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High temperature activation of noble metal catalysts supported on carbon multi-walled nanotubes for selective hydrogenation of unsaturated aldehydes

Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, Joaquim
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
47.615244%
Selective catalytic hydrogenation of α,β-unsaturated aldehydes represents today an important route in the industrial preparation of fine chemicals. Heterogeneous catalysts are normally less selective than the homogeneous, but easier to handle. Therefore, there is still room for improvement especially regarding catalyst selectivity to the unsaturated alcohol. Our work shows that the surface chemistry also plays an important role on selectivity. We describe an activation procedure for platinum and iridium metal catalysts supported on carbon nanotubes, which improves significantly both selectivity and activity. In the case of platinum, selectivity towards the unsaturated alcohol increased 8 times to a maximum of 66% at 79% conversion.

Size-dependent effects in supported metal catalysts for liquid phase hydrogenation reactions

Faria, Joaquim; Machado, Bruno; Gomes, Helder
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
48.111997%
Environmental awareness is pushing the development of more efficient and more selective heterogeneous catalysts for the production of fine chemicals and pharmaceuticals. The goal is to reduce the number of by-products and the consumption of hazardous solvents, making the processes efficient at molecular level. Heterogeneous catalysts can be tailored to specific needs, are easier to handle and lead to less amounts of waste chemicals in a given process. As preparation method, photochemical deposition of noble metals in different supports is gaining importance due to its simplicity and advantages. Its main advantage is the ability of spreading very effectively the metal throughout the support, leading to very high dispersions, resulting in higher molecular control, with a positive effect on both activity and selectivity.Hydrogenation of the carbonyl function in α,β-unsaturated olefins still attracts too much attention due to the importance of the unsaturated alcohol as intermediate in many synthetic routes [1]. The concepts of chemoselectivity and diastereoselectivity are extremely important issues in steroid hydrogenation. Noble metal catalysts (Pt and Ir) supported on titania, with different loads (1 and 5%wt) were prepared by liquid phase photodeposition of the appropriate precursors. Calcination (under N2) and reduction (H2) at various temperatures provided materials with variable particle sizes at the nanometer scale. In order to explore the possibility of a metal-support interaction two types of titania were used: Degussa P25 (crystal mean diameter of 30 nm) and a sample of TiO2 prepared by a modified acid-catalyzed sol–gel method from alkoxide precursors (crystal mean diameter of 8 nm). These parameters will be discussed in terms of the performance of the catalytic materials in the hydrogenation of cinnamaldehyde. As a representative example...

"Aplicação de catalisadores de níquel e cobalto preparados via precursores do tipo hidrotalcita nas reações de reforma a vapor, oxidação parcial e reforma oxidativa do metano"; "Application of nickel and cobalt catalysts prepared via hydrotalcite-type precursors in the reactions of steam reforming, partial oxidation and oxidative reforming of methane"

Lucredio, Alessandra Fonseca
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/02/2007 PT
Relevância na Pesquisa
48.18777%
Uma das principais aplicações do metano é a produção de gás de síntese, mistura de hidrogênio e monóxido de carbono. Três processos podem levar à formação de gás de síntese a partir do metano: reforma a vapor, reforma com CO2 e oxidação parcial. Vários catalisadores de metais não-preciosos foram estudados para os processos de reforma, embora a deposição de carbono ou a sinterização do metal sempre esteja presente. Catalisadores obtidos de precursores do tipo hidrotalcita têm se mostrado resistentes à coqueificação nas reações de reforma a vapor do metano, podendo ser aplicados ao processo combinado de reforma e oxidação parcial de metano para obtenção de gás de síntese, com potencial para minimizar as dificuldades inerentes aos processos: altas temperaturas e desativação do catalisador. Catalisadores de níquel e de cobalto, obtidos a partir de precursores do tipo hidrotalcita, com a adição de cério e de lantânio como promotores, foram preparados, caracterizados e aplicados em testes catalíticos nas reações de reforma a vapor, oxidação parcial e reforma oxidativa do metano, com o intuito de avaliar a atividade e estabilidade destes catalisadores e o efeito dos promotores. Os catalisadores não-promovidos foram obtidos por três métodos: método tradicional...

