H-Spillover and SMSI Effects in Paraffin Hydroisomerization over Pt/WOx/ZrO2Bifunctional Catalysts

Santiesteban, J.G.; Calabro, David C.; Borghard, W.S.; Chang, Clarence D.; Vartuli, J.C.; Tsao, Yuchi; Natal-Santiago, M.A.; Bastian, Robert

doi:10.1006/jcat.1999.2435

Cited by 72 publications

(31 citation statements)

References 32 publications

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“…The data reported here confirm the exceptionally high activity and selectivity of PtWZ in the presence of H 2 (7,8,(20)(21)(22)(23)(24)(25)(26). Our data show that the conversion of n-pentane in the presence of PtWZ is 60 times higher than the maximum conversion observed for WZ under identical conditions, and the isopentane selectivity is greater than 95% (Fig.…”

Section: N-pentane Conversion Catalyzed By Ptwz In the Presence Of Hsupporting

confidence: 85%

“…Consequently, most literature reports of platinum-promoted WZ present data for the catalyst operating in the presence of H 2 (7,8,(20)(21)(22)(23)(24)(25)(26), and there is little literature of the unpromoted catalysts, although they are active for the isomerization reaction (9,19). Even for the platinum-promoted catalyst, full analyses of the reaction products are usually lacking, and the role of H 2 in the reaction is not well known, although some investigations have reported its positive effects (7,8,(20)(21)(22)(23)(24)(25)(26).…”

Section: Introductionmentioning

confidence: 99%

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Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Kuba

Lukinskas

Ahmad

et al. 2003

Journal of Catalysis

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The catalytic isomerization of n-pentane catalyzed by tungsted zirconia (WZ) was investigated to elucidate the effects of H2 in the feed and platinum in the catalyst. In the reaction catalyzed by WZ with or without platinum, when no H2 was present, a complex reaction network was observed, associated with organic deposits on the catalyst, giving mainly cracked products. The alkane is inferred to be activated in a redox step forming W 5+ on the catalyst and unsaturated intermediates that react to form polyalkenylic surface species, which were detected by in-situ UVvisible spectroscopy. Promotion of WZ with platinum dramatically improved the catalytic activity and the isomerization selectivity in n-pentane conversion. The improvement was only marginal in the absence of H2, but it became substantial in the presence of H2, with the conversion increasing from 3 to 55% for the platinum-promoted catalyst, which underwent only little deactivation. The selectivity for isopentane was about 95% at 523 K. The results indicate that the complex reaction network operative with the WZ catalyst is suppressed on the platinum-containing catalysts in the presence of H2. A fast and selective monomolecular isomerization reaction takes over in this case. The adsorbed unsaturated C5 intermediates are rapidly desorbed via hydrogenation on the reduced tungstate surface. This rapid desorption minimizes the formation of highermolecular-weight organic species such as polyalkenyls that are necessary for the complex reaction path observed with the unpromoted catalyst. The observed side products are interpreted not as cracking products accompanying the acid-catalyzed isomerization reaction but instead as hydrogenolysis products formed directly on the platinum particles.

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Section: N-pentane Conversion Catalyzed By Ptwz In the Presence Of Hsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Kuba

Lukinskas

Ahmad

et al. 2003

Journal of Catalysis

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“…The remarkably high H 2 /Pt molar ratio over both catalysts indicates that H 2 is adsorbed not only by Pt but also by WO 3 and/or Al-ZrO x through H 2 spillover. [14] It has been reported that H 2 spillover takes place very readily in the Pt/WO 3 system. [15] However, the large difference in H 2 uptake between Pt/WO 3 /Al-ZrO x and Pt/WO 3 /ZrO 2 can be best explained by the role of Al-ZrO x in H 2 storage, which would typically occur only at very high temperatures in undoped ZrO 2 .…”

