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1

Methanesulfonamide: a cosolvent and a general acid catalyst in sharpless asymmetric dihydroxylations.  

PubMed

To obtain information about the effect that methanesulfonamide has in the hydrolysis step in Sharpless asymmetric dihydroxylation, a series of aliphatic and conjugated aromatic olefins were dihydroxylated with and without methanesulfonamide. The hypothesis in this study was that methanesulfonamide is a cosolvent that aids in the transfer of the hydroxide ions from the water phase to the organic phase. A plot of t90% versus the computational partition coefficient clog P of the intermediate osmate ester of nonterminal aliphatic olefins revealed that the polarity of the intermediate osmate ester has a significant effect on the reaction time and methanesulfonamide effect. The more polar the intermediate osmate ester, the faster is the reaction without methanesulfonamide and the smaller the accelerating methanesulfonamide effect. Methanesulfonamide had no accelerating effect in the asymmetric dihydroxylation of short chain terminal aliphatic olefins as a result of easier accessibility of terminal osmate ester groups to the water phase. A cosolvent hypothesis was found not to be valid in asymmetric dihydroxylations of conjugated aromatic olefins. In the reaction conditions used in Sharpless asymmetric dihydroxylation, weakly acidic methanesulfonamide was found to be a general acid catalyst that protonates the intermediate osmate esters of conjugated aromatic olefins in the hydrolysis step. PMID:19301884

Junttila, Mikko H; Hormi, Osmo O E

2009-04-17

2

The lactate dehydrogenase catalyzed pyruvate adduct reaction: simultaneous general acid-base catalysis involving an enzyme and an external catalyst.  

PubMed

The pH dependence of the reaction catalyzed by lactate dehydrogenase, where pyruvate adds covalently to NAD to yield a NAD-Pyr adduct, together with published data on the pH dependence of parameters in the normal redox reaction suggests similar binding modes for enolpyruvate and lactate in their complexes with E X NAD (where E is one-fourth of the tetramer), for ketopyruvate in its complexes with the protonated species, E X H X NAD and E X H X NADH, and for the NAD--Pyr adduct and NADH plus pyruvate in their complexes with E X H. These similarities, together with previous data, suggest a reaction scheme for the formation of the enzyme-adduct complex that includes the relevant proton-transfer steps. Seven different amine chloride buffers were used in a study of the reverse adduct reaction, i.e., the decomposition of E X H X NAD--Pyr. These act with varying efficiencies as external general acid catalysts; the enzyme apparently acts as a (internal) general base. The involvement of the amine chloride buffers as external general catalysts is supported by the concentration dependence of the buffer effect, by a Brönsted plot, and by solvent deuterium isotope effects. The involvement of the enzyme as an internal general catalyst is inferred from the pH dependence of the reaction and the identities of the nearby groups in the E X H X NAD--Pyr complex (from crystallographic studies). The dependence of the adduct reaction on chloride concentration indicates the presence of dead-end inhibitor complexes of E X H X Cl and E X H X NAD X Cl. Chloride also accelerates the decomposition of the adduct in the complex E X H X NAD--Pyr by binding to this complex. PMID:6477888

Burgner, J W; Ray, W J

1984-07-31

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

Catalysts for direct formic acid fuel cells  

NASA Astrophysics Data System (ADS)

Previous work has demonstrated that formic acid fuel cells show interesting properties for micro power generation. In this paper the effects of the anode catalyst composition on fuel cell performance is investigated. In particular, the performance of Pt, Pt/Pd and Pt/Ru catalysts for direct formic acid fuel cells is investigated and their effect on cell power density output at 30 °C are compared. It is found that the open cell potential varies significantly with the catalyst composition. The Pt/Pd catalyst shows an open cell potential of 0.91 V compared to 0.71 V with pure platinum and 0.59 V with Pt/Ru. The current at a cell potential of 0.5 V is 62 mA/cm 2 with Pt/Pd compared to 33 mA/cm 2 with pure platinum and 38 mA/cm 2 with Pt/Ru. Interestingly, the Pt/Ru catalyst gives the most power at low voltage 70 mW/cm 2 at 0.26 V, compared to 43 mW/cm 2 for pure platinum and 41 mW/cm 2 for Pt/Pd. All of the catalysts showed stable operation during several hour tests. Analysis of the data indicates that the addition of palladium enhances the rate of formic acid electrooxidation via a direct reaction mechanism, while ruthenium additions suppress the direct pathway and enhance electrooxidation via a reactive CO intermediate.

Rice, C.; Ha, S.; Masel, R. I.; Wieckowski, A.

7

Polyamino Acids as Man-Made Catalysts  

Microsoft Academic Search

Polyamino acids are easy to prepare by nucleophile-initiated polymerisation of amino acid N-carboxyanhydrides. Polymers such as poly-(l)-leucine act as robust catalysts for the epoxidation of a wide range of electron-poor alkenes, such as ?-substituted ?,?-unsaturated ketones. The optically active epoxides so formed may be transformed into heterocyclic compounds, polyhydroxylated\\u000a materials and biologically active compounds such as diltiazem and taxol side

Joanne V. Allen; Stanley M. Roberts; Natalie M. Williamson

8

Tungstophosphoric and tungstosilicic acids on carbon as acidic catalysts  

Microsoft Academic Search

Tungstophosphoric (TPA) and tungstosilicic acid (TSA) catalysts supported on carbon were studied. They were prepared by equilibrium and incipient wetness impregnation techniques. Solutions of TPA and TSA in 50% v\\/v ethanol–water were used to impregnate carbon at 20°C. The Fourier transform infrared and 31P nuclear magnetic resonance spectroscopies of TPA and TSA supported catalysts dried at 70°C showed that the

Marcelo E Chimienti; Luis R Pizzio; Carmen V Cáceres; Mirta N Blanco

2001-01-01

9

Industrial application of solid acid–base catalysts  

Microsoft Academic Search

A statistical survey of industrial processes using solid acid–base catalysts is presented. The number of processes such as alkylation, isomerization, amination, cracking, etherification, etc., and the catalysts such as zeolites, oxides, complex oxides, phosphates, ion-exchange resins, clays, etc., are 127 and 180, respectively. The classification of the types of catalysts into solid acid, solid base, and solid acid–base bifunctional catalysts

Kozo Tanabe; Wolfgang F. Hölderich

1999-01-01

10

Hydrocracking with new solid acid catalysts: Model compounds studies  

SciTech Connect

Two new solid acid catalysts have been prepared by supporting zinc chloride on silica gel and acid-exchanged montmorillonite. The acid properties of these catalysts were determined by Hammett indicator method which showed that highly Bronsted acidic sites were present. SEM/EDS studies indicated a uniform distribution of silicon, zinc, and chlorine in the silica gel-zinc chloride catalyst. The activities of these catalysts in the hydrocracking of bibenzyl, polybenzyl, alkylbenzenes, and other heteroatom substituted aromatics were investigated. Their results with model compounds account for the effectiveness of these solid acid catalysts for conversion of coals to lower molecular weight materials.

Sharma, R.K.; Diehl, J.W.; Olson, E.S. (Univ. of North Dakota, Grand Forks (USA))

1990-01-01

11

Activation and reactivity of epoxides on solid acid catalysts  

Microsoft Academic Search

The aminolysis of epoxides over novel solid catalysts (Brönsted-acidic SBA-15 functionalized with propylsulfonic acid and Lewis-acidic Ti-MCM-41) is reported. The acidic properties of these catalysts were determined by FTIR spectroscopy and temperature-programmed desorption of pyridine and NH3, respectively. The mesoporous solid acids of the present study are reusable and exhibit significantly higher catalytic activities than known catalysts for opening of

L. Saikia; J. K. Satyarthi; D. Srinivas; P. Ratnasamy

2007-01-01

12

Differential thermal analysis as an acidity probe in zeolite catalysts  

SciTech Connect

Differential thermal analysis is used as an acidity strength probe for a series of mordenite (zeolite) catalysts via determining the temperature at which presorbed pyridine completely desorbs from the catalyst. The findings obtained for metal(s) containing mordenite catalysts have been correlated with the Pearson's assumption concerning Lewis acids and bases and the Pauling's electronegativity of the metals contained and found compatible.

Aboul-Gheit, A.K.; Al-Hajjaji, M.A.; Menoufy, M.F.; Abdel-Hamid, S.M.

1986-01-01

13

Hydrocracking with new solid acid catalysts: Model compounds studies  

Microsoft Academic Search

Two new solid acid catalysts have been prepared by supporting zinc chloride on silica gel and acid-exchanged montmorillonite. The acid properties of these catalysts were determined by Hammett indicator method which showed that highly Bronsted acidic sites were present. SEM\\/EDS studies indicated a uniform distribution of silicon, zinc, and chlorine in the silica gel-zinc chloride catalyst. The activities of these

R. K. Sharma; J. W. Diehl; E. S. Olson

1990-01-01

14

A catalyst system for the formation of amides by reaction of carboxylic acids with blocked isocyanates  

Microsoft Academic Search

A catalyst for the reaction of blocked isocyanates (blocking agent diisopropylamine and dimethyl pyrazole) and carboxylic acids was identified. Magnesium and in some instances calcium salts proved to be highly active as catalyst. This reaction gives amides in quantitative yield and excellent selectivity and is suitable for coating and general chemical purposes.

R. Gertzmann; C. Gürtler

2005-01-01

15

Catalyst and electrode research for phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

An account is given of the development status of phosphoric acid fuel cells' high performance catalyst and electrode materials. Binary alloys have been identified which outperform the baseline platinum catalyst; it has also become apparent that pressurized operation is required to reach the desired efficiencies, calling in turn for the use of graphitized carbon blacks in the role of catalyst supports. Efforts to improve cell performance and reduce catalyst costs have led to the investigation of a class of organometallic cathode catalysts represented by the tetraazaannulenes, and a mixed catalyst which is a mixture of carbons catalyzed with an organometallic and a noble metal.

Antoine, A. C.; King, R. B.

1987-01-01

16

Effects of water on the esterification of free fatty acids by acid catalysts  

Microsoft Academic Search

To maximize the production of biodiesel from soybean soapstock, the effects of water on the esterification of high-FFA (free fatty acid) oils were investigated. Oleic acid and high acid acid oil (HAAO) were esterified by reaction with methanol in the presence of Amberlyst-15 as a heterogeneous catalyst or sulfuric acid as a homogeneous catalyst. The yield of fatty acid methyl

Ji-Yeon Park; Zhong-Ming Wang; Deog-Keun Kim; Jin-Suk Lee

2010-01-01

17

Silicotungstic acid supported zirconia: An effective catalyst for esterification reaction  

Microsoft Academic Search

A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of silicotungstic acid on hydrous zirconia (ZSTA). The prepared catalysts were characterized by PXRD, FTIR, UV–vis DRS, EPMA, BET surface area, acid sites, etc. FTIR and UV–vis DRS studies indicate that the material retain the Keggin-type structure of silicotungstic acid up to 500°C.

K. M. Parida; Sujata Mallick

2007-01-01

18

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 ...

19

Surface acidity and degree of carburization of modified silver catalysts  

SciTech Connect

The effect has been studied of some compounds as modifying additives on the surface acidity, degree of carburization, aggregation and silver entrainement of silver-pumice catalysts for methanol oxidation. Catalyst samples have been tested in an industrial reactor. The probable mechanism of modifying action of the additives is discussed.

Pestryakov, A.N.; Belousova, V.N.; Roznina, M.I. [Tomsk Institute of Construction Engineering (Russian Federation)

1993-11-10

20

Phosphorylated Mesoporous Carbon as a Solid Acid Catalyst  

SciTech Connect

Mesoporous carbon catalyst supports are attractive due to their wide chemical stability while potentially increasing masstransport through and providing a path for larger molecules to access catalytic sites. Herein we report the synthesis of a 10 phosphorylated mesoporous carbon solid-acid catalyst characterized by NH3-TPD and isopropanol dehydration.

Dai, Sheng [ORNL; Mayes, Richard T [ORNL; Fulvio, Pasquale F [ORNL; Ma, Zhen [ORNL

2011-01-01

21

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

22

Acid and base characteristics of molybdenum carbide catalysts  

Microsoft Academic Search

The acid and base properties of a high surface area Mo2C catalyst were characterized using the temperature programmed desorption of CO2 and NH3, the decomposition of isopropyl alcohol (IPA) as a test reaction and monitoring changes in the associated rates and product selectivities on the addition of acid and base site poisons. The Mo2C catalyst was prepared using the temperature

Shyamal K Bej; Christopher A Bennett; Levi T Thompson

2003-01-01

23

Solid acid catalysts for biodiesel production - towards sustainable energy  

Microsoft Academic Search

The advantages of biodiesel as an alterna- tive fuel and the problems involved in its manufactur- ing are outlined. The pros and cons of making biodie- sel via fatty acid esterification using solid acid cata- lysts are examined. The main problem is finding a suitable catalyst that is active, selective, and stable un- der the process conditions. Various solid acids

Gadi Rothenberg

2006-01-01

24

Continuous mode linoleic acid hydrogenation on Pd\\/sibunit catalyst  

Microsoft Academic Search

Catalytic hydrogenation of linoleic acid and oleic acid to stearic acid over palladium on mesoporous carbon sibunit (Pd\\/sibunit)\\u000a catalyst was studied in a continuous trickle-bed reactor with the weight hourly space velocity 5.4 h?1 at 120°C and 30 bar using tall oil fatty acid (TOFA) as reactor feed. Stearic acid preparation using TOFA as a raw material\\u000a is of industrial

A. Bernas; I. L. Simakova; K. Eränen; J. Myllyoja; T. Salmi; D. Yu. Murzin

2010-01-01

25

Enantioselective Iodolactonization of Disubstituted Olefinic Acids Using a Bifunctional Catalyst  

PubMed Central

The enantioselective iodolactonizations of a series of diversely-substituted olefinic carboxylic acids are promoted by a BINOL-derived, bifunctional catalyst. Reactions involving 5-alkyl- and 5-aryl-4(Z)-pentenoic acids and 6-alkyl- and 6-aryl-5(Z)-hexenoic acids provide the corresponding ?- and ?-lactones having stereogenic C–I bonds in excellent yields and >97:3 er. Significantly, this represents the first organocatalyst that promotes both bromo- and iodolactonization with high enantioselectivities. The potential of this catalyst to induce kinetic resolutions of racemic unsaturated acids is also demonstrated.

Fang, Chao; Paull, Daniel H.; Hethcox, J. Caleb; Shugrue, Christopher R.; Martin, Stephen F.

2012-01-01

26

Reductive amination of N-linked oligosaccharides using organic acid catalysts  

Microsoft Academic Search

The reductive amination of oligosaccharides with 8-aminopyrene-1,3,6-trisulfonate in several organic acids of varying strength was examined by capillary electrophoresis using laser-induced fluorescence detection. The relationship between the derivatization yield and the pKa of the catalyst (organic acids) is in agreement with the general acid catalysis of the hemiacetal ring opening and the Shiff base formation, one of which is considered

Ramon A. Evangelista; Fu-Tai A. Chen; András Guttman

1996-01-01

27

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

28

Structured catalysts for photo-Fenton oxidation of acetic acid  

Microsoft Academic Search

In this work photo-Fenton oxidation of acetic acid, was carried out on perovskites based structured catalysts, in the presence or in the absence of low amounts of Pt. Homogeneous photo-Fenton reaction by ferrioxalate complex has been also performed. The comparison of homogeneous and heterogeneous photo-Fenton oxidation indicates that the use of a heterogeneous structured catalyst greatly improves the total organic

Diana Sannino; Vincenzo Vaiano; Paolo Ciambelli; Lyubov A. Isupova

2011-01-01

29

Xanthan Sulfuric Acid: An Efficient and Recyclable Solid Acid Catalyst for Pechmann Condensation  

Microsoft Academic Search

In this report, substituted coumarins are formed via Pechmann condensation using various substituted phenols and ethyl acetoacetates in the presence of xanthan sulfuric acid as a solid acid catalyst under solvent-free conditions. This method is very simple, cost-effective, and has shorter reaction times, and the catalyst could be reused.

B. Suresh Kuarm; J. Venu Madhav; B. Rajitha

2012-01-01

30

Xanthan Sulfuric Acid: An Efficient and Recyclable Solid Acid Catalyst for Pechmann Condensation  

Microsoft Academic Search

In this paper, substituted coumarins are reported via Pechmann condensation by using various substituted phenols and ethyl acetoacetates in presence of Xanthan sulfuric acid as a solid acid catalyst under solvent-free conditions. This method is very simple, cost effective, shorter reaction times and the catalyst could be reused.

B. Suresh Kuarm; J. Venu Madhav; B. Rajitha

2011-01-01

31

A One-Bead-One-Catalyst Approach to Aspartic Acid-Based Oxidation Catalyst Discovery  

PubMed Central

We report an approach to the high-throughput screening of asymmetric oxidation catalysts. The strategy is based on application of the one-bead-one-compound library approach, wherein each of our catalyst candidates is based on a peptide scaffold. For this purpose we rely on a recently developed catalytic cycle that employs an acid-peracid shuttle. In order to implement our approach, we developed a compatible linker and demonstrated that the library format is amenable to screening and sequencing of catalysts employing partial Edman degradation and MALDI mass spectrometry analysis. The system was applied to the discovery (and re-discovery) of catalysts for the enantioselective oxidation of a cyclohexene derivative. The system is now poised for application to unprecedented substrate classes for asymmetric oxidation reactions.

Lichtor, Phillip A.; Miller, Scott J.

2011-01-01

32

Evaluation of catalyst acidity and substrate electronic effects in a hydrogen bond-catalyzed enantioselective reaction.  

PubMed

A modular catalyst structure was applied to evaluate the effects of catalyst acidity in a hydrogen bond-catalyzed hetero Diels-Alder reaction. Linear free energy relationships between catalyst acidity and both rate and enantioselectivity were observed, where greater catalyst acidity leads to increased activity and enantioselectivity. A relationship between reactant electronic nature and rate was also observed, although there is no such correlation to enantioselectivity, indicating the system is under catalyst control. PMID:20919686

Jensen, Katrina H; Sigman, Matthew S

2010-11-01

33

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

34

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

35

Functionalized carbon nanofibers as solid-acid catalysts for transesterification.  

PubMed

Carbon nanofibers (CNFs) were functionalized with aryl sulfonic acid groups using in situ diazonium coupling. The use of diazonium coupling yielded an acidic carbon material, in which the introduced acidic groups are readily accessible to the triglyceride substrate. The material is an efficient catalyst for the transesterification of triolein and methanol, outperforming conventional sulfonated carbons in both stability and activity per acid site. Upon comparing CNFs with varying degrees of functionalization, a linear correlation between sulfonic acid sites and catalytic performance was found. PMID:23908100

Stellwagen, Daniel R; van der Klis, Frits; van Es, Daan S; de Jong, Krijn P; Bitter, Johannes H

2013-09-01

36

Evaluation of acidity of strong acid catalysts. 1. Derivation of an acidity function from carbon-13 NMR measurements  

Microsoft Academic Search

The limitations of the Hammett indicator method for acidity measurements of liquid acid catalysts of practical importance and the inapplicability in principle of the Hammett acidity concept to solid acid catalysts are discussed. Evaluation of acidities from the hydronation equilibrium of two simple alcohols, methanol and ethanol, and an α,β-unsaturated detone, 4-methyl-3-penten-2-one (mesityl oxide, I), by carbon-13 NMR is demonstrated

D. Farcasiu; A. Ghenciu; G. Miller

1992-01-01

37

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

38

Corrosion-resistant catalyst supports for phosphoric acid fuel cells  

NASA Astrophysics Data System (ADS)

High-surface-area carbon blacks such as Vulcan XC-72 (Cabot Corp.) and graphitized carbon blacks such as 2700 C heat-treated Black Pearls 2000 (HTBP) (Cabot Corp.) have found widespread applications as catalyst supports in phosphoric acid fuel cells (PAFCs). However, due to the operating temperatures and pressures being utilized in PAFCs currently under development, the carbon-based cathode catalyst supports suffer from corrosion, which decreases the performance and life span of a PAFC stack. The feasibility of using alternative, low-cost, corrosion-resistant catalyst support (CRCS) materials as replacements for the cathode carbon support materials was investigated. The objectives of the program were to prepare high-surface-area alternative supports and to evaluate the physical characteristics and the electrochemical stability of these materials. The O2 reduction activity of the platinized CRCS materials was also evaluated.

Kosek, J. A.; Cropley, C. C.; Laconti, A. B.

39

Corrosion-resistant catalyst supports for phosphoric acid fuel cells  

SciTech Connect

High-surface-area carbon blacks such as Vulcan XC-72 (Cabot Corp.) and graphitized carbon blacks such as 2700{degree}C heat-treated Black Pearls 2000 (HTBP) (Cabot Corp.) have found widespread applications as catalyst supports in phosphoric acid fuel cells (PAFCs). However, due to the operating temperatures and pressures being utilized in PAFCs currently under development, the carbon-based cathode catalyst supports suffer from corrosion, which decreases the performance and life span of a PAFC stack. The feasibility of using alternative, low-cost, corrosion-resistant catalyst support (CRCS) materials as replacements for the cathode carbon support materials was investigated. The objectives of the program were to prepare high-surface-area alternative supports and to evaluate the physical characteristics and the electrochemical stability of these materials. The O{sub 2} reduction activity of the platinized CRCS materials was also evaluated. 2 refs., 3 figs.

Kosek, J.A.; Cropley, C.C.; LaConti, A.B.

1990-01-01

40

Layered and nanosheet tantalum molybdate as strong solid acid catalysts  

Microsoft Academic Search

Layered and nanosheet aggregates of HTaMoO6 were examined as solid acid catalysts. The HTaMoO6 aggregated nanosheets were formed by soft chemical processing of layered HTaMoO6 using tetra (n-butylammonium) hydroxide. The catalytic activity and acid properties of the HTaMoO6 compounds were compared with those of layered HNbMoO6 and a range of conventional solid acids. The catalytic activity of HTaMoO6 for Friedel–Crafts

Caio Tagusagawa; Atsushi Takagaki; Kazuhiro Takanabe; Kohki Ebitani; Shigenobu Hayashi; Kazunari Domen

2010-01-01

41

Dehydration of xylose into furfural over micro-mesoporous sulfonic acid catalysts  

Microsoft Academic Search

Surfactant-templated micro-mesoporous silicas possessing sulfonic acid groups (SAGs) have been prepared, characterized, and tested as catalysts in the dehydration of d-xylose to furfural. All of the materials possessed catalytic activity. In general, selectivity to furfural was lower for a poorly ordered microporous hybrid material, prepared via the co-condensation of (3-mercaptopropyl)trimethoxysilane with bis(trimethoxysilylethyl)benzene, than for mesoporous MCM-41 silica anchored with SAGs

Ana S. Dias; Martyn Pillinger; Anabela A. Valente

2005-01-01

42

Enhanced life of proton exchange membrane fuel cell catalysts using perfluorosulfonic acid stabilized carbon support  

Microsoft Academic Search

We report a new and simple solution to increase life of Pt\\/C catalysts using the proton-conducting polymer (perfluorosulfonic acid, PFSA) stabilized carbon support (denoted these catalysts as Pt\\/NFC catalysts) as compared to conventional Pt\\/C catalysts commonly used in PEM fuel cells. A high catalytic activity of the catalyst is observed by both CV (cyclic voltammetry) and ORR (oxygen reduction reaction)

Niancai Cheng; Shichun Mu; Xiaojing Chen; Haifeng Lv; Mu Pan; Peter P. Edwards

2011-01-01

43

PaaSiCats: novel polyamino acid catalysts.  

PubMed

The abilities of five polyamino acids (Paa's) to catalyse the asymmetric epoxidation of enones 1-7 under three sets of reaction conditions were compared: polyneo-pentylglycine and polyleucine showed distinct advantages in most circumstances. All five polymers were adsorbed onto silica and from this further study, immobilised polyneo-pentylglycine (PLNSi) and polyleucine (PLLSi) were shown to be the catalysts of choice for the asymmetric epoxidation of less-reactive alpha,beta-unsaturated ketones. PMID:10824145

Dhanda, A; Drauz, K H; Geller, T; Roberts, S M

2000-06-01

44

Catalytic cracking process employing an acid-reacted metakaolin catalyst  

SciTech Connect

This patent describes a method for cracking hydrocarbons. It comprises: reacting a hydrocarbon feedstock under catalytic cracking conditions with a catalyst which comprises an acid reacted metakaolin composition having a mole composition of about 0.8 to 1.0 Al{sub 2}O{sub 3}.2 SiO{sub 2} and characterized by a surface area of above bout 150 m{sup 2}/g.

Lussier, R.J.

1990-07-10

45

Butyric acid esterification kinetics over Amberlyst solid acid catalysts: the effect of alcohol carbon chain length.  

PubMed

The liquid phase esterification of butyric acid with a series of linear and branched alcohols is examined. Four strong cation exchange resins, Amberlyst™ 15, Amberlyst™ 36, Amberlyst™ BD 20, and Amberlyst™ 70, were used along with para-toluenesulfonic acid as a homogeneous catalyst. The effect of increasing alcohol carbon chain length and branching on esterification rate at 60°C is presented. For all catalysts, the decrease in turnover frequency (TOF) with increasing carbon chain length of the alcohol is described in terms of steric hindrance, alcohol polarity, and hydroxyl group concentration. The kinetics of butyric acid esterification with 2-ethylhexanol using Amberlyst™ 70 catalyst is described with an activity-based, pseudo-homogeneous kinetic model that includes autocatalysis by butyric acid. PMID:23380294

Pappu, Venkata K S; Kanyi, Victor; Santhanakrishnan, Arati; Lira, Carl T; Miller, Dennis J

2013-02-01

46

[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

47

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

Tungsten carbide, which is active for hydrogen oxidation, is CO tolerant and has a hexagonal structure is discussed. Titanium carbide is inactive and has a cubic structure. Four different samples of the cubic alloys W sub x-1Ti sub XC sub 1-y were found to be active and CO tolerant. When the activities of these cubic alloys are weighted by the reciprocal of the square to those of highly forms of WC. They offer important insight into the nature of the active sites on W-C anode catalysts for use in phosphoric acid fuel cells.

Mcalister, A. J.

1981-01-01

48

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

Four different samples of the cubic alloys W sub x-1 Ti sub x C sub 1-y were prepared and found to be active and CO tolerant. When the activities of these cubic alloys were weighted by the reciprocal of the square of the W exchange, they displayed magnitudes and dependence on bulk C deficiency comparable to those of highly active forms of WC. It is concluded that they may offer important insight into the nature of the active sites on, and means for improving the performance of, W-C anode catalysts for use in phosphoric acid fuel cells.

Mcalister, A. J.

1981-01-01

49

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

Tungsten carbide, which is known to be active for hydrogen oxidation and CO tolerant has a hexagonal structure. Titanium carbide is inactive and has a cubic structure. Four different samples of the cubic alloys Wx-1TixC were prepared and found to be active and CO tolerant. These alloys are of interest as possible phosphoric acid fuel cell catalysts. They also are of interest as opportunities to study the activity of W in a different crystalline environment and to correlate the activities of the surface sites with surface composition.

Mcalister, A. J.

1980-01-01

50

Prompt gamma activation analysis of solid acid catalysts  

SciTech Connect

Zeolite molecular sieves are important catalysts due to their porous structures, which lead to the size-selective transport of chemical products and reactants. One potential application of the size-selective molecular adsorption properties of zeolites is in the purification of hydrofluorocarbons (HFCs), which are replacing ozone-destroying chlorofluorocarbons in a wide range of uses, e.g., as refrigerants. A first step in understanding adsorption of these HFC molecules by zeolites is obtaining accurate measurements of the number of adsorbate molecules per zeolite supercage. Another class of catalysts, solid superacids, is important for chemical reactions such as isomerization of hydrocarbons, conversion of methanol into hydrocarbons, and polymerization of alkenes. For example, ZrO{sub 2} and TiO{sub 2} have been observed to behave as solid superacids when small amounts of sulfate and hydrogen are incorporated on their surfaces. The acidity of these materials can exceed 104 times that of liquid H{sub 2}SO{sub 4}. One explanation for the {open_quotes}superacid{close_quotes} properties of these materials is that hydrogen ions (Bronstead acid sites) bound to surface oxygens are rendered more acidic by electron withdrawal due to nearby sulfate (SO{sub 4}{sup 2-}) groups. There is much 4 current interest in the synthesis and properties of solid super-acids because they may ultimately replace liquid acids such as H{sub 2}SO{sub 4}, HF, and AICl{sub 3} in industrially important syntheses and thereby reduce the waste streams generated. Characterization of solid acids requires measurements of the hydrogen and sulfate concentrations for correlation with the catalytic properties. We have utilized prompt gamma neutron activation analysis to characterize a number of these materials because of its unique ability to quantitatively measure hydrogen concentrations in addition to a number of other elements.

Crawford, M.K.; Corbin, D.R.; VerNooy, P.D. [DuPont, Wilmington, DE (United States)

1994-12-31

51

sp³ -linked amorphous carbon with sulfonic acid groups as a heterogeneous acid catalyst.  

PubMed

SO?H-bearing amorphous carbon prepared from polyvinyl chloride (PVC) is studied as a heterogeneous Brønsted acid catalyst. Sulfonation of partially carbonized PVC produces amorphous carbon consisting of small SO?H-bearing carbon sheets linked by sp³ -based aliphatic hydrocarbons. This carbon material exhibits much higher catalytic performance in the hydrolysis of cellobiose than conventional heterogeneous Brønsted acid catalysts with SO?H groups, including SO?H-bearing amorphous carbon derived from cellulose. This can be attributed to a high density of SO?H groups and the fast diffusion of reactants and products enabled by a flexible carbon network. PMID:22740285

Suganuma, Satoshi; Nakajima, Kiyotaka; Kitano, Masaaki; Hayashi, Shigenobu; Hara, Michikazu

2012-09-01

52

Cathode catalysts for primary phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

Alkylation or carbon Vulcan XC-72, the support carbon, was shown to provide the most stable bond type for linking cobalt dehydrodibenzo tetraazannulene (CoTAA) to the surface of the carbon; this result is based on data obtained by cyclic voltammetry, pulse voltammetry and by release of 14C from bonded CoTAA. Half-cell tests at 100 C in 85% phosphoric acid showed that CoTAA bonded to the surface of carbon (Vulcan XC-72) via an alkylation procedure is a more active catalyst than is platinum based on a factor of two improvement in Tafel slope; dimeric CoTAA had catalytic activity equal to platinum. Half-cell tests also showed that bonded CoTAA catalysts do not suffer a loss in potential when air is used as a fuel rather than oxygen. Commercially available polytetrafluroethylene (PTFE) was shown to be unstable in the fuel cell environment with degradation occurring in 2000 hours or less. The PTFE was stressed at 200 C in concentrated phosphoric acid as well as electrochemically stressed in 150 C concentrated phosphoric acid; the surface chemistry of PTFE was observed to change significantly. Radiolabeled PTFE was prepared and used to verify that such chemical changes also occur in the primary fuel cell environment.

1981-01-01

53

Enhancing the efficiency and regioselectivity of p450 oxidation catalysts by unnatural amino Acid mutagenesis.  

PubMed

The development of effective strategies for modulating the reactivity and selectivity of cytochrome P450 enzymes represents a key step toward expediting the use of these biocatalysts for synthetic applications. We have investigated the potential of unnatural amino acid mutagenesis to aid efforts in this direction. Four unnatural amino acids with diverse aromatic side chains were incorporated at 11 active-site positions of a substrate-promiscuous CYP102A1 variant. The resulting "uP450s" were then tested for their catalytic activity and regioselectivity in the oxidation of two representative substrates: a small-molecule drug and a natural product. Large shifts in regioselectivity resulted from these single mutations, and in particular, for para-acetyl-Phe substitutions at positions close to the heme cofactor. Screening this mini library of uP450s enabled us to identify P450 catalysts for the selective hydroxylation of four aliphatic positions in the target substrates, including a C(sp(3) )?H site not oxidized by the parent enzyme. Furthermore, we discovered a general activity-enhancing effect of active-site substitutions involving the unnatural amino acid para-amino-Phe, which resulted in P450 catalysts capable of supporting the highest total turnover number reported to date on a complex molecule (34?650). The functional changes induced by the unnatural amino acids could not be reproduced by any of the 20 natural amino acids. This study thus demonstrates that unnatural amino acid mutagenesis constitutes a promising new strategy for improving the catalytic activity and regioselectivity of P450 oxidation catalysts. PMID:24692265

Kolev, Joshua N; Zaengle, Jacqueline M; Ravikumar, Rajesh; Fasan, Rudi

2014-05-01

54

Degradation of polyethylene and polypropylene into fuel oil by using solid acid and non-acid catalysts  

Microsoft Academic Search

The thermal and catalytic degradation of plastic polymers, polyethylene (PE) at 430°C and polypropylene (PP) at 380°C into fuel oil were carried out by batch operation. The catalysts employed were acid-catalysts silica–alumina (SA-1, SA-2), zeolite ZSM-5 and non acidic mesoporous silica catalysts (silicalite, mesoporous silica gel and mesoporous folded silica (FSM). The yields of product gas, liquid and residues; recovery

Yusaku Sakata; Akinori Muto

1999-01-01

55

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

56

Direct hydrogenation of aromatic carboxylic acids to their corresponding aldehydes with zinc oxide catalysts  

Microsoft Academic Search

High yields of aromatic aldehydes were obtained by direct hydrogenation of aromatic carboxylic acids over different zinc oxide catalysts having distinctive surface properties. The reaction is carried out in a fixed bed reactor in gas phase at 330–350°C. High selectivity of 96% of benzaldehyde at 100% conversion of benzoic acid was achieved using a zinc oxide catalyst having very weakly

W. F. Hölderich; J. Tjoe

1999-01-01

57

Preparation and characterization of biomass carbon-based solid acid catalyst for the esterification of oleic acid with methanol.  

PubMed

A solid acid catalyst, prepared by sulfonating carbonized corn straw, was proved to be an efficient and environmental benign catalyst for the esterification of oleic acid and methanol. Various synthetic parameters, such as carbonization temperature and time were systematically examined. It was found that the catalyst exhibited the highest acid density of 2.64 mmol/g by NaOH titration. A quantitative yield (98%) of ester was achieved, using the most active sulfonated catalyst at 333 K with a 7 wt.% catalyst/oleic acid ratio for 4h, at a 7:1 M ratio of methanol/oleic acid, while the commercial available Amberlyst-15 only gave 85% yield under the same reaction condition. PMID:23453798

Liu, Tiantian; Li, Zhilong; Li, Wei; Shi, Congjiao; Wang, Yun

2013-04-01

58

Chemoselective Tetrahydropyranylation of Alcohols and Their Detetrahydropyranylation Using Silicasulphuric Acid as a Reusable Catalyst  

Microsoft Academic Search

A simple, mild, and efficient protocol for chemoselective protection of alcohols over phenols as tetrahydropyranyl ethers and their deprotection using silicasulphuric acid as a reusable solid acid catalyst is described.

D. M. Pore; Uday V. Desai; R. B. Mane; P. P. Wadgaonkar

2004-01-01

59

n-hydrocarbons conversions over metal-modified solid acid catalysts  

NASA Astrophysics Data System (ADS)

The quality of a straight-run fuel oil can be improved if saturated n-hydrocarbons of low octane number are converted to their branched counterparts. Poor reactivity of traditional catalysts in isomerization reactions imposed the need for the development of new catalysts among which noble metal promoted acid catalysts, liquid and/or solid acid catalysts take a prominent place. Sulfated zirconia and metal promoted sulfated zirconia exhibit high activity for the isomerization of light alkanes at low temperatures. The present paper highlights the original results which indicate that the modification of sulfated zirconia by incorporation of metals (platinum and rhenium) significantly affects catalytic performances in n-hydrocarbon conversion reactions. Favourable activity/selectivity of the promoted sulfated zirconia depends on the crystal phase composition, critical crystallites sizes, platinum dispersion, total acidity and type of acidity. Attention is also paid to the recently developed solid acid catalysts used in other conversion reactions of hydrocarbons.

Zarubica, A.; Ran?elovi?, M.; Mom?ilovi?, M.; Radulovi?, N.; Putanov, P.

2013-12-01

60

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

61

SURFACE ACIDITY OF PALYGORSKITE-SUP PORTED RHODIUM CATALYSTS  

Microsoft Academic Search

Infrared spectra of adsorbed pyridine have been used to obtain qualitative information on the nature of the interaction of pyridine with different rhodium catalysts supported on palygorskite and silica. Based on these data, qualitative definitions of the adsorption sites of these catalysts have been deduced. The catalysts were prepared with natural palygorskite, and palygorskite dehydrated in vacuo at 150~ and

JUANA HERRERO; JESUS A. PAJARES; CARMEN BLANCO

62

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

63

Catalysts  

Microsoft Academic Search

A hydrotreating catalyst which is resistant to carbonaceous deposits and is particularly useful for hydrotreating coal derived liquids, is molybdenum or tungsten disulphide in an amount of 0.1 to 10% by weight, substantially completely on the outer surface of an active carbon support having a surface area in excess of 800 m2\\/g. The catalyst can be made by absorbing molybdenum

D. G. Gavin; M. A. Jones

1982-01-01

64

High-temperature sulfuric acid decomposition over complex metal oxide catalysts  

SciTech Connect

Activity and stability of FeTiO3, MnTiO3, NiFe2O4, CuFe2O4, NiCr2O4, 2CuO•Cr2O3, CuO and Fe2O3 for the atmospheric decomposition of concentrated sulfuric acid in sulfur-based thermochemical water splitting cycles are presented. Catalyst activity was determined at temperatures from 725 to 900 °C. Catalytic stability was examined at 850 °C for up to one week of continuous operation. The results were compared to a 1.0 wt% Pt/TiO2 catalyst. Surface area by nitrogen physisorption, X-ray diffraction analyses, and temperature programmed desorption and oxidation were used to characterize fresh and spent catalyst samples. Over the temperature range, the catalyst activity of the complex oxides followed the general trend: 2CuO•Cr2O3 > CuFe2O4 > NiCr2O4 ˜ NiFe2O4 > MnTiO3 ˜ FeTiO3. At temperatures less than 800 °C, the 1.0 wt% Pt/TiO2 catalyst had higher activity than the complex oxides, but at temperatures above 850 °C, the 2CuO•Cr2O3 and CuFe2O4 samples had the highest activity. Surface area was found to decrease for all of the metal oxides after exposure to reaction conditions. In addition, the two complex metal oxides that contained chromium were not stable in the reaction environment; both leached chromium into the acid stream and decomposed into their individual oxides. The FeTiO3 sample also produced a discoloration of the reactor due to minor leaching and converted to Fe2TiO5. Fe2O3, MnTiO3 and NiFe2O4 were relatively stable in the reaction environment. In addition, CuFe2O4 catalyst appeared promising due to its high activity and lack of any leaching issues.

