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Catalisadores nanoparticulados de níquel e níquel-paládio obtidos a partir de precursores organometálicos; Nickel and nickel-palladium supported nanocatalysts obtained from organometallic precursors

Costa, Natália de Jesus da Silva
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 31/08/2012 PT
Relevância na Pesquisa
49.26506%
A catálise é a chave para o desenvolvimento de processos químicos sustentáveis e, portanto, o preparo de catalisadores que sejam mais ativos e seletivos é sempre uma questão atual. Utilizando as propriedades diferenciadas de nanopartículas metálicas e as vantagens de separação e estabilidade de um catalisador heterogêneo, este trabalho descreve novos catalisadores de níquel e de níquel-paládio em escala nanométrica, suportados em sólidos magnéticos, para hidrogenação de olefinas. Os catalisadores de níquel apresentados neste trabalho foram preparados pela metodologia de decomposição do precursor organometálico Ni(COD)2 (COD = ciclo-octadieno), que apresenta o metal em estado de oxidação zero e permite a formação de nanopartículas metálicas após a hidrogenação das ligações C=C do ligante. O catalisador de níquel aprimorado, composto por nanoagregados de níquel, apresentou atividade superior a qualquer outro reportado na literatura para o mesmo tipo de reação. Além disso, mesmo com a facilidade de oxidação do Ni(0), este novo catalisador teve apenas sua superfície oxidada a NiO ao ser armazenado em ar. O NiO formado foi facilmente reduzido por hidrogênio a Ni(0) em condições brandas (75°C) se comparado ao NiO bulk (270-520°C). Os catalisadores bimetálicos de níquel-paládio foram sintetizados por uma reação de substituição galvânica com Pd(OAc)2 em um catalisador de Ni(0) suportado e por decomposição simultânea dos precursores organometálicos Ni(COD)2 e Pd2(dba)3 (dba = dibenzilideno acetona) em diferentes frações molares. Os catalisadores bimetálicos preparados por substituição galvânica não resultaram em estruturas core(Ni)-shell(Pd) como o esperado...

Conversão catalítica de celulose utilizando catalisadores de carbeto de tungstênio suportado em carvão ativo e promovido por paládio; Catalytic conversion of cellulose using catalysts of tungsten carbide supported on activated carbon and promoted by palladium

Leal, Glauco Ferro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/08/2014 PT
Relevância na Pesquisa
38.896235%
A celulose é o biopolímero mais abundante na natureza e apresenta grande potencial para ser processada e produzir de maneira sustentável biocombustíveis e produtos químicos. A conversão catalítica é um dos meios mais promissores para transformação da celulose. A separação entre produtos e catalisadores é uma etapa importante para indústria, o que coloca a catálise heterogênea em posição privilegiada como via de conversão, devido à facilidade de separação entre produto e catalisador. A hidrogenólise é uma via de transformação que promove a quebra de ligações C-C e a retirada de átomos de oxigênio, levando a uma gama de combustíveis e produtos químicos. Os carbetos de metais de transição suportados em carvão ativo são efetivos na quebra de ligações C-C, enquanto o paládio atua tanto na quebra de ligações C-C como em etapas de hidrogenação. Assim, este trabalho estudou as propriedades estruturais e catalíticas de catalisadores de carbeto de tungstênio suportados em carvão ativado e promovidos com paládio. Foram preparados e caracterizados catalisadores de WXC sem promotor e com 1 e 2% de Pd. As medidas de fisissorção de N2 revelou que os catalisadores são formados por uma mistura de micro e mesoporos. A análise de difração de raios X revelou predominância da fase W2C nos catalisadores promovidos por Pd...

