01

424

Ru-assisted synthesis of {111}-faceted Pd truncated bipyramids: a highly reactive, stable and restorable catalyst for formic acid oxidation.  

PubMed

{111}-Faceted Pd truncated triangular bipyramids (TTBPs) are first presented under the assistance of Ru. Attributed to their unique shape, the TTBPs are highly active and stable for formic acid oxidation. The electrochemical active surface area (ECSA) can be restored to its initial value after a harsh degradation test. PMID:25220420

Wu, Dongshuang; Cao, Minna; Cao, Rong

2014-11-01

425

Regeneration of Three-Way Automobile Catalysts using Biodegradable Metal Chelating Agent ? S, S-Ethylenediamine Disuccinic Acid (S, S-EDDS)  

EPA Science Inventory

Regeneration of the activity of three-way catalytic converters (TWCs) was tested for the first time using a biodegradable metal chelating agent (S, S. Ethylenediamine disuccinic acid (S, S-EDDS). The efficiency of this novel environmentally friendly solvent in removing various c...

426

Characteristics of Polyaniline Cobalt Supported Catalysts for Epoxidation Reactions  

PubMed Central

A study of polyaniline (PANI) doping with various cobalt compounds, that is, cobalt(II) chloride, cobalt(II) acetate, and cobalt(II) salen, is presented. The catalysts were prepared by depositing cobalt compounds onto the polymer surface. PANI powders containing cobalt ions were obtained by one- or two-step method suspending PANI in the following acetonitrile/acetic acid solution or acetonitrile and then acetic acid solution. Moreover different ratios of Co(II)?:?PANI were studied. Catalysts obtained with both methods and at all ratios were investigated using various techniques including AAS and XPS spectroscopy. The optimum conditions for preparation of PANI/Co catalysts were established. Catalytic activity of polyaniline cobalt(II) supported catalysts was tested in dec-1-ene epoxidation with molecular oxygen at room temperature. The relationship between the amount of cobalt species, measured with both AAS and XPS techniques, and the activity of PANI-Co catalysts has been established. PMID:24701183

Kowalski, Grzegorz; Pielichowski, Jan; Grzesik, Miroslaw

2014-01-01

427

Catalyst inventory control in an ebullated bed process  

SciTech Connect

A method of maintaining a selected weight of catalyst in a reactor in a continuous process for treating a fluid hydrocarbon feedstock with a hydrogen-containing gas at elevated catalytic reaction temperatures and pressures in the presence of a bed of particulate solid catalyst is described, said process comprising introducing the hydrogen-containing gas and feedstock into the lower end of a generally vertical catalyst containing reaction vessel at sufficient velocity whereby the catalyst is placed in random motion within the fluid hydrocarbon whereby the catalyst bed is expanded to a volume greater than its static volume, wherein the mixture of feedstock, gas and catalyst constitutes a turbulent zone from which zone aged catalyst is removed and fresh catalyst is added, the upper portion of which turbulent zone is defined by an interface with a substantially catalyst depleted zone from which zone hydrocracked hydrocarbon is removed, wherein the improvement comprises: 1. determining an interface height (H2) from a point adjacent the bottom of the bed (h0) to a point corresponding to the interface (h2), 2. determining an effective bed height (H1) from h0 to an intermediate fixed point (h1) in the bed adjacent the interface, and 3. determining a reactor height (H3) from a point adjacent the catalyst depleted zone top (h3) to h0, 4. measuring a first differential pressure (DP1) between h0 and h1, 5. measuring a second differential pressure (DP2) between the point adjacent the catalyst depleted zone top (h3) and h1, 6. determining a value for a catalyst inventory characterization factor (Wc) in accordance with the formula given in this patent, 7. removing aged catalyst, thereby changing the value of Wc, and 8. adding fresh catalyst in an amount to return to said value of Wc.

Nelson, G.V.; Nongbri, G.

1993-06-01

428

Sulphuric Acid Manufacture  

Microsoft Academic Search

The raw material for sulphuric acid manufacture is clean SO2 gas. It comes from (i) burning molten by-product sulphur; (ii) roasting or smelting metal sulphide concentrates, and (iii) decomposing contaminated organic chemical process sulphuric acid catalyst. Efficient gas cleaning is required for metallurgical and contaminated acid decomposition gases, especially the former. Sulphuric acid is made from SO2 gas by (i)

W. G. Davenport; M. J. King; B. Rogers; A. Weissenberger

2006-01-01

429

Structures of bacterial polynucleotide kinase in a Michaelis complex with GTP•Mg2+ and 5'-OH oligonucleotide and a product complex with GDP•Mg2+ and 5'-PO4 oligonucleotide reveal a mechanism of general acid-base catalysis and the determinants of phosphoacceptor recognition.  