Daniel M. Ginosar; Harry W. Rollins; Lucia M. Petkovic; Kyle C. Burch; Michael J. Rush

2009-05-01

65

Kinetics of esterification of propanoic acid with methanol over a fibrous polymer-supported sulphonic acid catalyst  

Microsoft Academic Search

Esterification kinetics of propanoic acid with methanol in the presence of a fibrous polymer-supported sulphonic acid catalyst as well as a conventional resin catalyst was studied. Kinetic experiments were carried out in a laboratory-scale batch reactor operating isothermally at 55, 60 and 63°C and with different initial molar ratios of propanoic acid and methanol (1:1, 2:3 and 3:2). The fibre

J. Lilja; J. Aumo; T. Salmi; D. Yu. Murzin; P. Mäki-Arvela; M. Sundell; K. Ekman; R. Peltonen; H. Vainio

2002-01-01

66

Study of a New Iron Phosphate Catalyst for Oxidative Dehydrogenation of Isobutyric Acid  

Microsoft Academic Search

A new method of preparation of iron phosphate-based catalysts has been developed. The catalysts obtained are characterized by a single phase which is very active and selective in methacrylic acid (MAA) formation. This phase, identified as Fe2(PO3OH)P2O7, is an selective but much more active than industrial iron phosphate-based catalysts prepared by another method. The similarities between the catalytic properties of

P. Bonnet; J. M. M. Millet; C. Leclercq; J. C. Védrine

1996-01-01

67

Role of dehydration catalyst acid properties on one-step DME synthesis over physical mixtures  

Microsoft Academic Search

The direct synthesis of dimethyl ether (DME) was studied in a continuous high-pressure unit composed basically of a Berty reactor and on-line gas chromatograph. A commercial methanol synthesis catalyst and some solid-acid catalysts (alumina, HZSM-5, tungsten–zirconia and sulfated-zirconia) were used as physical mixtures. The dehydration catalysts were characterised by pyridine adsorption followed by IR spectroscopy and tested in the methanol

F. S. Ramos; A. M. Duarte de Farias; L. E. P. Borges; J. L. Monteiro; M. A. Fraga; E. F. Sousa-Aguiar; L. G. Appel

2005-01-01

68

Preyssler-Structured Tungstophosphoric Acid Catalyst on Functionalized Silica for Esterification of n Butanol with Acetic Acid  

Microsoft Academic Search

The Preyssler-structured tungstophosphoric acid catalyst supported on functionalized silica (Preyssler\\/F-silica) was prepared\\u000a by means of grafting technique with amine group as coupling media, and its catalytic behavior was investigated in the esterification\\u000a of n-butanol with acetic acid. The catalyst was characterized by infra-red spectroscopy, UV–Vis spectroscopy, Hammett indicator\\u000a and N2 adsorption techniques. Catalysts prepared directly by impregnating Preyssler acid on

Shanshan Wu; Weihong Zhang; Jun Wang; Xiaoqian Ren

2008-01-01

69

Conversion of xylose into furfural using lignosulfonic Acid as catalyst in ionic liquid.  

PubMed

Preparation of biopolymer-based catalysts for the conversion of carbohydrate polymers to new energies and chemicals is a hot topic nowadays. With the aim to develop an ecological method to convert xylose into furfural without the use of inorganic acids, a biopolymer-derived catalyst (lignosulfonic acid) was successfully used to catalyze xylose into furfural in ionic acid ([BMIM]Cl). The characteristics of lignosulfonic acid (LS) and effects of solvents, temperature, reaction time, and catalyst loading on the conversion of xylose were investigated in detail, and the reusability of the catalytic system was also studied. Results showed that 21.0% conversion could be achieved at 100 °C for 1.5 h. The method not only avoids pollution from conventional mineral acid catalysts and organic liquids but also maked full use of a byproduct (lignin) from the pulp and paper industry, thus demonstrating an environmentally benign process for the conversion of carbohydrates into furfural. PMID:25007384

Wu, Changyan; Chen, Wei; Zhong, Linxin; Peng, Xinwen; Sun, Runcang; Fang, Junjie; Zheng, Shaobo

2014-07-30

70

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

71

Silica supported phosphomolybdic acid: an efficient heterogeneous catalyst for Friedlander synthesis of quinolines.  

PubMed

Silica supported phosphomolybdic acid, an eco-friendly heterogeneous catalyst, has been found to be highly efficient for Friedlander synthesis of quinolines in excellent yields. A variety of ketones afford the quinolines smoothly. The catalyst can be easily recovered and reused. PMID:18591832

Das, Biswanath; Krishnaiah, Martha; Laxminarayana, Keetha; Nandankumar, Duddukuri

2008-07-01

72

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

73

Preparation of MCM-41 supported phosphoric acid catalyst for thiophenic compounds alkylation in FCC gasoline  

Microsoft Academic Search

The alkylation of thiophenic sulfur compounds with olefins in FCC gasoline followed by distillation of heavy compounds is a good alternative to classical desulfurization technologies. In this study, the preparation condition of MCM-41 supported phosphoric acid catalyst was optimized and the activity tests in real gasoline proved that the optimal catalyst was promising to be applied in the alkylation transfer

Rong Wang; Yonghong Li

2010-01-01

74

Determination of the acid strength of solid catalysts in water by means of a kinetic tracer  

Microsoft Academic Search

The kinetic analysis of the hydrolysis of acetals in the presence of various solid acid catalysts, dealuminated H-form mordenites, H-montmorillonite and strong ion exchange resins has been carried out. Experiments performed in water as the solvent at different agitation speeds, catalyst weights and acetal concentrations show that the reaction is not controlled by external diffusion, nor by internal diffusion as

Claude Moreau; Robert Durand; Patrick Geneste; Samir Mseddi

1996-01-01

75

Catalysts  

SciTech Connect

A hydrotreating catalyst which is resistant to carbonaceous deposits and is particularly useful for hydrotreating coal derived liquids, is molybdenum or tungsten disulphide in an amount of 0.1 to 10% by weight, substantially completely on the outer surface of an active carbon support having a surface area in excess of 800 m2/g. The catalyst can be made by absorbing molybdenum or tungsten trisulphide onto the active carbon support and reducing the trisulphide to the disulphide.

Gavin, D.G.; Jones, M.A.

1982-02-02

76

Evaluation of acidity of strong acid catalysts. 1. Derivation of an acidity function from carbon-13 NMR measurements  

SciTech Connect

The limitations of the Hammett indicator method for acidity measurements of liquid acid catalysts of practical importance and the inapplicability in principle of the Hammett acidity concept to solid acid catalysts are discussed. Evaluation of acidities from the hydronation equilibrium of two simple alcohols, methanol and ethanol, and an {alpha},{beta}-unsaturated detone, 4-methyl-3-penten-2-one (mesityl oxide, I), by carbon-13 NMR is demonstrated for sulfuric acid-water mixtures. The latter compound is particularly useful because the signal for its carbon atom C-4 shifts downfield upon hydronation by almost 50 ppm, whereas the signal for C-3 moves upfield by 3 ppm. The comparison of the chemical shift difference {delta}(C-4)-{delta}(C-3) ({Delta}{delta}) for two different solutions allows a comparison of acidities of the two solutions from which other medium effects upon chemical shifts have been canceled out. The variation of {Delta}{delta} with concentration of I, or the ratio of base (I) to acid, is linear, at least between 1 and 0.5 M of I. Extrapolation of {Delta}{delta} of I to (B)/(AH) = 0 ({Delta}{delta}{sup 0}) allows the use of {sup 13}C NMR spectroscopy to establish a thermodynamically meaningful acidity scale, such as the traditional acidity function H{sub 0}. The slope of {Delta}{delta} vs (B)/(AH) plot changes with acid strength; it is lowest (most negative) for the acidity at which I is half-protonated. The acidity required for half-protonation can thus be accurately determined from this slope. On the other hand, {Delta}{delta} can be also measured at the stoichiometric ratio of the indicator base to acid molecules or sites. The latter approach must be used for comparison of strength of solid acids.

Farcasiu, D.; Ghenciu, A.; Miller, G. (Univ. of Pittsburgh, PA (United States))

1992-03-01

77

Acid and Base Catalysts in the Hybrid Silica Sol–Gel Process  

Microsoft Academic Search

Sol–gel silicas were synthesized from the hydrolysis of tetraethoxysilane andN-?-aminoethyl-?-aminopropyltrimethoxysilane in the presence of water and ethanol by using ammonium hydroxide or hydrochloric acid as base or acid catalysts, respectively. The influence of the type of the catalyst employed was studied by comparing the surface areas and pore sizes and volumes for both sol–gel silicas. Nitrogen elemental analysis and13C and29Si

Cesar R. Silva; Claudio Airoldi

1997-01-01

78

Preparation of microspherical ?-zirconium phosphate catalysts for conversion of fatty acid methyl esters to monoethanolamides  

Microsoft Academic Search

The performance of solid catalysts and catalyst supports is generally believed to be dependent on their morphology, surface area, and architecture. In order to fully exploit their attractive properties in actual practical applications, layered zirconium phosphate materials should be fabricated into macroscopic form. Here, we report the fabrication of microscopic spheres of ?-zirconium phosphate (?-ZrP) by a spray-drying process. The

Fazhi Zhang; Yaru Xie; Wei Lu; Xiaoying Wang; Sailong Xu; Xiaodong Lei

2010-01-01

79

Metal-organic frameworks of vanadium as catalysts for conversion of methane to acetic acid.  

PubMed

A catalytic system combining the high activity of homogeneous catalysts and the ease of use of heterogeneous catalysts for methane activation is reported. The vanadium-containing metal-organic frameworks (MOFs) MIL-47 and MOF-48 are found to have high catalytic activity and chemical stability. They convert methane selectively to acetic acid with 70% yield (490 TON) based on K(2)S(2)O(8) as an oxidant. Isotopic labeling experiments showed that two methane molecules are converted to the produced acetic acid. The MOF catalysts are reusable and remain catalytically active for several recycling steps without losing their crystalline structures. PMID:21766786

Phan, Anh; Czaja, Alexander U; Gándara, Felipe; Knobler, Carolyn B; Yaghi, Omar M

2011-08-15

80

Amberlyst 15: A Practical, Mild and Selective Catalyst for Methyl Esterification of Carboxylic Acids  

Microsoft Academic Search

Mild and selective methyl esterification of carboxylic acids are realized using Amberlyst 15 as acid catalyst in methanol. No race mization, epimerization or ketalization products have been observed with this method. Excellent results are obtained in the esterifications of bile acids.

Marino Petrini; Roberto Ballini; Enrico Marcantoni; Goffredo Rosini

1988-01-01

81

Stability of supported platinum sulfuric acid decomposition catalysts for use in thermochemical water splitting cycles  

Microsoft Academic Search

The activity and stability of several metal oxide supported platinum catalysts were explored for the sulfuric acid decomposition reaction. The acid decomposition reaction is common to several sulfur based thermochemical water splitting cycles. Reactions were carried out using a feed of concentrated liquid sulfuric acid (96wt%) at atmospheric pressure at temperatures between 800 and 850?C and a weight hour space

Daniel M. Ginosar; Lucia M. Petkovic; Anne W. Glenn; Kyle C. Burch

2007-01-01

82

40 CFR 76.3 - General Acid Rain Program provisions.  

Code of Federal Regulations, 2010 CFR

... 2009-07-01 false General Acid Rain Program provisions. 76.3 Section... AIR PROGRAMS (CONTINUED) ACID RAIN NITROGEN OXIDES EMISSION REDUCTION PROGRAM § 76.3 General Acid Rain Program provisions. The...

2009-07-01

83

40 CFR 76.3 - General Acid Rain Program provisions.  

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false General Acid Rain Program provisions. 76.3 Section... AIR PROGRAMS (CONTINUED) ACID RAIN NITROGEN OXIDES EMISSION REDUCTION PROGRAM § 76.3 General Acid Rain Program provisions. The...

2010-07-01

84

Preparation, characterization and catalytic activity of tin oxide-supported 12-tungstophosphoric acid as a solid catalyst  

Microsoft Academic Search

A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of 12-tungstophosphoric acid (TPA) on tin oxide. The prepared catalysts were characterized by thermal analysis, XRD, FT-IR and BET surface area. The acidity of the catalyst was measured by different techniques. The suitability of the materials was studied for acid-catalyzed esterification reaction using

Abd El Rahman S. Khder

2008-01-01

85

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

86

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.

2011-01-01

87

Transition metal sulfide hydrogen evolution catalysts for hydrobromic acid electrolysis.  

PubMed

Mixed metal sulfides containing combinations of W, Fe, Mo, Ni, and Ru were synthesized and screened for activity and stability for the hydrogen evolution reaction (HER) in aqueous hydrobromic acid (HBr). Co- and Ni-substituted RuS(2) were identified as potentially active HER electrocatalysts by high-throughput screening (HTS), and the specific compositions Co(0.4)Ru(0.6)S(2) and Ni(0.6)Ru(0.4)S(2) were identified by optimization. Hydrogen evolution activity of Co(0.4)Ru(0.6)S(2) in HBr is greater than RuS(2) or CoS(2) and comparable to Pt and commercial Rh(x)S(y). Structural and morphological characterizations of the Co-substituted RuS(2) suggest that the nanoparticulate solids are a homogeneous solid solution with a pyrite crystal structure. No phase separation is detected for Co substitutions below 30% by X-ray diffraction. In 0.5 M HBr electrolyte, the Co-Ru electrode material synthesized with 30% Co rapidly lost approximately 34% of the initial loading of Co; thereafter, it was observed to exhibit stable activity for HER with no further loss of Co. Density functional theory calculations indicate that the S(2)(2-) sites are the most important for HER and the presence of Co influences the S(2)(2-) sites such that the hydrogen binding energy at sufficiently high hydrogen coverage is decreased compared to ruthenium sulfide. Although showing high HER activity in a flow cell, the reverse reaction of hydrogen oxidation is slow on the RuS(2) catalysts tested when compared to platinum and rhodium sulfide, leaving rhodium sulfide as the only suitable tested material for a regenerative HBr cell due its stability compared to platinum. PMID:23205859

Ivanovskaya, Anna; Singh, Nirala; Liu, Ru-Fen; Kreutzer, Haley; Baltrusaitis, Jonas; Nguyen, Trung Van; Metiu, Horia; McFarland, Eric

2013-01-01

88

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

89

Hydrothermal preparation and characterization of novel corncob-derived solid Acid catalysts.  

PubMed

Novel corncob-derived solid acid catalysts were successfully synthesized for the first time by the hydrothermal method. The influences of different preparation conditions were investigated, and the structure-function relationships of the resulting catalysts were also discussed on the basis of the analysis of structure and composition. In comparison to conventional solid acid catalysts, the corncob-derived catalyst synthesized under optimized conditions exhibited higher catalytic activity in esterification reactions, yielding nearly 90% methyl oleate in only 2 h. The catalyst retained satisfactory catalytic activity for esterification, even after 8 reaction cycles. Solid-state magic angle spinning (MAS) (13)C nuclear magnetic resonance (NMR) investigations further indicated that the catalyst was composed of polycyclic aromatic carbon sheets bearing -SO3H, -COOH, and -OH groups in adequate amounts and with proper proportions, contributing to its excellent catalytic activity. This work provides a green method to synthesize solid acid catalysts from biomass wastes and may contribute to a holistic approach for biomass conversion. PMID:24820344

Ma, Huan; Li, Jiabao; Liu, Weiwei; Cheng, Beijiu; Cao, Xiaoyan; Mao, Jingdong; Zhu, Suwen

2014-06-11

90

Solid catalysts for multistep reactions: one-pot synthesis of 2,3-dihydro-1,5-benzothiazepines with solid acid and base catalysts.  

PubMed

1,5-Benzothiazepines derivatives were obtained first by starting from 1,3-diphenylpropenone derivatives (chalcones) and 2-aminothiophenol by using aluminosilicate solid catalysts. However, diffusional limitations and the strong adsorption of products on the catalyst are deleterious for catalyst activity and life. Then a structured amorphous mesoporous catalyst with large pores and mild acidity that works at higher temperatures allowed us to obtain high conversions (99 %) and selectivities (98 %) of the desired product. A one-pot synthesis of 1,5-benzothiazepines that starts from benzaldehyde, acetophenone, and 2-aminothiophenol with 95 % yield was performed by combining optimized solid base and acid catalysts in batch mode as well as in a continuous-flow reactor system. Much better conversion and selectivity as well as process intensification has been achieved with the structured mesoporous materials by avoiding intermediate and final neutralization and purification steps required in the synthesis reported previously that uses homogeneous catalysts. PMID:24616280

Climent, Maria J; Corma, Avelino; Iborra, Sara; Martí, Laura

2014-04-01

91

Chemical rescue, multiple ionizable groups, and general acid-base catalysis in the HDV genomic ribozyme.  

PubMed

In the ribozyme from the hepatitis delta virus (HDV) genomic strand RNA, a cytosine side chain is proposed to facilitate proton transfer in the transition state of the reaction and, thus, act as a general acid-base catalyst. Mutation of this active-site cytosine (C75) reduced RNA cleavage rates by as much as one million-fold, but addition of exogenous cytosine and certain nucleobase or imidazole analogs can partially rescue activity in these mutants. However, pH-rate profiles for the rescued reactions were bell shaped, and only one leg of the pH-rate curve could be attributed to ionization of the exogenous nucleobase or buffer. When a second potential ionizable nucleobase (C41) was removed, one leg of the bell-shaped curve was eliminated in the chemical-rescue reaction. With this construct, the apparent pK(a) determined from the pH-rate profile correlated with the solution pK(a) of the buffer, and the contribution of the buffer to the rate enhancement could be directly evaluated in a free-energy or Brønsted plot. The free-energy relationship between the acid dissociation constant of the buffer and the rate constant for cleavage (Brønsted value, beta, = approximately 0.5) was consistent with a mechanism in which the buffer acted as a general acid-base catalyst. These data support the hypothesis that cytosine 75, in the intact ribozyme, acts as a general acid-base catalyst. PMID:16690998

Perrotta, Anne T; Wadkins, Timothy S; Been, Michael D

2006-07-01

92

[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

93

Influence of solid acid catalyst on DME production directly from synthesis gas over the admixed catalyst of Cu\\/ZnO\\/Al 2O 3 and various SAPO catalysts  

Microsoft Academic Search

This study focused on the effect of solid acid catalyst on the catalytic performance in direct DME synthesis. The various SAPO catalysts were prepared to perform methanol dehydration and direct DME synthesis. In methanol dehydration, SAPO-34 and -18 with strong acid sites and showed high initial activity, but deactivated rapidly. This is mainly attributed to the formation of coking materials

Kye Sang Yoo; Ji-Hyun Kim; Min-Jo Park; Sun-Jin Kim; Oh-Shim Joo; Kwang-Deog Jung

2007-01-01

94

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

95

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) [Cambridge, MA; Lahr, David L. (Cambridge, MA) [Cambridge, MA

2010-11-09

96

MCF-supported boronic acids as efficient catalysts for direct amide condensation of carboxylic acids and amines.  

PubMed

For efficient direct amide condensations, a new class of catalysts are developed by immobilizing boronic acids on mesocellular siliceous foam. Associated with their large pores, the microenvironments surrounding the immobilized active species greatly influence the catalytic activity. The fluoroalkyl moieties on the silica surface significantly enhance the catalytic performance along with easy recovery and reuse. This approach proposes a potential way to optimize various types of silica-supported catalysts. PMID:24848459

Gu, Liuqun; Lim, Jaehong; Cheong, Jian Liang; Lee, Su Seong

2014-07-01

97

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

Microsoft Academic Search

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

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

1998-01-01

98

Zirconium phosphonates layered structure catalysts with organic acid pendants 2. Catalytic properties  

Microsoft Academic Search

Catalytic properties of Zirconium phosphonates layered structure (ZPLS) catalysts with organic sulfonic acid pendant groups\\u000a have been studied. The NaOH titration demonstrated the presence of sulfonic acid groups. The ZPLS contained acid sites per\\u000a weight similar to or slightly less than those for cation exchanged resins. The hydrolysis of ethyl acetate and the esterification\\u000a of acetic acid with ethanol were

Chang Mo Nam; Young Gul Kim; Jae Sung Lee

1995-01-01

99

Kinetic study of the esterification of free fatty acids in non-edible Pongamia pinnata oil using acid catalyst  

Microsoft Academic Search

Pre treatment of high free fatty acid containing Pongamia pinnata oil using sulfuric acid catalyst has been optimized. The kinetics of the pre treatment esterification process was studied. The experimental results were found to fit a Pseudo first-order kinetics. The influence of temperature on the rate constants was determined by fitting the results to the Arrhenius equation. The activation energy

J. Nandagopal; V. Sathya; Selva Bala; S. Dinesh Kirupha; P. Vijayalakshmi; S. Sivanesan

2009-01-01

100

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

101

Development of heterogeneous catalysts for the conversion of levulinic acid to ?-valerolactone.  

PubMed

?-Valerolactone (GVL) has been identified as a potential intermediate for the production of fuels and chemicals based on renewable feedstocks. Numerous heterogeneous catalysts have been used for GVL production, alongside a range of reaction setups. This Minireview seeks to outline the development of heterogeneous catalysts for the targeted conversion of levulinic acid (LA) to GVL. Emphasis has been placed on discussing specific systems, including heterogeneous noble and base metal catalysts, transfer hydrogenation, and application of scCO? as reaction medium, with the aim of critically highlighting both the achievements and remaining challenges associated with this field. PMID:22890968

Wright, William R H; Palkovits, Regina

2012-09-01

102

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

103

Esterification reaction using solid heterogeneous acid catalysts under solvent-less condition  

Microsoft Academic Search

The preparation of di-2-ethylhexylphthalate (DOP) via esterification reaction of phthalic anhydride by 2-ethylhexanol in the presence of solid acidic catalysts has been investigated. The used catalysts were natural zeolite, synthetic zeolites (ZEOKAR-2, ASHNCH-3), heteropolyacid H4Si(W3O10)4 and sulfated ZrO2. The reactions were carried out under solvent-less conditions. It was observed that sulfated ZrO2 has higher reactivity and efficiency among the investigated

Firdovsi Tataroglu Sejidov; Yagoub Mansoori; Nadereh Goodarzi

2005-01-01

104

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

105

Phosphotungstic acid supported on magnetic nanoparticles as an efficient reusable catalyst for epoxidation of alkenes  

SciTech Connect

Highlights: ? Phosphotungstic acid supported on functionalized cobalt ferrite was prepared. ? Silica coated cobalt ferrite nanoparticles were used as support. ? This composite was successfully used as catalyst for epoxidation of alkenes. ? Oxidation reactions were carried out in the presence of t-BuOOH as oxidant. ? The catalyst can be readily separated from solution by magnetic field. -- Abstract: A new magnetically separable catalyst consisting of phosphotungstic acid supported on imidazole functionalized silica coated cobalt ferrite nanoparticles was prepared. The synthesized catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). This immobilized phosphotungstic acid was shown to be an efficient heterogeneous catalyst for the epoxidation of various alkenes using tert-butylhydroperoxide (t-BuOOH) as oxidant. The catalyst is readily recovered by simple magnetic decantation and can be recycled several times with no significant loss of catalytic activity.

Kooti, M., E-mail: m_kooti@scu.ac.ir [Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz 61357- 43169 (Iran, Islamic Republic of); Afshari, M. [Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz 61357- 43169 (Iran, Islamic Republic of)] [Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz 61357- 43169 (Iran, Islamic Republic of)

2012-11-15

106

Effect of calcination temperature of Ni\\/?-Al2O3 catalyst on the steam reforming of acetic acid  

Microsoft Academic Search

Ni\\/?-Al2O3-550 and Ni\\/?-Al2O3-800 catalysts (calcined at 550°C and 800°C in the catalyst preparation) were prepared with a impregnation method. Steam reforming of acetic acid as a model compound of bio-oil for hydrogen production had been investigated on the catalysts. The fresh catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR-H2) and specific surface area analysis (BET). The spent

Lu An; Changqing Dong; Junjiao Zhang; Yongping Yang

2009-01-01

107

Development of a kinetic model for the esterification of acetic acid with methanol in the presence of a homogeneous acid catalyst  

Microsoft Academic Search

The esterification kinetics of acetic acid with methanol in the presence of hydrogen iodide as a homogeneous acid catalyst was studied with isothermal batch experiments at 30–60°C. The catalyst concentration was varied between 0.05 and 10.0 wt%. The experiments revealed that besides the main reaction, the esterification of acetic acid, a side reaction appeared: the catalyst, hydrogen iodide, was esterified

Robert Rönnback; Tapio Salmi; Antti Vuori; Heikki Haario; Juha Lehtonen; Anna Sundqvist; Esko Tirronen

1997-01-01

108

Evaluating acid and base catalysts in the methylation of milk and rumen fatty acids with special emphasis on conjugated dienes and total trans fatty acids  

Microsoft Academic Search

Milk analysis is receiving increased attention. Milk contains conjugated octadecadienoic acids (18?2) purported to be anticarcinogenic,\\u000a low levels of essential fatty acids, and trans fatty acids that increase when essential fatty acids are increased in dairy rations. Milk and rumen fatty acid methyl esters\\u000a (FAME) were prepared using several acid-(HCl, BF3, acetyl chloride, H2SO4) or base-catalysts (NaOCH3, tetramethylguanidine, diazomethane), or

John K. G. Kramer; Vivek Fellner; Michael E. R. Dugan; Frank D. Sauer; Magdi M. Mossoba; Martin P. Yurawecz

1997-01-01

109

General acid catalysis of monochloramine disproportionation  

SciTech Connect

A fundamental understanding of chloramine chemistry is important in the control of water and waste water disinfection, biofouling in power plants, and in assessing the fate of chlorinated effluents discharged into the environment. This paper presents experimental results showing that monochloramine disproportionation, which results in the formation of dichloramine, involves a general acid catalyzed reaction pathway. Rate constants characterizing the effect of hydrogen ion, phosphate, and sulfate were determined by measuring the rate of monochloramine disappearance under pH conditions, which simplified interpretation of results. These rates constants were used to develop a linear free energy relationship that was used to predict the effect of carbonate and silicate. Predictions indicate that carbonate, and possibly silicate, may significantly increase the rate of acid-catalyzed disproportionation at concentrations and pH values typical of many drinking waters. Since this reaction may govern the overall rate of oxidant loss, appropriate consideration must be given to the presence of potential proton donors when predictions relating to chloramine speciation and fate are made on the basis of reaction models or when the results of studies with chloramine solutions are evaluated.

Valentine, R.L.; Jafvert, C.T.

1988-06-01

110

Comparison of acidic and alkaline catalysts for preparation of fatty acid methyl esters from ovine muscle with emphasis on conjugated linoleic acid  

Microsoft Academic Search

Methanolic reagents containing acidic catalysts, HCl (0.5 M, 1 h, 80° C) or BF3 (14%, 1 h, 80° C), or alkaline catalysts, KOH (0.2 M, 15–60 min, 50° C) or NaOCH3 (0.5 M, 15–60 min, 50° C), were compared for use in preparation of fatty acid methyl esters for GC analysis of total lipids from freeze-dried semitendinosus muscle of lambs

C. M. Murrieta; B. W. Hess; D. C. Rule

2003-01-01

111

Organo-niobate Ionic Liquids: Synthesis, Characterization and Application as Acid Catalyst in Pechmann Reactions  

PubMed Central

The combinations of 1-butyl-3-methylimidazolium chloride with NbCl5 yielded ionic mixtures with different melting point temperatures and acidity depending on the niobium molar fraction. The mixtures were characterized by thermal (DSC) and spectroscopic (FT-IR and 1H NMR) analysis. The Pechmann reactions of different phenols with ethylacetoacetate, producing coumarins, was used as model to evaluate the catalytic behavior of these mixtures as acid Lewis catalyst. These reactions were carried out using acidic mixtures of 60 mol%.

Soares, Valerio C. D.; Alves, Melquizedeque B.; Souza, Ernesto R.; Pinto, Ivana O.; Rubim, Joel C.; Andrade, Carlos Kleber Z.; Suarez, Paulo A. Z.

2007-01-01

112

Application of a supported iron oxyhydroxide catalyst in oxidation of benzoic acid by hydrogen peroxide  

Microsoft Academic Search

Oxidation of benzoic acid was studied via Fenton-like reaction using an innovative supported ?-FeOOH catalyst. The decomposition kinetics of hydrogen peroxide was investigated first. Oxidation of benzoic acid by hydrogen peroxide was performed to understand the effects of initial pH and hydrogen peroxide dosage. The treatment efficiency of benzoic acid at an initial pH of 3.2 was higher than at

Shanshan Chou; Chihpin Huang

1999-01-01

113

Preparation of mesoporous polyoxometalate–tantalum pentoxide composite catalyst for efficient esterification of fatty acid  

Microsoft Academic Search

Mesoporous polyoxometalate–tantalum pentoxide composite catalyst, H3PW12O40\\/Ta2O5, was prepared by a one-step sol–gel-hydrothermal method in the presence of triblock copolymer surfactant. Structure, morphology and surface textural property of the composite were characterized. As-prepared H3PW12O40\\/Ta2O5 was applied as a solid acid catalyst for esterification reaction of lauric acid with ethanol, an important pretreatment step in the production of biodiesel from renewable feedstocks.

Leilei Xu; Xia Yang; Xiaodan Yu; Yihang Guo; Maynurkader

2008-01-01

114

Effect of carbon material on Pd catalyst for formic acid electrooxidation reaction  

NASA Astrophysics Data System (ADS)

Effect of several usually used carbon materials on Pd catalyst for formic acid electrooxidation reaction is studied by physical characterization and electrochemical measurements. New active sites are formed due to the Pd and carbon interaction which is confirmed by the XPS measurements, and electrochemical impedance spectroscopy confirms that the presence of the carbon material reduced the charge transfer resistance. Further, an improved fuel cell performance is observed when integrating the carbon-modified Pd catalyst in to a direct formic acid fuel cell. The results reveal that the carbon material is not only used as support, but also involves the new active sites formation.

Chang, Jinfa; Li, Songtao; Feng, Ligang; Qin, Xiujuan; Shao, Guangjie

2014-11-01

115

A designed organic–zeolite hybrid acid–base catalyst  

Microsoft Academic Search

An organic–zeolite hybrid catalyst was synthesised via solid-state impregnation of the zeolite with an amount of melamine corresponding to 20mol% of the aluminium content. A high density of basic sites is formed in the zeolite. From infrared spectroscopy and TGA measurements we infer that melaminium cations are formed in the zeolite which are highly thermally stable. IR spectroscopic and TGA

Andrew C. Brooks; Liam France; Cecile Gayot; Jerry Pui Ho Li; Ryan Sault; Andrew Stafford; John D. Wallis; Michael Stockenhuber

116

The roles of BrØnsted and Lewis surface acid sites in acid-treated montmorillonite supported ZnCl 2 alkylation catalysts  

Microsoft Academic Search

The catalyst known as “clayzic” (ZnCl2 supported on acid-treated montmorillonite) exhibits both BrØnsted and Lewis surface acidities. The relative catalytic activities of these two types of acid site have been determined in a range of reactions, by comparing the activities of clayzic with those of related catalysts which exhibit only one type of surface acidity. Acid-treated montmorillonite has been used

J. Massam; D. R. Brown

1995-01-01

117

Liquid phase nitration of benzene over supported ammonium salt of 12-molybdophosphoric acid catalysts prepared by sol-gel method.  

PubMed

A mild and clean liquid nitration of benzene with 65% nitric acid as nitrating agent over silica supported ammonium salt of 12-molybdophosphoric acid catalysts has been investigated. These catalysts with different loadings were prepared by sol-gel method and characterized by X-ray diffraction (XRD) and FTIR spectra. The acidity of these catalysts was measured by the potentiometric titration method. The XRD and IR analysis revealed that supported catalysts possess the Keggin structure which is similar to 12-molybdophosphoric acid. And it can be found that the supported catalysts had high nitration reaction catalytic activity and selectivity over nitrobenzene. The effects of various parameters such as nitric acid/benzene volume ratio, temperature and time of reaction have also been systematically studied. PMID:20185228

Gong, Shuwen; Liu, Lijun; Cui, Qingxin; Ding, Junhong

2010-06-15

118

Electrode catalyst  

SciTech Connect

An electrode catalyst for a fuel cell comprising at least one boride of molybdenum is disclosed. The electrode catalyst is far more excellent than conventional catalysts such as platinum black in that the resistance to acids is very high, that the polarization is little, that the price is low, etc. It is particularly suitable as an electrode catalyst for a fuel cell employing an acidic electrolyte.

Kudo, T.; Obayashi, H.

1980-12-30

119

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

120

Catalytic conversion of cellulose to 5-hydroxymethyl furfural using acidic ionic liquids and co-catalyst.  

PubMed

Efficient catalytic conversion of microcrystalline cellulose (MCC) to 5-hydroxymethyl furfural (HMF), is achieved using acidic ionic liquids (ILs) as the catalysts and metal salts as co-catalysts in the solvent of 1-ethyl-3-methylimidazo-lium acetate ([emim][Ac]). A series of acidic ILs has been synthesized and tested in conversion of MCC to HMF. The effect of reaction conditions, such as reaction time, temperature, catalyst dosage, metal salts, water dosage, Cu(2+) concentration and various acidic ILs are investigated in detail. The results show that CuCl(2) in 1-(4-sulfonic acid) butyl-3-methylimidazolium methyl sulfate ([C(4)SO(3)Hmim][CH(3)SO(3)]), is found to be an efficient catalyst for catalytic conversion of MCC to HMF, and 69.7% yield of HMF is obtained. A mechanism to explain the high activity of CuCl(2) in [C(4)SO(3)Hmim][CH(3)SO(3)] is proposed. To the best of our knowledge, this report first proposes that the Cu(2+) and [C(4)SO(3)Hmim][CH(3)SO(3)] show better catalytic performance in catalytic conversion of MCC to HMF. PMID:22840003

Ding, Zhen-Dong; Shi, Jin-Cai; Xiao, Jing-Jing; Gu, Wen-Xiu; Zheng, Chang-Ge; Wang, Hai-Jun

2012-10-01

121

Improved hydrogen production from formic acid on a Pd/C catalyst doped by potassium.  

PubMed

The rate of hydrogen production from vapour-phase formic acid decomposition can be increased by 1-2 orders of magnitude by doping a Pd/C catalyst with potassium ions. Surface potassium formate and/or bicarbonate species could be involved in the rate-determining step of this reaction. PMID:22447125

Bulushev, Dmitri A; Jia, Lijun; Beloshapkin, Sergey; Ross, Julian R H

2012-05-01

122

[Catalytic ozonation of oxalic acid in water with Pt/graphite catalyst].  

PubMed

Pt/graphite catalyst was prepared by incipient wetness impregnation using H2PtCl6 x 6H2O as precursor substance. The removal efficiencies of oxalic acid by Pt/graphite, graphite catalyzed ozonation and ozonation alone were compared. It was found that the removal efficiency of oxalic acid in ozonation alone, graphite and Pt/graphite catalyzed ozonation was 3.0%, 47.6% and 99.3% respectively under the present experimental conditions. Results showed that loading of Pt could significantly increase the catalytic activity of graphite. Taking oxalic acid degradation efficiency as indication, the preparation conditions of Pt/graphite were optimized. The pretreatment of graphite had no favor to improve the activity of Pt/graphite catalyst. The optimal preparation conditions of Pt/graphite catalyst are as follow: impregnant, distilled water; impregnation time, 24 h; the loading amount of Pt, 1.0%; reduction temperature, 35 degrees C. The Pt/graphite catalyst was used for five times with no significant decrease of its activity and more than 90% oxalic acid removal was obtained. PMID:17674732

Liu, Zheng-Qian; Ma, Jun; Zhao, Lei

2007-06-01

123

Oxidizing of ferulic acid with the use of polyoxometalates as catalysts  

NASA Astrophysics Data System (ADS)

The kinetics of catalytic oxidation for ferulic acid with polyoxometalates used as catalysts was studied. The effect of pH and concentrations of the principal reacting components on the process kinetics was studied. A kinetic scheme of oxidation is proposed, and the values of a number of kinetic parameters of the process are determined.

Povarnitsyna, T. V.; Popova, N. R.; Bogolitsyn, K. G.; Beloglazova, A. L.; Pryakhin, A. N.; Lunin, V. V.

2010-12-01

124

The behavior of palladium catalysts in direct formic acid fuel cells  

NASA Astrophysics Data System (ADS)

Previous work has considered the behavior of platinum based catalysts in direct methanol and Direct Formic Acid Fuel Cells (DFAFCs). In this paper, we explore the behavior of palladium-based anode catalyst for DFAFCs. The palladium catalysts produce significant performance enhancements. DFAFCs operated with dry air and zero back-pressure can generate power densities of 255˜230 mW cm -2 at relatively high voltages of 0.40˜0.50 V in a concentration range of formic acid from 3.0 to 15.0 M at a room temperature of 20 °C, which are not quite different from a hydrogen-air polymer exchange membrane (PEM) fuel cell with power density of 320 mW cm -2 obtained under the comparable conditions, and much higher than a direct methanol fuel cell (DMFC) with power density of 50 mW cm -2. The stability of the membrane electrode assembly (MEA) with palladium catalyst has also been evaluated. There is some decay in performance over several hours. However, the performance loss of DFAFCs can be fully recovered by applying a positive potential at the fuel cell anode after short-term life test. These results demonstrate that DFAFCs with palladium anode catalyst have exceptional properties for portable power applications.

Zhu, Yimin; Khan, Zakia; Masel, R. I.