A hidrogenação do adipato de dimetila utilizando catalisadores suportados em argilas pilarizadas; Hydrogenation of dimethyl adipate at presence of pillared clay based catalysts

Flavia Camargo Alves Figueiredo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/02/2009 PT
Relevância na Pesquisa
48.66637%
Vários métodos de síntese das argilas pilarizadas foram testados. Obtivemos os materiais pilarizados com alumínio em condições distintas: suspensões diluídas (Al-PILC 02), suspensões concentradas (Al-PILC 03), soluções pilarizantes concentradas (Al-PILC 04) e o uso de microondas no processo de envelhecimento (Al-PILC 05). Este último demonstrou ser o processo mais adequado, já que permitiu a obtenção da argila pilarizada em maior quantidade e menor tempo de síntese. As argilas pilarizadas apresentaram um significativo aumento na área superficial, principalmente relacionada aos microporos, e uma elevada capacidade de dispersão dos metais ativos platina e paládio. A exceção é o rutênio, que manteve a baixa dispersão já observada em outros suportes utilizados. A acidez dos suportes e catalisadores foi avaliada por diferentes técnicas, indicando que os materiais apresentam acidez de Brönsted e de Lewis. Esta acidez pode ser efetivamente reduzida por tratamento dos sólidos com bário, enquanto um tratamento com lítio se mostrou ineficaz. Os testes catalíticos de hidrogenação do adipato de dimetila demonstraram que todos os sistemas estudados apresentam uma elevada conversão, tipicamente superior a 95%, atribuída a uma atividade do suporte. Nos catalisadores monometálicos os valores de seletividade permanecem reduzidos. A redução da acidez...

Estudo das propriedades físico-químicas de sistemas Pd, Pd-Fe e Pd-Co suportados em CeO2/Al2O3; Study of the physico-chemical properties of the Pd, Pd-Fe and Pd-Co systems supported at CeO2/Al2O3

Eleonora Maria Pereira de Luna Freire
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 2005/08/3 PT
Relevância na Pesquisa
49.255044%
Os catalisadores à base de paládio apresentam particular interesse para o tratamento de gases de exaustão automotiva, notadamente no caso da combustão do etanol. O presente trabalho tem o objetivo de estudar as propriedades físico- químicas de catalisadores Pd - Fe e Pd - Co suportados em alumina modificada pelo óxido de cério. Para tanto, catalisadores modelo foram preparados através do método de impregnação por via úmida, empregando-se sais precursores à base de nitrato dos metais, e os suportes Al2O3, CeO2 e CeO2/Al2O3. Os catalisadores obtidos tiveram seus teores metálicos determinados por meio de espectrofotometria de absorção atômica, tendo sido caracterizados através de adsorção de nitrogênio (método B.E.T), espectroscopia no infravermelho, difração de raio-X, redução à temperatura programada. Os sistemas preparados foram avaliados pela reação catalítica de oxidação do etanol em fase gasosa em um microreator tubular de leito fixo, operando a pressão atmosférica e a temperatura de 3500 C. Os catalisadores preparados apresentam frações mássicas em torno de 2 % para o Pd, e de 1% para os aditivos Fe ou Co. A adição de Pd, Pd-Fe e Pd-Co aos suportes Al2O3 e CeO2/Al2O3 não levou a modificações...

Palladium-supported catalysts in methane combustion: comparison of alumina and zirconia supports

Domingos,Daniela; Rodrigues,Lílian Maria Tosta Simplício; Brandão,Soraia Teixeira; Rocha,Maria da Graça Carneiro da; Frety,Roger
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
Relevância na Pesquisa
48.923394%
Palladium catalysts supported on alumina and zirconia were prepared by the impregnation method and calcined at 600 and 1000 ºC. Catalysts were characterized by BET measurements, XRD, XPS, O2-TPD and tested in methane combustion through temperature programmed surface reaction. Alumina supported catalysts were slightly more active than zirconia supported catalysts, but after initial heat treatment at 1000 ºC, zirconia supported palladium catalyst showed better performance above 500 ºC A pattern between temperature interval stability of PdOx species and activity was observed, where better PdOx stability was associated with more active catalysts.

