In situ catalyst activity control in a novel membrane reactor-Reaction driven wireless electrochemical promotion of catalysis

A dual chamber membrane reactor was used in order to study the effect of macroscopically applied oxygen chemical potential differences to a platinum catalyst supported on a mixed oxygen ion and electronic conducting membrane. It is believed that the oxygen chemical potential difference imposed by the use of an oxygen sweep in one of the reactor chambers causes the back-spillover of oxygen species from the support onto the catalyst surface, resulting in the modification of the catalytic activity. The use of different sweep gases, such as ethylene and hydrogen was investigated as the means to reverse the rate modification by removing the spilt over species from the catalyst surface and returning the system to its initial state. Oxygen sweep in general had a positive effect on the reaction rate with rate increases up to 20% measured. Experimental results showed that hydrogen is a more potent sweep gas than ethylene in terms of the ability to reverse rate modification. A 10% rate loss was observed when using an ethylene sweep as compared with an almost 60% rate decrease when hydrogen was used as the sweep gas. © 2009 Elsevier Ltd. All rights reserved.

Remote control of the activity of a Pt catalyst supported on a mixed ionic electronic conducting membrane

A novel configuration for the in situ control of the catalytic activity of a polycrystalline Pt catalyst supported on a mixed ionic electronic conducting (MIEC) substrate is investigated. The modification of the catalytic activity is achieved by inducing the reverse spillover of oxygen promoting species from the support onto the catalyst surface, thus modifying the chemisorptive bond energy of the gas phase adsorbed reactants. This phenomenon is known as Electrochemical Promotion of Catalysis (EPOC). In this work we investigate the use of a wireless system that takes advantage of the mixed ionic electronic conductivity of the catalyst support (internally short-circuiting the system) in a dual chamber reactor. In this wireless configuration, the reaction takes place in one chamber of the membrane reactor while introduction of the promoting species is achieved by the use of an appropriate sweep gas (and therefore control of the oxygen chemical potential difference across the membrane) on the other chamber. Experimental results have shown that the catalytic rate can be enhanced by using an oxygen sweep, while a hydrogen sweep can reverse the changes. Total rate enhancement ratios of up to 3.5 were measured. © 2008 Elsevier B.V. All rights reserved.

The effect of niobium and tantalum on physicochemical and catalytic properties of silver and platinum catalysts based on MCF mesoporous cellular foams

MCF, NbMCF and TaMCF Mesostructured Cellular Foams were used as supports for platinum and silver (1 wt%). Metallic and bimetallic catalysts were prepared by grafting of metal species on APTMS (3-aminopropyltrimethoxysilane) and MPTMS (2-mercaptopropyltrimethoxysilane) functionalized supports. Characterizations by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) spectroscopy, and in situ Fourier Transform Infrared (FTIR) spectroscopy allowed to monitor the oxidation state of metals and surface properties of the catalysts, in particular the formation of bimetallic phases and the strong metal–support interactions. It was evidenced that the functionalization agent (APTMS or MPTMS) influenced the metals dispersion, the type of bimetallic species and Nb/Ta interaction with Pt/Ag. Strong Nb–Ag interaction led to the reduction of niobium in the support and oxidation of silver. MPTMS interacted at first with Pt to form Pt–Ag ensembles highly active in CH3OH oxidation. The effect of Pt particle size and platinum–silver interaction on methanol oxidation was also considered. The nature of the functionalization agent strongly influenced the species formed on the surface during reaction with methanol and determined the catalytic activity and selectivity.

Cystathionine beta-synthase variants : identification, characterization and modulation by thiol compounds

Tese de doutoramento, Farmácia (Bioquímica), Universidade de Lisboa, Faculdade de Farmácia, 2014

Iridium(I) complexes of phenanthroline-derived benzimidazolylidenes : synthetic, structural and catalytic studies

N-heterocyclic carbenes (NHCs) have undergone rapid development in recent years. Due to their strong a-electron donation and structural variability properties, NHCs are becoming a major class of ligands in organometallic chemistry. Compared with the other two types of NHCs (imidazolylidenes and imidazolinylidenes), benzimidazolylidenes have not been well represented. Limited synthetic approaches may impede the development ofbenzimidazolylidenes. This thesis is focused on the synthesis of phenanthroline-derived benzimidazolylidene ligands and their metal complexes. A series of benzimidazolylidene-iridium complexes were synthesized and characterized spectroscopically and crystallographic ally. All of the new complexes showed varying degrees of catalytic activity and enantioselectivity toward transfer hydrogenation and asymmetric hydrogenation. The best results were achieved in hydrogenation of methyl-2-acetamidoacrylate, which afforded (-)-(R)-methyl-2-acetamidopropanoate in 97% yield and 81 % ee.