125

Esterification of free fatty acids using water-tolerable Amberlyst as a heterogeneous catalyst  

Microsoft Academic Search

To produce biodiesel from high free fatty acid (FFA) oils, the esterification characteristics of two kinds of heterogeneous acid catalysts, Amberlyst 15 and Amberlyst BD20, were compared. When the FFA contents of oils were 50.0 and 99.8wt%, the activity of Amberlyst 15 gradually decreased with recycling, whereas the activity of Amberlyst BD20 was maintained during recycling. The activity of Amberlyst

Ji-Yeon Park; Deog-Keun Kim; Jin-Suk Lee

2010-01-01

126

Esterification of maleic acid with ethanol over cation-exchange resin catalysts  

Microsoft Academic Search

Diethyl maleate is an important intermediate extensively used in the production of latex emulsion polymers, thermoplast and thermoset plastics. The current paper delineates the efficacy of several heterogeneous catalysts, such as Indion-170, Amberlyst-36, Amberlyst-15, Amberlite IRA 120, 20% DTP\\/K-10 (dodecatungstophosphoric acid supported on K-10 clay) in the esterification of maleic acid with ethanol at reflux. Amongst these Indion-170, Amberlyst-36, Amberlyst-15

G. D. Yadav; M. B Thathagar

2002-01-01

127

Support effect in hydrotreating catalysts: hydrogenation properties of molybdenum sulfide supported on ?-zeolites of various acidities  

Microsoft Academic Search

In order to better understand the role of the acidity of the support on the hydrogenation properties of a molybdenum sulfide phase, a ?-zeolite with a nominal Si\\/Al = 13.8 was partially (Si\\/Al = 15.0 and 18.7) and fully dealuminated (Si\\/Al ?800, no Brönsted acidity). To achieve a reasonable Mo loading with a high Mo dispersion, the Mo\\/? catalysts were prepared by

Claude-Emmanuel Hédoire; Catherine Louis; Anne Davidson; Michèle Breysse; Françoise Maugé; Michel Vrinat

2003-01-01

128

Long chain cellulose esters with very low DS obtained with non-acidic catalysts  

Microsoft Academic Search

Long-chain cellulose esters with very low degree of substitution (DS<0.3), useful for specialty applications, were obtained\\u000a by reaction with fatty acids (FAs) without solvent for cellulose. Non-acidic catalysts such as FA salts were used to limit\\u000a the cellulose degradation when subjected to reaction at high temperatures. The surfactant character of this type of molecules\\u000a was employed to create an emulsion

J. Peydecastaing; S. Girardeau; C. Vaca-Garcia; M. E. Borredon

2006-01-01

129

Preparation of ruthenium supported catalysts for wet air oxidation of p-hydroxybenzoic acid  

Microsoft Academic Search

Ru\\/TiO2 and Ru\\/ZrO2 catalysts were prepared by incipient-wetness method of sol-gel supports. They were characterized by means of nitrogen adsorption-desorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Catalytic properties of the samples were determined in the wet air oxidation of p-hydroxybenzoic acid chosen as a model compound of olive oil wastewaters. The effect of the acid used for the

Mohamed Triki; Doan Pham Minh; Zouhaier Ksibi; Abdelhamid Ghorbel; Pierre Gallezot; Michèle Besson

2006-01-01

130

Deactivation of carbon supported palladium catalyst in direct formic acid fuel cell  

NASA Astrophysics Data System (ADS)

A new carbon black supported palladium catalyst for direct formic acid fuel cell applications has been prepared and characterized by X-ray diffraction. Bi-modal distribution of Pd crystallite sizes was observed. The average Pd size for crystallites in small size and large size ranges were about 2.7 nm and 11.2 nm, respectively. The initial activity of the catalyst in the oxidation of formic acid tested in a fuel cell was similar to a commercial well dispersed 20 wt.% Pd/Vulcan. The rates of the fuel cell power decay were measured for formic acid of two purities for various current loadings. The results showed that various mechanisms contribute to the decrease of cell power with time. In direct formic acid fuel cell (DFAFC) fed with a very pure HCOOH accumulation of CO 2 gas bubbles in anode catalyst layer is responsible for observed power decay. In DFAFC fed with a pure for analysis (p.a.) grade formic acid the formation of CO ads poison from the formic acid impurities is the main deactivation reason.

Miko?ajczuk, A.; Borodzinski, A.; Kedzierzawski, P.; Stobinski, L.; Mierzwa, B.; Dziura, R.

2011-07-01

131

Chemical mechanism of hydrocarbon cracking over solid acidic catalysts  

SciTech Connect

The article analyzes cracking reactions of isoalkanes and isoolefins over zeolite-based catalysts and discusses formation mechanisms of light reaction products under very mild conditions, at 150-250{degrees}C. Cracking patterns of 28 methyl- and ethyl-branched isoalkanes show that the compositions of light products can be described by an empirical rule: (1) the reaction site is formed at the tertiary carbon atom in an isoalkane molecule, (2) the predominant fission reaction involves the weakest C-C bond in the {alpha}-position to the reaction site, (3) the primary fission products are olefins. None of the cracking mechanisms described in the literature and involving reactions of carbonium and carbonium ions can adequately predict the observed product structures. A new cracking mechanism of isoalkanes which includes reactions between isoalkanes and Bronsted centers on the catalyst surface with the formation of transient hydrosiloxonium ions > Si-O{sup +} (H)-C< is proposed. The ions undergo the scission of the C-C bond in their alkyl groups in the {beta}-position of O{sup +} with the formation of olefin molecules (which rapidly isomerize) and smaller hydrosiloxonium ions. Comparison of cracked products from olefins and alkanes with the same skeletons and the same expected carbocations shows that the respective products are drastically different when they are formed under very mild conditions, i.e., that the cracking mechanisms of olefins and alkanes are also different. Studies of olefins with low oligomerization abilities (to prevent scrambling of the product structures) show that the olefin cracking can indeed be explained by fragmentation of carbenium ions via the {beta}-C-C bond scission mechanism. 40 refs., 2 figs., 12 tabs.

Kissin, Y.V. [Gulf Research and Development Co., Pittsburgh, PA (United States)] [Gulf Research and Development Co., Pittsburgh, PA (United States)

1996-09-15

132

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

133

Mechanism of hydrodenitrogenation (Part 4) infrared spectroscopy of acidic molybdena catalysts  

SciTech Connect

Mo oxide catalysts supported over a complete series of silica-aluminas have been characterized in the oxidic and reduced states, by means of total acidity measurements and by infrared spectroscopy. Ammonia chemisorption was used to titrate the total acidity of the catalysts, and IR absorption of adsorbed pyridine to distinguish Bronsted from Lewis acid sites. The formation of new acidity upon deposition of molybdena on silica-alumina supports was then explained on the basis of a simple surface model. The new acidity is of both Lewis and Bronsted type, the preponderance of one over the other depending on support composition, as well as loading and state of oxidation of Mo. High-alumina supports and low Mo loading favor dispersed Mo species, in particular bidentate and monodentate di-oxo Mo species. The latter is responsible for the new Bronsted acidity. Coordinative unsaturation of polymolybdates is responsible for the new Lewis acidity, which is increased upon reduction of Mo. High-silica supports favor monodentate species (high Bronsted acidity) up to 4 wt % MoO{sub 3}. Beyond that, polymolybdates species and Lewis acidity predominate. 7 refs., 4 figs.

Miranda, R.

1990-01-01

134

Biodiesel production in a membrane reactor using MCM-41 supported solid acid catalyst.  

PubMed

Production of biodiesel from the transesterification between soybean oil and methanol was conducted in this study by a membrane reactor, in which ceramic membrane was packed with MCM-41 supported p-toluenesulfonic acid (PTSA). Box-Behnken design and response surface methodology (RSM) were used to investigate the effects of reaction temperature, catalyst amount and circulation velocity on the yield of biodiesel. A reduced cubic model was developed to navigate the design space. Reaction temperature was found to have most significant effect on the biodiesel yield while the interaction of catalyst amount and circulation velocity have minor effect on it. 80°C of reaction temperature, 0.27 g/cm(3) of catalyst amount and 4.15 mL/min of circulation velocity were proved to be the optimum conditions to achieve the highest biodiesel yield. PMID:24657760

Xu, Wei; Gao, Lijing; Wang, Songcheng; Xiao, Guomin

2014-05-01

135

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

NASA Astrophysics Data System (ADS)

The feasibility of adapting phosphoric acid fuel cells to operate on coal gas fuels containing significant levels of contaminants such as CO, H2S and COS was investigated. The overall goal was the development of low-cost, carbon-supported anode fuel cell catalysts that can efficiently operate with a fossil fuel-derived hydrogen gas feed contaminated with carbon monoxide and other impurities. This development would reduce the cost of gas cleanup necessary in a coal gas-fueled PAFC power plant, thereby reducing the final power cost of the electricity produced. The problem to date was that the contaminant gases typically adsorb on catalytic sites and reduce the activity for hydrogen oxidation. An advanced approach investigated was to modify these alloy catalyst systems to operate efficiently on coal gas containing higher levels of contaminants by increasing the alloy catalyst impurity tolerance and ability to extract energy from the CO present through (1) generation of additional hydrogen by promoting the CO/H2 water shift reaction or (2) direct oxidation of CO to CO2 with the same result. For operation on anode gases containing high levels of CO, a Pt-Ti-Zn and Pt-Ti-Ni anode catalyst showed better performance over a Pt baseline or G87A-17-2 catalyst. The ultimate aim was to allow PAFC-based power plants to operate on coal gas fuels containing increased contaminant concentrations, thereby decreasing the need for and cost of rigorous coal gas cleanup procedures.

Kackley, N. D.; McCatty, S. A.; Kosek, J. A.

1990-07-01

136

Efficiencies of acid catalysts in the hydrolysis of lignocellulosic biomass over a range of combined severity factors  

Microsoft Academic Search

Dicarboxylic organic acids have properties that differ from those of sulfuric acid during hydrolysis of lignocellulose. To investigate the effects of different acid catalysts on the hydrolysis and degradation of biomass compounds over a range of thermochemical pretreatments, maleic, oxalic and sulfuric acids were each used at the same combined severity factor (CSF) values during hydrolysis. Xylose and glucose concentrations

Jae-Won Lee; Thomas W. Jeffries

2011-01-01

137

Zr mesoporous molecular sieves as novel solid acid catalysts in synthesizing nitrile and caprolactam.  

PubMed

Zr mesoporous materials with different Si/Zr ratio were synthesized by the surfactant-templated method involving cetyl trimethyl ammonium bromide (CTAB) as template and tetraethyl ortho silicate (TEOS) as organic source of silicon. The synthesized materials were labeled as SiZrMx (where x is Si/Zr = 10, 20 and 30). The BET analysis showed bimodal distribution of pores in SiZrMx structure. An attempt was made to generate super acidity on SiZrM20 by sulfation using sulfuric acid and ammonium sulfate (wt% = 4, 8 and 12). The NH3-TPD results revealed the presence of strong acidity in sulfated Zr-MCM-41. To understand the nature of acidity in Sulfated Zr-MCM-41, the efficiency of the materials is investigated in dehydration of Oximes. The industrially important materials caprolactam and intermediate nitrile were synthesized from their oximes in liquid phase system. Due to strong acidity in sulfated Zr-MCM-41, fast deactivation was observed during the synthesis of caprolactam but, the catalyst showed 96% nitrile selectivity. The strong acidity and medium strong acidity favoured the formation of nitrile and caprolactam respectively. This study revealed the molecular sieves were effective and eco-friendly solid acid catalysts for synthesizing caprolactam and nitrile. PMID:24734693

Nedumaran, D; Pandurangan, A

2014-04-01

138

Solid acid catalysts from clays: preparation of mesoporous catalysts by chemical activation of metakaolin under acid conditions.  

PubMed

Natural kaolin was treated at 850 or 950 degrees C in air flow to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90 degrees C with a 1 M solution of H(2)SO(4), for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to the high density of acid sites, while MK9 gave an ordered mesoporous material with a low density of acid sites. The materials were characterized by several techniques, X-ray powder diffraction, thermogravimetric analysis, N(2) physisorption, scanning electron microscopy, and temperature-programmed desorption of ammonia. The 1-butene isomerization was used as test reaction to evaluate the acidity of the samples. PMID:17451736

Lenarda, M; Storaro, L; Talon, A; Moretti, E; Riello, P

2007-07-15

139

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

140

Hydrogenation of succinic acid to 1,4-butanediol over rhenium catalyst supported on copper-containing mesoporous carbon.  

PubMed

Copper-containing mesoporous carbon (Cu-MC) was prepared by a single-step surfactant-templating method. For comparison, copper-impregnated mesoporous carbon (Cu/MC) was also prepared by a surfactant-templating method and a subsequent impregnation method. Rhenium catalysts supported on copper-containing mesoporous carbon and copper-impregnated mesoporous carbon (Re/Cu-MC and Re/Cu/MC, respectively) were then prepared by an incipient wetness method, and they were applied to the liquid-phase hydrogenation of succinic acid to 1,4-butanediol (BDO). It was observed that copper in the Re/Cu-MC catalyst was well incorporated into carbon framework, resulting in higher surface area and larger pore volume than those of Re/Cu/MC catalyst. Therefore, Re/Cu-MC catalyst showed higher copper dispersion than Re/Cu/MC catalyst, although both catalysts retained the same amounts of copper and rhenium. In the liquid-phase hydrogenation of succinic acid to BDO, Re/Cu-MC catalyst showed a better catalytic activity than Re/Cu/MC catalyst. Fine dispersion of copper in the Re/Cu-MC catalyst was responsible for its enhanced catalytic activity. PMID:24245272

Hong, Ung Gi; Park, Hai Woong; Lee, Joongwon; Hwang, Sunhwan; Kwak, Jimin; Yi, Jongheop; Song, In Kyu

2013-11-01

141

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.

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

2014-01-01

142

ZnCl 2Zn 2+Montmorillonite composite: efficient solid acid catalyst for benzylation of benzene  

Microsoft Academic Search

A newer type of metal salt–metal ion exchanged Montmorillonite (Mont), MCl2-Mn+-Mont (M=Ni, Cu, Zn; n=2) have been prepared and evaluated as solid acid catalysts for Friedel–Crafts reactions particularly for benzylation of benzene. The activity of such composites depends upon the amount of loading of metal salts on the metal ion exchanged-Mont support and 1.5mmol loading per mole of the support

Anjali Phukan; Jatindra Nath Ganguli; Dipak Kumar Dutta

2003-01-01

143

Synthesis of bis(2-ethylhexyl) phthalate over methane sulfonic acid catalyst. Kinetic investigations  

Microsoft Academic Search

The kinetic model for the synthesis of bis(2-ethylhexyl) phthalate from phthalic anhydride and 2-ethylhexanol in the presence\\u000a of methane sulfonic acid as a catalyst has been derived, based on the investigation carried out in an isothermal, semibatch\\u000a reactor. The first step, the formation of mono(2-ethylhexyl) phthalate, is very fast and irreversible. The second step, the\\u000a esterification of monoester with 2-ethylhexanol,

Jerzy Skrzypek; Maria Lachowska; Maria Kulawska; Henryk Moroz

2008-01-01

144

Influence of the carrier on steam reforming of acetic acid over Ru-based catalysts  

Microsoft Academic Search

The reaction of steam reforming of acetic acid (HAc), a model compound of pyrolysis-oil, over ruthenium catalysts supported on Al2O3 and MgO\\/Al2O3 carriers has been investigated employing transient and steady-state techniques. Main objective is the establishment of the reaction network over a wide temperature range and the elucidation of the role of MgO on intrinsic catalytic activity. It has been

Aristides C. Basagiannis; Xenophon E. Verykios

2008-01-01

145

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

146

Pt/TiO2 (Rutile) Catalysts for Sulfuric Acid Decomposition in Sulfur-Based Thermochemical Water-Splitting Cycles  

SciTech Connect

Thermochemical cycles consist of a series of chemical reactions to produce hydrogen from water at lower temperatures than by direct thermal decomposition. All the sulfur-based cycles for water splitting employ the sulfuric acid decomposition reaction. This work reports the studies performed on platinum supported on titania (rutile) catalysts to investigate the causes of catalyst deactivation under sulfuric acid decomposition reaction conditions. Samples of 1 wt% Pt/TiO2 (rutile) catalysts were submitted to flowing concentrated sulfuric acid at 1123 K and atmospheric pressure for different times on stream (TOS) between 0 and 548 h. Post-operation analyses of the spent catalyst samples showed that Pt oxidation and sintering occurred under reaction conditions and some Pt was lost by volatilization. Pt loss rate was higher at initial times but total loss appeared to be independent of the gaseous environment. Catalyst activity showed an initial decrease that lasted for about 66 h, followed by a slight recovery of activity between 66 and 102 h TOS, and a period of slower deactivation after 102 h TOS. Catalyst sulfation did not seem to be detrimental to catalyst activity and the activity profile suggested that a complex dynamical situation involving platinum sintering, volatilization, and oxidation, along with TiO2 morphological changes affected catalyst activity in a non-monotonic way.

L. M. Petkovic; D. M. Ginosar; H. W. Rollins; K. C. Burch; P. J. Pinhero; H. H. Farrell

2008-04-01

147

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.

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

2012-01-01

148

The influence of acidic and alkaline precursors on Pt Ru\\/C catalyst performance for a direct methanol fuel cell  

Microsoft Academic Search

This research aims to increase the activity of platinum–ruthenium alloy (PtRu\\/C) catalysts for methanol electrooxidation. The direct methanol fuel cell (DMFC) anodic PtRu\\/C catalysts were prepared from acidic and alkaline Pt(NH3)2(NO2)2 solutions as Pt precursors, respectively, and with the same acidic Ru compound but without Cl? ion as the Ru precursor by thermal reduction. The phase structures, lattice parameters, particle

Zhen-Bo Wang; Ge-Ping Yin; Peng-Fei Shi

2007-01-01

149

Activity and stability of pyrolyzed iron ethylenediaminetetraacetic acid as cathode catalyst in microbial fuel cells.  

PubMed

A low-cost and effective iron-chelated catalyst was developed as an electrocatalyst for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). The catalyst was prepared by pyrolyzing carbon mixed iron-chelated ethylenediaminetetraacetic acid (PFeEDTA/C) in an argon atmosphere. Cyclic voltammetry measurements showed that PFeEDTA/C had a high catalytic activity for ORR. The MFC with a PFeEDTA/C cathode produced a maximum power density of 1122 mW/m(2), which was close to that with a Pt/C cathode (1166 mW/m(2)). The PFeEDTA/C was stable during an operation period of 31 days. Based on X-ray diffraction and X-ray photoelectron spectroscopy measurements, quaternary-N modified with iron might be the active site for the oxygen reduction reaction. The total cost of a PFeEDTA/C catalyst was much lower than that of a Pt catalyst. Thus, PFeEDTA/C can be a good alternative to Pt in MFC practical applications. PMID:21324675

Wang, Li; Liang, Peng; Zhang, Jian; Huang, Xia

2011-04-01

150

Solid acid catalysts from clays: Preparation of mesoporous catalysts by chemical activation of metakaolin under acid conditions  

Microsoft Academic Search

Natural kaolin was treated at 850 or 950?°C in air flow to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90?°C with a 1 M solution of H2SO4, for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to

M. Lenarda; L. Storaro; A. Talon; E. Moretti; P. Riello

2007-01-01

151

Electrocatalytic performance of carbon supported Pd catalyst modified with Keggin type of Sn-substituted polyoxometalatate for formic acid oxidization  

NASA Astrophysics Data System (ADS)

The carbon supported Pd(Pd/C) catalyst modified by the new polyoxometalate with Keggin type of Sn-Substituted structure K7CoIIW11O39SnIVOH (Pd/C-K7) catalyst is prepared with the simple impregnation-reduction method. This work investigates the effects of Pd/C-K7 catalyst for direct formic acid fuel cells (DFAFCs). The morphology, structure, size and composition of the Pd/C-K7 catalyst are characterized by transmission electron microscopy (TEM) energy dispersive spectrum (EDS), X-ray diffraction (XRD). Cyclic voltammetry, chronoamperometry and CO-stripping voltammetry tests demonstrate the Pd/C-K7 catalyst have higher electrocatalytic activity, better electrochemical stability, and higher resistance to CO poisoning over the unmodified Pd/C catalyst for the formic acid oxidation reaction (FAOR) owing to K7CoIIW11O39SnIVOH with Keggin structure. Therefore, the Pd/C-K7 catalyst could be used as the excellent anodic catalyst in DFAFCs.

Ji, Yun; Shen, Liping; Wang, Anxing; Wu, Min; Tang, Yawen; Chen, Yu; Lu, Tianhong

152

Nano scale magnetically recoverable supported heteropoly acid as an efficient catalyst for the synthesis of benzimidazole derivatives in water.  

PubMed

12-Tungstophosphoric acid supported on silica-coated magnetic nano particles was prepared and characterized by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction and inductively coupled plasma atomic emission spectroscopy. Acidity of the catalysts was measured by potentiometric titration with n-butylamine. Catalytic activity of the prepared sample was evaluated in the model synthesis of 1,2-disubstituted benzimidazole derivatives in water. The catalyst showed excellent catalytic activity and the corresponding products were obtained in good to excellent yields under mild reaction conditions. Furthermore, the catalyst could be easily recovered using an external magnet and reused several times. The leaching and surface acidity of the recovered catalyst were also investigated. PMID:24664342

Rafiee, Ezzat; Rahpeima, Nasibeh; Eavani, Sara

2014-01-01

153

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

Microsoft Academic Search

Biodiesel could be synthesized using Brønsted acidic ionic liquid N-methyl-2-pyrrolidonium methyl sulfonate ([NMP][CH3SO3]) 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

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

2009-01-01

154

Esterification of free fatty acids using water-tolerable Amberlyst as a heterogeneous catalyst.  

PubMed

To produce biodiesel from high free fatty acid (FFA) oils, the esterification characteristics of two kinds of heterogeneous acid catalysts, Amberlyst 15 and Amberlyst BD20, were compared. When the FFA contents of oils were 50.0 and 99.8 wt%, the activity of Amberlyst 15 gradually decreased with recycling, whereas the activity of Amberlyst BD20 was maintained during recycling. The activity of Amberlyst 15 was inhibited by the water produced during the esterification process, but the activity of Amberlyst BD20 was not similarly affected by water. In images obtained with a scanning electron microscope (SEM), many pores were seen within the Amberlyst 15 catalyst, whereas Amberlyst BD20 showed few pores. Despite the fact that the pores of the catalyst play a role in increasing the number of active sites, Amberlyst BD20, which had fewer pores, was deemed to have more desirable performance in reducing the inhibition by water of the esterification of high FFA oils. PMID:19362818

Park, Ji-Yeon; Kim, Deog-Keun; Lee, Jin-Suk

2010-01-01

155

Graphene-Based Non-Noble-Metal Catalysts for Oxygen Reduction Reaction in Acid  

SciTech Connect

Non-noble-metal catalysts based on Fe-N-C moieties have shown promising oxygen reduction reaction (ORR) activity in proton exchange membrane fuel cells (PEMFCs). In this study, we report a facile method to prepare a Fe-N-C catalyst based on modified graphene (Fe-N-rGO) from heat treatment of a mixture of Fe salt, graphitic carbon nitride (g-C{sub 3}N{sub 4}), and chemically reduced graphene (rGO). The Fe-N-rGO catalyst was found to have pyridinic N-dominant heterocyclic N (40% atomic concentration among all N components) on the surface and have an average Fe coordination of {approx}3 N (Fe-N{sub 3,average}) in bulk. Rotating disk electrode measurements revealed that Fe-N-rGO had high mass activity in acid and exhibited high stability at 0.5 V at 80 C in acid over 70 h, which was correlated to low H{sub 2}O{sub 2} production shown from rotating ring disk electrode measurements.

H Byon; J Suntivich; Y Shao-Horn

2011-12-31

156

Characterization of iron counter-ion environment in bulk and supported phosphomolybdic acid based catalysts  

NASA Astrophysics Data System (ADS)

Extended X-ray absorption fine structure (EXAFS) was used to characterize the environment of iron counter-cations in Keggin type phosphomolybdic compounds used as catalysts for oxidation reactions. Iron doped compounds corresponding to bulk acid and to acid supported on the cesium salt were prepared and studied. Iron formed hexa-hydrated complex of both Fe3+ and Fe2+ in the bulk acid, whereas it was present as Fe(OH)2+ hydroxy-cations in the acid supported on the cesium salt. Upon heating the hexa-hydrated complex lost one molecule of water to bind to the Keggin anion through a terminal oxygen. (Fe O Mo bond). The environment of the iron hydroxy-cation changed upon heating while its closer coordination append to remained unchanged.

Huynh, Q.; Millet, J. M. M.

2005-05-01

157

Comparison between liquid and solid acids catalysts on reducing sugars conversion from furfural residues via pretreatments.  

PubMed

Liquid sulphuric acid is adopted and compared with carbon-based sulfonated solid acids (coal tar-based and active carbon-based) for furfural residues conversion into reducing sugars. The optimum hydrolysis conditions of liquid acid are at 4% of sulphuric acid, 25:1 of liquid and solid ratio, 175°C of reaction temperature and 120min of reaction time. The reducing sugar yields are reached over 60% on liquid acid via NaOH/H2O2, NaOH/microwave and NaOH/ultrasonic pretreatments, whereas only over 30% on solid acids. The TOFs (turnover number frequency) via NaOH/H2O2 pretreatments are 0.093, 0.020 and 0.023h(-1) for liquid sulphuric acid, coal tar-based and active carbon-based solid acids catalysts, respectively. Considering the efficiency, cost and environment factors, the liquid and solid acids have their own advantages of potential commercial application values. PMID:24976491

Lin, Keying; Ma, Baojun; Sun, Yuan; Liu, Wanyi

2014-09-01

158

Factors Affecting the Relative Efficiency of General Acid Catalysis  

ERIC Educational Resources Information Center

A simple framework for evaluating experimental kinetic data to provide support for Specific Acid Catalysis (SAC) and General Acid Catalysis (GAC) is described based on the factors affecting their relative efficiency. Observations reveal that increasing the SAC-to-GAC rate constant ratio reduces the effective pH range for GAC.

Kwan, Eugene E.

2005-01-01

159

A general nickel-catalyzed hydroamination of 1,3-dienes by alkylamines: catalyst selection, scope, and mechanism.  

PubMed

A simple colorimetric assay of various transition-metal catalysts showed that the combination of DPPF, Ni(COD)(2), and acid is a highly active catalyst system for the hydroamination of dienes by alkylamines to form allylic amines. The scope of the reaction is broad; various primary and secondary alkylamines react with 1,3-dienes in the presence of these catalysts. Detailed mechanistic studies revealed the individual steps involved in the catalytic process. These studies uncovered unexpected thermodynamics for the addition of amines to pi-allyl nickel complexes: instead of the thermodynamics favoring the reaction of a nickel allyl with an amine to form an allylic amine, the thermodynamics favored reaction of a nickel(0) complex with allylic amine in the presence of acid to form a Ni(II) allyl. The realization of these thermodynamics led us to the discovery that nickel and some palladium complexes in the presence or absence of acid catalyze the exchange of the amino groups of allylic amines with free amines. This exchange process was used to reveal the relative thermodynamic stabilities of various allylic amines. In addition, this exchange reaction leads to racemization of allylic amines. Therefore, the relative rate for C-N bond formation and cleavage influences the enantioselectivity of diene hydroaminations. PMID:11929257

Pawlas, Jan; Nakao, Yoshiaki; Kawatsura, Motoi; Hartwig, John F

2002-04-10

160

Which controls the depolymerization of cellulose in ionic liquids: the solid acid catalyst or cellulose?  

PubMed

Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires--as the first-step--its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100 degrees C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented. PMID:20155777

Rinaldi, Roberto; Meine, Niklas; vom Stein, Julia; Palkovits, Regina; Schüth, Ferdi

2010-02-22

161

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 (6.18g/100g) could be obtained at 180°C for 120min with 6.80g/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

162

Expeditious Pechmann Condensation by Using Biodegradable Cellulose Sulfuric Acid as a Solid Acid Catalyst  

Microsoft Academic Search

A facile synthesis of coumarins was performed in excellent yields via Pechmann condensation by using different type of phenols and ethylacetoacetates under solvent–free media using both conventional method and microwave irradiation in short reaction times is described. The reaction workup is very simple, and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent

B. Suresh Kuarm; J. Venu Madhav; S. Vijaya Laxmi; B. Rajitha; Y. Thirupathi Reddy; P. Narsimha Reddy; Peter A. Crooks

2010-01-01

163

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

164

Effect of water on silica-supported phosphotungstic acid catalysts for 1-butene double bond shift and alkane skeletal isomerization  

Microsoft Academic Search

The thermal stability, acidity, catalytic activity and regenerability of silica-supported phosphotungstic acid were evaluated in reference to the bulk solid acid. Samples were prepared with 5, 10, and 25wt.% heteropolyacid (HPA) on fumed silica to examine the effect of loading on the properties of supported acid catalysts. X-ray absorption spectroscopy indicated that the supported heteropolyacids did not completely decompose when

Billy B Bardin; Robert J Davis

2000-01-01

165

Magnetic Solid Sulfonic Acid Decorated with Hydrophobic Regulators: A Combinatorial and Magnetically Separable Catalyst for the Synthesis of ?-Aminonitriles.  

PubMed

A three-component, Strecker reaction of a series of aldehydes or ketones, amines, and trimethylsilyl cyanide for the synthesis of ?-aminonitriles in the presence of a catalytic amount of a magnetic solid sulfonic acid catalyst, Fe3O4@SiO2@Me&Et-PhSO3H under solvent-free conditions have been investigated. This catalyst, with a combination of hydrophobicity and acidity on the Fe3O4@SiO2 core-shell of the magnetic nanobeads, as well as its water-resistant property, enabled easy mass transfer and catalytic activity in the Strecker reaction. The catalyst was easily separated by an external magnet and the recovered catalyst was reused in 6 successive reaction cycles without any significant loss of activity. PMID:24932543

Mobaraki, Akbar; Movassagh, Barahman; Karimi, Babak

2014-07-14

166

Supported zirconium sulfate on carbon nanotubes as water-tolerant solid acid catalyst  

SciTech Connect

A new solid acid of zirconium sulfate (CZ) was successfully supported on carbon nanotube (CNT) for esterification reaction. Preparation conditions of the supported CZ have been investigated, to obtain highest catalytic activity for esterification reaction. XRD, TEM, BET, X-ray photoelectron spectra (XPS) and in situ FTIR analysis has also been carried out to understand the characteristics of the catalyst. In the esterification of acrylic acid with n-octanol, the supported CZ exhibited high catalytic activity and stability. The catalytic activity was nearly unchanged during four times of reuse. XRD and TEM analysis indicated that CZ was finely dispersed on CNT. XPS analysis shows that the CZ species was preserved and the chemical environment of the CZ has changed after loaded on CNT. This finding show that CNT as CZ support is an efficient water-tolerant solid acid.

Juan, Joon Ching [Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Ministry of Education, Beijing 100029 (China); Advanced Catalysis Technology Laboratory, School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600 (Malaysia); Jiang Yajie [Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Ministry of Education, Beijing 100029 (China); Meng Xiujuan [Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Ministry of Education, Beijing 100029 (China); Cao Weiliang [Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Ministry of Education, Beijing 100029 (China); Yarmo, Mohd Ambar [Advanced Catalysis Technology Laboratory, School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600 (Malaysia); Zhang Jingchang [Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Ministry of Education, Beijing 100029 (China)]. E-mail: zhangjc1@mail.buct.edu.cn

2007-07-03

167

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

168

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

169

Preparation and properties of new acid catalysts obtained by grafting alkoxides and derivatives on the most common supports. Part II: Grafting zirconium and silicon alkoxides on ?-alumina  

Microsoft Academic Search

In this work, the preparation and properties of the acid catalysts obtained by grafting zirconium and silicon alkoxides and zirconium-sulfated alkoxide on ?-alumina were studied. The catalysts prepared were examined with electrochemical techniques to evaluate the hydroxyl density, the ZPC (zero point charge) and the intrinsic surface ionization constants. The catalysts were also submitted to TPD (temperature-programmed desorption) analysis using

P Iengo; M Di Serio; V Solinas; D Gazzoli; G Salvio; E Santacesaria

1998-01-01

170

Photoassisted Fenton mineralisation of Acid Violet 7 by heterogeneous Fe(III)–Al 2O 3 catalyst  

Microsoft Academic Search

Photoassisted Fenton mineralisation of an azo dye Acid Violet 7 was studied in detail using a Fe(III) loaded Al2O3 as a heterogeneous catalyst in the presence of H2O2 and UV-A light. The catalyst ferrioxalate–Al2O3 is more efficient than ferricnitrate–Al2O3. 35% Fe3+ loaded Al2O3 shows maximum efficiency in the degradation. The effects of reaction parameters such as catalyst loading, H2O2 concentration,

Inbasekaran Muthuvel; Meenakshisundaram Swaminathan

2007-01-01

171

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

172

Acid catalysts based on Cu/Ru alumina: Conversion of butyraldehyde to dibutyl ether  

SciTech Connect

A system made by combining two nonalloying metals, ruthenium and copper, using alumina as the oxide support was studied. This bimetallic supported catalyst has been used mainly in hydrogenoloysis, dehydrogenation, and oxidation reactions of hydrocarbons. The preparation of such materials has been proposed to effect the selectivity and activity of a highly active metal by inclusions of a second less active metal. The samples were characterized by electron paramagnetic resonance spectrometry (EPR), X-ray diffraction (XRD), surface area, and surface acidities. The techniques EPR and XRD are ideal for studying the electronic and structural changes of the samples at different temperatures and concentrations. The primary reaction involved in this study was the hydrogenation of an aldehyde to the corresponding alcohol. A secondary reaction occurred as well. The acid catalyzed, substitution or bimolecular dehydration of the alcohol to the dibutyl ether was observed under certain catalytic conditions. These catalysts appeared to act as acid/base. Therefore this reaction to produce the ether is of special importance. A correlation between the electronic, structural and catalytic properties has been made to understand molecular processes` role in catalytic phenomena. 44 refs., 6 figs., 5 tabs.

Jansen, S.; Palmieri, M.; Gomez, M. [Temple Univ., Philadelphia, PA (United States)] [Temple Univ., Philadelphia, PA (United States); Lawrence, S. [Saginaw Valley State Univ., University Center, MI (United States)] [Saginaw Valley State Univ., University Center, MI (United States)

1996-10-01

173

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

2014-06-19

174

A Mild and Efficient Chemoselective Tetrahydropyranylation of Alcohols Using Bronsted Acidic Ionic Liquid as Catalyst Under Solvent-Free Conditions  

Microsoft Academic Search

A straightforward and efficient method for preparation of morpholinium bisulfate ([mroH] HSO4) as a novel acidic IL is reported. The application of this efficient and inexpensive acidic ionic liquid catalyst for tetrahydropyranylation of alcohols under mild and solvent-free conditions at room was investigated.

Abdol R. Hajipour; Zahra. Nasresfahani

2011-01-01

175

Aromatic Compounds Mannich Reaction Using Economical Acidic Ionic Liquids Based on Morpholinium Salts as Dual Solvent-Catalysts  

Microsoft Academic Search

Economical acidic ionic liquids containing an alkanesulfonic acid group in a morpholinium cation were found to be effective catalysts for the Mannich reactions of various kinds of aromatic aldehydes, acetophenone and aromatic amines at mild reaction conditions. The satisfactory results were obtained with short reaction time, good yields of the Mannich bases and simplicity in the experimental procedure. These ionic

Caibo Yue

2010-01-01

176

Mild and Efficient Chemoselective Tetrahydropyranylation of Alcohols Using Brønsted Acidic Ionic Liquid as Catalyst Under Solvent-Free Conditions  

Microsoft Academic Search

A straightforward and efficient method for preparation of morpholinium bisulfate ([mroH]HSO4) as a novel acidic ionic liquid is reported. The application of this efficient and inexpensive acidic ionic liquid catalyst for tetrahydropyranylation of alcohols under mild and solvent-free conditions at room was investigated.

Abdol R. Hajipour; Zahra Nasresfahani

2012-01-01

177

One-Pot synthesis of phosphorylated mesoporous carbon heterogeneous catalysts with tailored surface acidity  

SciTech Connect

Soft-templated phosphorylated mesoporous carbons with homogeneous distributions of phosphate groups were prepared by a 'one-pot' synthesis method using mixtures of phosphoric acid with hydrochloric, or nitric acids in the presence of Pluronic F127 triblock copolymer. Adjusting the various ratios of phosphoric acid used in these mixtures resulted in carbons with distinct adsorption, structural and surface acidity properties. The pore size distributions (PSDs) from nitrogen adsorption at -196 C showed that mesoporous carbons exhibit specific surface areas as high as 551 m{sup 2}/g and mesopores as large as 13 nm. Both structural ordering of the mesopores and the final phosphate contents were strongly dependent on the ratios of H{sub 3}PO{sub 4} in the synthesis gels, as shown by transmission electron microscopy (TEM), X-ray photoelectron (XPS) and energy dispersive X-ray spectroscopy (EDS). The number of surface acid sites determined from temperature programmed desorption of ammonia (NH{sub 3}-TPD) were in the range of 0.3-1.5 mmol/g while the active surface areas are estimated to comprise 5-54% of the total surface areas. Finally, the conversion temperatures for the isopropanol dehydration were lowered by as much as 100 C by transitioning from the least acidic to the most acidic catalysts surface.

Fulvio, Pasquale F [ORNL; Mahurin, Shannon Mark [ORNL; Mayes, Richard T [ORNL; Bauer, Christopher [ORNL; Wang, Xiqing [ORNL; Veith, Gabriel M [ORNL; Dai, Sheng [ORNL

2012-01-01

178

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

179

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

180

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

181

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

182

Carbon supported platinum catalysts for catalytic wet air oxidation of refractory carboxylic acids  

Microsoft Academic Search

Carbon supported platinum (1% wt) catalysts were prepared by the incipient wetness impregnation method and by organometallic chemical vapor deposition. Catalyst characterization was carried out by means of adsorption and thermogravimetric techniques, and by electron microscopy. The catalyst with higher metal dispersion was produced by incipient wetness impregnation. The catalysts were tested in the catalytic wet air oxidation (200°C and

H. T. Gomes; Ph. Serp; Ph. Kalck; J. L. Figueiredo; J. L. Faria

2005-01-01

183

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

184

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

185

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

186

Direct amidation of carboxylic acids catalyzed by ortho-iodo arylboronic acids: catalyst optimization, scope, and preliminary mechanistic study supporting a peculiar halogen acceleration effect.  

PubMed

The importance of amides as a component of biomolecules and synthetic products motivates the development of catalytic, direct amidation methods employing free carboxylic acids and amines that circumvent the need for stoichiometric activation or coupling reagents. ortho-Iodophenylboronic acid 4a has recently been shown to catalyze direct amidation reactions at room temperature in the presence of 4A molecular sieves as dehydrating agent. Herein, the arene core of ortho-iodoarylboronic acid catalysts has been optimized with regards to the electronic effects of ring substitution. Contrary to the expectation, it was found that electron-donating substituents are preferable, in particular, an alkoxy substituent positioned para to the iodide. The optimal new catalyst, 5-methoxy-2-iodophenylboronic acid (MIBA, 4f), was demonstrated to be kinetically more active than the parent des-methoxy catalyst 4a, providing higher yields of amide products in shorter reaction times under mild conditions at ambient temperature. Catalyst 4f is recyclable and promotes the formation of amides from aliphatic carboxylic acids and amines, and from heteroaromatic carboxylic acids and other functionalized substrates containing moieties like a free phenol, indole and pyridine. Mechanistic studies demonstrated the essential role of molecular sieves in this complex amidation process. The effect of substrate stoichiometry, concentration, and measurement of the catalyst order led to a possible catalytic cycle based on the presumed formation of an acylborate intermediate. The need for an electronically enriched ortho-iodo substituent in catalyst 4f supports a recent theoretical study (Marcelli, T. Angew. Chem. Int. Ed.2010, 49, 6840-6843) with a purported role for the iodide as a hydrogen-bond acceptor in the orthoaminal transition state. PMID:23013456

Gernigon, Nicolas; Al-Zoubi, Raed M; Hall, Dennis G

2012-10-01

187

Magnesium oxide-supported ziegler catalyst modified with acid and higher alkanol, and process for preparing narrow MWD HDPE  

Microsoft Academic Search

This patent describes a coordination-catalyst suitable for the polymerization of olefins. It comprises a titanium component and an organoaluminum compound reducing agent on a magnesium oxide support which has been pre-treated with a molar deficiency of a carboxylic acid with respect to the magnesium oxide support. The titanium component is the reaction product of an alkanol having 5 to 12

J. T. T

1989-01-01

188

SO?H-functionalized acidic ionic liquids as catalysts for the hydrolysis of cellulose.  