Effects of Cu over Pd based catalysts supported on silica or niobia

Roma,M.N.S.C.; Cunha,D.S.; Cruz,G.M.; Cobo,A.J.G.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2000 EN
Relevância na Pesquisa
38.829329%
Palladium and palladium-copper catalysts supported on silica and niobia were characterized by H2 chemisorption and H2-O2 titration. Systems over silica were also analyzed by transmission electron microscopy and EXAFS. The metallic dispersion decreased from 20% to 7% when the content of Pd was increased from 0.5wt.-% to 3wt.-% in monometallic catalysts. The addition of 3 wt.-% Cu to obtain Pd-Cu catalysts caused a remarkable capacity loss of hydrogen chemisorption. TPR analysis suggested an interaction between the two metals and EXAFS characterization of the catalyst supported on silica confirmed the formation of Pd-Cu alloy. Pd/Nb2O5 catalysts showed turnover numbers higher than those obtained with the Pd/SiO2 systems in the cyclohexane dehydrogenation. However, the bimetallic catalysts showed very low turnover numbers.

Phospha-adamantanes as ligands for palladium-catalyzed cross-coupling reactions

Adjabeng, George Maclean.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
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New and robust methodologies have been designed for palladium-catalyzed crosscoupling reactions involving·a novel·class oftertiary phosphine ligand incorporating a phospha-adamantane framework. It has been realized that bulky, electron-rich phosphines, when used as ligands for palladium, allow for cross-coupling reactions involving even the less reactive aryl halide substrates with a variety of coupling partners. In an effort to design new ligands suitable for carrying out cross-coupling transformations, the secondary phosphine, 1,3,5,7-tetramethyl-2,4,8-trioxa-6phosphaadamantane was converted into a number of tertiary phosphine derivatives. The ability of these tertiary phosphaadamantanes to act as effective ligands in the palladiumcatalyzed Suzuki cross-coupling was examined. 1,3,5,7-Tetramethyl-6-phenyl-2,4,8trioxa- 6-phosphaadamantane (PA-Ph) used in combination with Pdz(dba)3permitted the reaction of an array of aryl iodides, bromides and chlorides with a variety arylboronic acids to give biaryls in good to excellent yields. Subsequently, palladium complexes of PA-Ph were prepared and isolated in high yields as air stable palladium bisphosphine complexes. Two different kinds of crystals were isolated and upon characterization revealed two complexes...

Phospha-adamantane ligands and phosphorous ionic liquids for palladium-catalyzed cross-coupling reactions /

Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
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New and robust methodologies have been designed for palladiumcatalyzed cross-coupling reactions involving a library of novel tertiary phosphine ligands incorporating a phospha-adamantane framework. The secondary phosphine, l,3,5,7-tetramethyl-2,4,8-trioxa-6-phospha-adamantane was converted into a small library of tertiary phosphine derivatives and the ability of these tertiary phosphaadamantanes to act as effective ligands in the palladium-catalyzed amination reaction and p-alkyl-Suzuki cross-coupling was examined. l,3,5,7-Tetramethyl-6- phenyl-2,4,8-trioxa-6-phosphaadamantane (PA-Ph) used in combination with Pd2(dba)3 CHCI3 facilitated the reaction of an array of aryl iodides, bromides and chlorides with a variety secondary and primary amines to give tertiary and secondary amines respectively in good to excellent yields. 8-(2,4-Dimethoxyphenyl)- l,3,5,7-tetramethyl-2,4,6-trioxa-8-phospha-tricyclo[3.3.1.1*3,7*]decane used in combination with Pd(0Ac)2 permitted the reaction of an array of alkyl iodides, and bromides with a variety aryl boronic acids and alkyl 9-BBN compounds in good to excellent yields. Subsequent to this work, the use of phosphorous based ionic liquids, specifically tetradecyltrihexylphosphonium chloride (THPC)...