PubMed

Clostridium thermocellum polynucleotide kinase (CthPnk), the 5' end-healing module of a bacterial RNA repair system, catalyzes reversible phosphoryl transfer from an NTP donor to a 5'-OH polynucleotide acceptor. Here we report the crystal structures of CthPnk-D38N in a Michaelis complex with GTP•Mg(2+) and a 5'-OH oligonucleotide and a product complex with GDP•Mg(2+) and a 5'-PO4 oligonucleotide. The O5' nucleophile is situated 3.0 Å from the GTP ? phosphorus in the Michaelis complex, where it is coordinated by Asn38 and is apical to the bridging ? phosphate oxygen of the GDP leaving group. In the product complex, the transferred phosphate has undergone stereochemical inversion and Asn38 coordinates the 5'-bridging phosphate oxygen of the oligonucleotide. The D38N enzyme is poised for catalysis, but cannot execute because it lacks Asp38-hereby implicated as the essential general base catalyst that abstracts a proton from the 5'-OH during the kinase reaction. Asp38 serves as a general acid catalyst during the 'reverse kinase' reaction by donating a proton to the O5' leaving group of the 5'-PO4 strand. The acceptor strand binding mode of CthPnk is distinct from that of bacteriophage T4 Pnk. PMID:24150947

Das, Ushati; Wang, Li Kai; Smith, Paul; Jacewicz, Agata; Shuman, Stewart

2014-01-01

430

The use of imidazolium ionic liquid/copper complex as novel and green catalyst for chemiluminescent detection of folic acid by Mn-doped ZnS nanocrystals.  

PubMed

A novel chemiluminescence (CL) method using water-soluble Mn-doped ZnS quantum dots (QDs) as CL emitter is proposed for the chemiluminometric determination of folic acid in pharmaceutical formulation. Water-soluble Mn-doped ZnS QDs were synthesized by using L-cysteine as stabilizer in aqueous solutions. The nanoparticles were structurally and optically characterized by X-ray powder diffraction (XRD), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), UV-Vis absorption spectroscopy and photoluminescence (PL) emission spectroscopy. The CL of ZnS QDs induced by directly chemical oxidation and its ionic liquid-sensitized effect in aqueous solution were then investigated. It was found that oxidants, especially hydrogen peroxide, could directly oxidize ZnS QDs to produce weak CL emission in basic conditions. In the presence of 1,3-dipropylimidazolium bromide/copper a drastic light emission enhancement is observed, related to a strong interaction between Cu(2+) and the imidazolium ring. Therefore, a new CL analysis system was developed for the determination of folic acid. Under the optimum conditions, there is a good linear relationship between the relative CL intensity and the concentration of folic acid in the range of 1×10(-9)-1×10(-)(6) M of folic acid with a correlation coefficient (R(2)) of 0.9991. The limit of detection of this system was found to be 1×10(-)(10) M. This method is not only simple, sensitive and low cost, but also reliable for practical applications. PMID:24322762

Azizi, Seyed Naser; Shakeri, Parmis; Chaichi, Mohammad Javad; Bekhradnia, Ahmadreza; Taghavi, Mehdi; Ghaemy, Mousa

2014-03-25

431

The role played by acid and basic centers in the activity of biomimetic catalysts of the catalase, peroxidase, and monooxidase reactions  

NASA Astrophysics Data System (ADS)

The acid-basic centers of heterogeneous carriers of catalase, peroxidase, and monooxigenase biomimetics, in particular, iron protoporphyrin deposited on active or neutral aluminum magnesium silicate, were studied. The catalytic activity of biomimetics was stabilized, which allowed us not only to synthesize fairly effective biomimetics but also to clarify certain details of the mechanism of their action and perform a comparative analysis of the functioning of biomimetics and the corresponding enzymes.

Magerramov, A. M.; Nagieva, I. T.