PubMed

The conversion of cellulose into valuable chemicals to deal with the depletion of fossil fuel has got much attention. Completing the hydrolysis of cellulose under mild conditions is the key step. In this study, six kinds of SO(3)H-functionalized acidic ionic liquids were used as acid catalyst to promote the hydrolysis of cellulose in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). All of them were efficient for the hydrolysis of cellulose, with the maximum total reducing sugars (TRS) yields over 83% at 100 °C. Acidic ionic liquids with analogous structures showed similar catalytic activities. Triethyl-(3-sulfo-propyl)-ammonium hydrogen sulfate (IL-5 in this study) was the optimum ionic liquid for cellulose hydrolysis, with the maximum TRS yield at 100 °C up to 99% when the dosage used was 0.2g. In addition, the water in [BMIM]Cl had negative effect on cellulose hydrolysis. Therefore, controlling the content of water in a comparatively low level is quite necessary. PMID:23218286

Liu, Yuanyuan; Xiao, Wenwen; Xia, Shuqian; Ma, Peisheng

2013-01-30

189

A humic-acid-like polycondensate produced with no use of catalyst.  

PubMed

The synthesis and physicochemical characterization of a water soluble humic-acid-like polycondensate (HALP), which mimics fundamental physicochemical and spectroscopic properties of natural humic acids is presented. The polymer can be synthesized under ambient O(2) by oxidative co-polymerization of gallic (GA) and protocatechuic (PA) acid at pH >9, with no need for a catalyst. Solid state (13)C NMR spectra for GA-PA-HALP show that ring-opening reactions of GA, PA monomers are involved in GA-PA-HALP formation. EPR spectroscopy shows that GA-PA-HALP contains stable phenol-based radicals, with pH-dependent concentration. The H-binding profile of GA-PA-HALP follows the NICA-Donnan model, with two sets of distributed pK(a) values in the range 4-6 corresponding to carboxyl groups, and 7-9 corresponding to phenolic groups, as in natural HA. GA-PA-HALP bears a permanent negative charge Q(0)=-2.3 equiv kg(-1) which is higher than the literature Q(0) values of -1 to -2 equiv kg(-1) observed for natural HAs. A critical comparison of the present data with literature data is provided. PMID:19394625

Giannakopoulos, Evangelos; Drosos, Marios; Deligiannakis, Yiannis

2009-08-01

190

Pt\\/TiO 2 (rutile) catalysts for sulfuric acid decomposition in sulfur-based thermochemical water-splitting cycles  

Microsoft Academic Search

Thermochemical cycles consist of a series of chemical reactions to produce hydrogen from water at lower temperatures than by direct thermal decomposition. All the sulfur-based cycles for water splitting employ the sulfuric acid decomposition reaction. This work reports the studies performed on 1wt% Pt\\/TiO2 (rutile) catalysts submitted to flowing concentrated sulfuric acid at 1123K and atmospheric pressure for different times

L. M. Petkovic; D. M. Ginosar; H. W. Rollins; K. C. Burch; P. J. Pinhero; H. H. Farrell

2008-01-01

191

Hydrogenation of unsaturated carboxylic acids on functional gel-type resin supported Pd catalysts: The effect of reactant structure  

Microsoft Academic Search

Functional gel-type resin-based palladium catalysts (0.5–2wt.% Pd) of well dispersed Pd nanoparticles were prepared and characterized by SEM, TEM techniques and swelling measurements. The role of specific properties of gel-type matrix was studied in the hydrogenation of unsaturated CC bonds in series of carboxylic acids, derivatives of acrylic acid. They differ in the type of substituents (methyl, phenyl and carboxyl

A. Knapik; A. Drelinkiewicz; M. Szaleniec; W. Makowski; A. Waksmundzka-Góra; A. Bukowska; W. Bukowski; J. Noworól

2008-01-01

192

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

193

Asymmetric Mukaiyama aldol reaction of silyl enol ethers with aldehydes using a polymer-supported chiral Lewis acid catalyst  

Microsoft Academic Search

Chiral N-sulfonylated ?-amino acid monomer (5) derived from (S)-tryptophan was copolymerized with styrene and divinylbenzene under radical polymerization conditions to give a polymer-supported N-sulfonyl-(S)-tryptophan (6). Treatment of the polymer-supported chiral ligand with 3,5-bis(trifluoromethyl)phenyl boron dichloride afforded a polymeric Lewis acid catalyst (16) effective for asymmetric Mukaiyama aldol reaction of silyl enol ethers and aldehydes. Various aldehydes were allowed to react

Shinichi Itsuno; Shinnosuke Arima; Naoki Haraguchi

2005-01-01

194

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

195

Acid-base properties of the active sites of the surface of a skeletal nickel and promoted skeletal nickel catalyst  

NASA Astrophysics Data System (ADS)

The acid-base and adsorption properties of the active sites of the surface of a skeletal nickel and promoted nickel catalyst in aqueous solutions were studied by the potentiometric and pKspectroscopy methods. Titanium added as a promoter resulted in an increased number of lines in the pK spectra, which may attest to higher chemical activity of the promoted catalyst. An increase in the pH value of the media was shown to cause a shift in the process equilibria toward the formation of atomic strongly-bound forms of adsorbed hydrogen.

Filippov, D. V.; Kravchenko, A. V.; Ulitin, M. V.; Ryazanov, M. A.

2010-03-01

196

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

197

Low-grade oils and fats: effect of several impurities on biodiesel production over sulfonic acid heterogeneous catalysts.  

PubMed

Different lipidic wastes and low-grade oils and fats have been characterized and evaluated as feedstocks for the acid-catalyzed production of FAME. The characterization of these materials has revealed significant contents of free fatty acids, Na, K, Ca, Mg, P, unsaponifiable matter and humidity. Arenesulfonic acid-functionalized SBA-15 silica catalyst has provided yields to FAME close to 80% in the simultaneous esterification-transesterification of the different feedstocks, regardless of their nature and properties, using methanol under the following reaction conditions: 160 °C, 2 h, methanol to oil molar ratio of 30, 8 wt.% catalyst loading, and 2000 rpm stirring rate. Nevertheless, reutilization of the catalyst is compromised by high levels of impurities, especially because of deactivation by strong interaction of unsaponifiable matter with the catalytic sites. The conditioning of these materials by aqueous washing in the presence of cationic-exchange resin Amberlyst-15, followed by a drying step, resulted in a lower deactivation of the catalyst. PMID:21862322

Morales, Gabriel; Bautista, L Fernando; Melero, Juan A; Iglesias, Jose; Sánchez-Vázquez, Rebeca

2011-10-01

198

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

199

Low-quality vegetable oils as feedstock for biodiesel production using K-pumice as solid catalyst. Tolerance of water and free fatty acids contents.  

PubMed

Waste oils are a promising alternative feedstock for biodiesel production due to the decrease of the industrial production costs. However, feedstock with high free fatty acids (FFA) content presents several drawbacks when alkaline-catalyzed transesterification reaction is employed in biodiesel production process. Nowadays, to develop suitable processes capable of treating oils with high free fatty acids content, a two-step process for biodiesel production is being investigated. The major problem that it presents is that two catalysts are needed to carry out the whole process: an acidic catalyst for free fatty acids esterification (first step) and a basic catalyst for pretreated product transesterification (second step). The use of a bifunctional catalyst, which allows both reactions to take place simultaneously, could minimize the production costs and time. In the present study, the behavior of pumice, a natural volcanic material used as a heterogeneous catalyst, was tested using oils with several FFA and water contents as feedstock in the transesterification reaction to produce biodiesel. Pumice as a bifunctional solid catalyst, which can catalyze simultaneously the esterification of FFA and the transesterification of fatty acid glycerides into biodiesel, was shown to be an efficient catalyst for the conversion of low-grade, nonedible oil feedstock into biodiesel product. Using this solid catalyst for the transesterification reaction, high FAME yields were achieved when feedstock oils presented a FFA content until approximately 2% wt/wt and a water content until 2% wt/wt. PMID:22799882

Díaz, L; Borges, M E

2012-08-15

200

Electrochemical catalyst recovery method  

DOEpatents

A method of recovering catalyst material from latent catalyst material solids includes: a) combining latent catalyst material solids with a liquid acid anolyte solution and a redox material which is soluble in the acid anolyte solution to form a mixture; b) electrochemically oxidizing the redox material within the mixture into a dissolved oxidant, the oxidant having a potential for oxidation which is effectively higher than that of the latent catalyst material; c) reacting the oxidant with the latent catalyst material to oxidize the latent catalyst material into at least one oxidized catalyst species which is soluble within the mixture and to reduce the oxidant back into dissolved redox material; and d) recovering catalyst material from the oxidized catalyst species of the mixture. The invention is expected to be particularly useful in recovering spent catalyst material from petroleum hydroprocessing reaction waste products having adhered sulfides, carbon, hydrocarbons, and undesired metals, and as well as in other industrial applications.

Silva, Laura J. (Richland, WA); Bray, Lane A. (Richland, WA)

1995-01-01

201

Electrochemical catalyst recovery method  

DOEpatents

A method of recovering catalyst material from latent catalyst material solids includes: (a) combining latent catalyst material solids with a liquid acid anolyte solution and a redox material which is soluble in the acid anolyte solution to form a mixture; (b) electrochemically oxidizing the redox material within the mixture into a dissolved oxidant, the oxidant having a potential for oxidation which is effectively higher than that of the latent catalyst material; (c) reacting the oxidant with the latent catalyst material to oxidize the latent catalyst material into at least one oxidized catalyst species which is soluble within the mixture and to reduce the oxidant back into dissolved redox material; and (d) recovering catalyst material from the oxidized catalyst species of the mixture. The invention is expected to be particularly useful in recovering spent catalyst material from petroleum hydroprocessing reaction waste products having adhered sulfides, carbon, hydrocarbons, and undesired metals, and as well as in other industrial applications. 3 figs.

Silva, L.J.; Bray, L.A.

1995-05-30

202

Ultrasound-assisted one-pot synthesis of substituted coumarins catalyzed by poly(4-vinylpyridinium) hydrogen sulfate as an efficient and reusable solid acid catalyst.  

PubMed

Poly(4-vinylpyridinium) hydrogen sulfate solid acid was found to be efficient catalyst for synthesis of substituted coumarins via Pechmann reaction using ultrasound irradiation at room temperature and neat condition in high yields with short reaction times. This methodology offers momentous improvements over various options for the synthesis of coumarins with regard to yield of products, simplicity in operation and green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused and recovered for several times. PMID:23395258

Khaligh, Nader Ghaffari

2013-07-01

203

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

204

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

205

Enantioselective fluorescent recognition of a soluble "supported" chiral acid: toward a new method for chiral catalyst screening.  

PubMed

The long-chain aliphatic-group-substituted mandelic acid 3c, which is soluble only in THF and insoluble in water and many polar/nonpolar organic solvents, has been synthesized. This unique solubility allows 3c to be easily isolated from reaction mixtures and makes it potentially useful for catalyst screening. The fluorescent sensors (R)- and (S)-1 can be used to determine the ees of various samples of 3c generated from a series of catalyst screening experiments. The fluorescence measurements correlate well with the conventional HPLC-chiral column analysis. This work demonstrates that the enantioselective fluorescent recognition of organic substrates can lead to a fundamentally new method for chiral catalyst screening. [reaction: see text] PMID:16048312

Li, Zi-Bo; Lin, Jing; Qin, Ying-Chuan; Pu, Lin

2005-08-01

206

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

207

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.

2010-01-01

208

An efficient and heterogeneous recyclable silicotungstic acid with modified acid sites as a catalyst for conversion of fructose and sucrose into 5-hydroxymethylfurfural in superheated water.  

PubMed

Acidity modified silver exchanged silicotungstic acid (AgSTA) catalyst was prepared and characterized by X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, FT-IR pyridine adsorption, SEM imaging, EDX mapping, and antimicrobial activity was also tested. The catalytic activity was evaluated for the dehydration of fructose and sucrose in superheated water. As a result, 98% conversion of fructose with 85.7% HMF yield and 87.4% HMF selectivity in 120 min reaction time at 120 °C reaction temperature using 10 wt.% of AgSTA catalyst was achieved. While, 92% sucrose conversion with 62.5% of HMF yield was obtained from sucrose at uniform condition in 160 min. The effect of reaction parameters, such as reaction temperature, time, catalyst dosage, and effect acidity on HMF yield was also investigated. The AgSTA catalyst was separated from the reaction mixture by filtration process at end of the reaction and reused eight times without loss of catalytic activity. PMID:23435221

Jadhav, Arvind H; Kim, Hern; Hwang, In Taek

2013-03-01

209

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

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

210

Double bond isomerization of olefin-containing feeds with minimal oligomerization using surface acidity deactivated zeolite catalysts  

SciTech Connect

A method is described for double bond isomerization of alpha-olefin-containing organic feedstock with minimal oligomerization which comprises contacting said feedstock under double bond isomerization conditions with a double bond isomerization catalyst comprising a zeolite having a Constraint Index of 1 to 12 whose surface has been at least partially deactivated for acid catalyzed reactions by chemisorption of an alkyl-substituted pyridine surface-deactivating agent which possesses an average cross section diameter greater than that of the zeolite pores.

Haag, W.O.; Heck, R.H.; Santiesteban, J.G.; Shihabi, D.S.

1993-08-17

211

Transesterification of triacetin with methanol on solid acid and base catalysts  

Microsoft Academic Search

Biodiesel is a particularly attractive renewable fuel as it can be used in existing engines, is environmentally friendly, and is readily synthesized from animal fats and vegetable oils. Heterogeneous catalysts offer exciting possibilities for improving the economics of biodiesel synthesis; however, few published investigations have addressed the use of such catalysts to date. The purpose of this research was to

Dora E. López; James G. Goodwin; David A. Bruce; Edgar Lotero

2005-01-01

212

Preparation of a carbon-based solid acid catalyst by sulfonating activated carbon in a chemical reduction process.  

PubMed

Sulfonated (SO(3)H-bearing) activated carbon (AC-SO(3)H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO(3)H density of 0.64 mmol·g-1 and a specific surface area of 602 m2·g-1. The catalytic properties of AC-SO(3)H were compared with that of two commercial solid acid catalysts, Nafion NR50 and Amberlyst-15. In a 10-h esterification reaction of acetic acid with ethanol, the acid conversion with AC-SO(3)H (78%) was lower than that of Amberlyst-15 (86%), which could be attributed to the fact that the SO(3)H density of the sulfonated carbon was lower than that of Amberlyst-15 (4.60 mmol·g-1). However, AC-SO(3)H exhibited comparable and even much higher catalytic activities than the commercial catalysts in the esterification of aliphatic acids with longer carbon chains such as hexanoic acid and decanoic acid, which may be due to the large specific surface area and mesoporous structures of the activated carbon. The disadvantage of AC-SO(3)H is the leaching of SO(3)H group during the reactions. PMID:20956883

Liu, Xiao-Yan; Huang, Miao; Ma, Hai-Long; Zhang, Zeng-Qiang; Gao, Jin-Ming; Zhu, Yu-Lei; Han, Xiao-Jin; Guo, Xiang-Yun

2010-01-01

213

Preparation of Keggin and Preyssler Heteropolyacid Catalysts on Amine-modified SBA15 and Their Catalytic Performances in Esterification of n Butanol with Acetic Acid  

Microsoft Academic Search

The Keggin and Preyssler-structured tungstophosphoric acid catalysts anchored on the surface of modified SBA-15 (KNS and PNS)\\u000a by grafting amine groups into system, and were characterized by infra-red spectroscopy, X-ray diffraction, N2-adsorption, Hammett indicator and UV-Vis spectroscopy. Their catalytic behaviors were investigated in the esterification\\u000a of n-butanol with acetic acid. Characterization results for obtained catalysts verified the ordered hexagonal mesostructure

Shanshan Wu; Jun Wang; Weihong Zhang; Xiaoqian Ren

2008-01-01

214

Alkylation of aromatic compounds with multi-component Lewis acid catalysts of ZnCl 2 and ionic liquids with different organic cations  

Microsoft Academic Search

Alkylation of aromatic compounds with various alkylating agents such as benzyl chloride, benzyl alcohol and isopropyl chloride\\u000a were investigated using ZnCl2 based ionic liquid (ILs) Lewis acid catalysts. Multi-component Lewis acid catalysts of ZnCl2 and ionic liquids such as 1-butyl-3-methylimidazolium bromide, 1-butylpyridinium bromide, cholin chloride and tetrabutylammonium\\u000a bromide were prepared, supported on silica gel, and compared for alkylation reactions with

Rajendra Srivastava; Shin-Ichiro Fujita; Shuhei Okamura; Masahiko Arai

2009-01-01

215

Green, One-Pot, Solvent-Free Synthesis of 1,2,4,5Tetrasubstituted Imidazoles Using a Brønsted Acidic Ionic Liquid as Novel and Reusable Catalyst  

Microsoft Academic Search

3-Methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate [(CH2)4SO3HMIM][HSO4], a Brønsted acidic ionic liquid, has been used as an efficient, green, and reusable catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles using benzil, an aromatic aldehyde, and a primary amine in the presence of ammonium acetate under solvent-free conditions. The catalyst could be recycled and reused several times without noticeably decreasing the catalytic activity.

Abolghasem Davoodnia; Majid M. Heravi; Zahra Safavi-Rad; Niloofar Tavakoli-Hoseini

2010-01-01

216

In situ fourier transform infrared study of crotyl alcohol, maleic acid, crotonic acid, and maleic anhydride oxidation on a V-P-O industrial catalyst  

SciTech Connect

Crotyl alcohol, maleic acid, crotonic (2-butenoic) acid, and maleic anhydride were fed to an in situ infrared cell at 300/sup 0/C containing a P/V = 1.1 vanadium-phosphorous-oxide (V-P-O) catalyst used for the selective oxidation of n-butane. Crotyl alcohol was used as a mechanistic probe for the formation of reactive olefin species observed during previous n-butane and 1-butene studies. Crotonic acid, maleic acid, and maleic anhydride were fed as probes for the existence of other possible adsorbed intermediates. Olefin species and maleic acid are proposed as possible reaction intermediates in n-butane selective oxidation to maleic anhydride. The involvement of peroxide species in the oxidation of butadiene to maleic acid is also discussed.

Wenig, R.W.; Schrader, G.L.

1987-10-22

217

Sulfonic acid functionalized nano-?-Al2O3: a new, efficient, and reusable catalyst for synthesis of 3-substituted-2H-1,4-benzothiazines.  

PubMed

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

218

Silica tungstic acid as an efficient and reusable catalyst for the one-pot synthesis of 2-amino-4H-chromene derivatives.  

PubMed

Silica tungstic acid (STA) has been found to be an efficient and reusable solid acid catalyst for the synthesis of 2-amino-4H-chromenes via the three-component reaction of aromatic aldehydes, malononitrile, and ?-naphthol. STA as a novel solid acid was characterized by X-ray fluorescence, X-ray diffraction, and Fourier transform infrared spectroscopy. PMID:24664332

Farahi, Mahnaz; Karami, Bahador; Alipour, Samambar; Moghadam, Leila Taghavi

2014-01-01

219

Comparative characterization of basicity and acidity of metal oxide catalysts for the oxidative coupling of methane by different methods  

Microsoft Academic Search

A comprehensive study of the surface basicity and acidity of alkaline earth metal oxides, La2O3\\/CaO, CeO2\\/CaO and ZnO-doped NaOH (11 mol-%)\\/CaO which had earlier been tested as catalysts for the oxidative coupling of methane was performed. For determining the acid-base properties two probe reactions, i.e., the decomposition of 2-propanol to acetone and propene and the retroaldolisation of diacetone alcohol, further

Petra Käßner; Manfred Baerns

1996-01-01

220

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

Code of Federal Regulations, 2010 CFR

...2010-07-01 false Acceptance of State Acid Rain programs-general. 72.71 Section...CONTINUED) PERMITS REGULATION Acid Rain Phase II Implementation § 72.71 Acceptance of State Acid Rain programsâgeneral. (a) Each...

2010-07-01

221

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

Code of Federal Regulations, 2010 CFR

...2009-07-01 false Acceptance of State Acid Rain programs-general. 72.71 Section...CONTINUED) PERMITS REGULATION Acid Rain Phase II Implementation § 72.71 Acceptance of State Acid Rain programsâgeneral. (a) Each...

2009-07-01

222

Esterification of oleic acid in a three-phase, fixed-bed reactor packed with a cation exchange resin catalyst.  

PubMed

Esterification of oleic acid was performed in a three-phase fixed-bed reactor with a cation exchange resin catalyst (Amberlyst-15) at high temperature, which was varied from 80 to 120 °C. The fatty acid methyl ester (FAME) yields in the fixed-bed reactor were increased with increases in the reaction temperature, methanol flow rate and bed height. Moreover, the FAME yields were higher than those obtained using a batch reactor due to an equilibrium shift toward the product that resulted from continuous evaporation of the produced water. In addition, there was no catalyst deactivation during the esterification of oleic acid. However, addition of sunflower oil to the oleic acid reduced the FAME yield obtained from simultaneous esterification and transesterification. The FAME yield was 97.5% at a reaction temperature of 100 °C in the fixed-bed with a height of 5 cm when the methanol and oleic acid feed rates were 8.6 and 9.0 mL/h, respectively. PMID:20855192

Son, Sung Mo; Kimura, Hiroko; Kusakabe, Katsuki

2011-01-01

223

Acid strength of proton donors in complexes of nontransition metal halides as a measure of the activity of electrophilic polymerisation catalysts  

NASA Astrophysics Data System (ADS)

Data on one of the most urgent problems in modern theoretical chemistry are reviewed: the calculation of the acid strength of the complexes formed by the interaction of Lewis acids with proton donors, and the correlation of the acid strength with the activity and selectivity of these complexes as catalysts of electrophilic processes. Complexes based on aluminium and magnesium chlorides and on boron fluorides are discussed. It is shown that increasing the acid strength of these complexes as catalysts of electrophilic polymerisation reactions increases their activity but lowers their selectivity. The bibliography includes 43 references.

Minsker, Karl S.; Babkin, Vasilii A.; Zaikov, Gennadii E.

1994-03-01

224

Process for catalyst recovery  

SciTech Connect

This patent describes a process for recovering a homogeneous catalyst from a catalytic reaction mixture. It comprises: removing the reaction mixture solvent using temperatures such that decomposition of the catalyst is minimized; simultaneously adding a lower alkanoic acid; and recovering the precipitated homogeneous catalyst.

Bodurow, C.C.

1990-08-21

225

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.

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

226

B-doped Pd catalyst: boosting room-temperature hydrogen production from formic acid-formate solutions.  

PubMed

Facile production of hydrogen at room temperature is an important process in many areas including alternative energy. In this Communication, a potent boron-doped Pd nanocatalyst (Pd-B/C) is reported for the first time to boost hydrogen generation at room temperature from aqueous formic acid-formate solutions at a record high rate. Real-time ATR-IR spectroscopy is applied to shed light on the enhanced catalytic activity of B-doping and reveals that the superior activity of Pd-B/C correlates well with an apparently impeded COad accumulation on its surfaces. This work demonstrates that developing new anti-CO poisoning catalysts coupled with sensitive interfacial analysis is an effective way toward rational design of cost-effective catalysts for better hydrogen energy exploitation. PMID:24635163

Jiang, Kun; Xu, Ke; Zou, Shouzhong; Cai, Wen-Bin

2014-04-01

227

7 Regulation of the yeast general amino acid control pathway in response to nutrient stress  

Microsoft Academic Search

In response to starvation for amino acids, yeast cells induce the expression of a collection of genes involved in amino acid metabolism. This pathway referred to as the general amino acid control is a true cross-pathway response that induces expression of genes contributing to the synthesis of all amino acids independent of which amino acid is limiting. In this review,

Ronald C. Wek; Kirk A. Staschke; Jana Narasimhan

228

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

229

Protic acid immobilized on solid support as an extremely efficient recyclable catalyst system for a direct and atom economical esterification of carboxylic acids with alcohols.  

PubMed

A convenient and clean procedure of esterification is reported by direct condensation of equimolar amounts of carboxylic acids with alcohols catalyzed by an easy to prepare catalyst system of perchloric acid immobilized on silica gel (HClO(4)-SiO(2)). The direct condensation of aryl, heteroaryl, styryl, aryl alkyl, alkyl, cycloalkyl, and long-chain aliphatic carboxylic acids with primary/secondary alkyl/cycloalkyl, allyl, propargyl, and long-chain aliphatic alcohols has been achieved to afford the corresponding esters in excellent yields. Chiral alcohol and N-t-Boc protected chiral amino acid also resulted in ester formation with the representative carboxylic acid or alcohol without competitive N-t-Boc deprotection and detrimental effect on the optical purity of the product demonstrating the mildness and chemoselectivity of the procedure. The esters of long-chain (>C(10)) acids and alcohols are obtained in high yields. The catalyst is recovered and recycled without significant loss of activity. The industrial application of the esterification process is demonstrated by the synthesis of prodrugs of ibuprofen and a few commercial flavoring agents. Other protic acids such as H(2)SO(4), HBr, TfOH, HBF(4), and TFA that were adsorbed on silica gel were less effective compared to HClO(4)-SiO(2) following the order HClO(4)-SiO(2) > H(2)SO(4)-SiO(2) > HBr-SiO(2) > TfOH-SiO(2) > HBF(4)-SiO(2) approximately TFA-SiO(2). When HClO(4) was immobilized on other solid supports the catalytic efficiency followed the order HClO(4)-SiO(2) > HClO(4)-K10 > HClO(4)-Al(2)O(3) (neutral) > HClO(4)-Al(2)O(3) (acidic) > HClO(4)-Al(2)O(3) (basic). PMID:19618958

Chakraborti, Asit K; Singh, Bavneet; Chankeshwara, Sunay V; Patel, Alpesh R

2009-08-21

230

Efficient and selective conversion of methyl lactate to acrylic acid using Ca 3(PO 4) 2–Ca 2(P 2O 7) composite catalysts  

Microsoft Academic Search

Calcium phosphate Ca3(PO4)2 and calcium pyrophosphate Ca2(P2O7) composite catalysts of different weight ratios were prepared by a slurry-mixing method. These composite catalysts were calcined at 500°C in air and characterized by N2 sorption for specific surface area by XRD for crystal phases and by TPD-NH3 (acidity), TPD-CO2 (basicity) and SEM for morphological features. All the Ca3(PO4)2–Ca2(P2O7) composite catalysts were found

Ju Hyeong Hong; Jong-Min Lee; Hyungrok Kim; Young Kyu Hwang; Jong-San Chang; Shiva B. Halligudi; Yo-Han Han

2011-01-01

231

Nanoporous PdNi Alloy Nanowires As Highly Active Catalysts for the Electro-Oxidation of Formic Acid.  

PubMed

Highly active and durable catalysts for formic acid oxidation are crucial to the development of direct formic acid fuel cell. In this letter, we report the synthesis, characterization, and electrochemical testing of nanoporous Pd(57)Ni(43) alloy nanowires for use as the electrocatalyst towards formic acid oxidation (FAO). These nanowires are prepared by chemically dealloying of Ni from Ni-rich PdNi alloy nanowires, and have high surface area. X-ray diffraction data show that the Pd(57)Ni(43) nanowires have the face-centered cubic crystalline structure of pure Pd, whereas X-ray photoelectron spectroscopy confirm the modification of electronic structure of Pd by electron transfer from Ni to Pd. Electrocatalytic activity of the nanowires towards FAO exceeds that of the state-of-the-art Pd/C. More importantly, the nanowires are highly resistant to deactivation. It is proposed that the high active surface area and modulated surface properties by Ni are responsible for the improvement of activity and durability. Dealloyed nanoporous Pd(57)Ni(43) alloy nanowires are thus proposed as a promising catalyst towards FAO. PMID:21192691

Du, Chunyu; Chen, Meng; Wang, Wengang; Yin, Geping

2011-02-01

232

Application of nanostuctured materials as acid-catalysts in rice straw pyrolysis for bio-oil production  

NASA Astrophysics Data System (ADS)

Rice straw, a waste agro-byproduct, which is abundant lignocellulose products from rice production, is a renewable energy sources in Vietnam. Bio-oil from rice straw is produced by thermal and catalytic pyrolysis using a fixed-bed reactor with heating rate 15oC/min, nitrogen as sweeping gas with flow rate 120ml/min. Final temperature of the pyrolysis reaction is a significantly influence on product yield. The gas yield increased and the solid yield decreased as the pyrolysis temperature increasing from 400oC to 600oC. The bio-oil yield reached a maximum of 48.3 % at the pyrolysis temperature of 550oC. Mesoporous Al-SBA-15 was used as acid catalyst in pyrolysis of rice straw. The obtained results showed that, in the presence of catalyst, yield of gas products increased, whereas liquid yield decreased and solid product remained the same as compared to the non-catalytic experiments. The effect of nanostructured catalysts on the product yields and distribution was investigated.

Dang, Phuong T.; Le, Hy G.; Dinh, Thang C.; Hoang, Thang V.; Bui, Linh H. T.; Hoang, Yen; Tran, Hoa K. T.; Vu, Tuan A.

2008-12-01

233

Hazardous waste to materials: recovery of molybdenum and vanadium from acidic leach liquor of spent hydroprocessing catalyst using alamine 308.  

PubMed

Recovery of valuable materials/metals from waste goes hand in hand with environmental protection. This paper deals with the development of a process for the recovery of metals such as Mo, V, Ni, Al from spent hydroprocessing catalyst which may otherwise cause a nuisance if dumped untreated. A detailed study on the separation of molybdenum and vanadium from the leach solution of spent hydroprocessing catalyst of composition: 27.15% MoO?, 1.7% V?O?, 3.75% NiO, 54.3% Al?O?, 2.3% SiO? and 10.4% LOI is reported in this paper. The catalyst was subjected to roasting under oxidizing atmosphere at a temperature of about 550 °C and leaching in dilute sulphuric acid to dissolve molybdenum, vanadium, nickel and part of aluminium. Metals from the leach solution were separated by solvent extraction. Both molybdenum and vanadium were selectively extracted with a suitable organic solvent leaving nickel and dissolved aluminium in the raffinate. Various parameters such as initial pH of the aqueous feed, organic to aqueous ratio (O:A), solvent concentration etc. were optimized for the complete extraction and recovery of Mo and V. Molybdenum and vanadium from the loaded organic were stripped by ammonia solution. They were recovered as their corresponding ammonium salt by selective precipitation, and were further calcined to get the corresponding oxides in pure form. PMID:23644591

Sahu, K K; Agrawal, Archana; Mishra, D

2013-08-15

234

Effects of acid catalyst type on structural, morphological, and optoelectrical properties of spin-coated TiO2 thin film  

NASA Astrophysics Data System (ADS)

The effects of different acid catalysts of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, acetic acid, and citric acid on structural, morphological, and optoelectrical properties of nanocrystalline spin-coated TiO2 thin films synthesized via alkoxide sol-gel route were investigated. It was found that only the sols with HNO3 and HCl are suitable for film preparation. The X-ray diffractometry and Raman analysis showed that crystalline phases could be controlled by the type of acid catalyst. Although the H2SO4 sol shows good stability, it causes extremely different morphology to form due to its different sol nature and high contact angle. Fourier transformed infrared spectra confirmed the presence of acid anion species in all samples even after calcination. Furthermore, it was inferred from UV-visable absorption spectra that although the band gap and thickness of the films are independent of acid catalyst type, the refractive index and porosity of the films are strongly affected by the type of acids.

Golobostanfard, Mohammad Reza; Abdizadeh, Hossein

2013-03-01

235

Effect of the catalyst composition in the Pt x (Ru–Ir) 1? x \\/C system on the electro-oxidation of methanol in acid media  

Microsoft Academic Search

The effect of variations in the composition for ternary catalysts of the type Ptx(Ru–Ir)1?x\\/C on the methanol oxidation reaction in acid media for x values of 0.25, 0.50 and 0.75 is reported. The catalysts were prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analyses.

K. I. B. Eguiluz; G. R. Salazar-Banda; D. Miwa; S. A. S. Machado; L. A. Avaca

2008-01-01

236

Perfluorosulfonic acid-functionalized Pt\\/carbon nanotube catalysts with enhanced stability and performance for use in proton exchange membrane fuel cells  

Microsoft Academic Search

To further improve lifetime and performance of carbon nanotube (CNT) supported Pt catalysts for proton exchange membrane fuel cells, perfluorosulfonic acid (PFSA) was introduced by a simple colloid route to functionalize Pt (PFSA-Pt\\/CNT) catalysts. Here the PFSA is available as a binder to tightly anchor Pt nano-particles onto the CNT surfaces, and as a proton conductor to increase the triple

Daping He; Shichun Mu; Mu Pan

2011-01-01

237

NMR-spectroscopic evidence of intermediate-dependent pathways for acetic acid formation from methane and carbon monoxide over a ZnZSM-5 zeolite catalyst.  

PubMed

Two ways: a Zn-modified ZSM-5 zeolite catalyst was developed for the reaction of methane with carbon monoxide to directly produce acetic acid under mild conditions (573-623 K), and two different intermediate-dependent reaction pathways were unambiguously identified for acetic acid formation by in situ solid-state NMR spectroscopy. PMID:22389151

Wang, Xiumei; Qi, Guodong; Xu, Jun; Li, Bojie; Wang, Chao; Deng, Feng

2012-04-16

238

Acid Strength of Support Materials as a Factor Controlling Oxidation State of Palladium Catalyst for Propane Combustion  

Microsoft Academic Search

The support effect on the low temperature catalytic combustion of propane over palladium catalyst was studied by using a series of metal oxides as support materials: MgO, ZrO2, Al2O3, SiO2, SiO2–ZrO2, SiO2–Al2O3, and SO42?–ZrO2. The catalytic activity varied with the kind of the support materials; a support material with moderate acid strength gave maximum conversion. In order to discuss more

Yoshiteru Yazawa; Hisao Yoshida; Nobuyuki Takagi; Shin-ichi Komai; Atsushi Satsuma; Tadashi Hattori

1999-01-01

239

Comparison of different Lewis acid supported on hydroxyapatite as new catalysts of Friedel–Crafts alkylation  

Microsoft Academic Search

ZnCl2, NiCl2 and CuCl2 supported on hydroxyapatite (HAP), as a new solid support, catalyse the Friedel–Crafts alkylation of benzene, toluene and p-xylene by benzyl chloride. The reaction proceeds selectively to monoalkyl-compounds and in a short reaction time. The best catalytic activities were observed with the zinc catalysts.

Rachid Tahir; Rachid Nazih

2001-01-01

240

Supported transition metal oxides as acid cracking catalysts: periodic trends and their relationship to activity and selectivity  

SciTech Connect

Surface phase oxides bonded to a support such as alumina have not been recognized previously to have acid cracking activities in the league of amorphous silica-alumina to the best of their knowledge. In this paper the relative gas-oil cracking activities of all Group IV, V, and VIB oxides supported on alumina (including alumina and rhenia on alumina) are reported. All of the supported oxides are at a surface coverage about one-third that of a monolayer. Tungsten oxide and niobium oxide on alumina have been identified as solids acids with high activity; while molybdenum oxide and rhenium oxide on alumina lead to high coke and gas make even with steam present as a cofeed in the cracking test. The periodic trends of cracking activity are those expected from the charge-to-radius ratio of the metal cation. This class of surface phase oxide solid acids has a wide range of activities (two orders of magnitude) and may prove useful for matching acid strength to specific reactions. In addition, this class of solid acids maintains surface area and cracking activity following high temperature steam treatment, in contrast to many conventional solid acid catalysts.

Murrell, L.L.; Grenoble, D.C.; Kim, C.J.; Dispenziere, N.C. Jr.

1987-10-01

241

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

242

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

243

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

244

Hollow Ag@Pd core-shell nanotubes as highly active catalysts for the electro-oxidation of formic acid  

NASA Astrophysics Data System (ADS)

Ag nanowires are prepared as templates by a polyol reduction process. Then Ag nanotubes coated with a thin layer of Pd are synthesized through sequential reduction accompanied with the galvanic displacement reaction. The products show a hollow core-shell nanotubular structure, as demonstrated by detailed characterizations. The Ag@Pd can significantly improve the electrocatalytic activity towards the electro-oxidation of formic acid and enhance the stability of the Pd component. It is proposed that the enhanced electrochemically active surface area and modulated electron structure of Pd by Ag are responsible for the improvement of electrocatalytic activity and durability. The results obtained in this work are different from those previous reports, in which alloy walls with hollow interiors are usually formed. This work provides a new and simple method for synthesizing novel bimetallic core-shell structure with a hollow interior, which can be applied as high-performance catalysts for the electro-oxidation of formic acid.

Jiang, Yuanyuan; Lu, Yizhong; Han, Dongxue; Zhang, Qixian; Niu, Li

2012-03-01

245

Catalytic Synthesis of Oxygenates: Mechanisms, Catalysts and Controlling Characteristics  

SciTech Connect

This research focused on catalytic synthesis of unsymmetrical ethers as a part of a larger program involving oxygenated products in general, including alcohols, ethers, esters, carboxylic acids and their derivatives that link together environmentally compliant fuels, monomers, and high-value chemicals. The catalysts studied here were solid acids possessing strong Br�������¸nsted acid functionalities. The design of these catalysts involved anchoring the acid groups onto inorganic oxides, e.g. surface-grafted acid groups on zirconia, and a new class of mesoporous solid acids, i.e. propylsulfonic acid-derivatized SBA-15. The former catalysts consisted of a high surface concentration of sulfate groups on stable zirconia catalysts. The latter catalyst consists of high surface area, large pore propylsulfonic acid-derivatized silicas, specifically SBA-15. In both cases, the catalyst design and synthesis yielded high concentrations of acid sites in close proximity to one another. These materials have been well-characterization in terms of physical and chemical properties, as well as in regard to surface and bulk characteristics. Both types of catalysts were shown to exhibit high catalytic performance with respect to both activity and selectivity for the bifunctional coupling of alcohols to form ethers, which proceeds via an efficient SN2 reaction mechanism on the proximal acid sites. This commonality of the dual-site SN2 reaction mechanism over acid catalysts provides for maximum reaction rates and control of selectivity by reaction conditions, i.e. pressure, temperature, and reactant concentrations. This research provides the scientific groundwork for synthesis of ethers for energy applications. The synthesized environmentally acceptable ethers, in part derived from natural gas via alcohol intermediates, exhibit high cetane properties, e.g. methylisobutylether with cetane No. of 53 and dimethylether with cetane No. of 55-60, or high octane properties, e.g. diisopropylether with blending octane No. of 105, and can replace aromatics in liquid fuels.