Emulsion Copolymerization of alpha-Olefins with Carbon Monoxide Using Water-Soluble Palladium(II) Complexes; Emulsionscopolymerisation von alpha-Olefinen und Kohlenmonoxid mit wasserlöslichen Palladium(II)-Komplexen

Sunjuk, Mahmoud Shaker Ahmed
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
39.201592%
The objective of this thesis was the development of stable dispersions for aqueous polyketone latices on the basis of the copolymers propene/undecenoic acid/CO, butene/undecenoic acid/CO, and propene/butene/undecenoic acid/CO. Therefore, attention has been focused on the design of new water-soluble palladium(II) catalysts for the production of stable polymer latices with (i) high solids contents, (ii) high molecular weights, (iii) particle sizes in the range between 50 and 500 nm, and (iv) glass transition temperatures with values below room temperature. In the first chapter of this thesis the synthesis and characterization of novel diphosphine ligands and their palladium(II) complexes is described. The diphosphines R2P(CH2)3PR2 [R = (CH2)nP(O)(OEt)2, n = 2-6, 8; (CH2)nOH, n = 6; (CH2)nNH2, n = 3] were obtained by heating P(OEt)3 with 1,3-dibromopropane according to a Michaelis-Arbuzov reaction, followed by reduction of the resulting diphosphate with LiAlH4 in diethyl ether to give H2P(CH2)3PH2. An excess of the corresponding olefin CH2=CH.(CH2)n.X (X = OH, n = 4; P(O)(OEt)2, n = 0-4, 6; NH2, n = 1) was photochemically hydrophosphinated with the diprimary phosphine H2P(CH2)3PH2 over night. This convenient synthesis is nearly quantitative and simplifies the purification of the products. Purification is achieved by removing excess alkene under reduced pressure. The alkenyl phosphonates CH2=CH.(CH2)n.P(O)(OEt)2 were obtained either from commercial suppliers (n = 0...

The selective hydrogenation of 1,3-butadiene in the presence of n-butenes over supported palladium catalysts

Riley, Mark G.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 152 p.; application/pdf
ENG
Relevância na Pesquisa
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The selective hydrogenation of 1,3-butadiene in the presence of n-butenes over supported palladium catalysts, an industrially important reaction, was investigated at atmospheric pressure between 308K and 393K. The study included measuring the reaction kinetics both in the presence and absence of CO, examining of the differences between palladium supported on six different carriers, testing for the effects of hydrogen spillover, and investigating the catalyst's aging behavior. Isotopic tracers (single $\sp{13}$C labeled 1-butene) provided direct information about the reaction network. The kinetics of butadiene hydrogenation were measured on a 0.02% Pd/alumina catalyst. Reaction orders were one in hydrogen and zero in butadiene. Addition of CO decreased the rate of butadiene hydrogenation; the reaction rate was proportional to the negative one-half power of the CO pressure in the range of 25 to 145 ppm CO. CO affects the hydrogenation rate by reducing the surface concentration of hydrogen. Activation energies for butadiene hydrogenation were 13.3 + 0.8 kcal/mole in the absence of CO and increased to 15.5 + 0.5 kcal/mole with the addition of 40 ppm CO. Six supports were tested to determine what effect the support might have on the catalytic properties of the supported palladium catalyst. The six materials tested were: activated carbon...

Characterization of Pd nanoparticles and of silica-supported Pd-catalysts for the Suzuki-Miyaura reaction.

HANIF, MOHAMMAD ABU
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
49.13351%
The importance of palladium (Pd) as a catalyst in organic coupling reactions is undeniable. Mesoporous silica is widely used as the support of Pd catalysts. But the porous structure of the mesoporous silica limits complete characterization. As a result, heterogeneous Pd catalysts are not fully understood. Model Suzuki-Miyaura reaction catalysts have been made by immobilizing Pd on a mercaptopropyltrimethoxysilane (MPTMS) functionalized Si substrate. Two types of Pd species were found on the fresh catalysts that may be attributed to a S-bound Pd (II) species and Pd nanoparticles. A sulfur species that has not been previously reported on this class of catalysts has also been observed. A systematic study of various palladium/sulfur complexes using XPS was carried out to identify this species, which may be assigned to high oxidation state sulfur formed by oxidation of thiol during the reduction of the Pd(OAc)2 used to load the catalyst with Pd. Shifts in binding energy observed for both Pd and S spectra of the used catalysts were examined in order to probe the change of electronic environment of reactive palladium center and the thiol ligand during the reaction. Electron and atomic force microscopic imaging of the surfaces demonstrates the formation of Pd nanoparticles on fresh catalysts and subsequent size reduction of the Pd nano-particles following reaction. Nanoparticles have gained increased attention due to their unique properties different from the bulk materials. Polyvinyl pyrrolidone (PVP) and dodecyl sulfide stabilized palladium nanoparticles have been synthesized with a size range of 3 to 10 nm and 2 to 5 nm respectively. XPS confirmed the conversion of Pd (II) to Pd (0) and presence of stabilizing agent on nanoparticles surface by observing Pd 3d...