Oxidação de carboidratos via catálise metálica não enzimática para aplicação em sensores

Magalhães, Jéssica Cleidiane Paraizo
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Trabalho de Conclusão de Curso
POR
Relevância na Pesquisa
47.750923%
This work has main aim of is to propose the synthesis and characterization of nanostructured materials for oxidation of carbohydrates such as glucose, with non-enzymatic catalysis. The proposed pathway of synthesis of metal catalysts is the polyol method and techniques of physical characterization proposals for analysis of prepared catalyst pass through diffraction technique of ray-x (DRX), scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy ray-x (EDX). Technical proposals for the electrochemical characterization of the synthesized catalysts are Cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The prospects of this work are compared by the catalytic activity of the sensor designed with non-enzymatic sensors and biosensors also known in the literature; Este trabalho tem como escopo propor a síntese e a caracterização de materiais nanoestruturados para a oxidação de carboidratos, como a glicose, através de catálise não enzimática. A proposta da via de síntese dos catalizadores metálicos é o método poliol e as técnicas de caracterização física propostas para análise do catalizador preparado passam pela técnica de Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Energia Dispersiva de Raios-X (EDX). As técnicas para a caracterização eletroquímica dos catalisadores são Voltametria Cíclica (CV) e Voltametria de Pulso Diferencial (DPV). As perspectivas deste trabalho passam pela comparação da atividade catalítica dos sensores não enzimáticos e também biossensores já conhecidos na literatura

Hidrogenólise seletiva do glicerol em catalisadores de rutênio suportado em nióbio, sílica e alumina; Selective hydrogenolysis of glycerol on ruthenium catalysts supported on niobium, silica and alumina

Michael Martinez Jorrín
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/09/2010 PT
Relevância na Pesquisa
47.83014%
Foram avaliados os catalisadores de Ru suportados em Nióbia, Sílica e Alumina na Hidrogenólise seletiva de Glicerol para a obtenção de propanodióis (1,2 e 1,3 - Propanodiol). O método de preparação utilizado para os três catalisadores foi o de impregnação úmida partindo-se de uma solução aquosa do sal precursor RuCl3.1,37H2O cuja porcentagem em peso do metal ativo foi de 2%. Os catalisadores foram caracterizados pelo método da Área Superficial Específica (método de B.E.T) e Microscopia Eletrônica de Varredura (M.E. V) com EDX. O maior valor de área superficial específica foi alcançado pelo catalisador de Ru/SiO2 seguido pelo catalisador de Ru/Al2O3, mas isto não foi o fator determinante para escolha do melhor sistema catalítico em termos de seletividade para o 1,2-propanodiol e conversão de substrato. A reação de hidrogenólise foi conduzida em um reator Parr, em atmosfera de H2 a qual foi avaliada ás temperaturas de 120°C, 140°C e 200°C, pressão de 50 bar, 0,75 g do catalisador e uma solução aquosa de glicerol de 0,2 g/mL, durante 6 h. Foram ainda realizados testes exploratórios variando a pressão (30 bar) e a quantidade de catalisador( 1,5 g), para avaliar a sua influência. Os resultados dos testes cinéticos mostraram que com os catalisadores utilizados ocorrem reações de degradação envolvendo a ruptura de ligações C-C e conseqüente formação de produtos tais como etilenoglicol...

Efeitos da adição de metais básicos aos catalisadores à base de Pd e Ru para a hidrodescloração do pentaclorofenol; Effects of base metals addition to the Pd and Ru catalysts for the pentachlorophenol hydrodechlorination

Marcio Wagner da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/12/2010 PT
Relevância na Pesquisa
47.89282%
Alguns compostos organoclorados são motivo de grande preocupação, em razão da elevada toxicidade e persistência, tanto no meio ambiente quanto em organismos vivos. Dentre tais compostos, encontra-se o pentaclorofenol, utilizado para a conservação de madeira e na proteção de lavouras. Uma das tecnologias mais promissoras para o tratamento dessa classe de compostos tóxicos é a hidrodescloração catalítica, através da qual é possível recuperar a matéria-prima utilizada na síntese do contaminante. Embora diferentes catalisadores possam ser utilizados nesta reação, destacam-se os sólidos à base de Pd e Ru, notadamente devido à maior atividade catalítica. No entanto, os elevados preços destes metais nobres podem aumentar significativamente os custos do processo. Nesse contexto, o objetivo do presente trabalho é estudar os efeitos da presença dos metais básicos Fe e Ni em catalisadores à base de Pd e Ru, destinados à hidrodescloração do pentaclorofenol em fase líquida. Para tanto, catalisadores monometálicos e bimetálicos, suportados em alumina (Al2O3) ou titânia (TiO2), foram preparados a partir dos precursores clorados, através do método de co-impregnação a seco. Os sólidos obtidos foram caracterizados por meio das técnicas de adsorção de N2 (método BET)...