Kamil Klier; Richard G. Herman

2005-11-30

246

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

247

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

248

Recovery of nickel from spent NiO/Al2O3 catalyst through sulfuric acid leaching, precipitation and solvent extraction.  

PubMed

Effective recovery of nickel (Ni) from spent NiO/Al(2)O(3) catalyst in a simple hydrometallurgical route is suggested. Nickel recovery of 99.5% was achieved with sulfuric acid leaching. The leach liquor was partly neutralized and nickel ammonium sulfate was precipitated by adding ammonia. The nickel in the supernatant was concentrated by solvent extraction using D2EHPA and subsequently stripped back into sulfuric acid and returned to the precipitation stage. Necessary counter current extraction and stripping stages were determined in McCabe-Thiele diagrams. The suggested method appears simple and very effective in recovering nickel from spent catalysts from the petrochemical industry. PMID:21930525

Nazemi, M K; Rashchi, F

2012-05-01

249

PROPIEDADES ACIDAS DE LOS CATALIZADORES DE Pt-Sn\\/Al2O3 PREPARADOS POR SOL-GEL ACIDIC PROPERTIES OF Pt-Sn\\/Al2O3 SOL-GEL PREPARED CATALYSTS  

Microsoft Academic Search

The acid properties in sol-gel catalysts were studied. Tin-alumina catalysts were prepared by cogeltion of aluminium tri-sec-butoxide and tetra-butyltin, tetra-ter-amil-oxide tin or tin tetrachloride. Aqueous platinum solutions were used for impregnation. The results shown that the specific surface area and the acidity of the catalysts were only alightly modified by the metal precursors used. The solids prepared with tetrabutyltin showed

R. Silva-Rodrigo; T. López-Goerne; V. Bertin-Mardel; R. Gómez-Romero

2005-01-01

250

Active sites in vanadia\\/titania catalysts for selective aerial oxidation of ?-picoline to nicotinic acid  

Microsoft Academic Search

Vanadia\\/titania catalysts with varying vanadium content were prepared by impregnation using three different titania carrier materials of varying surface area. The structure of active vanadium species for ?-picoline oxidation was investigated. Vanadium is mainly in the +5 oxidation state as revealed by electron paramagnetic resonance (EPR) and 51V magic-angle spinning nuclear magnetic resonance (51V MAS NMR) spectroscopy techniques. Diffuse reflectance

Darbha Srinivas; Wolfgang F. Hölderich; Steffen Kujath; Michael H. Valkenberg; Thirumalaiswamy Raja; Lakshi Saikia; Ramona Hinze; Veda Ramaswamy

2008-01-01

251

Hydroisomerization and hydrocracking of alkanes. 7. Influence of the balance between acid and hydrogenating functions on the transformation of n-decane on PtHY catalysts  

SciTech Connect

The transformation of n-decane was studied at 473 K, 101 kPa and pH{sub 2}/p{sub n-decane} = 9 on a series of PtHY catalysts containing from 0.02 to 1.5 wt% platinum and with Si/Al atomic ratios of 3, 9, or 35. The ratio between the number of accessible Pt atoms and the number of acid sites on which the heat of ammonia adsorption is greater than 100 kJ mol{sup -1} (n{sub Pt}/n{sub A}) was chosen for characterizing the balance between the hydrogenating and the acid functions. The activities, stabilities, and selectivities of the catalysts are definitely governed by this balance. For low values of N{sub Pt}/n{sub A} (<0.03), the activity per acid site is low, the deactivation is rapid and n-decane leads directly to all the isomerization and cracking products. For high values ({ge}0.17) the activity per acid sites is maximal, the deactivation is very slow and n-decane transforms successively into monobranched isomers, dibranched isomers, and tribranched isomers plus cracking products. In this latter case the catalyst can be considered as an ideal bifunctional catalyst, namely a catalyst on which only one transformation of the alkene intermediates on the acid sites can occur during their diffusion from the platinum sites on which they are generated to those on which they are hydrogenated. Therefore the reaction scheme of n-decane transformation matches the reaction scheme of olefinic intermediates. From the product distribution established on ideal catalysts the mechanism of the transformation of olefinic intermediates can be deduced. Branching isomerization occurs through protonated cyclopropane and cyclobutane intermediates. 29 refs., 9 figs., 5 tabs.

Alvarez, F.; Ribeiro, F.R. [Instituto Superior Tecnico, Lisboa Codex (Portugal)] [Instituto Superior Tecnico, Lisboa Codex (Portugal); Perot, G.; Thomazeau, C. [Universite de Poitiers (France)] [Universite de Poitiers (France)

1996-09-01

252

Two-Stage Conversion of High Free Fatty Acid Jatropha curcas Oil to Biodiesel Using Br?nsted Acidic Ionic Liquid and KOH as Catalysts  

PubMed Central

Biodiesel was produced from high free fatty acid (FFA) Jatropha curcas oil (JCO) by two-stage process in which esterification was performed by Brønsted acidic ionic liquid 1-(1-butylsulfonic)-3-methylimidazolium chloride ([BSMIM]Cl) followed by KOH catalyzed transesterification. Maximum FFA conversion of 93.9% was achieved and it reduced from 8.15?wt% to 0.49?wt% under the optimum reaction conditions of methanol oil molar ratio 12?:?1 and 10?wt% of ionic liquid catalyst at 70°C in 6?h. The ionic liquid catalyst was reusable up to four times of consecutive runs under the optimum reaction conditions. At the second stage, the esterified JCO was transesterified by using 1.3?wt% KOH and methanol oil molar ratio of 6?:?1 in 20?min at 64°C. The yield of the final biodiesel was found to be 98.6% as analyzed by NMR spectroscopy. Chemical composition of the final biodiesel was also determined by GC-MS analysis.

Das, Subrata; Thakur, Ashim Jyoti; Deka, Dhanapati

2014-01-01

253

Partial oxidation of methane on silica-supported silicomolybdic acid catalysts in an excess amount of water vapor  

SciTech Connect

Partial oxidation of methane into oxygenates such as methanol and formaldehyde on highly dispersed MoO{sub 3}/SiO{sub 2} catalysts was studied in an excess amount of water vapor. The reaction was carried out at 873 K using gases consisting of oxygen, methane, and water vapor. The selectivity of oxygenates was found to be a strong function of water vapor, and increased as the fraction of water vapor in a feed gas increased. Inversely, the selectivity of CO and CO{sub 2} in the products decreased as the fraction of water vapor increased. This is ascribed to the formation of silicomolybdic acid (SMA:H{sub 4}SiMo{sub 12}O{sub 40}) over the silica surface during the reaction, partially evidenced by IR measurements. Accordingly, silica-supported SMA catalysts were prepared and applied to the partial oxidation of methane under the same conditions as described above to see if SMA works as the active species for the reaction. Although SMA easily decomposed into SiO{sub 2} and MoO{sub 3} at 873 K without water vapor, it worked well for the production of oxygenates when the fraction of water vapor was more than 50% in the feed gas. The yield of oxygenates increased up to 20% of methane as the fraction of water vapor was around 60%; methane conversion was about 25% and the selectivity of oxygenates was 90%. In this paper, the authors will emphasize that SMA formed on the silica surface are the active species of silica-supported MoO{sub 3} catalysts for the partial oxidation of methane in an excess amount of water vapor.

Sugino, Tomomi; Kido, Ayako; Azuma, Naoto; Ueno, Akifumi; Udagawa, Yasuo

2000-02-15

254

Bio-inspired amino acid oxidation by a non-heme iron catalyst.  

PubMed

This study reports the kinetics and mechanism of Fe(III)-catalyzed oxidative decarboxylation and deamination of a series of acyclic (?-aminoisobutyric acid, ?-(methylamino)isobutyric acid, alanine, norvaline, and 2-aminobutyric acid) and cyclic (1-aminocyclopropane-1-carboxylic acid, 1-amino-1-cyclobutanecarboxylic acid, 1-aminocyclopentanecarboxylic acid, and 1-aminocyclohexanecarboxylicacid) amino acids using hydrogen peroxide, t-butyl hydroperoxide, iodosylbenzene, m-chloroperbenzoic acid, and peroxomonosulphate as oxidant in 75% DMF-25% water solvent mixture. Model complex [Fe(IV)O(SALEN)](•+) (SALENH2: N,N'-bis(salicylidene)ethylenediamine) was generated by the reaction of Fe(III)(SALEN)Cl and H2O2 in CH3CN at 278 K as reported earlier. This method provided us high-valent oxoiron species, stable enough to ensure the direct observation of the reaction with amino acids. PMID:23528571

Góger, Szabina; Bogáth, Dóra; Baráth, Gábor; Simaan, A Jalila; Speier, Gábor; Kaizer, József

2013-06-01

255

Functional gel-type resin based palladium catalysts: The role of polymer properties in the hydrogenation of the C C bond of maleic and fumaric acids, the isomers of dicarboxylic acids  

Microsoft Academic Search

Functional gel-type resins (OFP) composed of 2-hydroxyethyl methacrylate (HEMA, 20mol%), styrene (60–77mol%) and diethylene glycol dimethacrylate, the crosslinking reagent (DEGDMA, 3–20mol%) are used as supports for palladium catalysts (0.25–2wt% Pd). The influence of polymer mass expansion on the activity of Pd\\/OFP catalysts in the hydrogenation of cis- and trans-isomers of unsaturated dicarboxylic acids, maleic (MA) and fumaric (FA), is examined.

A. Drelinkiewicz; A. Knapik; A. Waksmundzka-Góra; A. Bukowska; W. Bukowski; J. Noworól

2008-01-01

256

Selective oxidation of propane to acrylic acid on K-doped MoVSbO catalysts: catalyst characterization and catalytic performance  

Microsoft Academic Search

K-doped MoVSb mixed oxides catalysts have been prepared by impregnation of a MoVSbO mixed oxide (previously prepared by hydrothermal synthesis) with an aqueous solution of potassium nitrate, characterized by XRD, SEM-EDX, EPR, XPS, XANES, and FTIR of adsorbed NH3, and tested in the selective oxidation of propane and propylene in the 593–693 K temperature range. The undoped MoVSbO catalysts presented

T. Blasco; P. Botella; P. Concepción; J. M. López Nieto; A. Martinez-Arias; C. Prieto

2004-01-01

257

Synthesis of fatty acid methyl ester from crude jatropha (Jatropha curcas Linnaeus) oil using aluminium oxide modified Mg-Zn heterogeneous catalyst.  

PubMed

The synthesis of fatty acid methyl esters (FAME) as a substitute to petroleum diesel was investigated in this study from crude jatropha oil (CJO), a non-edible, low-cost alternative feedstock, using aluminium modified heterogeneous basic oxide (Mg-Zn) catalyst. The transesterification reaction with methanol to methyl esters yielded 94% in 6h with methanol-oil ratio of 11:1, catalyst loading of 8.68 wt.% at 182°C and the properties of CJO fuel produced were determine and found to be comparable to the standards according to ASTM. In the range of experimental parameters investigated, it showed that the catalyst is selective to production of methyl esters from oil with high free fatty acid (FFA) and water content of 7.23% and 3.28%, respectively in a single stage process. Thus, jatropha oil is a promising feedstock for methyl ester production and large scale cultivation will help to reduce the product cost. PMID:21486692

Olutoye, M A; Hameed, B H

2011-06-01

258

Photo-degradation of acid green dye over Co-ZSM-5 catalysts prepared by incipient wetness impregnation technique.  

PubMed

Co-ZSM-5 catalysts with different Co-loadings (2-30wt.%) were prepared by incipient wetness impregnation method. The prepared solid catalysts were characterized by X-ray diffraction, FTIR, in situ FTIR of pyridine adsorption and surface area measurements. The XRD data presented disintegration in the zeolitic crystalline structure accompanied by an increase in particle size of the prepared solids. New phases, Co(3)O(4) and Co(2)SiO(4), were detected with increasing the Co-loading, which indicate the strong interaction of cobalt ions with the ZSM-5 zeolite. FTIR study proved the presence of Co ions in stabilized sites inside the ZSM-5 framework. The in situ FTIR of adsorbed pyridine determined the type and relative strength of acidity on the surface of the prepared solids. The acidity switched from B-acid sites to L-acid sites with impregnation of cobalt ions in ZSM-5 zeolite. The acidity decreased with increasing Co-loading, which might be due to the destruction of zeolite framework and presence of new phases such as cobalt silicate and cobalt oxide on the surface. The surface texture characteristics changed with the promotion of ZSM-5 by cobalt ions, since a decrease of surface area, mean pore radius and pore volume was observed. The assessment of the catalytic activity was performed by the use of the photo-degradation of acid green (AG) dye as a probe reaction in presence of H(2)O(2) as an oxidant. The pH value controlled the degradation rate since a gradual increase of AG degradation rate was observed with increasing pH value and the optimum H(2)O(2) concentration was 61.6 mmol/l. It was found that, the AG degradation rate increased until an optimum value of Co-loading (ca. 10 wt.%), beyond which a monotonic decrease of reaction rate was recognized. The experimental data pointed to the importance of both the cobalt moieties and the zeolite framework structure in the AG degradation reaction. PMID:17904732

El-Bahy, Zeinhom M; Mohamed, Mohamed M; Zidan, Farouk I; Thabet, Mohamed S

2008-05-01

259

Preparation and characterization of mesoporous N-doped and sulfuric acid treated anatase TiO{sub 2} catalysts and their photocatalytic activity under UV and Vis illumination  

SciTech Connect

Nitrogen-doped TiO{sub 2} catalysts were prepared by a precipitation method. The samples were calcined at 400 deg. C for 4 h in air. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature N{sub 2}-adsorption was used for structural characterization and UV-diffuse reflectance (UV-DR) was applied to investigate the optical properties of the as-prepared samples. It was found that microporous N-doped catalysts have solely anatase crystalline structure. Acidic treatment of the calcined samples was performed using sulfuric acid agitation. The crystalline structure remained unchanged due to surface treatment, while the porosity and the surface areas (a{sub BET}{sup S}) were decreased dramatically. Optical characterization of the doped catalysts showed that they could be excited by visible light photons in the 400-500 nm wavelength range (lambda{sub g,1}={approx}390 nm, lambda{sub g,2}={approx}510 nm). It was also established that surface treatment enhances the Vis-light absorption of the N-TiO{sub 2} powders. Finally the catalysts were tested in the photocatalytic degradation of phenol in aqueous suspensions. Two different light sources were used; one of them was a UV-rich high pressure Hg-lamp, while the other was a tubular visible light source. We found that using visible light illumination N-doped, acid treated TiO{sub 2} samples were more catalytically active than non-doped TiO{sub 2} catalysts. - Graphical abstract: The effect of the acid treatment on the visible-light-driven photocatalytic activity of the N-doped, anatase TiO{sub 2} catalysts.

Kun, Robert [Supramolecular and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, University of Szeged, Aradi vt. 1, H-6720 Szeged (Hungary); Tarjan, Sandor [Department of Colloid Chemistry, University of Szeged, Aradi vt. 1, H-6720 Szeged (Hungary); Oszko, Albert [Department of Solid State and Radiochemistry, University of Szeged, Aradi vt. 1, H-6720 Szeged (Hungary); Seemann, Torben; Zoellmer, Volker; Busse, Matthias [Fraunhofer Institute for Manufacturing Technology and Applied Materials Research, IFAM, Wienerstrasse 12, 28359 Bremen (Germany); Dekany, Imre, E-mail: i.dekany@chem.u-szeged.h [Supramolecular and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, University of Szeged, Aradi vt. 1, H-6720 Szeged (Hungary); Department of Colloid Chemistry, University of Szeged, Aradi vt. 1, H-6720 Szeged (Hungary)

2009-11-15

260

Hydrocracking of polyolefins to liquid fuels over strong solid acid catalysts  

SciTech Connect

Post-consumer plastic makes up about 13 wt% of the 48 million tons of total packaging wastes generated annually. Plastics are non-biodegradable, constitute a increasingly large volume of solid wastes (20 vol. % in 1990), and are not being recycled to a significant extent. Pyrolysis, as an alternative for plastic waste recycling, usually results in unsaturated and unstable oils of low yield and value. Significant amounts of char are formed on pyrolyzing plastic wastes. This paper describes the results of hydrocracking of polyolefins over sulfated zirconia catalysts.

Venkatesh, K.R.; Hu, J.; Tierney, J.W.; Wender, I. [Univ. of Pittsburgh, PA (United States)

1995-12-31

261

Simultaneous formation of nitrogen and sulfur-doped transition metal catalysts for oxygen reduction reaction through pyrolyzing carbon-supported copper phthalocyanine tetrasulfonic acid tetrasodium salt  

NASA Astrophysics Data System (ADS)

In this work, we report a spontaneous formation of copper (Cu-N-S/C) catalysts containing both nitrogen (N) and sulfur (S) elements using a one-step pyrolysis of carbon supported copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc/C). The obtained catalysts exhibit high catalytic activities for oxygen reduction reaction (ORR) in alkaline media. Through electrochemical measurements and physical characterizations, several observations are reached as follows: (1) different pyrolysis temperatures can result in different catalyst structures and performances, and the optimum pyrolysis temperature is found to be 700 °C; (2) the electron transfer number of the ORR process catalyzed by the unpyrolyzed catalyst is about 2.5, after the pyrolysis, this number is increased to 3.5, indicating that the pyrolysis process can change the ORR pathway from a 2-electron transfer dominated process to a 4-electron transfer dominated one; (3) increasing catalyst loading from 40 ?g cm-2 to 505 ?g cm-2 can effectively improve the catalytic ORR activity, under which the percentage of H2O2 produced decreases sharply from 39.5% to 7.8%; and (4) the Cu ion can bond on pyridinic-N, graphite-N and C-Sn-C to form Cu-N-S/C catalyst active sites, which play the key role in the ORR activity.

Qing, Xin; Shi, Jingjing; Ma, Chengyu; Fan, Mengyang; Bai, Zhengyu; Chen, Zhongwei; Qiao, Jinli; Zhang, Jiujun

2014-11-01

262

Materials and Molecular Research Division, Effects of Lewis Acid Catalysts on the Hydrogenation and Cracking of Two-Ring Aromatic and Hydroaromatic Structures Related to Coal.  

National Technical Information Service (NTIS)

An investigation was carried out of the hydrogenation and cracking of two-ring aromatic and hydroaromatic compounds catalyzed by ZnCl(sup 2) and AlCl(sup 3). The rates of both processes are strongly affected by the Bronsted acidity of the active catalyst ...

A. T. Bell S. S. Salim

1980-01-01

263

Sulfur and iron co-doped titanoniobate nanosheets: a novel efficient solid acid catalyst for alcoholysis of styrene epoxide at room temperature.  

PubMed

Sulfur and iron co-doped titanoniobate nanosheets were prepared and evaluated in alcoholysis of styrene epoxide. The resultant co-doped catalyst exhibited excellent catalytic performance (yield of 99% with methanol as the nucleophile in only 1 h at room temperature) and may act as a promising candidate in many acid-catalyzed reactions. PMID:23856976

Zhang, Lihong; Hu, Chenhui; Zhang, Junfeng; Cheng, Liyuan; Zhai, Zheng; Chen, Jing; Ding, Weiping; Hou, Wenhua

2013-09-01

264

Synthesis of 3-Mono-Substituted Binaphthyl-Based Secondary Amine Catalysts via Monobromination of an Axially Chiral Dicarboxylic Acid Derivative.  

PubMed

A facile synthetic route to a 3-bromo binaphthyl-based secondary amine through the monobromination of an axially chiral dicarboxylic acid derivative has been developed. The combination of this new procedure with coupling reactions established an efficient synthetic approach to a series of binaphthyl-based secondary amine catalysts containing various functional groups in an efficient way. PMID:24708270

Kano, Taichi; Takeda, Momotaro; Sakamoto, Ryu; Maruoka, Keiji

2014-05-01

265

Chiral magnesium(II) binaphtholates as cooperative Brønsted/Lewis acid-base catalysts for the highly enantioselective addition of phosphorus nucleophiles to ?,?-unsaturated esters and ketones.  

PubMed

A little cooperation goes a long way: The cooperative Brønsted/Lewis acid-base supramolecular catalysts formed in situ from simple chiral magnesium(II) binaphtholate aqua complexes promoted the highly enantioselective 1,4-hydrophosphinylation of ?,?-unsaturated esters with diaryl phosphine oxides and 1,2-hydrophosphonylation of ?,?-unsaturated ketones with dialkyl phosphites (see scheme). PMID:23495237

Hatano, Manabu; Horibe, Takahiro; Ishihara, Kazuaki

2013-04-22

266

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

267

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

268

Mineralization of clofibric acid by electrochemical advanced oxidation processes using a boron-doped diamond anode and Fe 2+ and UVA light as catalysts  

Microsoft Academic Search

This work shows that aqueous solutions of clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid), the bioactive metabolite of various lipid-regulating drugs, up to saturation at pH 3.0 are efficiently and completely degraded by electrochemical advanced oxidation processes such as electro-Fenton and photoelectro-Fenton with Fe2+ and UVA light as catalysts using an undivided electrolytic cell with a boron-doped diamond (BDD) anode and an O2-diffusion

Ignasi Sirés; Francesc Centellas; José Antonio Garrido; Rosa María Rodríguez; Conchita Arias; Pere-Lluís Cabot; Enric Brillas

2007-01-01

269

Cu nanoclusters supported on nanocrystalline SiO2-MnO2: 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

2014-07-29

270

Nano TiO 2 photo-catalyst and sodium hypophosphite for cross-linking cotton with poly carboxylic acids under UV and high temperature  

Microsoft Academic Search

The present research attempts to accomplish a cross-linking finish on the bleached cotton fabric by using a nano titanium dioxide photo-catalyst which can effectively operate under UV irradiation. In this study, the bleached cotton fabrics were treated with two cross-linking agents including 1,2,3,4-butane tetracarboxylic acid (BTCA) and citric acid (CA) in the presence of sodium hypophosphite (SHP) and nano TiO2

A. Nazari; M. Montazer; A. Rashidi; M. Yazdanshenas; M. Anary-Abbasinejad

2009-01-01

271

Effects of structural defects and acid–basic properties on the activity and selectivity of isopropanol decomposition on nanocrystallite sol–gel alumina catalyst  

Microsoft Academic Search

The surface acid–basic properties of sol–gel alumina catalysts were studied by Fourier transform infrared (FTIR) spectroscopy of pyridine adsorption and temperature-programmed desorption of CO2 and NH3. The number of acid and basic sites on the samples varied with the calcination temperatures of the samples. The populations of the three different aluminum ions—tetrahedral, pentacoordinated and octahedral, which were identified by the

J. A. Wang; X. Bokhimi; O. Novaro; T. López; F. Tzompantzi; R. Gómez; J. Navarrete; M. E. Llanos; E. López-Salinas

1999-01-01

272

Influence of Acid Modification on Selective Phenol Hydrogenation Over Pd\\/Activated Carbon Catalysts  

Microsoft Academic Search

The influence of the acid treatment on cyclohexanone selectivity of phenol hydrogenation over Pd on active carbon was studied\\u000a in liquid phase reaction and by temperature-programmed desorption. Acid treatment of activated carbon led to an increased\\u000a cyclohexanone\\/cyclohexanol ratio. Acid modification of the carbon support enriched the electron density of Pd, and enhanced\\u000a the desorption of the phenoxy species, which resulted

Shingo Watanabe; Venu Arunajatesan

2010-01-01

273

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

274

Alkylation catalyst regeneration  

SciTech Connect

Described is a novel acid-soluble oil composition produced as a by-product from an alkylation reaction catalyzed by a sulfone-containing catalyst. Also described is a novel process for regenerating an alkylation catalyst which contains a sulfone component. 2 figs.

Eastman, A.D.; Abbott, R.G.

1994-01-04

275

Cycloisomerization of acetylenic acids to ?-alkylidene lactones using a palladium(II) catalyst supported on amino-functionalized siliceous mesocellular foam.  

PubMed

Cycloisomerization of various ?-acetylenic acids to their corresponding ?-alkylidene lactones by the use of a heterogeneous Pd(II) catalyst supported on amino-functionalized siliceous mesocellular foam is described. Substrates containing terminal as well as internal alkynes were cyclized in high to excellent yields within 2–24 h under mild reaction conditions. The protocol exhibited high regio- and stereoselectivity, favoring the exo-dig product with high Z selectivity. Moreover, the catalyst displayed excellent stability under the employed reaction conditions, as demonstrated by its good recyclability and low leaching. PMID:24467515

Nagendiran, Anuja; Verho, Oscar; Haller, Clémence; Johnston, Eric V; Bäckvall, Jan-E

2014-02-01

276

Preparation of Butyl Chloride from Butanol and Hydrochloric Acid Using Ionic Liquids as Catalyst * * Supported by the National Natural Science Foundation of China (No.20376004)  

Microsoft Academic Search

The catalytic performance of some quaternary ammonium salts for the liquid phase reaction of butanol and hydrochloric acid at different conditions was studied experimentally and compared with the traditional catalyst (ZnCl2). The organic ammonium catalysts investigated include ionic liquids N-butyl-N-methyl imidazolium fluoborate ([BMIM][BF4]) and N-butyl-N-methylimidazolium chloride ([BMIM]Cl) as well as hydrochloric salts of N-methylimidazol ([HMIM]Cl), pyridine ([HPy]Cl) and triethylamine ([HEt3N]Cl).

Aijun SUN; Yi NIE; Chunxi LI; Zihao WANG

2008-01-01

277

Experimental evidence for the all-up reactive conformation of chiral rhodium(II) carboxylate catalysts: enantioselective synthesis of cis-cyclopropane alpha-amino acids.  

PubMed

Useful empirical insights onto the enantioinduction process of chiral Rh(II)-carboxylate catalysts are described in the first catalytic asymmetric cyclopropanation of alkenes with alpha-nitro diazoacetophenones. X-ray, solution NMR, and reactivity studies made on these complexes suggest that the level of asymmetric induction strongly depends on their active symmetry, which in turn relies on the nature of the chiral ligands' substituents. The catalyst's 'All Up' reactive conformation resulted in being necessary to obtain good stereoselectivity, and the resulting products are shown to be key intermediates in a concise synthesis of highly enantioenriched cis-cyclopropane alpha-amino acids. PMID:19860407

Lindsay, Vincent N G; Lin, Wei; Charette, André B

2009-11-18

278

Chiral derivatives of 1,2-benzenedisulfonimide as efficient Brønsted acid catalysts in the Strecker reaction.  

PubMed

Two chiral derivatives of 1,2-benzenedisulfonimide, namely 4-methyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide and 4,5-dimethyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide, have been easily synthesized in good overall yields (respectively 34% and 41%) by means of an eleven-step synthetic protocol from commercially available 2-methyl-6-nitroaniline or 2,3-dimethyl-6-nitroaniline. 4,5-Dimethyl-3,6-bis(1-naphthyl)-1,2-benzenedisulfonimide was also synthesized, but the overall yield from 2,3-dimethyl-6-nitroaniline was lower (9%). The atropisomers of these compounds have been resolved and (-)atropisomers have been demonstrated to be efficient chiral catalysts in the Strecker reaction. PMID:24788654

Barbero, Margherita; Cadamuro, Silvano; Dughera, Stefano; Torregrossa, Roberta

2014-06-21

279

Deactivator for olefin polymerization catalyst  

SciTech Connect

A method is described comprising deactivating an olefin polymerization catalyst selected from the group consisting of Ziegler-Natta transition element catalysts and catalysts based on transition metal oxides by contacting the catalyst with a copolymer. The copolymer consists of an alpha-olefin having from 2 to about 12 carbon atoms and an unsaturated ester of a carboxylic acid. The deactivating copolymer is present in an amount such that the molar ratio of the unsaturated ester thereof to the sum of the transition element component of the polymerization catalyst and a cocatalyst for the transition element catalyst is in the range of between about 0.1 and about 6.

Rekers, L.J.; Speca, A.N.; Mayhew, H.W.

1987-03-10

280

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Electro-oxidation of Formic Acid on Carbon Supported Edge-Truncated Cubic Platinum Nanoparticles Catalysts  

NASA Astrophysics Data System (ADS)

The oxidation of formic acid on edge-truncated cubic platinum nanoparticles/C catalysts is investigated. X-ray photoelectron spectroscopy analysis indicates that the surface of edge-truncated cubic platinum nanoparticles is composed of two types of coordination sites. The oxidation behavior of formic acid on edge-truncated cubic platinum nanoparticles/C is investigated using cyclic voltammetry. The apparent activation energies are found to be 54.2, 55.0, 61.8, 69.5, 71.9, 69.26, 65.28kJ/mol at 0.15, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7V, respectively. A specific surface area activity of 1.76 mA·cm-2 at 0.4 V indicates that the edge-truncated cubic Platinum nanoparticles are a promising anode catalyst for direct formic acid fuel cells.

Li, She-Qiang; Fu, Xing-Qiu; Hu, Bing; Deng, Jia-Jun; Chen, Lei

2009-11-01

281

Kinetic resolution of racemic alpha-arylalkanoic acids with achiral alcohols via the asymmetric esterification using carboxylic anhydrides and acyl-transfer catalysts.  

PubMed

A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic alpha-substituted carboxylic acids using achiral alcohols, aromatic or aliphatic carboxylic anhydrides, and chiral acyl-transfer catalysts. The combination of 4-methoxybenzoic anhydride (PMBA) or pivalic anhydride with the modified benzotetramisole-type catalyst ((S)-beta-Np-BTM) is the most effective for promotion of the enantioselective coupling reaction between racemic carboxylic acids and a novel nucleophile, bis(alpha-naphthyl)methanol, to give the corresponding esters with high ee's. This protocol was successfully applied to the production of nonracemic nonsteroidal anti-inflammatory drugs from racemic compounds utilizing the transacylation process to generate the mixed anhydrides from the acid components with the suitable carboxylic anhydrides. PMID:20681552

Shiina, Isamu; Nakata, Kenya; Ono, Keisuke; Onda, Yu-suke; Itagaki, Makoto

2010-08-25

282

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

283

Low Temperature Thermoconversion of Biomass to Useful Chemicals by Lewis Acid Catalysts. Phase I.  

National Technical Information Service (NTIS)

The goal of this study was to convert biomass into useful organic chemicals at reasonable cost. Lewis acids such as aluminum chloride (AlCl3) were used for thermoconversion of lignocellulosic materials (biomass) into useful organic materials. Temperatures...

V. R. Koch G. H. Schnaper

1980-01-01

284

Br?nsted Acid Co-catalysts in Photocatalytic Radical Addition of ?-Amino C-H Bonds Across Michael Acceptors  

PubMed Central

In marked contrast to the variety of strategies available for oxidation and nucleophilic functionalization of methylene groups adjacent to amines, relatively few approaches for modification of this position with electrophilic reaction partners have been reported. In the course of an investigation of the reactions of photogenerated ?-amino radicals with electrophiles, we made the surprising observation that the efficiency of radical photoredox functionalization of N-aryl tetrahydroisoquinolines is dramatically increased in the presence of a Brønsted acid co-catalyst. Optimized conditions provide high yields and efficient conversion to radical addition products for a range of structurally modified tetrahydroisoquinolines and enones using convenient household light sources and commercially available Ru(bpy)3Cl2 as a photocatalyst. Our investigations into the origins of this unexpected additive effect have demonstrated that the carbon–carbon bond-forming step is accelerated by TFA and is a rare example of Brønsted acid catalysis in radical addition reactions. Moreover, a significant conclusion arising from these studies is the finding that product formation is dominated by radical chain processes and not by photocatalyst turnover. Together, these findings have important implications for the future design and mechanistic evaluation of photocatalytic radical processses.

Espelt, Laura Ruiz; Wiensch, Eric M.; Yoon, Tehshik P.

2013-01-01

285

Physical methods of nucleic acid transfer: general concepts and applications  

PubMed Central

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future. This article is part of a themed section on Vector Design and Drug Delivery. For a list of all articles in this section see the end of this paper, or visit: http://www3.interscience.wiley.com/journal/121548564/issueyear?year=2009

Villemejane, Julien; Mir, Lluis M

2009-01-01

286

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.

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

2014-01-01

287

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

288

General Acid Catalysis: A Flexible Experiment, Adaptable to Student Ability and Various Teaching Approaches.  

ERIC Educational Resources Information Center

The acid-catalyzed hydrolysis of N-vinyl pyrrolidone provides a simple spectrophotometric kinetic experiment to introduce general acid catalysis, solvent isotope effects, and other aspects of ionic reactions in solution in advanced courses. The Bronsted equation and concept of linear free-energy changes is also covered. (SK)

Bulmer, R. S.; And Others

1981-01-01

289

Relationships between microstructure and surface acidity of Ti-Si mixed oxide catalysts  

SciTech Connect

The surface acidities and reactivities of titania, silica, and a series of Ti-Si mixed oxides have been investigated with a variety of surface-sensitive techniques, including temperature-programmed desorption/reaction of ammonia and 2-propanol, IR spectroscopy of adsorbed ammonia, and catalytic reaction of 1-butene. Results from TPD, TPR, and IR spectroscopy indicated that total acidity and relative acid strength decreased as silica was incorporated into titania. However, the areal rate of 1-butene isomerization was almost four times greater over a titania-rich mixed oxide than over pure titania. Infrared spectroscopy of adsorbed ammonia revealed that all of the acid sites on pure titania were of the Lewis type, whereas about 80% of the sites on the mixed oxides were of the Broensted type. Therefore, the enhancement of butene isomerization activity over titania-rich mixed oxides was attributed to the Broensted acid sites that were not present on pure titania. The appearance of Broensted acidity in titania-rich mixed oxides was due to the local charge imbalance associated with tetrahedrally coordinated silica chemically mixing with the octahedral titania matrix. In silica-rich mixed oxides, Ti substituted isomorphously for Si in the tetrahedral silica matrix, thus eliminating the local charge imbalance that caused Broensted acidity. The molar ratio of NH{sub 3(ads)}/Ti for a silica-rich mixed oxide was approximately 0.3, which was nearly the same as the fraction of nontetrahedrally coordinated Ti in the sample. 33 refs., 7 figs., 2 tabs.

Liu, Z.; Tabora, J.; Davis, R.J. [Univ. of Virginia, Charlottesville, VA (United States)] [Univ. of Virginia, Charlottesville, VA (United States)

1994-09-01

290

Process of making supported catalyst  

DOEpatents

Oxide supported metal catalysts have an additional metal present in intimate association with the metal catalyst to enhance catalytic activity. In a preferred mode, iridium or another Group VIII metal catalyst is supported on a titania, alumina, tungsten oxide, silica, or composite oxide support. Aluminum ions are readsorbed onto the support and catalyst, and reduced during calcination. The aluminum can be added as aluminum nitrate to the iridium impregnate solution, e.g. chloroiridic acid.

Schwarz, James A. (Fayetteville, NY); Subramanian, Somasundaram (Melvindale, MI)

1992-01-01

291

Sulfonic acid functionalized poly (ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole) as an efficient catalyst for the synthesis of methyl propionate  

Microsoft Academic Search

Sulfonic acid functionalized poly (ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole), poly (EGDMA–VTAZ–SO3H) (average diameter 1.0–1.5mm), was found to be efficient solid acid catalyst for the esterification of methanol and propionic acid under heterogeneous reaction conditions. The pristine polymer, poly (EGDMA–VTAZ), was produced by suspension polymerization and then proton-conducting polymer was obtained by blending of poly (EGDMA–VTAZ) with different percentage of H2SO4 solutions. The

Beyhan Erdem; Ali Kara

2011-01-01

292

The identification of the acid-base catalyst of alpha-arabinofuranosidase from Geobacillus stearothermophilus T-6, a family 51 glycoside hydrolase.  

PubMed

The alpha-L-arabinofuranosidase from Geobacillus stearothermophilus T-6 (AbfA T-6) belongs to the retaining family 51 glycoside hydrolases. The conserved Glu175 was proposed to be the acid-base catalytic residue. AbfA T-6 exhibits residual activity towards aryl beta-D-xylopyranosides. This phenomenon was used to examine the catalytic properties of the putative acid-base mutant E175A. Data from kinetic experiments, pH profiles, azide rescue, and the identification of the xylopyranosyl azide product provide firm support to the assignment of Glu175 as the acid-base catalyst of AbfA T-6. PMID:11943144

Shallom, Dalia; Belakhov, Valery; Solomon, Dmitry; Gilead-Gropper, Sara; Baasov, Timor; Shoham, Gil; Shoham, Yuval

2002-03-13

293

Direct synthesis of 1,6-hexanediol from HMF over a heterogeneous Pd/ZrP catalyst using formic acid as hydrogen source.  

PubMed

A new approach is developed for hydrogenolytic ring opening of biobased 5-hydroxymethylfurfural (HMF), dehydration product of hexoses, towards 1,6-hexanediol (HDO) under atmospheric pressure. The highest yield of HDO, 43%, is achieved over reusable Pd/zirconium phosphate (ZrP) catalyst at 413 K in the presence of formic acid as hydrogen source. In comparison with various Brønsted and/or Lewis acidic supports, the specific Brønsted acidity on ZrP support effectively accelerated the cleavage of C-O bond in a furan ring. PMID:24259303

Tuteja, Jaya; Choudhary, Hemant; Nishimura, Shun; Ebitani, Kohki

2014-01-01

294

Solid Sulfonic Acid Catalysts Based on Porous Carbons and Carbon-Silica Composites  

NASA Astrophysics Data System (ADS)

Mesoporous carbons prepared using a templating method under different carbonization temperatures are sulfonated with concentrated H2SO4. Without the moving of silica template carbon-silica composites were prepared, which can maintain the pore structure well during sulfonation reaction process. The resultant samples are characterized using nitrogen adsorption, transmission electron microscope, field-emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and elemental analysis techniques. The catalytic performances of the sulfonated carbons and composites are evaluated by esterification reaction of methanol with acetic acid. The results show that a low-temperature carbonization process is favorable for improving the reaction conversion of acetic acid. In addition, the sulfonated carbon-silica composites show a higher acetic acid conversion than the sulfonated mesoporous carbons.