Combustão catalitica de metano usando paladio suportado em peneiras moleculares; Catalytic combustion of methane by palladium-supported molecular sieves

Juan Alberto Chavez Ruiz
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/03/2005 PT
Relevância na Pesquisa
49.03223%
A participação do gás natural na geração de energia vem crescendo significativamente nos últimos anos, tanto no Brasil como no mundo. O seu uso na combustão gera menor emissão de poluentes quando comparado aos outros combustíveis fósseis. Isto é muito importante numa época em que países do mundo inteiro concentram esforços para atender a meta do protocolo de Kyoto. Neste sentido o governo brasileiro vem incentivando o uso do gás natural visando atingir, em 2010, uma participação de até 12 % deste combustível na matriz energética do país. Esta Tese teve como objetivo determinar a utilidade das peneiras moleculares como suporte de catalisadores de paládio, na reação de combustão catalítica de metano com fins de geração de energia em baixas temperaturas. Para isso, foram sintetizadas peneiras moleculares micro e mesoporosas do tipo ETS-10, (Si e AI)-MCM-41 e meso-SAPO. As estabilidades térmicas dessas peneiras moleculares indicaram que para a reação de interesse, somente o MCM-41 seria útil, tanto puramente silícico (Si-MCM-41) como com alumínio (AI-MCM-41). Também foram estudados os efeitos causados por aditivos como cério, lantânio e zircônio, introduzidos por impregnação nos suportes antes da impregnação do paládio. A estrutura dos suportes do tipo MCM-41 apresentaram uma boa estabilidade térmica até 900°C e o suporte a base de silicato demonstrou ser mais estável do que o AI-MCM-41. A caracterização realizada permitiu verificar a presença de óxido de paládio (PdO) nos catalisadores. Os catalisadores de ambas as séries Si-MCM-41 e AI-MCM-41 foram ativos na reação de interesse. O paládio suportado na série Si-MCM-41 apresentou maior atividade que quando suportado na série AI-MCM-41. Este fato pode estar relacionado com a diferença no caráter hídrofílico/hidrofóbico do suporte. A acidificação dos suportes antes da impregnação do paládio melhorou performance catalítica enquanto que a presença de aditivos não apresentaram a melhora esperada...

A interação metal-suporte em catalizadores de paládio-óxido de lantânio

Paulo Roberto Britto Guimarães
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/08/1991 PT
Relevância na Pesquisa
49.02574%
Neste trabalho foram estudadas as modificações introduzidas nas propriedades dos catalisadores de Paládio em função do teor de 'LA' 'O IND. 3' (óxido de Lantânio) presente nos mesmos. Para tanto foram preparados catalisadores de 5% Pd/'AL IND. 2' 'O IND. 3', 5% Pd-1% 'La IND. 2' 'O IND. 3'/ 'AL IND. 2' 'O IND. 3', 5% Pd/'AL IND. 2' 'O IND. 3'-'LA IND. 2' 'O IND. 3'. O método de preparação utilizado foi o da impregnação por via seca, tendo-se usado o Pd'CL IND.2', dissolvido em HCl 1N, como precursor. Após secagem a 393 K ('120 GRAUS'C) por 12h, e calcinação a 773 K ('500 GRAUS'C) por 4h, os catalisadores foram caracterizados através dos métodos de B.E.T., T.P.R., T.P.D., Quimissorção Seletiva de 'H IND. 2', Espectroscopia de Infra-vermelho, X.P.S.(E.S.C.A.), Difração de Raios-X, e um teste de atividade, através da hidrogenação do Etileno ('C IND. 2' 'H IND. 4'). Os resultados experimentais obtidos demonstraram que um alto teor de 'LA IND. 2' 'O IND. 3' modifica significativamente os perfis de redução e de dessorção de 'H IND. 2' dos catalisadores de Paládio, além de inibir fortemente a quimissorção de CO, não afetando, porém, a quimissorção de 'H IND. 2'. Além disso, verifica-se que as dispersçoes metálicas observadas nesses catalisadores são maiores que as obtidas naqueles com pouco (1%) ou nenhum 'LA IND. 2' 'O IND. 3'. Por fim...