2010-11-01

432

A preliminary study on iron species as heterogeneous catalysts for the degradation of linear alkylbenzene sulphonic acids by H 2O 2  

Microsoft Academic Search

Different eco-sustainable methods based on the activation of H2O2 promoted by iron species in homogeneous and heterogeneous phase, in the presence and absence of solar irradiation was compared in order to evaluate their effectiveness in the wastewater treatment. Commercial linear alkylbenzene sulphonic acids (LAS) have been chosen as model compound, being a pollutant largely used in different fields. Supported iron

Angela Cuzzola; Maristella Bernini; Piero Salvadori

2002-01-01

433

Spectroscopic monitoring of photocatalytic degradation of the insecticide acetamiprid and its degradation product 6-chloronicotinic acid on TiO2 catalyst  

Microsoft Academic Search

Two spectroscopic methods, H NMR and FTIR, were developed for the monitoring of the photocatalytic degradation of acetamiprid, a widely used pyridine-based neonicotinoid insecticide, in UV-irradiated aqueous suspensions of O2\\/TiO2. The H NMR method allowed also the identification of the intermediates such as 6-chloronicotinic and formic acids, as well as separate monitoring of the kinetics of degradation of acyclic and

Valéria Guzsvány; Ljiljana Raji?; Branislav Jovi?; Dejan Or?i?; János Csanádi; Sanja Lazi?; Biljana Abramovi?

2012-01-01

434

The use of imidazolium ionic liquid/copper complex as novel and green catalyst for chemiluminescent detection of folic acid by Mn-doped ZnS nanocrystals  

NASA Astrophysics Data System (ADS)

A novel chemiluminescence (CL) method using water-soluble Mn-doped ZnS quantum dots (QDs) as CL emitter is proposed for the chemiluminometric determination of folic acid in pharmaceutical formulation. Water-soluble Mn-doped ZnS QDs were synthesized by using L-cysteine as stabilizer in aqueous solutions. The nanoparticles were structurally and optically characterized by X-ray powder diffraction (XRD), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), UV-Vis absorption spectroscopy and photoluminescence (PL) emission spectroscopy. The CL of ZnS QDs induced by directly chemical oxidation and its ionic liquid-sensitized effect in aqueous solution were then investigated. It was found that oxidants, especially hydrogen peroxide, could directly oxidize ZnS QDs to produce weak CL emission in basic conditions. In the presence of 1,3-dipropylimidazolium bromide/copper a drastic light emission enhancement is observed, related to a strong interaction between Cu2+ and the imidazolium ring. Therefore, a new CL analysis system was developed for the determination of folic acid. Under the optimum conditions, there is a good linear relationship between the relative CL intensity and the concentration of folic acid in the range of 1 × 10-9-1 × 10-6 M of folic acid with a correlation coefficient (R2) of 0.9991. The limit of detection of this system was found to be 1 × 10-10 M. This method is not only simple, sensitive and low cost, but also reliable for practical applications.

Azizi, Seyed Naser; Shakeri, Parmis; Chaichi, Mohammad Javad; Bekhradnia, Ahmadreza; Taghavi, Mehdi; Ghaemy, Mousa

2014-03-01

435

A comparison of the electrophilic reactivities of Zn2+ and acetic acid as catalysts of enolization: imperatives for enzymatic catalysis of proton transfer at carbon.  

PubMed

The deprotonation of the alpha-CH3 and alpha-CH2OD groups of hydroxyacetone and the alpha-CH3 groups of acetone in the presence of acetate buffer and zinc chloride in D2O at 25 degrees C was followed by monitoring the incorporation of deuterium by 1H NMR spectroscopy, and the rate laws for catalysis of these reactions by acetate anion and zinc dication were evaluated. Relative to solvent water at a common standard state of 1 M, Zn2+ provides 6.3 and 4.4 kcal/mol stabilizations, respectively, of the transition states for deprotonation of the alpha-CH2OD and alpha-CH3 groups of hydroxyacetone by acetate anion, and a smaller 3.3 kcal/mol stabilization of the transition state for deprotonation of the alpha-CH3 group of acetone. There is only a 1.4 kcal/mol smaller stabilization of the transition state for the acetate-ion-promoted deprotonation of acetone by the Brønsted acid acetic acid than by Zn2+, which shows that, in the absence of a chelate effect, there is no large advantage to the use of a metal dication rather than a Brønsted acid to stabilize the transition state for deprotonation of alpha-carbonyl carbon. PMID:15099099