Tian, Xiao Ning; Luo, Lijuan; Jiang, Zhongqing; Zhao, X. S.

295

Presynaptic GABA Band ?-hydroxybutyric acid-mediated mechanisms in generalized absence seizures  

Microsoft Academic Search

?-Hydroxybutyric acid (GHB) is a naturally occurring compound which has the ability to induce generalized absence seizures when given to animals. This effect of GHB may be blocked by either GHB or GABAB receptor antagonists. We sought to test the hypothesis that pre-synaptic GHB- and GABAB-mediated mechanisms in thalamus and cortex are operative in the GHB model of generalized absence

O. C. Snead

1996-01-01

296

Solid phase synthesis of a diketopiperazine catalyst containing the unnatural amino acid ( S)-norarginine  

Microsoft Academic Search

A cyclic dipeptide containing the unnatural amino acid (S)-norarginine, recently shown to display useful catalytic activity, has been synthesized in good yield and high chemical purity using a solid phase protocol. All reactions in the sequence, including a Hofmann rearrangement and cyclization to diketopiperazine, were performed on the Merrifield polystyrene resin and proceed in high yield. In addition to its

Jennifer Kowalski; Mark A. Lipton

1996-01-01

297

The oxidation of tetrabromobisphenol A by potassium monopersulfate with an iron(III)-phthalocyanine-tetrasulfonic acid catalyst in the presence of humic acid.  

PubMed

Tetrabromobisphenol A (TBBPA), a type of brominated flame retardant that shows endocrine disruption effects, has been identified in leachates from landfills. Iron(III)-porphyrins that mimic the active site of peroxidases have been shown to be effective in oxidizing halogenated phenols, such as TBBPA. In the present study, TBBPA was subjected to oxidation with potassium monopersulfate (KHSO5) using an iron(III)-phthalocyanine-tetrasulfonic acid (FePcTS), structural analogue of iron(III)-porphyrin, in the presence of humic acid (HA), a major component in landfill leachates. When TBBPA was oxidized using the above system, the levels of degradation and debromination increased with increasing pH in the presence of HA. Because of landfill leachates are weakly alkaline (around pH 8), oxidation products derived from TBBPA were investigated at pH 8. Approximately 48% of the bromine in the degraded TBBPA was incorporated into HA, and hydroxy-tribromobisphenol A was determined to be the major brominated intermediate in the HA fraction. In the iron(III)-porphyrin catalytic systems, the brominated intermediate incorporated into HA is mainly TBBPA, and no hydroxy-substituted bromophenols are found. Thus, the catalytic power of FePcTS is higher than that of iron(III)-porphyrin catalysts. PMID:24798896

Maeno, Shohei; Mizutani, Yusuke; Zhu, Qianqian; Miyamoto, Takafumi; Fukushima, Masami; Kuramitz, Hideki

2014-07-29

298

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

299

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

300

Preparation and evaluation of advanced catalysts for phosphoric acid fuel cells  

NASA Technical Reports Server (NTRS)

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 with the influence of low concentrations of carbon monoxide in the fuel gas stream. In a similar way, these platinum on carbon electrocatalysts were evaluated for oxygen reduction in hot phosphoric acid. Binary noble metal alloys were prepared for anodic oxidation of hydrogen and noble metal-refractory metal mixtures were prepared for oxygen reduction. An exemplar alloy of platinum and palladium (50/50 atom %) was discovered for anodic oxidation of hydrogen in the presence of carbon monoxide, and patent disclosures were submitted. For the cathode, platinum-vanadium alloys were prepared showing improved performance over pure platinum. Preliminary experiments on electrocatalyst utilization in electrode structures showed low utilization of the noble metal when the electrocatalyst loading exceeded one weight percent on the carbon.

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

1984-01-01

301

Development of efficient Lewis acid catalysts for intramolecular cycloaddition reactions of ester-tethered substrates.  

PubMed

We have developed novel bidentate Lewis acids that efficiently promote the intramolecular cycloaddition reactions of ester-tethered substrates. Bis-aluminated triflic amide derivatives [TfN(AlR(1)R(2))2], which are generated by simply mixing triflic amide and 2 equiv of methyl aluminum or aluminum hydride, catalyzed intramolecular Diels-Alder (DA) reactions of ester-tethered 1,7,9-trienes and intermolecular DA reactions of alpha,beta-unsaturated lactones. We also found that bimetallic Lewis acid derived from 1,1'-biphenyl-2,2'-di(triflyl)amide and dimethylaluminum chloride promoted the intramolecular [3 + 2] cycloaddition reaction of acrylate derivatives having an allylsilane part. PMID:17549689

Taguchi, Takeo; Saito, Akio; Yanai, Hikaru

2007-01-01

302

Kinetic studies of potential bifuntional acid-base catalysts in aqueous solution. The iodination of acetone  

Microsoft Academic Search

The catalysis of the iodination of acetone by a series of general bases was studied in HâO and in DâO at 25.0°C and at an ionic strength of 0.1M. Catalytic rate coefficients were determined for general bases which possess removable protons: monohydrogen phosphate dianion, k\\/sub HPOâ\\/sup 2 -\\/\\/ = 1.56 x 10⁻³ M⁻¹ min⁻¹; monohydrogen arsenate dianion, k\\/sub HAsOâ\\/sup 2

J. Spaulding; J. E. Stein; J. E. Meany

1977-01-01

303

Synthesis of fructone over dealmuinated USY supported heteropoly acid and its salt catalysts  

Microsoft Academic Search

12-Phosphotungstic acid (PW) and cesium salt of PW supported on dealuminated ultra-stable Y zeolite (DUSY) with various loadings were prepared by impregnation method, and their physicochemical properties were characterized by X-ray powder diffraction (XRD), N2 adsorption, solid state 31P and 29Si MAS NMR, Hammett indicator and SEM techniques. Their catalytic performances were evaluated in the liquid-phase acetalization of ethyl acetoacetate

Fumin Zhang; Chaoshu Yuan; Jun Wang; Yan Kong; Haiyang Zhu; Chunyan Wang

2006-01-01

304

Polycondensation reaction and its mechanism during lignocellulosic liquefaction by an acid catalyst: a review  

Microsoft Academic Search

The increase in the residue content resulting from polycondensation would be adverse to the utilization of lignocellulose\\u000a and to the quality of products obtained from liquefied lignocellulosic material. The yield of the residue formed from liquefaction\\u000a and the mechanism of polycondensation were reported mainly by Lin, Yamada and Kobayashi. The major products of cellulosic\\u000a liquefaction are levulinic acid and hydroxymethylfurfural

Min Niu; Guang-jie Zhao; Mehmet Hakki Alma

2011-01-01

305

Characterization of Palladium Nanoparticles Adsorpt on Polyacrylic Acid Particles as Hydrogenation Catalyst  

Microsoft Academic Search

Palladium particles can be prepared in sizes of a few nanometers from Pd(OAc)2in the presence of a block copolymer in aromatic unpolar solvents with suitable reducing agents like NaBH4 or LiAlH4. After mixing the organic metal solution with a polyacrylic acid (PAA) dispersion of defined concentration and following a crosslinking process with an epoxide, reactive membranes with a well-defined pore

Lothar Gröschel; Rami Haidar; Andreas Beyer; Karl-Heinz Reichert; Reinhard Schomäcker

2004-01-01

306

Study on Preparation Process of Lubrication from 1-Decene with Acidic Ionic Liquid Catalyst  

Microsoft Academic Search

Poly-alpha-olefin (PAO) was researched over acidic ionic liquid catalyzed the oligomerization of 1-decene. Ionic liquid used was 1-butyl-3-methyl imidazolium as a cation and aluminum chloride as an anion, which could effectively catalyze oligomerization and had a higher selectivity. The optimum process conditions for the synthesis of PAO were that the reaction temperature was 160°C, the reaction time was 3 h,

H. Ding; B. Y. Zhang; J. Liu

2009-01-01

307

Ketones from carboxylic acids over supported magnesium oxide and related catalysts  

Microsoft Academic Search

Silica-supported alkaline earth oxides revealed excellent activity to convert acetic acid selectively into acetone in a vapor-phase fixed-bed flow system. Acetone was obtained through the cyclic formation of alkaline earth acetate followed by decomposition. Magnesium oxide should be supported on the silica surface without formation of magnesium silicate, which was inactive for the present reaction. Attempted syntheses of benzophenone and

Shigeru Sugiyama; Kiyozumi Sato; Seiji Yamasaki; Katsuhiro Kawashiro; Hiromu Hayashi

1992-01-01

308

Mechanism of 1-butene hydration over acidic zeolite and ion-exchange resin catalysts  

Microsoft Academic Search

Vapour-phase hydration of 1-butene at atmospheric pressure above 373 K shows similar features on both H-clinoptilolite and sulphonic acid ion-exchange resin: the initial reaction rate linearly increases with the partial pressure of 1 -butene and passes through a maximum as a function of water pressure. Kinetics was evaluated accordingly. A decrease in the 1-butene isomerization rate indicated that under hydration

Dénes Kalló; R. Magdolna Mihályi

1995-01-01

309

Combination of best promoter and micellar catalyst for more than kilo-fold rate acceleration in favor of chromic acid oxidation of D-galactose to D-galactonic acid in aqueous media at room temperature  

NASA Astrophysics Data System (ADS)

Picolinic acid, 2,2'-bipyridine and 1,10-phenanthroline promoted Cr(VI) oxidation of D-galactose to D-galactonic acid in three representative aqueous micellar media has been studied. The anionic surfactant (SDS) accelerated the rate of reaction while the cationic surfactant (CPC) and neutral surfactant (TX-100) retarded the reaction rate. Combination of bipy and SDS is the best choice for chromic acid oxidation of D-galactose to D-galactonic acid in aqueous media although 1,10-phenanthroline is best promoter in absence of micellar catalyst.

Saha, Rumpa; Ghosh, Aniruddha; Sar, Pintu; Saha, Indrajit; Ghosh, Sumanta K.; Mukherjee, Kakali; Saha, Bidyut

2013-12-01

310

Studies of the effect of pivalic acid on the hydrogenation rate and the enantio-differentiating ability for the hydrogenation of 2-octanone over a tartaric acid-NaBr-modified nickel catalyst  

Microsoft Academic Search

The effects of the addition of pivalic acid to the reaction media on the hydrogenation rate and the enantio-differentiating\\u000a ability (e.d.a.) for the hydrogenation of 2-octanone were studied over an (R,R)-tartaric acid-NaBr-in-situ-modified nickel catalyst. It was revealed that the modification with both tartaric acid and NaBr\\u000a was necessary for increasing the e.d.a. by the addition of pivalic acid to the

Tsutomu Osawa; Yuki Nakagawa; Tadao Harada; Osamu Takayasu

2006-01-01

311

Catalyst-free tandem Michael addition/decarboxylation of (thio)coumarin-3-carboxylic acids with indoles: facile synthesis of indole-3-substituted 3,4-dihydro(thio)coumarins.  

PubMed

The tandem Michael addition/decarboxylation of (thio)coumarin-3-carboxylic acids with indoles has been developed and the biologically important indole-3-substituted dihydrocoumarins were obtained in good to excellent yields under catalyst-free conditions. PMID:24589942

Shao, Zhuzhou; Xu, Lubin; Wang, Liang; Wei, Hongtao; Xiao, Jian

2014-04-14

312

Acidic ionic liquid [NMP]H 2PO 4 as dual solvent-catalyst for synthesis of ?-alkoxyketones by the oxa-Michael addition reactions  

Microsoft Academic Search

Acidic ionic liquid N-methyl-2-pyrrolidonium dihydrogen phosphate [NMP]H2PO4 was prepared and used as efficient catalyst and reaction medium to synthesize ?-alkoxyketones by the oxa-Michael addition reactions for the first time. The effect of anions and cations, amount of ionic liquid on the reaction was investigated. Various alcohols and phenols proceeded smoothly and led to corresponding ?-alkoxyketones with high yields under mild

Hui Guo; Xia Li; Jun-Liang Wang; Xiao-Han Jin; Xian-Fu Lin

2010-01-01

313

Hydrofining activity and acid–base properties of nickel–molybdenum catalysts incorporated on sodium and magnesium ions-modified alumina  

Microsoft Academic Search

In the study of a series of NiMo catalysts incorporated on alumina modified with sodium and magnesium ions, decomposition of isopropyl or diacetone alcohol and ethylbenzene were used as model reactions. Hydrofining of coal liquid was performed at the pressure of 9.0MPa and at 400°C. Modification of alumina with sodium and magnesium ions leads to a decrease in the acidity

M Lewandowski; Z Sarbak

1998-01-01

314

Influence of the acid-base character of supported vanadium catalysts on their catalytic properties for the oxidative dehydrogenation of n-butane  

SciTech Connect

The oxidative dehydrogenation of n-butane on supported vanadium catalysts has been studied. Al{sub 2}O{sub 3}, sepiolite, hydrotalcite (Mg/Al atomic ratio of 3.0), and MgO were used as supports. The vanadium content of supported catalysts was varied to obtain dispersed vanadium species. The strength and number of Lewis acid sites (determined by FTIR of adsorbed pyridine) decreases in the following trend: V/Al{sub 2}O{sub 3} > V/Sepiolite > V/ hydrotalcite > V/MgO. {sup 51}V NMR spectroscopy indicates that tetrahedral V{sup 5+}-species (with different distortion degree and/or environment) are the main vanadium species. Temperature-programmed reduction results show that the reducibility of catalysts, determined from the onset temperature of H{sub 2}-consumption, decreases in the order V/Al{sub 2}O{sub 3} > V/MgO (first peak) > V/Sepiolite > V/MgO (second peak) {approx} V/hydrotalcite. The catalytic activity for n-butane oxidation follows a trend similar to that observed in TPR, concluding that the catalytic activity is related to the reducibility of surface vanadium species in the catalysts. However, the selectivity to dehydrogenated products, as well as the distribution of C{sub 4}-olefins, can be tentatively related to the acid-base character of catalysts. Thus, the selectivities to 1-butene and butadiene decrease in the order V/MgO > V/Hydrotalcite > V/Sepiolite > V/Al{sub 2}O{sub 3}, while the selectivities to 2-butene and carbon oxides present the opposite trend. 48 refs., 10 figs., 4 tabs.

Blasco, T.; Lopez Nieto, J.M. [Instituto de Tecnologia Quimi ca, Valencia (Spain)] [Instituto de Tecnologia Quimi ca, Valencia (Spain); Dejoz, A. [Universidade de Valencia, Burjasot (Spain)] [and others] [Universidade de Valencia, Burjasot (Spain); and others

1995-12-01

315

Kinetic Demonstration of Intermolecular General Acid (GA) Catalysis in Thiolysis of 9-Anilinoacridine  

NASA Astrophysics Data System (ADS)

All acids other than hydronium ion (known as specific acid) are called general acids (GA) and all bases other than hydroxide ion (known as specific base) are defined as general bases (GB). If a reaction is sensitive to acid catalysis, it may involve both specific acid and GA catalysis. It is now generally believed that most enzyme-catalyzed reactions involve the occurrence of intramolecular and intermolecular general acid-base (GA-GB) catalysis (1). Since this fact was realized a huge amount of work has been carried out using simpler nonenzymatic reactions with the purpose of developing an understanding of the mechanistic aspects of such catalysis (2). After nearly five decades of active research and numerous publications on GA-GB catalysis, introduction of an experiment on GA for students majoring in enzymology/physical organic chemistry at advanced undergraduate/postgraduate level is appropriate. A kinetic experiment involving the reaction of 2-mercaptoethanol (2-ME) with 9-anilinoacridine (9-ANA) is designed to demonstrate intermolecular GA catalysis.

Niyaz Khan, Mohammad

1998-05-01

316

Engelhard expands oxidation catalysts portfolio  

SciTech Connect

Engelhard says its agreement earlier this month to market Amoco Chemical`s proprietary maleic anhydride catalyst reflects an effort to expand its speciality catalysts business (CW, Feb. 19, p.5). In particular, the company says it is looking for additional alliances to bolster its oxidation catalysts portfolio. {open_quotes}There are some areas of oxidation catalysis that are reasonably attractive,{close_quotes} says Paul Lamb, marketing director/chemical catalysts. He says that while Engelhard is not interested in commodity oxidation catalysts, such as those used to make sulfuric acid, it does want to boost offerings for higher-value oxidation catalysts. Engelhard is collaborating with Geon to offer oxychlorination catalysts for making ethylene dichloride. It also markets oxidation catalysts for vinyl acetate production.

Rotman, D.

1997-02-26

317

Mesoporous H 3PW 12O 40-silica composite: Efficient and reusable solid acid catalyst for the synthesis of diphenolic acid from levulinic acid  

Microsoft Academic Search

Mesoporous H3PW12O40-silica composite catalysts with controllable H3PW12O40 loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H3PW12O40 loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0m2g?1), larger and well-distributed pore

Yihang Guo; Kexin Li; Xiaodan Yu; James H. Clark

2008-01-01

318

Improved catalysts and method  

SciTech Connect

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. 8 figs., 3 tabs.

Taylor, C.E.; Noceti, R.P.

1990-12-31

319

Generalized gangliosidosis: Acid ?-galactosidase deficiency with early onset, rapid mental deterioration and minimal bone dysplasia  

Microsoft Academic Search

This report concerns a 3-month-old girl with rapidly progressive psychomotor retardation, hepatomegaly, vacuolated lymphocytes, minimal bone dysplasia and normal excretion of acid mucopolysaccharides. A deficiency of acid ß-galactosidase was demonstrated in isolated leucocytes and in a liver biopsy. The diagnosis of generalized gangliosidosis due to deficiency of ß-galactosidase was also based on the absence of the enzyme activity from cultured

H. Fricker; J. S. O'Brien; F. Vassella; E. Gugler; J. P. Mühlethaler; M. Spycher; U. N. Wiesmann; N. Herschkowitz

1976-01-01

320

Highly Reactive, General and Long-Lived Catalysts for Palladium-Catalyzed Amination of Heteroaryl and Aryl Chlorides, Bromides and Iodides: Scope and Structure-Activity Relationships  

PubMed Central

We describe a systematic study of the scope and relationship between ligand structure and activity for a highly efficient and selective class of catalysts for the amination of heteroaryl and aryl chlorides, bromides and iodides containing sterically hindered chelating alkylphosphines. In the presence of this catalyst, aryl and heteroaryl chlorides, bromides and iodides react with many primary amines in high yields with part-per-million quantities of palladium precursor and ligand. Many reactions of primary amines with both heteroaryl and aryl chlorides, bromides and iodides occur to completion with 0.0005-0.05 mol % catalysts. A comparison of the reactivity of this catalyst for coupling of primary amines at these loadings is made with catalysts generated from hindered monophosphines and carbenes, and these data illustrate the benefits of chelation. Thus, these complexes constitute a fourth-generation catalyst for the amination of aryl halides, whose activity complements catalysts based on monophosphines and carbenes.

Shen, Qilong; Ogata, Tokutaro; Hartwig, John F.

2010-01-01

321

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

PubMed Central

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 acids are abundant Gap1p is sorted from the trans-Golgi through the multivesicular endosome (MVE) and to the vacuole. Here we test the hypothesis that Gap1p itself is the sensor of amino acid abundance by examining the trafficking of Gap1p mutants with altered substrate specificity and transport activity. We show that trafficking of mutant Gap1pA297V, which does not transport basic amino acids, is also not regulated by these amino acids. Furthermore, we have identified a catalytically inactive mutant that does not respond to complex amino acid mixtures and constitutively sorts Gap1p to the plasma membrane. Previously we showed that amino acids govern the propensity of Gap1p to recycle from the MVE to the plasma membrane. Here we propose that in the presence of substrate the steady-state conformation of Gap1p shifts to a state that is unable to be recycled from the MVE. These results indicate a parsimonious regulatory mechanism by which Gap1p senses its transport substrates to set an appropriate level of transporter activity at the cell surface.

Cain, Natalie E.; Kaiser, Chris A.

2011-01-01

322

Theoretical mechanistic study of the formic acid decomposition assisted by a Ru(II)-phosphine catalyst.  

PubMed

A density functional theory (DFT) study of formic acid decomposition, catalyzed by a model of the trans-[Ru(TPPTS)?(H?O)?]²? complex, has been performed. A mechanism comprising two competitive catalytic cycles, which have as a common intermediate a monohydride ruthenium complex, has been hypothesized in literature on the basis of high pressure NMR experiments. To explain the observed increase in H? production rate during the process, it has been suggested by the same authors that the reaction occurs entering the second proposed cycle (Cycle 2), although none of the complexes assumed to be formed have been experimentally observed. To gain more insights into the reaction mechanism, a detailed investigation of both the proposed catalytic cycles has been carried out. To describe the energy profiles, different accurate computational protocols have been employed. Our computations reveal that molecular hydrogen cannot be produced more rapidly following cycle 2, since it requires a larger amount of energy to occur. Moreover, the release of molecular hydrogen has been found to be the step that limits the reaction rate in both cycles, instead of the CO? dissociation as hypothesized by the authors. PMID:24810464

Mazzone, Gloria; Alberto, Marta E; Sicilia, Emilia

2014-05-01

323

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

324

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

325

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

326

Immobilized bisdiazaphospholane catalysts for asymmetric hydroformylation.  

PubMed

Condensation reactions of enantiopure bis-3,4-diazaphospholanes (BDPs) that are functionalized with carboxylic acids enable covalent attachment to bead and silica supports. Exposure of tethered BDPs to the hydroformylation catalyst precursor, Rh(acac)(CO)2, yields catalysts for immobilized asymmetric hydroformylation (iAHF) of prochiral alkenes. Compared with homogeneous catalysts, catalysts immobilized on Tentagel resins exhibit similarly high regioselectivity and enantioselectivity. When corrected for apparent catalyst loading, the activity of the immobilized catalysts approaches that of the homogeneous analogues. Excellent recyclability with trace levels of rhodium leaching are observed in batch and flow reactor conditions. Silica-bound catalysts exhibit poorer enantioselectivities. PMID:24742285

Adint, Tyler T; Landis, Clark R

2014-06-01

327

EFFECTS OF LEWIS ACID CATALYSTS ON THE HYDROGENATION AND CRACKING OF TWO-RING AROMATIC AND HYDROAROMATIC STRUCTURES RELATED TO COAL  

SciTech Connect

An investigation was carried out of the hydrogenation and cracking of two-ring aromatic and hydroaromatic compounds catalyzed by ZnCl{sub 2} and AlCl{sub 3}. The rates of both processes are strongly affected by the Bronsted acidity of the active catalyst [e.g., H{sup +}(MX{sub n}Y){sup -}] and the Bronsted basicity of the aromatic portions of the reactant, the latter characteristic being enhanced by either methyl or hydroxyl substitution. The source of hydrogen used for hydrogenation depends on the choice of catalyst. In the presence of AlCl{sub 3}, Scholl condensation of aromatic nuclei serves as the principle source of hydrogen. Molecular hydrogen is used exclusively, though, when hydrogenation is catalyzed by ZnCl{sub 2}. The formation of reaction products and the trends in reactant reactivity are discussed on the basis of carbonium ion mechanisms.

Salim, Sadie S.; Bell, Alexis T.

1980-11-01

328

Kinetics of Mo, Ni, V and Al leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide.  

PubMed

The kinetics of molybdenum, nickel, vanadium and aluminium leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide was investigated. The effects of temperature and particle size were examined. In addition, the reaction mechanism for the dissolution of the spent catalyst was discussed. The results of the kinetic analysis for various experimental conditions indicated that the reaction rate of leaching process is controlled by chemical reaction at the particle surface. The values of the activation energies of 31±2, 36±4, 30±4 and 57±3 kJ mol(-1) for Mo, Ni, V and Al, respectively, are characteristic for mechanism controlled by chemical reaction. PMID:21167639

Szymczycha-Madeja, Anna

2011-02-28

329

Photodegradation of acid green dye over Co–ZSM-5 catalysts prepared by incipient wetness impregnation technique  

Microsoft Academic Search

Co–ZSM-5 catalysts with different Co-loadings (2–30wt.%) were prepared by incipient wetness impregnation method. The prepared solid catalysts were characterized by X-ray diffraction, FTIR, in situ FTIR of pyridine adsorption and surface area measurements. The XRD data presented disintegration in the zeolitic crystalline structure accompanied by an increase in particle size of the prepared solids. New phases, Co3O4 and Co2SiO4, were

Zeinhom M. El-Bahy; Mohamed M. Mohamed; Farouk I. Zidan; Mohamed S. Thabet

2008-01-01

330

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

331

Knowledge about folic acid and the prevention of neural tube defects in two general practice populations.  

PubMed Central

Knowledge about the link between folic acid supplementation in pregnancy and the prevention of neural tube defects was assessed in women from two contrasting general practices using a questionnaire. The persisting lack of awareness, particularly in the more at-risk group from the inner city area, lends support to the argument in favour of the fortification of flour.

Krischer, J

1997-01-01

332

95—A GENERALIZED THEORY FOR THE COMBINATION OF ACID OR ALKALI WITH WOOL KERATIN  

Microsoft Academic Search

A generalized Donnan theory (assuming ions to be adsorbed at sites) is developed to describe the titration curve of an insoluble protein which possesses unequal numbers of carboxyl and amino groups. The equations derived apply to combination with acid or alkali and include a treatment of the isoelectric point. From the constancy of the isoelectric pH of keratin it is

L. Peters

1960-01-01

333

Catalytic performance of Fe 3O 4CoO\\/Al 2O 3 catalyst in ozonation of 2-(2,4-dichlorophenoxy)propionic acid, nitrobenzene and oxalic acid in water  

Microsoft Academic Search

Fe3O4-CoO\\/Al2O3 catalyst was prepared by incipient wetness impregnation using Fe(NO3)3-9H2O and Co(NO3)2-6H2O as the precursors, and its catalytic performance was investigated in ozonation of 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), nitrobenzene and oxalic acid. The experimental results indicated that Fe3O4-CoO\\/Al2O3 catalyst enabled an interesting improvement of ozonation efficiency during the degradation of each organic pollutant, and the Fe3O4-CoO\\/Al2O3 catalytic ozonation system followed a

Shaoping Tong; Rui Shi; Hua Zhang; Chunan Ma

2010-01-01

334

Epoxidation catalyst and process  

DOEpatents

Disclosed herein is a catalytic method of converting alkenes to epoxides. This method generally includes reacting alkenes with oxygen in the presence of a specific silver catalyst under conditions suitable to produce a yield of the epoxides. The specific silver catalyst is a silver nanocrystal having a plurality of surface planes, a substantial portion of which is defined by Miller indices of (100). The reaction is performed by charging a suitable reactor with this silver catalyst and then feeding the reactants to the reactor under conditions to carry out the reaction. The reaction may be performed in batch, or as a continuous process that employs a recycle of any unreacted alkenes. The specific silver catalyst has unexpectedly high selectivity for epoxide products. Consequently, this general method (and its various embodiments) will result in extraordinarily high epoxide yields heretofore unattainable.

Linic, Suljo (Ann Arbor, MI); Christopher, Phillip (Ann Arbor, MI)

2010-10-26

335

Degradation of H-acid in aqueous solution by microwave assisted wet air oxidation using Ni-loaded GAC as catalyst.  

PubMed

A novel process, microwave assisted catalytic wet air oxidation (MW-CWO), was applied for the degradation of H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) in aqueous solution. Ni-loaded granular activated carbon (GAC), prepared by immersion-calcination method, was used as catalyst. The results showed that the MW-CWO process was very effective for the degradation of H-acid in aqueous solution under atmospheric pressure with 87.4% TOC (total organic carbon) reduction in 20 min. Ni on GAC existed in the form of NiO as specified by XRD. Loss of Ni was significant in the initial stage, and then remained almost constant after 20 min reaction. BET surface area results showed that the surface property of GAC after MW-CWO process was superior to that of blank GAC. PMID:16083118

Zhang, Yao-Bin; Quan, Xie; Zhao, Hui-Min; Chen, Shuo; Yang, Feng-Lin

2005-01-01

336

Tungstic acid functionalized mesoporous SBA-15: a novel heterogeneous catalyst for facile one-pot synthesis of 2-amino-4H-chromenes in aqueous medium.  

PubMed

A new highly ordered mesoporous tungstic acid functionalized SBA-15, TAFMC-1 has been synthesized via post-synthesis modification of mesoporous SBA-15 with (3-chloropropyl) triethoxysilane followed by substitution reaction of chlorine atom of the 3-chloropropyl group by tungstic acid group under refluxing conditions in n-hexane. The tungstic acid functionalized mesoporous silica material has been characterized by using small angle powder X-ray diffraction, N2 sorption, HR-TEM, FE-SEM, FT-IR and solid state MAS NMR studies. TAFMC-1 catalyzes the facile one-pot catalytic three-component condensation reaction of resorcinol, aromatic aldehyde and malononitrile for the synthesis of a diverse range of 2-amino-4H-chromenes in aqueous medium. This heterogeneous catalyst can be recycled very efficiently for six consecutive reaction cycles without significant loss of catalytic activity. PMID:23760225

Kundu, Sudipta K; Mondal, John; Bhaumik, Asim

2013-08-01

337

General acid-base catalysis mediated by nucleobases in the hairpin ribozyme  

PubMed Central

The catalytic mechanism by which the hairpin ribozyme accelerates cleavage or ligation of the phosphodiester backbone of RNA has been incompletely understood. There is experimental evidence for an important role for an adenine (A38) and a guanine (G8), and it has been proposed that these act in general acid-base catalysis. In this work we show that a large reduction in cleavage rate on substitution of A38 by purine (A38P) can be reversed by replacement of the 5?-oxygen atom at the scissile phosphate by sulfur (5?-PS), which is a much better leaving group. This is consistent with A38 acting as the general acid in the unmodified ribozyme. The rate of cleavage of the 5?-PS substrate by the A38P ribozyme increases with pH log-linearly, indicative of a requirement for a deprotonated base with a relatively high pKa. On substitution of G8 by diaminopurine, the 5?-PS substrate cleavage rate at first increases with pH and then remains at a plateau, exhibiting an apparent pKa consistent with this nucleotide acting in general base catalysis. Alternative explanations for the pH dependence of hairpin ribozyme reactivity are discussed, from which we conclude that general acid-base catalysis by A38 and G8 is the simplest and most probable explanation consistent with all the experimental data.

Kath-Schorr, Stephanie; Wilson, Timothy J.; Li, Nan-Sheng; Lu, Jun; Piccirilli, Joseph A.; Lilley, David M. J.

2012-01-01

338

pH-dependent release of trace elements including platinum group elements (PGEs) from gasoline and diesel catalysts  

NASA Astrophysics Data System (ADS)

The release of trace metals and platinum group elements (PGEs) from automobile exhaust catalysts represents a remarkable source of higly dispersed environmental contamination. Especially, PGEs have shown increasing research interest due to their possible bioaccessibility. In our research, we focused on leaching behaviour of trace metals from gasoline and diesel automobile catalysts. While catalysts for gasoline engines contain a mixture of Pt-Pd-Rh or Pd-Rh, catalysts for diesel engines are composed only of Pt. We used dust from two crushed gasoline and two crushed diesel catalysts (new and aged). The dust of gasoline catalysts contains significant concentrations of Pt (700 mg.kg-1), Pd (11 000 mg.kg-1) and Rh (700 mg.kg-1). And the dust of diesel catalysts are composed of Pt (3 900 mg.kg-1) and they contains negligible amounts of Pd dan Rh (< 0.5 mg.kg-1, < 0.1 mg.kg-1, respectively). To evaluate leaching of trace metals from dust we used pH-stat leaching test according to the European standard CEN/TS 14997. The concentrations of cations: PGEs (Pt, Pd a Rh), K, Na, Ca, Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, La and Ce were determined by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS), and anions: F-, Cl-, SO42- and NO3- by high-performance liquid chromatography. Although the dusts from catalysts were relatively stable to acid/base influence, the leaching of trace metals from catalysts showed a dependence on pH. Generally, the highest concentrations were released under acidic conditions. The leaching of PGEs was higher for Pt in diesel catalysts and for Pd and Rh in gasoline catalysts. The highest concentrations of Zn and Pb were observed in old catalysts. The rare earth metals were released more from gasoline catalysts. Catalysts particles represent health risk especially with respect to their PGEs contents.

Sucha, Veronika; Mihaljevic, Martin; Ettler, Vojtech; Strnad, Ladislav

2014-05-01

339

Solvent-free selective oxidation of primary alcohols-to-aldehydes and aldehydes-to-carboxylic acids by molecular oxygen over MgO-supported nano-gold catalyst  

Microsoft Academic Search

Magnesium oxide supported nano-gold catalyst (prepared by the homogeneous deposition precipitation technique) showed high activity\\/selectivity and excellent reusability in the oxidation of different primary alcohols and aldehydes to corresponding aldehydes and carboxylic acids, respectively, by molecular oxygen (under atmospheric pressure) in the absence of any solvent. Influence of the catalyst calcination temperature (400–900°C), reaction temperature (50–120°C) and use of different

Vasant R. Choudhary; Deepa K. Dumbre

2011-01-01

340

Hydrogen production via sulfur-based thermochemical cycles: Part 1: Synthesis and evaluation of metal oxide-based candidate catalyst powders for the sulfuric acid decomposition step  

Microsoft Academic Search

The present work concerns the synthesis of various single and mixed oxide materials and their study as catalysts for the sulfuric acid dissociation reaction via which the production of SO2 and O2 is achieved. This is the most energy intensive step of sulfur-based thermochemical cycles for the production of hydrogen. Commercial (i.e. FeO, Fe3O4, Fe2O3, CuO, Cr2O3, ?-Al2O3, Pt\\/?-Al2O3) and

George Karagiannakis; Christos C. Agrafiotis; Alexandra Zygogianni; Chrysoula Pagkoura; Athanasios G. Konstandopoulos

2011-01-01

341

Two-dimensional hybrid germanium zeotype formed by selective coordination of the trans-1,2-diaminocyclohexane isomer to the ge atom: heterogeneous acid-base bifunctional catalyst.  

PubMed

[C 6H 10(NH 2) 2Ge 3O 6] ICMM9 is a two-dimensional germanate in which the metallic atoms are covalently bonded to chelating diamines. Its layered structure having some similitude with that of the pyroxene mineral, presents a totally new topology with two 4-c nodes. The solvothermal synthesis reaction allows the separation in situ of the two 1,2-diaminocyclohexane isomers by selective coordination of the trans isomer to octahedral Ge atoms of the ICMM9 framework. This material behaves as an active and selective heterogeneous acid-base bifunctional catalyst. PMID:18593111

Gándara, Felipe; Medina, Manuela E; Snejko, Natalia; Gómez-Lor, Berta; Iglesias, Marta; Gutiérrez-Puebla, Enrique; Monge, M Angeles

2008-08-01

342

Vapor phase oxidation of benzoic acid to phenol over a novel catalyst system consisting of NiO and NiFe{sub 2}O{sub 4}  

SciTech Connect

NiO and Fe{sub 2}O{sub 3} were found to show the catalytic activities for the vapor phase oxidation of benzoic acid to form phenol. Furthermore, the enhancement of the activity and phenol selectivity were achieved by combined Ni and Fe components prepared by precipitation. The calcination temperature and the atomic ratio of Ni to Fe were found to be important for the enhancement of activity. The homogeneous distribution profile of NiO and NiFe{sub 2}O{sub 4} on the surface and in the bulk of the catalyst is essential for the optimization of phenol formation. 32 refs., 7 figs., 4 tabs.

Miki, Jun; Asanuma, Minoru; Tachibana, Yakudo [NKK Corporation, Kawasaki (Japan)] [and others] [NKK Corporation, Kawasaki (Japan); and others

1995-02-01

343

Kinetic resolution of racemic 2-hydroxy-?-butyrolactones by asymmetric esterification using diphenylacetic acid with pivalic anhydride and a chiral acyl-transfer catalyst.  

PubMed

Various optically active 2-hydroxy-?-butyrolactone derivatives are produced via the kinetic resolution of racemic 2-hydroxy-?-butyrolactones with diphenylacetic acid using pivalic anhydride and (R)-benzotetramisole ((R)-BTM), a chiral acyl-transfer catalyst. Importantly, the substrate scope of this novel protocol is fairly broad (12 examples, s-value; up to over 1000). In addition, we succeeded in disclosing the reaction mechanism to afford high enantioselectivity using theoretical calculations and expounded on the substituent effects at the C-3 positions in 2-hydroxylactones. PMID:23461674

Nakata, Kenya; Gotoh, Kouya; Ono, Keisuke; Futami, Kengo; Shiina, Isamu

2013-03-15

344

Microwave assisted catalytic wet air oxidation of H-acid in aqueous solution under the atmospheric pressure using activated carbon as catalyst.  

PubMed

Catalytic wet air oxidation (CWAO) is a promising method for the treatment of heavily contaminated wastewater. However, its application is restricted due to severe operation conditions (high pressure and high temperature). A microwave (MW) assisted oxidation method was investigated aiming to treat heavily contaminated wastewater under milder conditions. H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) was selected as target compound to evaluate the performance of this novel process. The removal of H-acid and TOC (total organic carbon) for H-acid solution of 3000 mg/L reached as high as 92.6% in 20 min and 84.2% in 60 min, respectively under optimal conditions. The existence of activated carbon and oxygen proved to be critical for effective treatment. The activated carbon acted not only as a catalyst for H-acid decomposition, but also as a special material for the absorption of MW energy. Air was supplied to the reactor as an oxygen source at constant flows. The amino group in H-acid was converted ultimately into nitrate, and sulfonic group into sulfate. This observation gave an evidence of H-acid mineralization although other organic intermediates were unable to be determined. The value of BOD(5)/COD (ratio of 5d biochemical oxygen demand to chemical oxygen demand) increased from 0.008 to 0.467 indicating a significant improvement of biodegradability for the solution, which is beneficial for the further biological treatment of the wastewater. PMID:16600490

Zhang, Yaobin; Quan, Xie; Chen, Shuo; Zhao, Yazhi; Yang, Fenglin

2006-09-01

345

Acute generalized exanthematous pustulosis (AGEP) due to exposure to sulfuric acid and bromic acid vapor: a case report.  