Methane combustion over Pd/SiO2 catalysts with different degrees of hydrophobicity

Gracia, F. J.; Guerrero, Sichem; Robertson, J.; Araya Figueroa, Paulo Enrique
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artículo de revista
EN
Relevância na Pesquisa
48.19773%
The combustion of methane has been studied over 1% Pd catalysts supported on commercial silica with different hydrophobicity, prepared by chlorine free precursors. It was found that, when no water is added to the feed, the degree of hydrophobicity of the silica does not affect significantly the behavior of the catalysts. The results show that the activation and deactivation processes are similar for both catalysts. Furthermore, contrary to what is observed on Pd/Al2O3 and Pd/ZrO2 catalysts, the apparent reaction order with respect to water for Pd/SiO2 catalysts is -0.25. When water is added to the feed, however, the different hydrophobicity of the supports affects the inhibition produced by the adsorption of water on the catalytic surface. Regardless of the hydrophobicity of the support, the addition of water also speeds up the deactivation process of the Pd catalysts supported on silica.

Combustion of butyl carbitol using supported palladium catalysts

Feio, Lílian S. F; Escritori, J. C.; Noronha, Fábio Bellot; Hori, Carla E
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
58.296177%
Catalysis Letters, 120(3-4):229-235 Jan. 2008; Abstract Palladium catalysts supported on CeO2, Ce0.75Zr0.25O2, ZrO2, TiO2, Nb2O5, Al2O3 were studied on the total oxidation of butyl carbitol. Several techniques were used to characterize the samples such as diffuse reflectance spectroscopy (DRS), temperature programmed reduction (TPR), cyclohexane dehydrogenation and CO temperature programmed desorption (TPD). DRS and TPR results revealed the presence of bulk PdO and PdO with strong interaction with the support. The catalytic tests showed the following order for decreasing activity: Pd/Ce0.75Zr0.25O2 > Pd/CeO2 > Pd/TiO2 > Pd/Nb2O5 > Pd/Al2O3 > Pd/ZrO2. However, when the turnover frequency (TOF) was calculated, all the samples had similar values.

Characterization of Graphite-Supported Palladium-Cobalt Catalysts by Temperature-Programmed Reduction and Magnetic Measurements

Noronha, Fábio Bellot; Schmal, Martin; Nicot, C.; Moraweck, B.; Fréty, R.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
38.86317%
Journal of catalysis, 168(1): 42-50, Maio 1997.; Graphite-supported cobalt, palladium, and cobalt-palladium systems were prepared by a simple impregnation technique and submitted to hydrogen reduction in a temperature-programmed mode. Using X-ray diffraction to define the structure of the calcined precursors, magnetic measurements to determine the amount of metallic cobalt formed after reduction, and analysis of the gaseous medium during the reduction, a general model for the reduction of the graphite supported catalysts has been suggested. At room temperature, both pure Pd~ and Pd~ associated with C0304 are reduced to the metallic state. In the case of bimetallic systems, a fraction of C0304 in close proximity or interfaced with Pd~ can be reduced to the metallic state and to CoO species, demonstrating a strong catalytic effect of palladium on the reduction of cobalt oxides. At temperatures between 298 and 500 K, depending on the catalyst formulation, the presence of metallic palladium promotes the reduction of a large fraction of oxidized cobalt. At higher reduction temperature, at least two competitive phenomena were detected: direct reduction of the residual oxidized cobalt by the graphite, leading to carbon monoxide and dioxide formation...