Influence du chondroïtine sulfate (CS) sur l’activité et l’expression de plusieurs isoformes du cytochrome P450 et de la NADPH P450 réductase

Le CS fait partie de la famille des SYSADOA (SYmptomatic Slow Acting Drugs for OsteoArthritis) et est utilisé par les patients avec de l’ostéoarthrose de façon chronique pour ses propriétés anti-inflammatoires. Étant donné que ces patients reçoivent d’autres médicaments, il était intéressant de documenter les effets du CS sur le cytochrome P450 et la NADPH-réductase (NADPH). Pour cette étude, deux modèles ont été utilisés: des lapins témoins (LT) et des lapins avec une réaction inflammatoire (LRI) afin de diminuer l’activité et l’expression du CYP. Six groupes contenant chacun cinq lapins ont été utilisés: un groupe sans CS et deux groupes qui ont pris oralement dans l’eau approximativement 20.5 mg/kg/jour de CS pendant 20 et 30 jours; les lapins des trois groupes restants ont pris du CS comme décrit plus haut, mais ont reçu 5 ml sous-cutanées de térébenthine afin de produire une réaction inflammatoire aseptique (RIA) deux jours avant leur sacrifice, c’est-à-dire aux jours -2, 18 et 28. Les hépatocytes ont été isolés pour évaluer l’activité et l’expression du CYP3A6, CYP1A2 et NADPH et aussi le ARNm de ces protéines. In vitro, nous avons étudié l’effet de différentes concentrations de CS-disaccharides sulfatés, 4S, 6S, et 4,6S de CS, sur l’activité et l’expression du CYP1A2 et du CYP3A6. Pour documenter la présence de la réaction inflammatoire, nous avons mesure les mucoprotéines, dans le sérum des lapins avec une réaction inflammatoire. Aussi nous avons mesuré la présence de l’oxide nitrique (NO) chez les hépatocytes de lapins contrôles et chez les hépatocytes des lapins avec une réaction inflammatoire. La translocation nucléaire du NF-κB a été etudiée par fluorescence chez les hépatocytes. Par comparaison aux lapins témoins, l’administration du CS pendant 20 et 30 jours n’affecte pas l’activité du CYP3A6 et du CYP1A2. La RIA a augmenté les mucoprotéines à 95,1±5,7 vs 8,4±1,6 mg/dl dans les lapins témoins (p<0,05). La RIA a diminué l’activité du CYP3A6 de 62% et l’activité du CYP 1A2 de 54%. Le CS n’empêché pas la diminution du CYP1A2 produite par la RIA. Par ailleurs, le CS n’affecte pas l’activité ni l’expression de la NADPH. La translocation nucléaire de NF-κB a été empêche par l’administration chronique de CS aux lapins avec RIA; en plus, la concentration de l’oxide nitrique n’a pas démontré une augmentation en présence de CS; par contre, CS n’empêche pas l’augmentation des séromucoïdes. Au contraire, CS affecte la diminution du CYP3A6 en fonction de temps et secondaire à la RIA. Dans ce group, CS a rétabli le niveau des protéines du CYP3A6 observé dans le group de lapins témoins. Pourtant cette croissance été independante de mRNA qui garde un niveau trés bas. Le plus remarcable a été la manière dont CS a augmenté la protéine du CYP3A6, sans avoir rétabli l’activité de cet isoforme. Finalement, in vitro, CS et ses trois disaccharides sulfatés (4S, 6S et 4,6S) n’affectent ni l’activité ni l’expression de CYP1A2, CYP3A6 et de la NADPH. En conclusion, l’administration chronique de CS n’affecte pas l’activité ni l’expression du CYP1A2, ou la diminution du CYP1A2 produite par la réaction inflammatoire. Le CS n’affecte pas l’activité ni l’expression du NADPH. Cependant, CS empêche la diminution du CYP3A6 en fonction de temps et secondaire à la RIA.

Effect of vanadia on physico-chemical and catalytic characteristics of dysprosia

Physico-chemical characterization of DY203/V2O5 systems prepared through wet impregnation method has been carried out using various techniques like EDX, XRD, FTIR. thermal studies, BET surface area, pore volume and pore size distribution analysis. The amount of vanadia incorporated has been found to influence the surface properties of dysprosia. The spectroscopic results combining with X-ray analysis reveal that vanadia species exist predominantly as isolated amorphous vanadyl units along with crystalline dysprosium orthovanadate. Basicity studies have been conducted by adsorption of electron acceptors and acidity and acid strength distribution by temperature programmed desorption of ammonia. Cyclohexanol decomposition has been employed as a chemical probe reaction to examine the effect of vanadia on the acid base property of Dy2O3. Incorporation of vanadia titrates thc Lewis acid and base sites of Dy2O3, while an enhancement of Bronsted acid sites has been noticed. Data have been correlated with the catalytic activity of these oxides towards the vapour phase methylation of phenol

A comparative study on aniline alkylation activity using methanol and dimethyl carbonate as the alkylating agents over Zn–Co–Fe ternary spinel systems

The catalyst compositions of the Zn1−xCOxFe2O4 (x= 0, 0.2, 0.5, 0.8 and 1.0) spiel series possessing ‘x’ values, x less than or equal to 0.5, are unique for selective N-monomethylation of aniline using methanol as the alkylating agent. Since dimethyl carbonate (DMC) is another potential non-toxic alkylating agent, alkylation of aniline was investigated over various Zn–Co ferrites using DMC as the alkylating agent. The merits and demerits of the two alkylating agents are compared. Catalytic activity followed a similar trend with respect to the composition of the ferrospinel systems. DMC is active at comparatively low temperature, where methanol shows only mild activity. However, on the selectivity basis, DMC as an alkylating agent could not compete with methanol, since the former gave appreciable amounts of N,N-dimethylaniline (NNDMA) even at low temperature where methanol gave nearly 99% N-methylaniline (NMA) selectivity. As in the case of methanol, DMC also did not give any C-alkylated products.