Hidrogenação de compostos aromáticos em fase líquida com catalisadores à base de metais do grupo VIII suportados em alumina via impregnação úmida; Hydrogenation of aromatics compounds in liquid phase with catalysts based on metals from group VIII supported on alumina via wet impregnation

Raphael Soeiro Suppino
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/03/2014 PT
Relevância na Pesquisa
48.25304%
A hidrogenação de compostos aromáticos é uma reação química de grande interesse industrial. Diante das crescentes restrições à presença desses compostos em combustíveis, a hidrodesaromatização catalítica é um dos processos mais importantes nas refinarias. Nesse contexto, o presente trabalho tem por objetivo estudar a hidrogenação de compostos aromáticos em fase líquida, empregando catalisadores à base de metais básicos (Fe, Co, Ni) e nobres (Ru, Pd, Pt) suportados em Al2O3 via impregnação úmida. Especificamente, buscou-se avaliar a influência da composição química, da redução sob H2 e do reuso de tais catalisadores sobre o desempenho catalítico. Catalisadores mono e bimetálicos foram preparados a partir de precursores clorados, através de coimpregnação úmida conduzida a 353 K (80 oC) e pH igual a 10. Durante a impregnação úmida, os sólidos foram reduzidos em fase líquida com formaldeído, sendo posteriormente reduzidos ex situ ou in situ sob H2. Os sólidos preparados foram caracterizados através das técnicas de titulação potenciométrica, adsorção de N2, espectroscopia de fotoelétrons excitados por raios X, microscopia eletrônica (varredura e transmissão) e redução à temperatura programada. O desempenho dos catalisadores foi avaliado na hidrogenação do tolueno e de uma mistura de aromáticos. As reações foram realizadas num reator Parr do tipo slurry...

Palladium/alumina catalysts: effect of the processing route on catalytic performance

Greca, Maria Conceição; Moraes, Caetano; Segadães, Ana Maria
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.87904%
Supported precious metal catalysts preparation usually includes two major steps, namely, the production of the ceramic support and its impregnation with the active species in the form of a salt solution, followed by a heat treatment. Alternatively, the active species can be incorporated simultaneously with the preparation of the support by combustion synthesis, which is a straightforward technique to produce homogeneous submicron crystalline oxide ceramic powders without the intermediate decomposition and/or calcination steps. In the present work, 0.5 and 1 wt.% of metallic palladium was incorporated through the impregnation technique in commercial Alcoa A-16 alumina and in alumina prepared by combustion synthesis. Moreover, alumina + Pd mixed powders, with the same nominal compositions, were prepared in a single step by combustion synthesis. All alumina-supported Pd catalysts are shown to be effective in ethanol oxidation reaction to acetic acid. The catalytic performance was investigated in terms of selectivity to acetic acid and total conversion of ethanol as a function of temperature (up to 200 degreesC). The effect of the addition of PdO on the sintering behavior and catalytic performance changes when the incorporation technique is changed. The results obtained suggest that...

Alkaline polymer electrolyte fuel cells completely free from noble metal catalysts

Lu, Shanfu; Pan, Jing; Huang, Aibin; Zhuang, Lin; Lu, Juntao
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
47.750923%
In recent decades, fuel cell technology has been undergoing revolutionary developments, with fundamental progress being the replacement of electrolyte solutions with polymer electrolytes, making the device more compact in size and higher in power density. Nowadays, acidic polymer electrolytes, typically Nafion, are widely used. Despite great success, fuel cells based on acidic polyelectrolyte still depend heavily on noble metal catalysts, predominantly platinum (Pt), thus increasing the cost and hampering the widespread application of fuel cells. Here, we report a type of polymer electrolyte fuel cells (PEFC) employing a hydroxide ion-conductive polymer, quaternary ammonium polysulphone, as alkaline electrolyte and nonprecious metals, chromium-decorated nickel and silver, as the catalyst for the negative and positive electrodes, respectively. In addition to the development of a high-performance alkaline polymer electrolyte particularly suitable for fuel cells, key progress has been achieved in catalyst tailoring: The surface electronic structure of nickel has been tuned to suppress selectively the surface oxidative passivation with retained activity toward hydrogen oxidation. This report of a H2–O2 PEFC completely free from noble metal catalysts in both the positive and negative electrodes represents an important advancement in the research and development of fuel cells.