Oxidation and reduction effects of propane-oxygen on Pd-chlorine/almnina catalysts

Schmal, Martin; Noronha, Fábio Bellot; Aranda, D. A. G.; Guimarães, A. L.; Monteiro, Robson de Souza
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
58.95654%
Catalysis letters, 64(2-4): 163-169, 2000.; Pd-chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd-OH) at the surface...

Pd/γ-Al2O3 monolithic catalysts for NOx reduction with CH4 in excess of O2: effect of precursor salt

Martín Pereira, Juan Carlos; Suárez Gil, Silvia; Yates Buxcey, Malcolm; Ávila García, Pedro
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 88 bytes; text/plain
ENG
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Article in press.; Palladium monolithic catalysts based on γ-Al2O3 were developed and their activities and selectivities for the Selective Catalytic Reduction of nitrogen oxides employing methane as the reducing agent in oxygen excess (CH4-SCR) for use at pilot plant scale, were determined. The alumina monoliths were sulphated to increase the activity of the support and subsequently impregnated with one of three precursor salts: palladium chloride, nitrate or acetate, respectively. The catalysts were characterised by XRF, XRD, TGA-DTA, H2-TPR, N2 ad/desorption and MIP. Significant differences in the catalytic activities, selectivity and stabilities were found. In the case of nitrate and acetate palladium precursors, multilayer sulphates for both and Al2(SO4) phase for the latter were observed that may inhibit the interaction of the reactants with the active phase, leading to catalysts with reduced activity. Palladium chloride was the most efficient precursor for NOx abatement, not only due to the stability of the surface sulphates that hinder the competitive CH4 oxidation reaction but also to the presence of Cl- ions that seem to play an important role in the reaction. This catalyst had the lowest tendency for the competing hydrocarbon oxidation reaction and also demonstrated the highest stability after forty hours of reaction in the chosen operating conditions.; The authors would like to thank the Comunidad Autónoma of Madrid CAM project GR/AMB/0751/2004SE505 and the Program "Ciencia y Tecnología para el Desarrollo" CYTED...

Influence of catalyst treatments on the decomposition of hydrogen peroxide on supported palladium catalysts

Voll,F.A.P.; Palú,F.; Santos,J.B.O.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 ES
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The decomposition of hydrogen peroxide was studied on Pd catalysts between 293 K and 313 K. The apparent activation energy value was calculated for all the catalysts and it varied between 27 and 55 kJ/mol. For all the catalysts tested, treatment with hydrogen resulted in a significant increase in the reaction rate, as well as a decrease in the apparent activation energy for the reaction. All the reactions were well represented by a first order rate law with respect to H2O2. The effect of the treatment with H2O2 was studied in successive reactions without catalyst exchange. A small deactivation was observed in the 5.0% Pd/AC and 0.5% Pd/AC catalysts after four H2O2 decomposition reactions.

Hydrogenation of cinnamaldehyde over an ionic cobalt promoted alumina-supported palladium catalyst

Erasmus,Elizabeth
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2013 EN
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Nano γ-alumina-supported transition metal-based mono- (Pd0/γ-Al2O3 or CoIII/γ-Al2O3) and bimetallic catalysts (Pd0CoIII/γ-Al2O3), were prepared by wet impregnation, oxidation and in situ reduction of the palladium. The palladium(II) acetate [PdII3(OOCCH3)6], cobalt(II) acetate [CoII(OOCCH3)2].4H2O and palladium, cobalt bridging tetraacetate [PdII CoII(OOCCH3)4].H2O.2CH3COOH, were used as catalyst precursors to prepare a 7.4 % mol catalyst/support loading. The oxidation states of these activated catalysts were studied by XPS. These catalysts were evaluated for hydrogenation of cinnamaldehyde in a biphasic reaction under 3 MPa of hydrogen at 80 °C. The Pd0/γ-Al2O3 selectively catalyzed the hydrogenation of C=C bond in cinnamaldehyde to form phenylpropanol (100 %). In contrast, catalysis with Pd0CoIII/γ-Al2O3 hydrogenated both C=C and C=O bonds consecutively, forming 65 % phenylpropanal and 35 % phenylpropanol with TOF = 47.2 h-1. No reaction occurred when CoIII/γ-Al2O3 was used.