Acid-Base, Surface electron donating and catalytic properties of binary oxides of Zr with rare earth elements

Department of Applied Chemistry, Cochin University of Science and Technology

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V2O5 loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies (29Si and 51V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V2O5 loading and formation of cerium orthovanadate (CeVO4) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO4 phase at higher loadings of V2O5. The oxidation activity increases with vanadia loading up to 8 wt.% V2O5, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.

Effect of pore size on the catalytic activities of K-I 0 clay and H-zeolites for the acetalization of ketones with methanol

One-pot acetalizations of cyclohexanone. acetophenone and benzophenone were carried out using methanol over H-montmorillonite clay (a mesoporous material). silica, alumina, and different zeolites such as HFAU-Y.HBeta, H-ZSM-5, and H-mordenite. In all the cases a single product-the corresponding dimethylacetal-was obtained in high yields. Hemiacetal formation was not observed with any catalyst. A comparison of catalytic activity indicated that montmorillonite K-10 is the most active catalyst for the reaction. As evidenced by the reaction time studies, the catalyst decay is greater over the zeolite catalyst than over the clay.

Acid base and catalytic properties of Zr02 - Y203 systems

The surface acidity and basicity of mixed oxides of Zr and Y and their mixed oxides have been determined by titration method using Hammett indicators. The acid base properties are evaluated on a common scale of acid strength. Liquid phase reduction of cyclohexanone has been selected as a model reaction to correlate catalytic activity.

Influence of residual cations (Na+, K+ and Mg2+) in the alkylation activity of benzene with 1-octene over rare earth metal ion exchanged FAU–Y zeolite

The effect of residual cations in rare earth metal modified faujasite–Y zeolite has been monitored using magic angle spinning NMR spectral analysis and catalytic activity studies. The second metal ions being used are Na+, K+ and Mg+. From a comparison of the spectra of different samples, it is concluded that potassium and magnesium exchange causes a greater downfield shift in the 29Si NMR peaks. Also, lanthanum exchanged samples show migration behavior from large cages to small cages, which causes the redistribution of second counter cations. It is also observed that Mg2+ causes the most effective migration of lanthanum ions due to its greater charge. The prepared systems were effectively employed for the alkylation of benzene with 1-octene in the vapor phase. From the deactivation studies it is observed that the as-exchanged zeolites possess better stability towards reaction condition over the pure HFAU zeolite.

Vanadia supported on ceria: Characterization and activity in liquid-phase oxidation of ethylbenzene

Vanadia/ceria catalysts (2–10 wt% of V2O5) were prepared by wet impregnation of ammonium metavanadate in oxalic acid solution. Structural characterization was done with energy dispersive X-ray analysis (EDX), powder X-ray diffraction (XRD), BET surface area measurements, FT-IR spectroscopy and nuclear magnetic spectral analysis (51V MASNMR). XRD and 51V MASNMR results show highly dispersed vanadia species at lower loadings and the formation of CeVO4 phase at higher V2O5 loading. The catalytic activity of catalysts was conducted in liquid phase oxidation of ethylbenzene with H2O2 as oxidant. The oxidation activity is increased with loading up to 8 wt% V2O5 and then decreased with further increase in V2O5 content to 10 wt%. Different vanadia species evidenced by various techniques were found to be selective towards ethylbenzene oxidation. The CeVO4 formation associated with increased concentration of vanadia on ceria results the production of acetophenone along with 2-hydroxyacetophenone.

Catalytic oxidation of alcohols using molecular oxygen mediated by poly(ethylene glycol)-supported nitroxyl radicals

The selective catalytic oxidation of alcohols over a mixture of copper(l) chloride and a number of linear 'linker-less' or 'branched' poly(ethylene glycol)-supported nitroxyl radicals of the 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) family as a catalyst system has been investigated in the presence of molecular oxygen in a batch reactor. It is found that the activity profile of the polymer-supported nitroxyl radicals is in good agreement with that of low-molecular weight nitroxyl catalysts, for example, allylic and benzylic alcohols are oxidised faster than aliphatic alcohols. The oxidations can be tuned to be highly selective such that aldehydes are the only oxidation products observed in the oxidation of primary alcohols and the oxidations of secondary alcohols yield the corresponding ketones. A strong structural effect of the polymeric nitroxyl species on catalytic activity that is dependent upon their spatial orientation of the nitroxyl radicals is particularly noted. The new soluble macromolecular catalysts can be recovered readily from the reaction mixture by solvent precipitation and filtration. In addition, the recycled catalysts demonstrate a similar selectivity with only a small decrease in activity compared to the fresh catalyst even after five repetitive cycles. (c) 2005 Elsevier B.V. All rights reserved.