Catalytic Ring Hydrogenation of Benzoic Acid with Supported Transition Metal Catalysts in scCO2

Wang, Hongjun; Zhao, Fengyu
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 12/07/2007 EN
Relevância na Pesquisa
47.40706%
The ring hydrogenation of benzoic acid to cyclohexanecarboxylic acid over charcoal-supported transition metal catalysts in supercritical CO2 medium has been studied in the present work. The cyclohexanecarboxylic acid can be produced efficiently in supercritical CO2 at the low reaction temperature of 323 K. The presence of CO2 increases the reaction rate and several parameters have been discussed.

Fabrication of vertical GaN/InGaN heterostructure nanowires using Ni-Au bi-metal catalysts

Ha, Ryong; Kim, Sung-Wook; Choi, Heon-Jin
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 26/06/2013 EN
Relevância na Pesquisa
47.750923%
We have fabricated the vertically aligned coaxial or longitudinal heterostructure GaN/InGaN nanowires. The GaN nanowires are first vertically grown by vapor–liquid-solid mechanism using Au/Ni bi-metal catalysts. The GaN nanowires are single crystal grown in the [0001] direction, with a length and diameter of 1 to 10 μm and 100 nm, respectively. The vertical GaN/InGaN coaxial heterostructure nanowires (COHN) are then fabricated by the subsequent deposition of 2 nm of InxGa1-xN shell on the surface of GaN nanowires. The vertical GaN/InGaN longitudinal heterostructure nanowires (LOHN) are also fabricated by subsequent growth of an InGaN layer on the vertically aligned GaN nanowires using the catalyst. The photoluminescence from the COHN and LOHN indicates that the optical properties of GaN nanowires can be tuned by the formation of a coaxial or longitudinal InGaN layer. Our study demonstrates that the bi-metal catalysts are useful for growing vertical as well as heterostructure GaN nanowires. These vertically aligned GaN/InGaN heterostructure nanowires may be useful for the development of high-performance optoelectronic devices.

Structural modulation of silicon nanowires by combining a high gas flow rate with metal catalysts

Seo, Dongjea; Lee, Jaejun; Kim, Sung Wook; Kim, Ilsoo; Na, Jukwan; Hong, Min-Ho; Choi, Heon-Jin
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 21/04/2015 EN
Relevância na Pesquisa
47.40706%
We grew silicon nanowires (SiNWs) by a vapor-liquid-solid (VLS) mechanism using metal catalysts of gold (Au), titanium (Ti), manganese (Mn), and iron (Fe) under a high flow rate of hydrogen (H2). This combination of catalyst types and high gas flow rate revealed the potential for growing various SiNWs, including kinked SiNWs (with Au), ultra-thin SiNWs having diameters about 5 nm (with Ti), rough-surfaced SiNWs (with Mn), and ribbon-shaped SiNWs tens of microns in width (with Fe). The high flow rate of gas affects the VLS mechanism differently for each combination; for example, it induces an unstable solid-liquid interfaces (with Au), active etching of the catalyst (with Ti), sidewall deposition by a vapor-solid (VS) mechanism, and an asymmetric precipitation of Si in the catalyst (with Fe). Our combinatorial approach may provide a new path for the structural modulation of SiNWs via the VLS mechanism.

Design and fabrication of non-noble-metal electrocatalysts for oxygen reduction reactions.