Section: +mentioning

confidence: 99%

“…Unlike conventional isomerization catalysts, which are designed as strong solid acids, the superior catalytic performance of Pt/WO 3 /M-ZrO x is associated with an unusually high surface density of spilt-over H 2 and a facile reverse process of H 2 spillover. [13][14][15] Nanocomposite processing can be used to develop unique catalysts with superior surface areas, ultrahigh dispersion of components, and excellent stability. [16,17] In this study, an easier method of simultaneously precipitating different metal cations, such as Al 3+ with Zr 4+ , under controlled pH conditions is employed to obtain metal hydroxides that are mixed at an atomic level.…”

mentioning

confidence: 99%

A Highly Active and Selective Nanocomposite Catalyst for C₇₊ Paraffin Isomerization

Ying

2006

Angew Chem Int Ed

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“…O tratamento HTR produz portanto uma forte interação metal-oxigênio. Essa interação já foi sugerida por outros, para o catalisador Pd/ Al 2 [20][21][22][23] . O efeito SMSI aumenta a densidade eletrônica do subnível d do metal disperso [23][24][25][26] , assim uma forte ligação pi (retrodoação) entre o paládio e a carbonila pode ser formada.…”

Section: Análise No Infravermelho (Ftir)unclassified

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Cunha¹,

Faccin²,

Moro³

et al. 2002

Quím. Nova

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Recebido em 24/4/01; aceito em 4/9/01 INFRARED AND X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF CHLORIDE EFFECT IN PALLADIUM CATALYSTS. Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bonded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d 5/2 binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al 2 O 3 reduced at 500 o C, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.Keywords: chloride poisoning effect; infrared; XPS. INTRODUÇÃOAs propriedades catalíticas de catalisadores metálicos suportados são geralmente influenciadas pela presença de aditivos, que podem ser tanto promotores 1,2 como também inibidores [3][4][5][6] . Alguns inibidores como cloreto, as vezes, podem estar presente no catalisador, não como aditivos, mas sim, como resíduo dos sais metálicos precursores do catalisador, e podem produzir a diminuição na atividade catalítica 3,7,8 .A influência do cloreto na atividade catalítica pode ser interpretada de duas formas: i) Como um efeito estérico, onde o haleto coordena-se aos sítios que são necessários a adsorção e ativação de outras espécies 9-11 . Nesse caso o cloreto produz o bloqueio dos sítios metálicos resultando na diminuição da acessibilidade dos reagentes a esses sítios 11,12 . ii) A outra interpretação é considerar o envenenamento do cloreto como um efeito eletrônico. Nesse caso cloreto metálico pode ser formado 13,14 . Para metais nobres como paládio, esses haletos são mais estáveis que os óxidos 13,15 . A atividade catalítica portanto diminui, pois os haletos metálicos são menos ativos que as partículas metálicas.Nesse trabalho, nossos resultados evidenciam que a presença de cloreto no catalisador metálico produz efeitos eletrônicos e que quando esse é reduzido a temperatura de 500 o C, a interação do paládio disperso com o oxigênio do suporte alumina pode também resultar em um efeito semelhante ao do cloreto. Uma redução parcial do efeito do envenenamento por cloreto pode ser obtida quando usa-se molibdênio/alumina como suporte. As interpretações foram feitas a partir da análise através da espectroscopia de fotoelétrons excitados por raios-X e também na análise das ligações por retro-doação pi entre o metal e a carbonila, que dependem da densidade eletrônica do metal. Essas ligações podem ser monitoradas a partir da espectroscopia no infravermelho. PARTE EXPERIMENTAL Síntese do Pd/Al 2 O 3 (sem cloreto)O su...

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H-Spillover and SMSI Effects in Paraffin Hydroisomerization over Pt/WOx/ZrO2Bifunctional Catalysts

Cited by 72 publications

References 32 publications

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

A Highly Active and Selective Nanocomposite Catalyst for C₇₊ Paraffin Isomerization

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

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H-Spillover and SMSI Effects in Paraffin Hydroisomerization over Pt/WOx/ZrO2Bifunctional Catalysts

Cited by 72 publications

References 32 publications

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

A Highly Active and Selective Nanocomposite Catalyst for C7+ Paraffin Isomerization

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

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A Highly Active and Selective Nanocomposite Catalyst for C₇₊ Paraffin Isomerization