PubMed

Acute generalized exanthematous pustulosis (AGEP, toxic pustuloderma, pustular drug eruption) is a not uncommon cutaneous reaction pattern that is usually related to drug administration. The eruption is of sudden onset and appears 7-10 days after the medication is started. A 22-year-old male patient who was a student at a chemical faculty attended our outpatient clinic with a complaint of pustular eruption on his face. According to his history, the eruption started with pruritus and erythema on his chin 3 days ago and spread to his face and chest. He explained that he had performed an experiment with sulfuric acid and bromic acid and was exposed to their vapor. His dermatological examination revealed erythema and pustules on his cheeks, on his chin, above his upper lip, and on his eyebrows. He also had a few pustules on his chest. There were no ocular, mucous membrane, or pulmonary symptoms. Histopathological examination of the skin biopsy specimen revealed superficial orthokeratosis, focal subcorneal pustule formation, and perivascular chronic inflammatory cell infiltration in superficial dermis. After administration of systemic antihistamines and wet dressing topically, we observed rapid healing of the lesions. Because there was no systemic drug intake in his history, we were concerned that exposure to sulfuric acid and bromic acid vapor caused AGEP in this patient. We present this rare case to show that the vapor of chemical materials may cause AGEP or other drug eruptions. PMID:18568897

Bilac, Dilek Bayraktar; Ermertcan, Aylin Turel; Ozturkcan, Serap; Sahin, M Turhan; Temiz, Peyker

2008-01-01

346

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.

2014-01-01

347

Evidence for a boroxinate based Brønsted acid derivative of VAPOL as the active catalyst in the catalytic asymmetric aziridination reaction.  

PubMed

Studies are described that were designed to determine the structure of the active catalyst in the asymmetric catalytic aziridination of imines with ethyl diazoacetate (AZ reaction). Evidence suggests that the active catalyst contains a boroxine ring in which one of the three boron atoms is spiro-fused with the two phenol groups of the VAPOL ligand. (11)B and (1)H NMR evidence supports the boroxinate structure B in which the counterion to the boroxinate is the protonated form of the imine. The boroxinate structure is also supported by two solid state structures of a VAPOL boroxinate in which the gegen cation is tetramethyl ammonium and 4-dimethylaminopyridinium. PMID:19813716

Hu, Gang; Huang, Li; Huang, Rui H; Wulff, William D

2009-11-01

348

Boron stress activates the general amino acid control mechanism and inhibits protein synthesis.  

PubMed

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

349

Influence of carbon–oxygen surface complexes on the surface acidity of tungsten oxide catalysts supported on activated carbons  

Microsoft Academic Search

Tungsten oxide catalysts supported on activated carbons were prepared by using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide as precursors. An activated carbon was obtained from olive stone by physical activation. A portion of this activated carbon was oxidized with ammonium peroxydisulfate in order to introduce different oxygen surface complexes. Subsequently, different portions of this oxidized activated carbon were heat

Carlos Moreno-Castilla; Agust??n F. Pérez-Cadenas; Francisco J. Maldonado-Hódar; Francisco Carrasco-Mar??n; José Luis G. Fierro

2003-01-01

350

Phosphomolybdic and phosphotungstic acids as efficient catalysts for the synthesis of bridged 1,2,4,5-tetraoxanes from ?-diketones and hydrogen peroxide.  

PubMed

Phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) efficiently catalyze the addition of H2O2 to ?-diketones to form bridged 1,2,4,5-tetraoxanes. These reactions are not accompanied by the formation of monocyclic peroxides containing hydroxy and hydroperoxide groups or polymeric peroxides. The use of these catalysts made it possible to obtain bridged tetraoxanes from easily oxidizable benzoylacetone derivatives and ?-unsubstituted ?-diketones. The syntheses are scaled up to ten grams. The resulting peroxides can be easily isolated from the reaction mixture by column chromatography. The yield of tetraoxanes depends on the structure of ?-diketone and varies from 12 to 83%. NMR monitoring of two bridged 1,2,4,5-tetraoxanes synthesis was carried out. PMID:23446630

Terent'ev, Alexander O; Yaremenko, Ivan A; Vil', Vera A; Moiseev, Igor K; Kon'kov, Sergey A; Dembitsky, Valery M; Levitsky, Dmitri O; Nikishin, Gennady I

2013-04-28

351

Deactivation Mechanism of Potassium on the V2O5/CeO2 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

352

Electron-Withdrawing Trifluoromethyl Groups in Combination with Hydrogen Bonds in Polyols: Brønsted Acids, Hydrogen-Bond Catalysts, and Anion Receptors  

SciTech Connect

Electron withdrawing trifluoromethyl groups were characterized in combination with hydrogen bond interactions in three polyols (i.e., CF3CH(OH)CH2CH(OH)CF3, 1; (CF3)2C(OH)C(OH)(CF3)2, 2; ((CF3)2C(OH)CH2)2CHOH, 3) by pKa measurements in DMSO and H2O, negative ion photoelectron spectroscopy and binding constant determinations with Cl–. Their catalytic behavior in several reactions were also examined and compared to a BrØnsted acid (HOAc) and a commonly employed thiourea ((3,5-(CF3)3C6H3NH)2CS). The combination of inductive stabilization and hydrogen bonds was found to afford potent acids which are effective catalysts. It also appears that hydrogen bonds can transmit the inductive effect over distance even in an aqueous environment, and this has far reaching implications.

Shokri, Alireza; Wang, Xue B.; Kass, Steven R.

2013-06-26

353

Extraction and separation of nickel(II) using bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex 301) and its recovery from spent catalyst and electroplating bath residue  

SciTech Connect

The paper embodies the details on the extraction behavior of Ni(II) along with Cr(III), Fe(III), Mn(II), Co(II), Cu(II) and Zn(II) from sulfuric acid media employing Cyanex 301-toluene system. The effect of various parameters like concentration of acid, metal ion and extractant and nature of diluent on the extraction of Ni(II) has been studied. On the basis of the distribution data the extracting species has been proposed. The recycling capacity of the extractant has been assessed. Some binary and ternary separations have also been achieved. The practical utility of the extractant has been demonstrated by recovering Ni(II) from spent catalyst and electroplating bath residue.

Singh, R.; Khwaja, A.R.; Gupta, B.; Tandon, S.N. [Univ. of Roorkee (India). Dept. of Chemistry

1999-03-01

354

Bioleaching of spent fluid catalytic cracking catalyst using Aspergillus niger.  

PubMed

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 gluconic acids), as well as a mixture of organic acids at the same concentrations as that biogenically produced. It was shown that bioleaching realised higher metal extraction than chemical leaching, with A. niger mobilizing Ni (9%), Fe (23%), Al (30%), V (36%) and Sb (64%) at 1% pulp density. Extraction efficiency generally decreased with increased pulp density. Compared with abiotic controls, bioleaching gave rise to higher metal extractions than leaching using fresh medium and cell-free spent medium. pH decreased during bioleaching, but remained relatively constant in both leaching using fresh medium and cell-free spent medium, thus indicating that the fungus played a role in effecting metal extraction from the spent catalyst. PMID:15664080

Aung, Khin Moh Moh; Ting, Yen-Peng

2005-03-16

355

H-Gallosilicate (MFI) propane aromatization catalyst Influence of calcination temperature on acidity, activity and deactivation due to coking  

Microsoft Academic Search

H-Gallosilicate (MFI) (bulk Si\\/Ga = 33) calcined at different temperatures (600–1100°C) has been characterized for its acidity\\/acid strength distribution (by step wise thermal desorption and chemisorption of pyridine at 100–400°C), acid function by acid catalyzed model reactions (viz. isooctane cracking (at 400°C) for external acid sites and o-xylene isomerization (at 400°C) and toluene disproportionation (at 500°C) for overall acid sites),

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

1996-01-01

356

Results of catalyst testing using iron-based catalysts.  

National Technical Information Service (NTIS)

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 ...

J. C. Linehan J. G. Darab D. W. Matson

1993-01-01

357

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

358

Catalyst of a metal heteropoly acid salt that is insoluble in a polar solvent on a non-metallic porous support and method of making  

DOEpatents

The present invention includes a catalyst having (a) a non-metallic support having a plurality of pores; (b) a metal heteropoly acid salt that is insoluble in a polar solvent on the non-metallic support; wherein at least a portion of the metal heteropoly acid salt is dispersed within said plurality of pores. The present invention also includes a method of depositing a metal heteropoly acid salt that is insoluble in a polar solvent onto a non-metallic support having a plurality of pores. The method has the steps of: (a) obtaining a first solution containing a first precursor of a metal salt cation; (b) obtaining a second solution containing a second precursor of a heteropoly acid anion in a solvent having a limited dissolution potential for said first precursor; (c) impregnating the non-metallic support with the first precursor forming a first precursor deposit within the plurality of pores, forming a first precursor impregnated support; (d) heating said first precursor impregnated support forming a bonded first precursor impregnated support; (e) impregnating the second precursor that reacts with the precursor deposit and forms the metal heteropoly acid salt.

Wang, Yong [Richland, WA; Peden, Charles H. F. [West Richland, WA; Choi, Saemin [Richland, WA

2002-10-29

359

Catalyst Of A Metal Heteropoly Acid Salt That Is Insoluble In A Polar Solvent On A Non-Metallic Porous Support And Method Of Making  

DOEpatents

The present invention includes a catalyst having (a) a non-metallic support having a plurality of pores; (b) a metal heteropoly acid salt that is insoluble in a polar solvent on the non-metallic support; wherein at least a portion of the metal heteropoly acid salt is dispersed within said plurality of pores. The present invention also includes a method of depositing a metal heteropoly acid salt that is insoluble in a polar solvent onto a non-metallic support having a plurality of pores. The method has the steps of: (a) obtaining a first solution containing a first precursor of a metal salt cation; (b) obtaining a second solution containing a second precursor of a heteropoly acid anion in a solvent having a limited dissolution potential for said first precursor; (c) impregnating the non-metallic support with the first precursor forming a first precursor deposit within the plurality of pores, forming a first precursor impregnated support; (d) heating said first precursor impregnated support forming a bonded first precursor impregnated support; (e) impregnating the second precursor that reacts with the precursor deposit and forms the metal heteropoly acid salt.

Wang. Yong (Richland, WA); Peden. Charles H. F. (West Richland, WA); Choi. Saemin (Richland, WA)

2004-11-09

360

Electro-catalytic oxidation of CO on Pt catalyst supported on carbon nanotubes pretreated with oxidative acids  

Microsoft Academic Search

Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO3, mixed HNO3+H2SO4 and H2SO4+K2Cr2O7 solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ?3nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques

Li Li; Gang Wu; Bo-Qing Xu

2006-01-01

361

Influence of support on the performance of molybdenum sulfide catalysts used to hydrotreat coal liquids  

SciTech Connect

Supports for molybdenum sulfide hydrotreating catalysts included silica, silica-magnesia, titania, chromia-alumina, activated carbon and nitrided activated carbon. The alumina supported Amocat 1A and Amocat 1C as well as the silica-alumina supported, Harshaw CoMo-0402 were also studied. Catalysts were characterized by BET surface area, mercury porosimetry and x-ray powder diffraction. Acidity was measured by the temperature programmed desorption of tert-butyl amine. Initial activity screening studies were conducted in a stirred autoclave batch reactor to determine appropriate metals loadings for the various supports. Initially active catalysts were then tested in a bench scale, trickle bed reactor to determine activity maintenance, coking tendency and selectivity at lined out conditions. Selectivities for hydrodenitrogenation and for the production of hydrogen donor molecules were of interest. The donatable hydrogen content of the produce was determined by {sup 1}H and {sup 13}C NMR spectroscopy. The results indicated a strong correlation between lined out hydrogenation activity and the volume in 60-200 {angstrom} diameter pores. A second correlation was observed between HDN activity and acid site density, indicating the importance of acid sites in denitrogenation. Low acidity catalysts appeared to produce a greater hydrogen donor content in the product oil than did high acidity catalysts but the results were not conclusive. The results also suggest that Bronsted acid sites can markedly reduce coking tendency but that in general, coke formation is related in a complex way to the acid/base chemistry of the surface.

McCormick, R.L.

1988-01-01

362

Fatty acid-based polyurethane films for wound dressing applications.  

PubMed

Fatty acid-based polyurethane films were prepared for use as potential wound dressing material. The polymerization reaction was carried out with or without catalyst. Polymer films were prepared by casting-evaporation technique with or without crosslink-catalyst. The film prepared from uncatalyzed reaction product with crosslink-catalyst gave slightly higher crosslink density. The mechanical tests showed that, the increase in the tensile strength and decrease in the elongation at break is due to the increase in the degree of crosslinking. All films were flexible, and resisted to acid solution. The films prepared without crosslink-catalyst were more hydrophilic, absorbed more water. The highest permeability values were generally obtained for the films prepared without crosslink catalyst. Both the direct contact method and the MMT test were applied for determination of cytotoxicity of polymer films and the polyurethane film prepared from uncatalyzed reaction product without crosslink-catalyst showed better biocompatibility property, closest to the commercial product, Opsite. PMID:18839285

Gultekin, Guncem; Atalay-Oral, Cigdem; Erkal, Sibel; Sahin, Fikret; Karastova, Djursun; Tantekin-Ersolmaz, S Birgul; Guner, F Seniha

2009-01-01

363

Reaction products and the mechanism in the dimerization of 2-methyl-1-alkenes over Lewis acid and Brønsted acid catalysts: anomalous reaction behaviors of 2-methyl-1-alkenes over Re 2O 7–Al 2O 3 metathesis catalyst  

Microsoft Academic Search

2-Methyl-1-alkenes have exhibited anomalous reaction behavior over a Re2O7–Al2O3 metathesis catalyst. Self-metathesis of 2-methyl-1-alkenes did not occur at all and several kinds of dimers were formed as major products. The dimer structures using 2-methyl-1-pentene as a model compound were identified by using various methods, such as ozonolysis, hydrogenation, gas chromatography–mass spectrometry (GC–MS) and 1H NMR and 13C NMR. The dimerization

Tadashi Kawai; Hiroyuki Kudo; Takehiko Suzuki; Tomokazu Iyoda

2000-01-01

364

Molecular water oxidation catalyst  

DOEpatents

A dimeric composition of the formula: ##STR1## wherein L', L", L'", and L"" are each a bidentate ligand having at least one functional substituent, the ligand selected from bipyridine, phenanthroline, 2-phenylpyridine, bipyrimidine, and bipyrazyl and the functional substituent selected from carboxylic acid, ester, amide, halogenide, anhydride, acyl ketone, alkyl ketone, acid chloride, sulfonic acid, phosphonic acid, and nitro and nitroso groups. An electrochemical oxidation process for the production of the above functionally substituted bidentate ligand diaqua oxo-bridged ruthenium dimers and their use as water oxidation catalysts is described.

Gratzel, Michael (St. Sulpice, CH) [St. Sulpice, CH; Munavalli, Shekhar (Bel Air, MD) [Bel Air, MD; Pern, Fu-Jann (Lakewood, CO) [Lakewood, CO; Frank, Arthur J. (Lakewood, CO) [Lakewood, CO

1993-01-01

365

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

366

SO2-4/TiO2-SiO2 Mixed Oxide Catalyst, I: Synthesis, Characterization, and Acidic Properties.  

PubMed

A series of sulfate-doped titania-silica mixed oxides have been prepared by immersing titania-silica gel in the required volume of sulfuric acid, followed by drying. The mixed oxide gel is obtained by hydrolyzing an equimolar mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBOT) at pH 3. The materials, after calcining at 723 K for 4 h, are characterized by XRD, FT-IR, the BET method, and surface acid strength by the Hammett indicator method. The catalytic activity tests are carried in a fixed bed catalytic reactor (i.d. = 10 mm) for alcohol conversion, whereas cumene cracking/dehydrogenation reactions are carried out in a micropulse reactor. XRD results shows that the titania-silica mixture is amorphous and the crystallization starts with sulfation. The surface of the mixed oxide contains both bridged and normal hydroxyl groups, as observed from FT-IR data. The surface area of the material is not much altered by sulfation and lies within 50 m2/g. The acid strength of 4 wt% SO2-4/TiO2-SiO2 is found to be stronger than that of 100% concentrated H2SO4. In the case of 2-propanol conversion, low acetone selectivity indicates the presence of weak basic sites, whereas methanol conversion over all solids shows that dehydration follows a parallel and consecutive pathway. A good correlation is found between the cumene cracking and the acidity of the catalysts. Copyright 1999 Academic Press. PMID:10395770

Parida; Samantaray; Mishra

1999-08-01

367

PseAAC-General: fast building various modes of general form of Chou's pseudo-amino acid composition for large-scale protein datasets.  

PubMed

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

368

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

369

A convenient catalyst system for microwave accelerated cross-coupling of a range of aryl boronic acids with aryl chlorides  

PubMed Central

A convenient microwave accelerated cross-coupling procedure between aryl chlorides with a range of boronic acids has been developed. An explanation for the low reactivity of highly fluorinated boronic acids in Suzuki coupling is provided.

Clarke, Matthew L; France, Marcia B; Fuentes, Jose A; Milton, Edward J; Roff, Geoffrey J

2007-01-01

370

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.

Preus, S?ren; Kilsa, Kristine; Miannay, Francois-Alexandre; Albinsson, Bo; Wilhelmsson, L. Marcus

2013-01-01

371

Synthesis of 3,4-Dihydropyrimidin-2(1H)-Ones and Their Corresponding 2(1H)Thiones Using Trichloroacetic Acid as a Catalyst under Solvent-Free Conditions  

PubMed Central

Trichloroacetic acid was found to be a convenient catalyst for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones and their corresponding 2(1H)-thiones through a one-pot three-component reaction of aldehydes, alkyl acetoacetate, and urea or thiourea at 70°C under solvent-free conditions.

Karimi-Jaberi, Zahed; Moaddeli, Mohammad Sadegh

2012-01-01

372

o-Benzenedisulfonimide and its chiral derivative as Brønsted acids catalysts for one-pot three-component Strecker reaction. Synthetic and mechanistic aspects.  

PubMed

o-Benzenedisulfonimide (OBS) has efficiently catalysed the one-pot three-component reaction of ketones and aromatic amines with trimethylsilyl cyanide (TMSCN) giving the corresponding ?-amino nitriles in excellent yields (23 examples; average yield 85%). Reaction conditions were very simple, green and efficient. Theoretical calculations have allowed us to explain the mechanism of this reaction which has been found to take place in two phases; the first consists of the nucleophilic addition of the aniline to the ketone and the subsequent dehydration to an imine; the second one consists of the formal addition of cyanide anion to the protonated imine. OBS acts in all steps of this mechanism. Without an acid catalyst, the reaction mechanism is more simple but barriers are sensibly higher. A chiral derivative of OBS was also used and gave fairly good results. PMID:22527016

Barbero, Margherita; Cadamuro, Silvano; Dughera, Stefano; Ghigo, Giovanni

2012-05-28

373

Two stage leaching of activated spent HDS catalyst and solvent extraction of aluminium using organo-phosphinic extractant, Cyanex 272  

Microsoft Academic Search

Spent catalyst generally contains valuable metals like Mo, Co, Ni on a supporting material, such as ?-A12O3. In the present study, a two stage alkali\\/acid leaching process is proposed to selectively target molybdenum and cobalt\\/nickel separately to facilitate the downstream processing. Prior to the leaching, the spent catalyst was calcined at 500°C to remove C and S; and to convert

Kyung Ho Park; Debasish Mohapatra; Chul-Woo Nam

2007-01-01

374

High-dose tranexamic acid is related to increased risk of generalized seizures after aortic valve replacement  

Microsoft Academic Search

Objective: To investigate the incidence of postoperative generalized seizures in patients undergoing aortic valve replacement (AVR) under extracorporeal circulation, who received either high-dose tranexamic acid (TXA) or epsilon aminocaproic acid (EACA) as an antifibrinolytic agent. Methods: This retrospective analysis comprised 682 consecutive patients undergoing AVR with or without simultaneous coronary artery bypass surgery. Patients operated on before March 2008 were

Cornelius Keyl; Reiner Uhl; Friedhelm Beyersdorf; Susanne Stampf; Cornelius Lehane; Christoph Wiesenack; Dietmar Trenk

2011-01-01

375

Metal chelate catalysts for fuel cells  

NASA Astrophysics Data System (ADS)

Various modified forms of several organometallic chelate compounds were synthesized and tested for their activity and stability as oxygen reduction electrocatalysts in sulfuric acid electrolyte. The most active catalysts found were cobalt tetraazaannulene (CoTAA), iron phthalocyanine (FePc) and cobalt tetraphenylporphyrin (CoTPP). However, these catalysts have limited stability in strong acids.

Darby, R.; Yamana, M.; Dhar, H.; White, R.

1982-10-01

376

Metal chelate catalysts for fuel cells  

Microsoft Academic Search

Various modified forms of several organometallic chelate compounds were synthesized and tested for their activity and stability as oxygen reduction electrocatalysts in sulfuric acid electrolyte. The most active catalysts found were cobalt tetraazaannulene (CoTAA), iron phthalocyanine (FePc) and cobalt tetraphenylporphyrin (CoTPP). However, these catalysts have limited stability in strong acids.

R. Darby; M. Yamana; H. Dhar; R. White

1982-01-01

377

The conversion of CO2 and CH4 to acetic acid over the Au-exchanged ZSM-5 catalyst: a density functional theory study.  

PubMed

The direct conversion of methane and carbon dioxide to acetic acid is one of the most challenging research topics. Using the density functional theory (M06-L) the study reveals the catalytic activity of the Au(I)-ZSM-5 zeolite in this reaction. The Au(I)-ZSM-5 is represented by a 34T quantum cluster model. The activation of the C-H bond over the Au-ZSM-5 zeolite would readily take place via the homolytic ?-bond activation with an energy barrier of 10.5 kcal mol(-1), and subsequent proton transfer from the Au cation to the zeolitic oxygen, yielding the stable methyl-gold complex adsorbed on the zeolite Brønsted acid. The conversion of CO(2) on this bi-functional catalyst involves the Brønsted acid site playing a role in the protonation of CO(2) and the methyl-gold complex acting as a methylating agent. The activation energy of 52.9 kcal mol(-1) is predicted. PMID:22903398

Panjan, Wasinee; Sirijaraensre, Jakkapan; Warakulwit, Chompunuch; Pantu, Piboon; Limtrakul, Jumras

2012-12-28

378

Cracking Activity of Zeolite Y Catalysts Synthesized from a South African Kaolinite.  

National Technical Information Service (NTIS)

Rare earth cation exchanged zeolite Y catalysts, rare earth acidic exchanged zeolite Y catalysts, and ultrastable zeolite Y catalysts with or without exchanged rare earth cations were prepared from ceramic microspheres which contained 24% NaY zeolites. A ...

M. G. Howden

1981-01-01

379

Sulfated titania [TiO 2\\/SO 4 2?]: A very active solid acid catalyst for the esterification of free fatty acids with ethanol  

Microsoft Academic Search

Sulfated titanias were prepared by using ammonium sulfate and sulfuric acid as sulfate precursors. Depending on the sulfation method, important effects on the acidity, textural properties as well as on activity were found. After ammonium sulfate was used, a large amount of SO linked to the titania surface was observed by FTIR spectroscopy. The acidity strength determined with Hammett indicators

J. L. Ropero-Vega; A. Aldana-Pérez; R. Gómez; M. E. Niño-Gómez

2010-01-01

380

Photo-oxidation catalysts  

DOEpatents

Photo-oxidation catalysts and methods for cleaning a metal-based catalyst are disclosed. An exemplary catalyst system implementing a photo-oxidation catalyst may comprise a metal-based catalyst, and a photo-oxidation catalyst for cleaning the metal-based catalyst in the presence of light. The exposure to light enables the photo-oxidation catalyst to substantially oxidize absorbed contaminants and reduce accumulation of the contaminants on the metal-based catalyst. Applications are also disclosed.

Pitts, J. Roland (Lakewood, CO); Liu, Ping (Irvine, CA); Smith, R. Davis (Golden, CO)

2009-07-14

381

CALCULATION OF THE SURFACE AREAS AND THE ACID STRENGTH OF NiSO4, CuSO4 AND CoSO4.H20 AND THE USE OF THESE CATALYSTS ON DEHYDRATION OF SOME ALCOHOLS  

Microsoft Academic Search

SUMMARY In this study; the surfaces of the catalysts were examined by electron microscope and their surface areas were calculated with gas adsorption method as a unit of m2g-1. In addition, the acid strength on solid catalysts (NiSO4, CuSO4, CoSO4.H2O) was determined by Hammett indicator adsorption method and also, dehydration reactions of 2,6-dimethyl-4-heptanol, 3,7-dimethyl-3-octanol and 2-octanol were investigated with the

MUSTAFA RIDVANLAR; ÜLKÜ OYMAN

382

General roles of abscisic and jasmonic acids in gene activation as a result of mechanical wounding.  

PubMed

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, ABA-responsive genes that encode two additional proteinase inhibitors, the proteolytic enzyme leucine aminopeptidase, and the biosynthetic enzyme threonine deaminase were isolated from potato plants. Wounding or treatment with ABA resulted in a pattern of accumulation of these mRNAs very similar to that of pin2. ABA-deficient plants did not accumulate any of the mRNAs upon wounding, although they showed normal levels of expression upon ABA treatment. Also, application of methyl jasmonate (MeJA) induced a strong accumulation of these transcripts, both in wild-type and in ABA-deficient plants, thus supporting a role for jasmonic acid as an intermediate in the signaling pathway that leads from ABA accumulation in response to wounding to the transcriptional activation of the genes. PMID:1392612

Hildmann, T; Ebneth, M; Peña-Cortés, H; Sánchez-Serrano, J J; Willmitzer, L; Prat, S

1992-09-01

383

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

384

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

385

Naturally occurring alkaline amino acids function as efficient catalysts on Knoevenagel condensation at physiological pH: a mechanistic elucidation.  

PubMed

To maintain biological functions, thousands of different reactions take place in human body at physiological pH (7.0) and mild conditions, which is associated with health and disease. Therefore, to examine the catalytic function of the intrinsically occurring molecules, such as amino acids at neutral pH, is of fundamental interests. Natural basic ?-amino acid of L-lysine, L-arginine, and L-histidine neutralized to physiological pH as salts were investigated for their ability to catalyze Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate. Compared with their free base forms, although neutralized alkaline amino acid salts reduced the catalytic activity markedly, they were still capable to perform an efficient catalysis at physiological pH as porcine pancreatic lipase (PPL), one of the best enzymes that catalyze Knoevenagel condensation. In agreement with the fact that the three basic amino acids were well neutralized, stronger basic amino acid Arg and Lys showed more obvious variation in NH bend peak from the FTIR spectroscopy study. Study of ethanol/water system and quantitative kinetic analysis suggested that the microenvironment in the vicinity of amino acid salts and protonability/deprotonability of the amine moiety may determine their catalytic activity and mechanism. The kinetic study of best approximation suggested that the random binding might be the most probable catalytic mechanism for the neutralized alkaline amino acid salt-catalyzed Knoevenagel condensation. PMID:24682854

Li, Weina; Fedosov, Sergey; Tan, Tianwei; Xu, Xuebing; Guo, Zheng

2014-05-01

386

A comparison of tiaprofenic acid, mefenamic acid and placebo in the treatment of dysmenorrhoea in general practice.  

PubMed

The efficiency and side-effects of tiaprofenic acid, mefenamic acid and placebo were compared in the treatment of primary dysmenorrhoea. The trial was a double-blind prospective randomized 3-way crossover study during 6 successive menstrual cycles following a 2-cycle run-in period and involved 50 women with primary dysmenorrhoea selected from 96 volunteers between 16 and 35 years of age. Overall pain was significantly less (p less than 0.05) on treatment with tiaprofenic acid than on treatment with mefanemic acid, placebo, or the women's usual treatments. Both active treatments were well tolerated but more side-effects were reported during treatment with mefenamic acid. PMID:1520205

Tilyard, M W; Dovey, S M

1992-05-01

387

SO{sub 4}{sup 2{minus}}/TiO{sub 2}-SiO{sub 2} mixed oxide catalyst. 1: Synthesis, characterization, and acidic properties  

SciTech Connect

A series of sulfate-doped titania-silica mixed oxides have been prepared by immersing titania-silica gel in the required volume of sulfuric acid, followed by drying. The mixed oxide gel is obtained by hydrolyzing an equimolar mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBOT) at pH 3. The materials, after calcining at 723 K for 4 h, are characterized by XRD, FT-IR, the BET method, and surface acid strength by the Hammett indicator method. The catalytic activity tests are carried in a fixed bed catalytic reactor (i.e. = 10 mm) for alcohol conversion, whereas cumene cracking/dehydrogenation reactions are carried out in a micropulse reactor. XRD results shows that the titania-silica mixture is amorphous and the crystallization starts with sulfation. The surface of the mixed oxide contains both bridged and normal hydroxyl groups, as observed from FT-IR data. The surface area of the material is not much altered by sulfation and lies within 50 m{sup 2}/g. The acid strength of 4 wt% SO{sub 4}{sup 2{minus}}/TiO{sub 2}-SiO{sub 2} is found to be stronger than that of 100% concentrated H{sub 2}SO{sub 4}. In the case of 2-propanol conversion, low acetone selectivity indicates the presence of weak basic sites, whereas methanol conversion over all solids shows that dehydration follows a parallel and consecutive pathway. A good correlation is found between the cumene cracking and the acidity of the catalysts.

Parida, K.M.; Samantaray, S.K.; Mishra, H.K. [CSIR, Orissa (India). Regional Research Lab.] [CSIR, Orissa (India). Regional Research Lab.

1999-08-01

388

Catalytic performance of Fe3O4-CoO/Al2O3 catalyst in ozonation of 2-(2,4-dichlorophenoxy)propionic acid, nitrobenzene and oxalic acid in water.  

PubMed

Fe3O4-CoO/Al2O3 catalyst was prepared by incipient wetness impregnation using Fe(NO3)3 x 9H2O and Co(NO3)2 x 6H2O as the precursors, and its catalytic performance was investigated in ozonation of 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), nitrobenzene and oxalic acid. The experimental results indicated that Fe3O4-CoO/Al2O3 catalyst enabled an interesting improvement of ozonation efficiency during the degradation of each organic pollutant, and the Fe3O4-CoO/Al2O3 catalytic ozonation system followed a radical-type mechanism. The kinetics of ozonation alone and Fe3O4-CoO/Al2O3 catalytic ozonation of three organic pollutants in aqueous solution were discussed under the mere consideration of direct ozone reaction and OH radical reaction to well investigate its performance. In the catalytic ozonation of 2,4-DP, the apparent reaction rate constants (k) were determined to be 1.456 x 10(-2) min(-1) for ozonation alone and 4.740 x 10(-2) min(-1) for O3/Fe3O4-CoO/Al203. And O3/Fe3O4-CoO/Al2O3 had a larger R(ct) (6.614 x 10(-9)) calculated by the relative method than O3 did (1.800 x 10(-9)), showing O3/Fe3O4-CoO/Al2O3 generated more hydroxyl radical. Similar results were also obtained in the catalytic ozonation of nitrobenzene and oxalic acid. The above results demonstrated that the catalytic performance of Fe3O4-CoO/Al2O3 in ozonation of studied organic substance was universal to a certain degree. PMID:21235195

Tong, Shaoping; Shi, Rui; Zhang, Hua; Ma, Chunan

2010-01-01

389

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

390

Cross-coupling of diarylborinic acids and anhydrides with arylhalides catalyzed by a phosphite/N-heterocyclic carbene co-supported palladium catalyst system.  

PubMed

A highly efficient cross-coupling of diarylborinic acids and anhydrides with aryl chlorides and bromides has been effected by using a palladium catalyst system co-supported by a strong ?-donor N-heterocyclic carbene (NHC), N,N'-bis(2,6-diisopropylphenyl) imidazol-2-ylidene, and a strong ?-acceptor phosphite, triphenylphosphite, in tert-BuOH in the present of K(3)PO(4)·3H(2)O. Unsymmetrical biaryls with a variety of functional groups could be obtained in good to excellent yields using as low as 0.01, 0.2-0.5, and 1 mol % palladium loadings for aryl bromides and activated and deactivated aryl chlorides, respectively, under mild conditions. A ligand synergy between the ?-donor NHC and the ?-acceptor phosphite in the Pd/NHC/P(OPh)(3) catalytic system has been proposed to be responsible for the high efficacy to arylchlorides in the cross-coupling. A scalable and economical process has therefore been developed for synthesis of Sartan biphenyl from the Pd/NHC/P(OPh)(3) catalyzed cross-coupling of di(4-methylphenyl)borinic acid with 2-chlorobenzonitrile. PMID:22860711

Chen, Xiaofeng; Ke, Haihua; Chen, Yao; Guan, Changwei; Zou, Gang

2012-09-01

391

Isobutane alkylation with C 4 olefins on a sulfonic solid acid catalyst system based on laminar clays  

Microsoft Academic Search

Natural clays were modified by means of the controlled attack of strong Brönsted acids in aqueous solution. The variations of the surface acidity of the solids, followed by IR of adsorbed pyridine and hammett indicators, indicated a population of Brönsted type sites above 800?mol\\/g, while the surface area increased from 23 up to 105m2\\/g. A series of solids (ATZ-L, ATZ-A

C. E Ramos-Galván; J. M Dom??nguez; G Sandoval-Robles; A Mantilla; G Ferrat

2001-01-01

392

Regioselective ?-Alkylation of Silyl Enolates using a Mild Catalyst ZnCl2 Doped on Acidic Alumina  

Microsoft Academic Search

ZnCl2 doped acidic alumina used as a solid support acts as a better Lewis acid in the SNl reaction of trimethyl silyl enol ethers with 3, allylic and benzylic halides to yield exclusively the substituted product in excellent yields. This method has been employed for the synthesis of monocyclic sesquitepene hydrocarbon, (±)-?-bisabolene and a monoterpene, 2,6-dimethyl-7-octen-4-one.

G. L. Kad; Vasundhara Singh; Anupam Khurana; Sangeeta Chaudhary; Jasvinder Singh

1999-01-01

393

Acidity and catalytic properties for methane conversion of Mo\\/HZSM-5 catalyst modified by reacting with organometallic complex  

Microsoft Academic Search

The selective modification of the external surface of HZSM-5 by large organometallic complexes was used to reduce the densities of external acid sites and MoOx species retained at external surfaces during the exchange process. The amounts of acid sites and the catalytic properties for non-oxidative aromatization of methane over modified and unmodified samples were studied by NH3-TPD, FT-IR of d3-acetonitrile

Peng Wu; Qiubin Kan; Xuxu Wang; Dongyang Wang; Haijun Xing; Piaoping Yang; Tonghao Wu

2005-01-01

394

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

395

Identification of a potential general acid/base in the reversible phosphoryl transfer reactions catalyzed by tyrosine recombinases: Flp H305  

PubMed Central

Summary Flp provides a unique opportunity to apply the tools of chemical biology to phosphoryl transfer reactions. Flp and other tyrosine recombinases catalyze site-specific DNA rearrangements via a phosphotyrosine intermediate, similar to the mechanism of type Ib topoisomerases [1]. Unlike most related enzymes, Flp’s nucleophilic tyrosine derives from a different protomer than the remainder of its active site [2, 3]. Because the tyrosine can be supplied exogenously, non-natural synthetic analogs can be used. Here we examine the catalytic role of Flp’s conserved H305. DNA cleavage was studied using a peptide containing either tyrosine (pKa?10), or 3-fluoro-tyrosine (pKa?8.4). Religation was studied using DNA substrates with 3’-phospho-cresol (pKa?10) or 3’-para-nitro-phenol (pKa?7.1) mimicking the covalent protein-DNA intermediate. In both cases, the tyrosine analog with the lower pKa specifically restored the activity of an H305 mutant. These results provide the first experimental evidence that this conserved histidine functions as a general acid/base catalyst in tyrosine recombinases.

Whiteson, Katrine L.; Chen, Yu; Chopra, Neeraj; Raymond, Amy C.; Rice, Phoebe A.

2007-01-01

396

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

2014-05-01

397

Supported olefin polymerization catalyst  

SciTech Connect

A solid, hydrocarbon-insoluble, alpha-olefin polymerization catalyst component is described comprising the product formed by: A. complexing a magnesium alkyl composition with an ortho disubstituted hindered carboxylic aromatic acid ester; B. reacting the resulting stable complex with a compatible precipitation agent to form a solid component; and C. reacting the resulting solid with a titanium compound in a suitable diluent containing a suitable electron donor compound.

Johnson, B.V.; Karayannis, N.M.; Hoppin, C.R.; Ornellas, L.

1986-04-08

398

Efficient combination of promoter and catalyst for chromic acid oxidation of propan-2-ol to acetone in aqueous acid media at room temperature  

NASA Astrophysics Data System (ADS)

Oxidation of propan-2-ol to acetone was carried out in aqueous media at room temperature. The effect of promoter (PA, bpy, phen), micellar catalyst (SDS, CPC, TX-100) and their combination has been studied. The reactions were performed under the condition [Propan-2-ol]T ? [Cr(VI)]T at 30 °C. Then kobs and half life of all the reaction were determined to identify which promoter and which combination are the most effective for this oxidation. Among the promoters phen accelerates the reaction most in aqueous media. In absence of promoters anionic surfactant SDS increases the rate more effectively than neutral surfactant TX-100. CPC retards the rate in comparison to aqueous media. The rate of the oxidation is highest in presence of the combination of bpy and SDS.

Mukherjee, Kakali; Saha, Rumpa; Ghosh, Aniruddha; Ghosh, Sumanta K.; Saha, Bidyut

2013-01-01

399

Generalized peroxisomal disorder in male twins: Fatty acid composition of serum lipids and response to n?3 fatty acids  

Microsoft Academic Search

Male, identical twins presented with hypotonia, hypoglycaemia, dysmorphic facies, feeding problems, discoloured stools, hepatomegaly, and nephrolithiasis. Elevated blood levels of very long-chain fatty acids and bile acids suggested a peroxisomal disorder. Plasmalogen biosynthesis in cultured fibroblasts was reduced. Morphologically distinct peroxisomes were undetectable in liver. Twin 1 suffered from nephrocalcinosis and severe infection, and died at 18 months of age.

O. Søvik; J.-E. Månsson; A.-L. Bjørke Monsen; E. Jellum; R. K. Berge

1998-01-01

400

Circulating Levels of Fatty Acid-Binding Protein Family and Metabolic Phenotype in the General Population  

PubMed Central

Objective Fatty acid-binding proteins (FABPs) are a family of 14-15-kDa proteins, and some FABPs have been to be used as biomarkers of tissue injury by leak from cells. However, recent studies have shown that FABPs can be secreted from cells into circulation. Here we examined determinants and roles of circulating FABPs in a general population. Methods From the database of the Tanno-Sobetsu Study, a study with a population-based cohort design, data in 2011 for 296 subjects on no medication were retrieved, and FABP1?5 in their serum samples were assayed. Results Level of FABP4, but not the other isoforms, showed a gender difference, being higher in females than in males. Levels of all FABPs were negatively correlated with estimated glomerular filtration rate (eGFR), but a distinct pattern of correlation with other clinical parameters was observed for each FABP isoform; significant correlates were alanine aminotransferase (ALT), blood pressure (BP), and brain natriuretic peptide (BNP) for FABP1, none besides eGFR for FABP2, age, BP, and BNP for FABP3, age, waist circumference (WC), BP, BNP, lipid variables, high-sensitivity C-reactive protein (hsCRP), and HOMA-R for FABP4, and age, WC, BP, ALT, BNP, and HOMA-R for FABP5. FABP4 is the most strongly related to metabolic markers among FABPs. In a multivariate regression analysis, FABP4 level was an independent predictor of HOMA-R after adjustment of age, gender, WC, BP, HDL cholesterol, and hsCRP. Conclusions Each FABP isoform level showed a distinct pattern of correlation with clinical parameters, although levels of all FABPs were negatively determined by renal function. Circulating FABP4 appears to be a useful biomarker for detecting pre-clinical stage of metabolic syndrome, especially insulin resistance, in the general population.