Liang, Ji
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
47.750923%
Fuel cell is a device that can directly convert the chemical energy in fuels into electricity and it has the advantages including high efficiency, high energy density and zero waste emission. However, a current fuel cell requires noble-metal catalysts (in most cased platinum, Pt) to accelerate the electrode reactions. As a result of the high cost of Pt, the commercialization of fuel cell has been severely hindered. Thus, it is exceptionally important to search for an alternative low-cost catalyst, especially on the cathode when the sluggish oxygen reduction reaction (ORR) occurs and much larger amount of Pt is employed, to bring down the over-all price of a fuel cell. With this aim, this Ph.D thesis has demonstrated the design and synthesis of a serial of high –performance Pt-free catalysts based on carbon materials. These researches include: (1) We firstly designed and constructed a series of porous g-C₃N₄/C composite with different pore size ranging from large mesopores (ca. 12 nm) to large macropores (ca. 400 nm) and studied the structural impact of these hybrid materials on their ORR performance. In this study, we have for the first time revealed that macropores would be more favorable for ORR in such materials rather than the conventionally believed mesopores. (2) Then...

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

Chen, Y.; Yu, J.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.40706%
Aligned carbon nanotubes(CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000°C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.; This work is supported in part by the Australian Research Council under Centre of Excellence and Discovery research projects.

Development and Kinetic Analysis of Homogeneous and Heterogeneous Transition Metal Catalysts for the Cleavage of Phosphate Esters in Methanol

MOHAMED, MARK
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
47.615244%
Described here are detailed kinetic studies probing the structural elements which are crucial for the catalytic activity of dinuclear Zn(II) complexes towards phosphate diester cleavage. First, two sets of dinuclear Zn(II) complexes (a member with and without a bridging oxyanion linker group) were synthesized and their ability to promote the cyclization of 2-hydroxypropyl-p-nitrophenyl phosphate, a common model for RNA, was compared. Kinetic studies indicated that the complexes without the oxyanion linker were more active in promoting the cyclization in methanol under pH controlled conditions at 25 degrees. Quantitative energetics analysis shows that the rate reduction is attributable to a decrease in the second-order rate constant for the cyclization reaction, which adds 3.7 and 6.5 kcal/mol of activation energy to the respective reactions mediated by the complex with the oxyanion linker. Secondly, we have investigated a series of dinuclear Zn(II) complexes that incorporate various substituents including hydrophobic and hydrogen-bonding ones. Analysis of the data at the pH optimum for each reaction indicates that the presence of the H-bonding groups and alkyl groups provides similar increases (at least an order of magnitude) of the kcat terms over the unfunctionalized complex. There is also no clear trend that H-bonding groups or the alkyl groups provide stronger binding to the substrate than the parent complex. We also describe here the preparation and kinetic analysis of a series of solid supported transition metal catalysts for the cleavage of P=O chemical warfare simulants and P=S pesticides. We report a kinetic study of a 1...

Transition metal catalyzed hydroborations with pinacolborane: new applications and mechanistic investigations

Hleba, Yonek Bryan
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 872156 bytes; application/pdf
EN; EN
Relevância na Pesquisa
47.834424%
A methodology for the catalytic asymmetric hydroboration of vinylarenes with pinacolborane has been developed. Use of pinacolborane in hydroboration, especially catalytic asymmetric hydroboration grants direct access to chiral boronate esters, without the cryogenic temperatures required for catalytic hydroboration with catecholborane and the subsequent transesterification with excess pinacol. These chiral boronate esters were then subjected to a homologation/oxidation sequence previously refined in our labs to prepare Naproxen™ in 66% yield and 88% enantiopurity from its corresponding vinyl arene precursor. A survey of metal catalysts, solvents and ligands revealed remarkable changes in regioselectivity with changes in metal. Rhodium catalysts in combination with pinacolborane were able to provide regioselectivity for the secondary branched isomer equivalent to those obtained with catecholborane. Iridium catalysts showed a near perfect regioselectivity for the primary linear isomer. With respect to the choice of chiral ligand, complete reversal in the enantiomer obtained was observed with the choice of hydroborating reagent from catecholborane to pinacolborane. In order to understand the regioselectivity observed under iridium catalysis...

Low metal loading catalysts used for the selective hydrogenation of styrene

Badano,Juan; Lederhos,Cecilia; Quiroga,Mónica; L'Argentière,Pablo; Coloma-Pascual,Fernando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
58.04932%
A series of Group VIII metal catalysts was obtained for the semi-hydrogenation of styrene. Catalysts were characterized by Hydrogen Chemisorption, TPR and XPS. Palladium, rhodium and platinum low metal loading prepared catalysts presented high activity and selectivity (ca. 98%) during the semi-hydrogenation of styrene, being palladium the most active catalyst. The ruthenium catalyst also presented high selectivity (ca. 98%), but the lowest activity. For the palladium catalyst, the influence of the precursor salt and of the reduction temperature on the activity and selectivity were studied. The following activity series was obtained: PdN-423 > PdCl-673 > PdCl-373> PtCl-673 > RhCl-673 >> RuCl-673. As determined by XPS, differences in activity could be attributed, at least in part, to electronic effects.