Crugeiras, Juan; Richard, John P

2004-04-28

436

CATALYSTS FOR HIGH CETANE ETHERS AS DIESEL FUELS  

SciTech Connect

A tungstena-zirconia (WZ) catalyst has been investigated for coupling methanol and isobutanol to unsymmetrical ethers, i.e. methyl isobutyl ether (MIBE) and compared with earlier studied sulfated-zirconia (SZ) and Nafion-H catalysts. In all cases, the ether synthesis mechanism is a dual site S{sub N}2 process involving competitive adsorption of reactants on proximal acid sites. At low reaction temperatures, methylisobutylether (MIBE) is the predominant product. However, at temperatures >135 C the WZ catalyst is very good for dehydration of isobutanol to isobutene. The surface acid sites of the WZ catalyst and a Nafion-H catalyst were diagnosed by high resolution X-ray photoelectron spectroscopy (XPS) of N 1s shifts after adsorption of amines. Using pyridine, ethylenediamine, and triethylamine, it is shown that WZ has heterogeneous strong Broensted acid sites. Theoretical study located the transition state of the alcohol coupling reaction on proximal Broensted acid sites and accounted well for XPS core-level shifts upon surface acid-base interactions. While computations have not been carried out with WZ, it is shown that the SZ catalyst is a slightly stronger acid than CF{sub 3}SO{sub 3}H (a model for Nafion-H) by 1.3-1.4 kcal/mol. A novel sulfated zirconia catalyst having proximal strong Broensted acid sites was synthesized and shown to have significantly enhanced activity and high selectivity in producing MIBE or isobutene from methanol/isobutanol mixtures. The catalyst was prepared by anchoring 1,2-ethanediol bis(hydrogen sulfate) salt precursor onto zirconium hydroxide, followed by calcination to remove the -(CH{sub 2}CH{sub 2})- bridging residues.

Kamil Klier; Richard G. Herman; Heock-Hoi Kwon; James G. C. Shen; Qisheng Ma; Robert A. Hunsicker; Andrew P. Butler; Scott J. Bollinger

2003-03-01

437

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s as high-efficiency catalysts for carbonyl-group transformation reactions.  

PubMed

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)(2)][OSO(2)C(8)F(17)](2)?nH(2)O?THF (M = Zr (2?a?3?H(2)O?THF), M = Ti (2?b?2?H(2)O?THF)) were synthesized by the reaction of [M(Cp)(2)]Cl(2) (M = Zr (1?a), M = Ti (1?b)) with nBuLi and C(8)F(17)SO(3)H (2?equiv) or with C(8)F(17)SO(3)Ag (2?equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry-differential scanning calorimetry (TG-DSC) analysis showed that 2?a and 2?b were thermally stable at 300 and 180?°C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2?a and 2?b) were ionic dissociation in CH(3)CN solution. X-ray analysis result confirmed 2?a?3?H(2)O?THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2?a. Fluorescence spectra showed that the Lewis acidity of 2?a fell between those of Sc(3+) (?(em)=474?nm) and Fe(3+) (?(em)=478?nm). ESR spectra showed the Lewis acidity of 2?a (0.91?eV) was at the same level as that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV), while the Lewis acidity of 2?b (1.06?eV) was larger than that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel-Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis. PMID:22504964

Qiu, Renhua; Xu, Xinhua; Peng, Lifeng; Zhao, Yalei; Li, Ningbo; Yin, Shuangfeng

2012-05-14

438

Bauxites as hydrotreatment catalysts  

Microsoft Academic Search

The effects of calcination temperature on structural and textural characteristics of two Greek bauxites were examined by different physicochemical techniques. Although the above minerals exhibited lower activity than a commercial CoMo\\/Al2O3 catalyst, they were evaluated as possible hydrotreating catalysts.

S. Alexandropoulos; A. Tsatsaronis; P. Haimalas; Ch. Kordulis

1991-01-01

439

Chemo-Enzymatic Synthesis of Each Enantiomer of Orthogonally-Protected 4,4-Difluoroglutamic Acid - A Candidate Monomer for Chiral Br?nsted-Acid Peptide-Based Catalysts  

PubMed Central

We have accomplished an asymmetric synthesis of each enantiomer of 4,4-difluoroglutamic acid. This ?-amino acid has been of interest in medicinal chemistry circles. Key features of the synthesis include highly scalable procedures, a Reformatsky-based coupling reaction, and straightforward functional group manipulations to make the parent amino acid. Enantioenrichment derives from an enzymatic resolution of the synthetic material. Conversion of the optically enriched compounds to orthogonally protected forms allows selective formation of peptide bonds. 4,4- Difluoroglutamic acid, in a suitably protected form, is also shown to exhibit enhanced catalytic activity in both an oxidation reaction and a reduction reaction, in comparison to the analogous glutamic acid derivative. PMID:22039908

Li, Yang

2011-01-01

440

Glutamic acid decarboxylase 65: a link between GABAergic synaptic plasticity in the lateral amygdala and conditioned fear generalization.  