Watanabe, Yuki; Hoshina, Kyoko; Fuseya, Takahiro; Mita, Tomohiro; Okazaki, Yusuke; Koyama, Masayuki; Tanaka, Marenao; Akasaka, Hiroshi; Ohnishi, Hirofumi; Yoshida, Hideaki; Saitoh, Shigeyuki; Miura, Tetsuji

2013-01-01

401

An infrared study of selective hydrogenation of carboxylic acids to corresponding aldehydes over a ZrO 2 catalyst: pivalic acid to 2,2-dimethylpropanal  

Microsoft Academic Search

A selective hydrogenation of pivalic acid ((CH3)3C-COOH) to 2,2-dimethylpropanal ((CH3)3C-CHO) was studied by infrared spectroscopy. While pivalic acid adsorbed on Cr2O3-ZrO2 as a carboxylate ((CH3)3C-COC-) above 303 K and decomposed at 773 K, it was reduced by H2 at 623 K. The adsorbed aldehyde changed into the carboxylic acid ion species above 523 K via several intermediate species observed below

Nan Ding; Junko Kondo; Ken ichi Maruya; Kazunari Domen; Toshiharu Yokoyama; Naoko Fujita; Takao Maki

1993-01-01

402

Laboratory and pilot scale synthesis, characterization and reactivity of multicomponent cobalt spinel catalyst for low temperature removal of N 2O from nitric acid plant tail gases  

Microsoft Academic Search

Synthesis of a multicomponent (K, Zn-doped) cobalt spinel deN2O catalyst developed in a laboratory was extended to a pilot scale. The optimal composition and morphology of the prototype catalyst elucidated in the laboratory conditions were successfully reproduced upon large scale synthesis and shaping. Tuning of the catalyst properties was guided by in situ work function measurements in conjunction with the

Marek Inger; Pawe? Kowalik; Magdalena Saramok; Marcin Wilk; Pawe? Stelmachowski; Gabriela Maniak; Pascal Granger; Andrzej Kotarba; Zbigniew Sojka

2011-01-01

403

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

404

Effects of particulates, heavy metals and acid gas on the removals of NO and PAHs by V2O5-WO3 catalysts in waste incineration system.  

PubMed

This study investigated the activities of prepared and commercial V(2)O(5)-WO(3) catalysts for simultaneous removals of NO and polycyclic aromatic hydrocarbons (PAHs) and the influences of particulates, heavy metals, SO(2), and HCl on the performances of catalysts. The experiments were carried out in a laboratory-scale waste incineration system equipped with a catalyst reactor. The DREs of PAHs by prepared and commercial V(2)O(5)-WO(3) catalysts were 64% and 72%, respectively. Increasing the particulate concentrations in flue gas suppressed the DRE of PAHs, but increasing the carbon content on surface of catalysts promotes the NO conversions. The DRE of PAHs by the catalysts was significantly decreased by the increased concentrations of heavy metal Cd, but was promoted by high concentration of Pb. The influence level of SO(2) was higher than HCl on the performances of V(2)O(5)-WO(3) catalysts for PAHs removal, but was lower than HCl for NO removal. Prepared and commercial V(2)O(5)-WO(3) catalysts have similar trends on the effects of particulates, heavy metals, SO(2), and HCl. The results of ESCA analysis reveal that the presence of these pollutants on the surface of catalysts did not change the chemical state of V and W. PMID:19500905

Chang, Feng-Yim; Chen, Jyh-Cherng; Wey, Ming-Yen; Tsai, Shih-An

2009-10-15

405

Amino Acid:Pyruvate Transaminase from Alcaligenes denitrificans Y2k-2: a New Catalyst for Kinetic Resolution of  Amino Acids and Amines  

Microsoft Academic Search

Alcaligenes denitrificans Y2k-2 was obtained by selective enrichment followed by screening from soil samples, which showed -amino acid:pyruvate transaminase activity, to kinetically resolve aliphatic -amino acid, and the corresponding structural gene (aptA) was cloned. The gene was functionally expressed in Escherichia coli BL21 by using an isopropyl--D-thiogalactopyranoside (IPTG)-inducible pET expression system (9.6 U\\/mg), and the recombinant AptA was purified to

Hyungdon Yun; Seongyop Lim; Byung-Kwan Cho; Byung-Gee Kim

2004-01-01

406

Ionic Liquids as Catalysts for Ethylbenzene Production  

Microsoft Academic Search

\\u000a Chloroaluminate ionic liquids have been assessed as liquid acid catalysts for the alkylation of benzene with ethylene to produce\\u000a ethylbenzene. Detailed comparisons with commercial aluminium(III) chloride catalyst have been carried out, using performance\\u000a indicators such as activity, selectivity and lifetime. Results of the study indicate inferior activity but superior recyclability\\u000a with current generations of ionic liquid catalysts. Calculations suggest that

M. P. Atkins; C. Bowlas; B. Ellis; F. Hubert; A. Rubatto; P. Wasserscheid

407

Cationic gold catalyst poisoning and reactivation.  

PubMed

High gold affinity impurities (halides, bases) in solvents, starting materials, filtration, or drying agents could affect the reactivity of gold catalyst adversely, which may significantly reduce the TON of cationic gold-catalyzed reactions. Use of a suitable acid activator (e.g., HOTf, In(OTf)3) reactivates the gold catalyst and makes the reaction proceed smoothly at low gold catalyst loading. PMID:24937566

Kumar, Manish; Hammond, Gerald B; Xu, Bo

2014-07-01

408

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

409

Synthesis and structural study of N-acetyl-1,2,3,4-tetrahydroisoquinoline-2-sulfonamide obtained using H6P2W18O62 as acidic solid catalyst  

NASA Astrophysics Data System (ADS)

At room temperature and under acidic conditions, acylation of sulfamides derivatives in various solvents using diverse solid catalysts has been investigated. The best yields are obtained in acetonitrile with a Wells-Dawson type heteropolyacid H6P2W18O62 as acidic solid catalyst. Crystals of N-acetyl-1,2,3,4-tetrahydroisoquinoline-2-sulfonamide suitable for X-ray study have been obtained after recrystallization in toluene. The detailed analysis of molecular and crystal structure is presented in comparison with the structure of 1,2,3,4-tetrahydroisoquinoline-2-sulfonamide, before acylation, previously studied by our team. The role of both intra- and intermolecular weak interactions is discussed. The Hirshfeld surfaces analysis in form of dnorm representation and decomposed fingerprint plots were used to find out different weak but directional hydrogen bonds and ? interactions. Both structures present similar sandwich structures with alternation of primary layers involving strong hydrogen bonds with secondary layers involving mostly weaker interactions.

Bougheloum, Chafika; Barbey, Carole; Berredjem, Malika; Messalhi, Abdelrani; Dupont, Nathalie

2013-06-01

410

Optimization of furfural production from D-xylose with formic acid as catalyst in a reactive extraction system.  

PubMed

Furfural is one of the most promising platform chemicals derived from biomass. In this study, response surface methodology (RSM) was utilized to determine four important parameters including reaction temperature (170-210°C), formic acid concentration (5-25 g/L), o-nitrotoluene volume percentage (20-80 vt.%), and residence time (40-200 min). The maximum furfural yield of 74% and selectivity of 86% were achieved at 190°C for 20 g/L formic acid concentration and 75 vt.% o-nitrotoluene by 75 min. The high boiling solvent, o-nitrotoluene, was recommended as extraction solvent in a reactive extraction system to obtain high furfural yield and reduce furfural-solvent separation costs. Although the addition of halides to the xylose solutions enhanced the furfural yield and selectivity, the concentration of halides was not an important factor on the furfural yield and selectivity. PMID:23434814

Yang, Wandian; Li, Pingli; Bo, Dechen; Chang, Heying; Wang, Xiaowei; Zhu, Tao

2013-04-01

411

Crosslinking of cotton cellulose with succinic acid in the presence of titanium dioxide nano-catalyst under UV irradiation  

Microsoft Academic Search

The nanometer titanium dioxide (TiO2), succinic acid (SUA), and the mixture of nano- TiO2 and SUA were dispersed or dissolved in pure water, then irradiated with UV at the wavelength of 254 nm under stirring for\\u000a different time periods respectively. The pH and conductivity values and UV-vis spectra of those solutions were recorded immediately.\\u000a The powders obtained from the filtrated and

Cheng-Chi Chen; Chyung-Chyung Wang

2006-01-01

412

SO 2? 4\\/TiO 2–SiO 2 Mixed Oxide Catalyst, I: Synthesis, Characterization, and Acidic Properties  

Microsoft Academic Search

A series of sulfate-doped titania–silica mixed oxides have been prepared by immersing titania–silica gel in the required volume of sulfuric acid, followed by drying. The mixed oxide gel is obtained by hydrolyzing an equimolar mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBOT) at pH 3. The materials, after calcining at 723 K for 4 h, are characterized by XRD, FT-IR, the

K. M. Parida; S. K. Samantaray; H. K. Mishra

1999-01-01

413

Potassium and Silver Salts of Tungstophosphoric Acid as Catalysts in Dehydration of Ethanol and Hydration of Ethylene  

Microsoft Academic Search

Potassium and silver salts of tungstophosphoric acid (HPW) with varying amounts of the cations KxH3?xPW12O40 and AgxH3?xPW12O40 have been prepared as pure or supported on silica using the incipient wetness method. Their catalytic properties in two reactions have been studied. The vapor-phase dehydration of ethanol carried out in a conventional flow-type reactor under atmospheric pressure at temperatures varying from 398

J. Haber; K. Pamin; L. Matachowski; B. Napruszewska; J. Po?towicz

2002-01-01

414

Preparing poly(aryl ethers) using alkaline earth metal carbonates, organic acid salts, and optionally copper compounds, as catalysts  

SciTech Connect

This patent describes an improved process for preparing poly(aryl ethers) and poly(aryl ether ketones) by the reaction of a mixture of at least one bisphenol and at least one dihalobenzenoid compound, and/or a halophenol. The improvement comprises providing to the reaction, a base which is a combination of an alkaline earth metal carbonate and/or bicarbonate and a potassium, rubidium, or cesium salt of an organic acid or combination of organic salts thereof.

Winslow, P.A.; Kelsey, D.R.; Matzner, M.

1988-09-27

415

?-Amino Acid:Pyruvate Transaminase from Alcaligenes denitrificans Y2k-2: a New Catalyst for Kinetic Resolution of ?-Amino Acids and Amines  

PubMed Central

Alcaligenes denitrificans Y2k-2 was obtained by selective enrichment followed by screening from soil samples, which showed ?-amino acid:pyruvate transaminase activity, to kinetically resolve aliphatic ?-amino acid, and the corresponding structural gene (aptA) was cloned. The gene was functionally expressed in Escherichia coli BL21 by using an isopropyl-?-d-thiogalactopyranoside (IPTG)-inducible pET expression system (9.6 U/mg), and the recombinant AptA was purified to show a specific activity of 77.2 U/mg for l-?-amino-n-butyric acid (l-?-ABA). The enzyme converts various ?-amino acids and amines to the corresponding ?-keto acids and ketones by using pyruvate as an amine acceptor. The apparent Km and Vmax for l-?-ABA were 56 mM and 500 U/mg, respectively, in the presence of 10 mM pyruvate. In the presence of 10 mM l-?-ABA, the apparent Km and Vmax for pyruvate were 11 mM and 370 U/mg, respectively. The enzyme exhibits high stereoselectivity (E > 80) in the kinetic resolution of 50 mM d,l-?-ABA, producing optically pure d-?-ABA (99% enantiomeric excess) with 53% conversion.

Yun, Hyungdon; Lim, Seongyop; Cho, Byung-Kwan; Kim, Byung-Gee

2004-01-01

416

omega-Amino acid:pyruvate transaminase from Alcaligenes denitrificans Y2k-2: a new catalyst for kinetic resolution of beta-amino acids and amines.  

PubMed

Alcaligenes denitrificans Y2k-2 was obtained by selective enrichment followed by screening from soil samples, which showed omega-amino acid:pyruvate transaminase activity, to kinetically resolve aliphatic beta-amino acid, and the corresponding structural gene (aptA) was cloned. The gene was functionally expressed in Escherichia coli BL21 by using an isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible pET expression system (9.6 U/mg), and the recombinant AptA was purified to show a specific activity of 77.2 U/mg for L-beta-amino-n-butyric acid (L-beta-ABA). The enzyme converts various beta-amino acids and amines to the corresponding beta-keto acids and ketones by using pyruvate as an amine acceptor. The apparent K(m) and V(max) for L-beta-ABA were 56 mM and 500 U/mg, respectively, in the presence of 10 mM pyruvate. In the presence of 10 mM L-beta-ABA, the apparent K(m) and V(max) for pyruvate were 11 mM and 370 U/mg, respectively. The enzyme exhibits high stereoselectivity (E > 80) in the kinetic resolution of 50 mM D,L-beta-ABA, producing optically pure D-beta-ABA (99% enantiomeric excess) with 53% conversion. PMID:15066855

Yun, Hyungdon; Lim, Seongyop; Cho, Byung-Kwan; Kim, Byung-Gee

2004-04-01

417

Novel Isopolyoxotungstate [H2W11O38](8-) Based Metal Organic Framework: As Lewis Acid Catalyst for Cyanosilylation of Aromatic Aldehydes.  

PubMed

A novel polyoxometalate-based metal organic framework (POMOF) constructed from isolated isopolyoxotungstate [H2W11O38](8-) cluster, {[Cu2(bpy)(H2O)5.5]2[H2W11O38]·3H2O·0.5CH3CN} (1, where bpy = 4,4'-bpydine), has been synthesized under solvothermal conditions and charaterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction. In 1, {W11} clusters are alternately linked by two [Cu(2)(H2O)1.5(Ot)3(N)](2+) cations in an unexpected end-to-end fashion leading to a one-dimensional (1D) chain. Adjacent 1D chains are linked through Cu(1)-bpy-Cu(2) in an opposite direction to form a two-dimensional (2D) wavelike sheet along the ab plane. These 2D sheets are further stacked in a parallel fashion giving rise to the 1D channels with copper(II) cations aligned in the channels. The resulting POMOF acted as a Lewis acid catalyst through a heterogeneous manner to prompt cyanosilylation with excellent efficiency. PMID:24903523

Han, Qiuxia; Sun, Xueping; Li, Jie; Ma, Pengtao; Niu, Jingyang

2014-06-16

418

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

419

Synthesis of ferromagnetic nanoparticles, formic acid oxidation catalyst nanocomposites, and late-transition metal-boride intermetallics by unique synthetic methods and single-source precursors  

NASA Astrophysics Data System (ADS)

The design, synthesis, and characterization of magnetic alloy nanoparticles, supported formic acid oxidation catalysts, and superhard intermetallic composites are presented. Ferromagnetic equatomic alloy nanoparticles of FePt, FePd, and CoPt were synthesized utilizing single-source heteronuclear organometallic precursors supported on an inert water-soluble matrix. Direct conversion of the precursor-support composite to supported ferromagnetic nanoparticles occurs under elevated temperatures and reducing conditions with metal-ion reduction and minimal nanoparticle coalescence. Nanoparticles were easily extracted from the support by addition of water and characterized in structure and magnetic properties. Palladium and platinum based nanoparticles were synthesized with microwave-based and chemical metal-ion reduction strategies, respectively, and tested for catalytic performance in a direct formic acid fuel cell (DFAFC). A study of palladium carbide nanocomposites with various carbonaceous supports was conducted and demonstrated strong activity comparable to commercially available palladium black, but poor catalytic longevity. Platinum-lead alloy nanocomposites synthesized with chemical reduction and supported on Vulcan carbon demonstrated strong activity, excellent catalytic longevity, and were subsequently incorporated into a prototype DFAFC. A new method for the synthesis of superhard ceramics on polymer substrates called Confined Plasma Chemical Deposition (CPCD) was developed. The CPCD method utilizes a tuned Free Electron Laser to selectively decompose the single-source precursor, Re(CO)4(B3H8), in a plasma-like state resulting in the superhard intermetallic ReB2 deposited on polymer substrates. Extension of this method to the synthesis of other hard of superhard ceramics; WB4, RuB2, and B4C was demonstrated. These three areas of research show new synthetic methods and novel materials of technological importance, resulting in a substantial advance in their respective fields.

Wellons, Matthew S.

420

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

421

Preparation of gold catalysts for glucose oxidation  

Microsoft Academic Search

The investigations focused on the influence of doping an alumina support with different base metal oxides on the catalytic performance of gold catalysts to oxidize glucose to gluconic acid. Sodium oxide and calcium oxide strongly enhanced the reaction rate for catalysts prepared by both the deposition–precipitation and incipient wetness method. Urea was used as the precipitation agent in the former.

Christine Baatz; Ulf Prüße

2007-01-01

422

Binary ferrihydrite catalysts  

DOEpatents

A method of preparing a catalyst precursor comprises dissolving an iron salt and a salt of an oxoanion forming agent, in water so that a solution of the iron salt and oxoanion forming agent salt has a ratio of oxoanion/Fe of between 0.0001:1 to 0.5:1. Next is increasing the pH of the solution to 10 by adding a strong base followed by collecting of precipitate having a binary ferrihydrite structure. A binary ferrihydrite catalyst precursor is also prepared by dissolving an iron salt in water. The solution is brought to a pH of substantially 10 to obtain ferrihydrite precipitate. The precipitate is then filtered and washed with distilled water and subsequently admixed with a hydroxy carboxylic acid solution. The admixture is mixed/agitated and the binary ferrihydrite precipitate is then filtered and recovered.

Huffman, Gerald P. (Lexington, KY); Zhao, Jianmin (Lexington, KY); Feng, Zhen (Lexington, KY)

1996-01-01

423

Binary ferrihydrite catalysts  

DOEpatents

A method of preparing a catalyst precursor comprises dissolving an iron salt and a salt of an oxoanion forming agent, in water so that a solution of the iron salt and oxoanion forming agent salt has a ratio of oxoanion/Fe of between 0.0001:1 to 0.5:1. Next is increasing the pH of the solution to 10 by adding a strong base followed by collecting of precipitate having a binary ferrihydrite structure. A binary ferrihydrite catalyst precursor is also prepared by dissolving an iron salt in water. The solution is brought to a pH of substantially 10 to obtain ferrihydrite precipitate. The precipitate is then filtered and washed with distilled water and subsequently admixed with a hydroxy carboxylic acid solution. The admixture is mixed/agitated and the binary ferrihydrite precipitate is then filtered and recovered. 3 figs.

Huffman, G.P.; Zhao, J.; Feng, Z.

1996-12-03

424

Process for Making a Noble Metal on Tin Oxide Catalyst  

NASA Technical Reports Server (NTRS)

To produce a noble metal-on-metal oxide catalyst on an inert, high-surface-area support material (that functions as a catalyst at approximately room temperature using chloride-free reagents), for use in a carbon dioxide laser, requires two steps: First, a commercially available, inert, high-surface-area support material (silica spheres) is coated with a thin layer of metal oxide, a monolayer equivalent. Very beneficial results have been obtained using nitric acid as an oxidizing agent because it leaves no residue. It is also helpful if the spheres are first deaerated by boiling in water to allow the entire surface to be coated. A metal, such as tin, is then dissolved in the oxidizing agent/support material mixture to yield, in the case of tin, metastannic acid. Although tin has proven especially beneficial for use in a closed-cycle CO2 laser, in general any metal with two valence states, such as most transition metals and antimony, may be used. The metastannic acid will be adsorbed onto the high-surface-area spheres, coating them. Any excess oxidizing agent is then evaporated, and the resulting metastannic acid-coated spheres are dried and calcined, whereby the metastannic acid becomes tin(IV) oxide. The second step is accomplished by preparing an aqueous mixture of the tin(IV) oxide-coated spheres, and a soluble, chloride-free salt of at least one catalyst metal. The catalyst metal may be selected from the group consisting of platinum, palladium, ruthenium, gold, and rhodium, or other platinum group metals. Extremely beneficial results have been obtained using chloride-free salts of platinum, palladium, or a combination thereof, such as tetraammineplatinum (II) hydroxide ([Pt(NH3)4] (OH)2), or tetraammine palladium nitrate ([Pd(NH3)4](NO3)2).

Davis, Patricia; Miller, Irvin; Upchurch, Billy

2010-01-01

425

Diseases associated with general amino acid transporters of the solute carrier 6 family (SLC6).  

PubMed

Amino acid transporters of the SLC6 family mediate the Na(+)-dependent uptake of neutral amino acids into neurons and epithelial cells of the intestine, kidney and other organs. They are integral parts of amino acid homeostasis in the whole body and the brain. In the intestine they are involved in protein absorption, while in the kidney they regulate plasma amino acid concentrations through reabsorption. The metabolic role of SLC6 amino acid transporters in the brain is less clear and most likely related to anaplerosis of the TCA cycle. Mutations in these transporters cause rare inherited disorders such as Hartnup disorder and iminoglycinuria. They may also play a role in complex traits such as depression, anxiety, obesity, diabetes and cancer. The review does not cover the transport of neurotransmitter amino acids. PMID:23876153

Broer, Stefan

2013-07-01

426

Characterisation of Catalysts by Transmission Electron Microscopy  

Microsoft Academic Search

Catalysts are one of the most important and the most widely used materials. Microstructures in heterogeneous catalysts are\\u000a closely related to the catalytic properties. TEM and related microanalytic techniques are powerful tools in characterising\\u000a catalysts at atomic level. The obtained structural information is essential to the understanding of correlations between microstructures\\u000a and catalytic properties. In this lecture note, the general

Di Wang

427

Keggin heteropolyacids as catalyst for the polymerization of ?-pinene  

Microsoft Academic Search

A series of Keggin-type heteropolyacids (HPAs) have been explored for cationic polymerization of ?-pinene in an attempt to\\u000a substitute traditional polymerization catalyst Lewis acids. The catalysts were characterized by XRD, FT-IR, TGA, acid strengths\\u000a of the catalysts were measured with Hammett indicators. Among them, 12-phosphotungstic acid (PW12) exhibits much higher catalytic activity. The effects of solvent, calcination temperature and reaction

Hualong Zhu; Zuguang Liu; Xinnan An; Fuhou Lei

2010-01-01

428

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.

Kim, YooJin; Feng, Xudong; Lippard, Stephen J.

2011-01-01

429

Influence of generated intermediates' interaction on heterogeneous Fenton's degradation of an azo dye 1-diazo-2-naphthol-4-sulfonic acid by using sludge based carbon as catalyst.  

PubMed

Sewage sludge based carbons have recently been used as novel catalyst in heterogeneous Fenton's reactions to degrade azo dye molecules. The carbons, functioning as both catalyst and adsorbent, play an important role in pollutants elimination, especially for those simultaneously generated organic intermediates. Different factors, i.e., H2O2 concentration, may influence the type and properties of those intermediates and may have great impacts on their elimination through the interactions with catalysts' surface. Thus, techniques including Temperature Programmed Desorption-Mass Spectrometer (TPD-MS), N2 adsorption isotherm and Scanning Electron Microscope (SEM) were used to probe the ways of the interaction between oxidation products and catalyst by using different initial H2O2 concentrations (10 and 20mM). The higher Chemical Oxygen Demand (COD) removal with 20mM H2O2 was found to be related not only to the higher hydroxyl radicals but also the specific interactions between the intermediates and catalyst' surface. The deep oxidation occurred in the conditions with higher oxidant amount enhances the intermediates' adsorption on catalyst, thus increasing the COD removal by large margin. Simulated adsorption experiments by using six primarily formed intermediates and three deeply mineralized products on three different catalysts also confirmed the assumption. Results suggested close relations between adsorption capacities and intermediates' properties such as polar surface area and octanol-water partition coefficient. PMID:24225585

Gu, Lin; Huang, Shouqiang; Zhu, Nanwen; Zhang, Daofang; Yuan, Haiping; Lou, Ziyang

2013-12-15

430

The general amino acid control pathway regulates mTOR and autophagy during serum/glutamine starvation.  

PubMed

Organisms have evolved elaborate mechanisms to adjust intracellular nutrient levels in response to fluctuating availability of exogenous nutrients. During starvation, cells can enhance amino acid uptake and synthesis through the general amino acid control (GAAC) pathway, whereas nonessential cellular contents are recycled by autophagy. How these two pathways are coordinated in response to starvation is currently unknown. Here we show that the GAAC pathway couples exogenous amino acid availability with autophagy. Starvation caused deactivation of mTOR, which then activated autophagy. In parallel, serum/glutamine starvation activated the GAAC pathway, which up-regulated amino acid transporters, leading to increased amino acid uptake. This elevated the intracellular amino acid level, which in turn reactivated mTOR and suppressed autophagy. Knockdown of activating transcription factor 4, the major transcription factor in the GAAC pathway, or of SLC7A5, a leucine transporter, caused impaired mTOR reactivation and much higher levels of autophagy. Thus, the GAAC pathway modulates autophagy by regulating amino acid uptake and mTOR reactivation during serum/glutamine starvation. PMID:25049270

Chen, Rui; Zou, Yilong; Mao, Dongxue; Sun, Daxiao; Gao, Guanguang; Shi, Jingwen; Liu, Xiaoqing; Zhu, Chen; Yang, Mingyu; Ye, Wanlu; Hao, Qianqian; Li, Ruiqiang; Yu, Li

2014-07-21

431

Improved catalysts for coal liquefaction: Final report  

SciTech Connect

Heterogeneous catalysts prepared from a variety of support materials were tested for activity and activity maintenance while processing coal-derived liquids under high severity conditions (P = 2000 psi, T = 800--825/degree/F, WHSV = 2-3). Conventional alumina supported hydrotreating catalysts were promoted with alkali and alkaline earth metals subjected to similar testing. Initial activity screening was conducted in a batch microautoclave reactor. Activity maintenance was evaluated in a continuous trickle bed reactor with run lengths of up to 500 hours. The feedstocks employed ranged from a hydrogen deficient light creosote oil to a mildly hydrogenated medium creosote oil spiked with ash-free, coal-derived-residuum material. The fresh and used catalysts were characterized structurally and subjected to analysis for carbon on catalyst, metals agglomeration and catalyst acidity. The benchmark commercial catalysts (Amocat 1A and Shell 324M) experienced minimal deactivation early in the run and maintained activity well despite the high severity conditions employed. Several of the laboratory preparations also performed well: most notably a NiMo/titania--alumina catalyst was competitive with the benchmark catalyst in terms of both activity and activity maintenance. A positive correlation was observed between ''lined out'' activity and pore volume in the 60--200 A diameter range. A correlation was also developed between carbon on catalyst and relative acid density. 116 refs., 100 figs., 94 tabs.

Haynes, H.W. Jr.

1988-04-01

432

Fresh catalyst container  

SciTech Connect

This patent describes a fresh catalyst container. It comprises: generally upright walls including substantially parallel side-walls and substantially parallel front and back walls; substantially parallel top and bottom walls extending between, intersecting, and connecting the upright walls and cooperating with the upright walls to define corners of the container; lock-receiving means comprising legs extending downwardly from aid bottom for matingly engaging and lockingly receiving lock pins of a flatbed truck trailer; lower folklift channels extending across and secured to the bottom wall for receiving tines of a folklift truck; upper monorail grab channels extending through the front and back walls for receiving grab hooks of a monorail; and substantially horizontal electrical limit switch-tripping means operatively connected to the walls for indicating the type of fresh catalyst in the container.

Erickson, M.E.; Plichta, R.T.

1990-08-07

433

Microscale Dehydration of Cyclohexanol Using a Macroreticular Cation Exchange Resin as Catalyst  

NASA Astrophysics Data System (ADS)

There are few experiments for the undergraduate laboratory involving ion exchange resins as catalysts. In this experiment, cyclohexanol is dehydrated to cyclohexene using Amberlyst 15 macroreticular resin as an acid catalyst. The procedure is carried out with partners, one student using phosphoric acid-sulfuric acid catalyst, the other student using the resin. Yields and ease of manipulation between the two options are compared.

Moeur, Harriet P.; Swatik, Sharon A.; Pinnell, Robert P.

1997-07-01

434

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

435

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

436

General and Facile Surface Functionalization of Hydrophobic Nanocrystals with Poly(amino acid) for Cell Luminescence Imaging  

PubMed Central

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

2013-01-01

437

Cracking of cumene on a radioactive tricalcium phosphate catalyst  

Microsoft Academic Search

1.The action of radioactive tricalcium phosphate catalysts containing the isotopes Ca45 and P32 in the cracking of cumene was investigated.2.The cracking of cumene on radioactive tricalcium phosphate catalysts is not acclerated in comparison with nonradioactive catalysts.3.The radioactivity of the catalysts, reaching 87 mCi\\/g, had no effect upon the nature and number of the acid centers of tricalcium phosphate, determined by

A. A. Balandin; Vikt I. Spitsyn; N. P. Dobrosel'skaya

1965-01-01

438

Bimetallic complexes and polymerization catalysts therefrom  

DOEpatents

Group 3-6 or Lanthanide metal complexes possessing two metal centers, catalysts derived therefrom by combining the same with strong Lewis acids, Bronsted acid salts, salts containing a cationic oxidizing agent or subjected to bulk electrolysis in the presence of compatible, inert non-coordinating anions and the use of such catalysts for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers are disclosed.

Patton, Jasson T. (Midland, MI); Marks, Tobin J. (Evanston, IL); Li, Liting (Evanston, IL)

2000-11-28

439

Degradation of polystyrene using montmorillonite clay catalysts  

Microsoft Academic Search

Summary The performance of acid-treated montmorillonite catalysts in the degradation of polystyrene (PS) was investigated in this study. The degradation was carried out in a semi-batch reactor with a mixture of PS and catalyst at 400-450oC. The commercial Süd Chemie acid-treated montmorillonite clays (K-series) showed good catalytic activity for the degradation of PS. The styrene monomer and ethylbenzene were major

Byung-Sik Jang; Kyo-Hyun Cho; Kyung-Hoon Kim; Dae-Won Park

2005-01-01

440

Scientific Literature Reviews on Generally Recognized as Safe (GRAS) Food Ingredients - Tallow and Stearic Acid.  

National Technical Information Service (NTIS)

The Scientific Literature Review summarizes the available scientific literature from 1920 to 1973 related to the safety of tallow and stearic acid as food ingredients. Chemical information, biological data, and biochemical aspects of tallow and stearic ac...

1973-01-01

441

[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

442

Polymerization of ?-Hydroxyacetylenes by Transition Metal Catalysts  

Microsoft Academic Search

?-Hydroxyacetylenes (2-propyn-1-ol, DL-3-butyn-2-ol, 1-octyn-3-ol, 2-phenyl-3-butyn-2-ol) with a hydroxy functional group were polymerized by various Mo- and W-based catalysts. In general, the catalytic activities of Mo-based catalysts were greater than those of W-based catalysts for these polymerizations. In the polymerization of 2-propyn-l-ol, MoCl5 alone and the MoCl5-EtAlCl2 catalyst system gave a quantitative yield of polymer. In the polymerization of 2-propyn-l-ol and

Yeong-Soon Gal; Bal Jung; Ji-Heung Kim; Won-Chul Lee; Sam-Kwon Choi

1994-01-01

443

Peculiarities of the behavior of a PdCoPt\\/C cathodic catalyst in an acidic environment: Formation of core-shell structures  

Microsoft Academic Search

A PdCoPt\\/C catalytic system is synthesized by modifying a commercial 20% Pd\\/C (ETEK) catalyst, and its morphology and composition\\u000a are determined. The stability of the catalyst is estimated by means of accelerated durability testing in a 0.5 M H2SO4 solution either using potential cycling or in the absence of polarization. The partial dissolution of Pd and Co components\\u000a is shown

D. V. Novikov; M. R. Tarasevich; V. A. Bogdanovskaya; V. M. Andoralov; G. V. Zhutaeva

2010-01-01

444

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

445

Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum  

Microsoft Academic Search

Mutants of Rhizobium leguminosarum were selected that were altered in the uptake activity of the general amino acid permease (Aap). The main class of mutant maps to sud and suct), which are part of a gene cluster mdh-sucCDAB, which codes for malate dehydrogenase (mdh), succinyl-CoA synthetase (sucCD) and components of the 2-oxoglutarate dehydrogenase complex (sudB). Mutation of either SUCC or

David L. Walshaw; Adam Wilkinson; Mathius Mundy; Mary Smith; Philip S. Poole

1997-01-01

446

Topologically unique heterometallic Cu(II)/Li coordination polymers self-assembled from N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid biobuffer: versatile catalyst precursors for mild hydrocarboxylation of alkanes to carboxylic acids.  

PubMed

The facile aqueous medium reactions of copper(II) nitrate with BES biobuffer [(HOCH(2)CH(2))(2)N(CH(2)CH(2)SO(3)H), hereinafter referred as H(3)bes] in the presence of various benzenecarboxylic acids [benzoic (Hba), 3-hydroxybenzoic (Hhba), and 3,5-dihydroxybenzoic (Hdhba) acid] and lithium hydroxide gave rise to the self-assembly generation of three new heterometallic Cu(II)/Li materials, [Li(H(2)O)(4)][Cu(4)(?(2)-Hbes)(4)(?(2)-ba)]·H(2)O (1) and [Cu(4)(?(3)-Hbes)(4)(L){Li(H(2)O)(2)}](n)·3nH(2)O {L = ?(2)-hba (2) and ?(2)-dhba (3)}. They were isolated as air-stable crystalline solids and fully characterized by infrared (IR) and UV-vis spectroscopy and electrospray ionization (ESI)-MS(±), elemental, thermal, and single-crystal X-ray diffraction analyses. The latter revealed that 1-3 have comparable packing patterns and unit cell parameters, being composed of similar [Cu(4)(?-Hbes)(4)(?-carboxylate)](-) cores and [Li(H(2)O)(4)](+) cations (in 1) or [?-Li(H(2)O)(2)](+) groups (in 2 and 3), which are arranged into discrete 0D aggregates in 1 or infinite 3D noninterpenetrating metal-organic networks in 2 and 3. The topological analysis of the coordination polymers 2 and 3 disclosed the trinodal 3,3,4-connected underlying nets with an unprecedented topology defined by the point symbol of (4.6.8)(4)(4(2).6)(2)(6(2).16(2).18(2)), further simplification of which resulted in the binodal 4,4-connected nets with the pts (PtS) topology. Apart from representing very rare examples of coordination compounds derived from H(3)bes, 1-3 feature solubility in water and were applied as efficient and versatile catalyst precursors for the mild (60 °C) single-pot hydrocarboxylation, by CO and H(2)O, of various gaseous, linear, and cyclic C(n) (n = 2-9) alkanes into the corresponding C(n+1) carboxylic acids, in H(2)O/MeCN medium under homogeneous conditions and in the presence of potassium peroxodisulfate. Total yields (based on alkane) of carboxylic acids up to 78% were achieved, which are remarkable in the field of alkane functionalization under mild conditions, especially for a C-C bond formation reaction in aqueous acid-solvent-free medium. PMID:22482365

Kirillova, Marina V; Kirillov, Alexander M; Martins, André N C; Graiff, Claudia; Tiripicchio, Antonio; Pombeiro, Armando J L

2012-05-01

447

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

448

Sequential hydrodistension and intravesical instillation of hyaluronic acid under general anaesthesia for treatment of refractory interstitial cystitis: a pilot study.  

PubMed

Pilot study looking at the combination of general anaesthetic hydrodistension and intravesical hyaluronic acid for treatment of refractory interstitial cystitis. Twenty-three treatment refractory patients were recruited with an average age 53.4 years. All underwent general anaesthetic cystoscopy, hydrodistension and instillation of hyaluronic acid (40 mg/50 ml). The bladder was then subsequently drained with the patient awake. Two initial treatments were carried out a month apart and duration between treatments increased depending upon symptom response. In the responders, the average number of treatments was 6.6 (median 4.5), duration between treatments was 3.1 months (median 2.6) and follow-up 15.8 months (median 16). Seventeen patients (74%) responded with immediate improvement in symptoms. In all responders, healing of ulceration and resolution of inflammation occurred. Average anaesthetic bladder capacity increased in the responder group from an average of 492 ml (median 500 ml) to an average of 776 ml (median 700 ml). Our pilot data suggests sequential hydrodistension and hyaluronic acid treatment under general anaesthesia may be considered for resistant cases of interstitial cystitis, especially those that cannot tolerate the instillation procedure under local anaesthesia. Further prospective trials are required. PMID:17874027

Ahmad, Imran; Sarath Krishna, Nalagatla; Meddings, Robert N

2008-04-01

449

Hydrofining catalysts  

SciTech Connect

A process is described for hydrotreating a hydrocarbon containing feed stream comprising the step of intimately contacting a substantially liquid hydrocarbon containing feed stream, which also contains compounds of sulfur, nickel, and vanadium, with a free hydrogen containing gas and a catalyst composition under such hydrotreating conditions as to produce a hydrocarbon containing stream having a reduced level of sulfur, nickel, and vanadium. The catalyst composition is prepared by a process comprising the steps of: (A) mixing (a) at least one vanadium and oxygen containing compound, (b) at least one nickel (II) compound, (c) ammonia and (d) water, in such amounts and under such conditions as to obtain a solution; (B) mixing the solution obtained in step (A) with alumina-containing support material; (C) heating the mixture obtained in step (B) at a first temperature under such conditions as to at least partially dry the mixture; and (D) heating the at least partially dried mixture obtained in step (C) at a second temperature, which is higher than the first temperature, under such conditions as to activate the mixture.

Kukes, S.G.; Parrott, S.L.; Brandes, K.K.

1986-06-24

450

The Acid-Base Chemistry of Nicotine: Extensions, Analogies, and a Generalization  

NASA Astrophysics Data System (ADS)

Some solutes can exist in aqueous solution in more than one form. Nicotine is an example of such a solute, as are amino acids and other substances that can exist in more than one state of ionization in water. This paper shows how to express the fractional concentrations of the two or more forms in which such substances can be present in an aqueous solution and how to figure out under what conditions any one form will be the major form present. Nicotine serves as the introductory example. Other examples include amino acids and enzymes.

Ault, Addison

2001-04-01

451

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