A study of the promoting effect of noble metal addition on niobia and niobia alumina catalysts

Schmal, Martin; Aranda, D. A. G.; Soares, R. R.; Noronha, Fábio Bellot; Frydman, A.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
48.019097%
Catalysis Today, 57 (3-4): 275-282 Abril 20, 2000.; The catalytic activity of Nb2O5 and Nb2O5/Al2O3-supported metal catalysts was evaluated in the n-heptane conversion, CO hydrogenation and butadiene hydrogenation. After high temperature of reduction (HTR), the metal adsorption capacity decreases on all the samples, due to the reduction of Nb2O5with subsequent blocking of metal atoms and bimetallic effect. It was also observed that the activity decay caused by metal-support interaction was remarkably inhibited on the bimetallics with respect to the monometallics by comparing reaction rates after HTR. Thus, the addition of Rh to Co, Cu to Pd and Sn to Pt on niobia catalysts significantly altered the product distribution in Fischer–Tropsch synthesis (FTS) and in the hydrogenation and dehydrogenation of hydrocarbons, respectively. In addition, an unusual bifunctional effect was obtained in Pt/Nb2O5/Al2O3 catalyst.

Towards a General Growth Model for Graphene CVD on Transition Metal Catalysts

Cabrero-Vilatela, Andrea; Weatherup, Robert S.; Braeuninger-Weimer, Philipp; Caneva, Sabina; Hofman, Stephan
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; accepted version
EN
Relevância na Pesquisa
47.40706%
This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the Royal Society of Chemistry.; The chemical vapour deposition (CVD) of graphene on three polycrystalline transition metal catalysts, Co, Ni and Cu, is systematically compared and a first-order growth model is proposed which can serve as a reference to optimize graphene growth on any elemental or alloy catalyst system. Simple thermodynamic considerations of carbon solubility are insufficient to capture even basic growth behaviour on these most commonly used catalyst materials, and it is shown that kinetic aspects such as carbon permeation have to be taken into account. Key CVD process parameters are discussed in this context and the results are anticipated to be highly useful for the design of future strategies for integrated graphene manufacture.; We wish to thank Dr. M.-B. Martin for careful reading of the manuscript. A.C.V. acknowledges the Conacyt Cambridge Scholarship and Roberto Rocca Fellowship. R.S.W. acknowledges a Research Fellowship from St. John?s College, Cambridge and a Marie Sk?odowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870) from the European Union?s Horizon 2020 research and innovation programme. S.C. acknowledges funding from EPSRC (Doctoral training award). S.H. acknowledges funding from ERC grant InsituNANO (No. 279342) and EPSRC under grant GRAPHTED (Ref. EP/K016636/1).

Embedding Covalency into Metal Catalysts for Efficient Electrochemical Conversion of CO_2

Lim, Hyung-Kyu; Shin, Hyeyoung; Goddard, William A., III; Hwang, Yun Jeong; Min, Byoung Koun; Kim, Hyungjun
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 13/08/2014
Relevância na Pesquisa
47.615244%
CO_2 conversion is an essential technology to develop a sustainable carbon economy for the present and the future. Many studies have focused extensively on the electrochemical conversion of CO_2 into various useful chemicals. However, there is not yet a solution of sufficiently high enough efficiency and stability to demonstrate practical applicability. In this work, we use first-principles-based high-throughput screening to propose silver-based catalysts for efficient electrochemical reduction of CO_2 to CO while decreasing the overpotential by 0.4–0.5 V. We discovered the covalency-aided electrochemical reaction (CAER) mechanism in which p-block dopants have a major effect on the modulating reaction energetics by imposing partial covalency into the metal catalysts, thereby enhancing their catalytic activity well beyond modulations arising from d-block dopants. In particular, sulfur or arsenic doping can effectively minimize the overpotential with good structural and electrochemical stability. We expect this work to provide useful insights to guide the development of a feasible strategy to overcome the limitations of current technology for electrochemical CO_2 conversion.