PubMed

An imbalance of the gamma-aminobutyric acid (GABA) system is considered a major neurobiological pathomechanism of anxiety, and the amygdala is a key brain region involved. Reduced GABA levels have been found in anxiety patients, and genetic variations of glutamic acid decarboxylase (GAD), the rate-limiting enzyme of GABA synthesis, have been associated with anxiety phenotypes in both humans and mice. These findings prompted us to hypothesize that a deficiency of GAD65, the GAD isoform controlling the availability of GABA as a transmitter, affects synaptic transmission and plasticity in the lateral amygdala (LA), and thereby interferes with fear responsiveness. Results indicate that genetically determined GAD65 deficiency in mice is associated with (1) increased synaptic length and release at GABAergic connections, (2) impaired efficacy of GABAergic synaptic transmission and plasticity, and (3) reduced spillover of GABA to presynaptic GABAB receptors, resulting in a loss of the associative nature of long-term synaptic plasticity at cortical inputs to LA principal neurons. (4) In addition, training with high shock intensities in wild-type mice mimicked the phenotype of GAD65 deficiency at both the behavioral and synaptic level, indicated by generalization of conditioned fear and a loss of the associative nature of synaptic plasticity in the LA. In conclusion, GAD65 is required for efficient GABAergic synaptic transmission and plasticity, and for maintaining extracellular GABA at a level needed for associative plasticity at cortical inputs in the LA, which, if disturbed, results in an impairment of the cue specificity of conditioned fear responses typifying anxiety disorders. PMID:24663011

Lange, Maren D; Jüngling, Kay; Paulukat, Linda; Vieler, Marc; Gaburro, Stefano; Sosulina, Ludmila; Blaesse, Peter; Sreepathi, Hari K; Ferraguti, Francesco; Pape, Hans-Christian

2014-08-01

441

Thermal Decomposition of Bulk K-CoMoSx Mixed Alcohol Catalyst Precursors and Effects on Catalyst Morphology and Performance  

Microsoft Academic Search

Cobalt molybdenum sulfide-type mixed alcohol catalysts were synthesized via calcination of precipitated bulk sulfides and studied with temperature programmed decomposition analysis. Precursors containing aqueous potassium were also considered. Precipitates thermally decomposed in unique events which released ammonia, carbon dioxide, and sulfur. Higher temperature treatments led to more crystalline and less active catalysts in general with ethanol productivity falling from 203

M. J. Menart; J. E. Hensley; K. E. Costelow

2012-01-01

442

The general anesthetic propofol increases brain N-arachidonylethanolamine (anandamide) content and inhibits fatty acid amide hydrolase  

PubMed Central

Propofol (2,6-diisopropylphenol) is widely used as a general anesthetic and for the maintenance of long-term sedation. We have tested the hypothesis that propofol alters endocannabinoid brain content and that this effect contributes to its sedative properties. A sedating dose of propofol in mice produced a significant increase in the whole-brain content of the endocannabinoid, N-arachidonylethanolamine (anandamide), when administered intraperitoneally in either Intralipid or emulphor-ethanol vehicles. In vitro, propofol is a competitive inhibitor (IC50 52 ?M; 95% confidence interval 31, 87) of fatty acid amide hydrolase (FAAH), which catalyzes the degradation of anandamide. Within a series of propofol analogs, the critical structural determinants of FAAH inhibition and sedation were found to overlap. Other intravenous general anesthetics, including midazolam, ketamine, etomidate, and thiopental, do not affect FAAH activity at sedative-relevant concentrations. Thiopental, however, is a noncompetitive inhibitor of FAAH at a concentration of 2 mM. Pretreatment of mice with the CB1 receptor antagonist SR141716 (1 mg kg?1, i.p.) significantly reduced the number of mice that lost their righting reflex in response to propofol. Pretreatment of mice with the CB1 receptor agonist, Win 55212-2 (1 mg kg?1, i.p.), significantly potentiated the loss of righting reflex produced by propofol. These data indicate that CB1 receptor activity contributes to the sedative properties of propofol. These data suggest that propofol activation of the endocannabinoid system, possibly via inhibition of anandamide catabolism, contributes to the sedative properties of propofol and that FAAH could be a novel target for anesthetic development. PMID:12839875

Patel, Sachin; Wohlfeil, Eric R; Rademacher, David J; Carrier, Erica J; Perry, LaToya J; Kundu, Abhijit; Falck, J R; Nithipatikom, Kasem; Campbell, William B; Hillard, Cecilia J

2003-01-01

443

Deactivation and poisoning of fuel cell catalysts, revision  

NASA Astrophysics Data System (ADS)

The unique aspects of catalysts in the electrical generating unit of fuel cells are discussed. Fuel cell catalysts suffer from deactivation and poisoning phenomena that are either identical to or strongly analogous to the processes which occur in heterogeneous catalysis. Fuel cell performance is degraded by poisoning from impurities, loss of surface area of noble metal, and physical deterioration of the catalyst structure. The fuel cell catalyst is an integral part of the physical structure of the electrical generator, and there are at present no designs which are able to employ catalyst regeneration. Therefore, catalyst deactivation and poisoning phenomena are even more serious technological problems in fuel cells than in conventional reactors. The deactivation and poisoning phenomena reviewed in this paper are: the poisoning of anode (fuel electrode) catalyst by carbon monoxide; the deactivation of the cathode (air electrode) catalyst by loss of Pt dispersion; and the deactivation of the cathode by corrosion processes. The fuel cell technology discussed in the context of this phenomena is the phosphoric acid fuel cell. The operating conditions for this technology are typically 180 to 210 C, 95 to 99% acid, and in pressurized versions 50 to 120 psig.

Ross, P. N., Jr.

1985-09-01

444

Probing the Active Site of MIO-dependent Aminomutases, Key Catalysts in the Biosynthesis of amino Acids Incorporated in Secondary Metabolites  

SciTech Connect

The tyrosine aminomutase SgTAM produces (S)-{beta}-tyrosine from L-tyrosine in the biosynthesis of the enediyne antitumor antibiotic C-1027. This conversion is promoted by the methylideneimidazole-5-one (MIO) prosthetic group. MIO was first identified in the homologous family of ammonia lyases, which deaminate aromatic amino acids to form {alpha},{beta}-unsaturated carboxylates. Studies of substrate specificity have been described for lyases but there have been limited reports in altering the substrate specificity of aminomutases. Furthermore, it remains unclear as to what structural properties are responsible for catalyzing the presumed readdition of the amino group into the {alpha},{beta}-unsaturated intermediates to form {beta}-amino acids. Attempts to elucidate specificity and mechanistic determinants of SgTAM have also proved to be difficult as it is recalcitrant to perturbations to the active site via mutagenesis. An X-ray cocrystal structure of the SgTAM mutant of the catalytic base with L-tyrosine verified important substrate binding residues as well as the enzymatic base. Further mutagenesis revealed that removal of these crucial interactions renders the enzyme inactive. Proposed structural determinants for mutase activity probed via mutagenesis, time-point assays and X-ray crystallography revealed a complicated role for these residues in maintaining key quaternary structure properties that aid in catalysis.

Cooke, H.; Bruner, S

2010-01-01

445

Deactivation and poisoning of fuel cell catalysts. Revision  

SciTech Connect

In this paper, we do not discuss the problems of catalyst deactivation in the fuel conditioning unit, since these are conventional catalysts and reactors that are covered by other papers. The discussion here is restricted to the unique aspects of catalysts in the electrical generating unit of fuel cells. Fuel cell catalysts suffer from deactivation and poisoning phenomena that are either identical to or strongly analogous to the processes which occur in heterogeneous catalysis. As in conventional catalytic reactors, fuel cell performance is degraded by poisoning from impurities, loss of surface area of noble metal, and physical deterioration of the catalyst structure. Unlike conventional catalytic reactors, where some catalyst regeneration capability is usually designed into the system, the fuel cell catalyst is an integral part of the physical structure of the electrical generator, and there are at present no designs which are able to employ catalyst regeneration. Therefore