Influence of the redox properties of ceria on the preparation of three-way automotive platinum—rhodium/ alumina—ceria catalysts

Marécot, P.; Pirault, L.; Mabilon, G.; Prigent, Michel; Barbier, J.

doi:10.1016/0926-3373(94)00038-7

Cited by 39 publications

(15 citation statements)

References 21 publications

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“…The promotion of catalytic activity and the oxygen storage capacity by CeO 2 is well-identified (Sayle et al, 1994;Marecot et al, 1994;Kalakkad et al, 1992;Ihara et al, 1990;Hepburn and Gandhi, 1992;Herrmann et al, 1989;Li et al, 1989). The synergetic mechanism may be explained by the following chain of reactions:…”

Section: Resultsmentioning

confidence: 95%

Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

Ding

Wade

et al. 1998

Ind. Eng. Chem. Res.

171

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Catalytic oxidation of ammonia in supercritical water (SCW) was studied using a continuous-flow, packed-bed reactor at temperatures ranging from 410 to 470 °C, a nominal pressure of 27.6 MPa, and reactor residence times of less than 1 s. The kinetics and catalyst performance of MnO2/CeO2 for oxidation of ammonia in SCW was evaluated. In this reaction environment, ammonia was predominantly converted into molecular nitrogen (N2), and the rate of ammonia conversion was enhanced by MnO2/CeO2. For example, 40% of the ammonia was converted when using the MnO2/CeO2 catalyst at a temperature of 450 °C and a reactor residence time of 0.8 s. It was reported that, without a catalyst, essentially no ammonia conversion was observed below 525 °C (Helling, R. K.; Tester, J. W. Environ. Sci. Technol. 1988, 22 (11), 1319) and 10% of the ammonia was converted at a temperature of 680 °C, a pressure of 24.6 MPa, and a reactor residence time of 10 s (Webley, P. A.; Tester, J. W.; Holgate, H. R. Ind. Eng. Chem. Res. 1991, 30 (8), 1745). Kinetic models developed for the gas-phase catalytic oxidation of ammonia were adopted and proven to be adequate for catalytic oxidation of ammonia in supercritical water. The best-fit global rate expression for catalytic supercritical water oxidation of ammonia by MnO2/CeO2 was obtained as follows: r = 1.14 × 1014 exp(−189 kJ/mol/RT) [NH3]0.63[O2]0.71. The BET surface area and X-ray diffraction analyses of the exposed catalyst indicated a significant reduction of surface area and changes in the crystalline structure of the catalyst.

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Section: Resultsmentioning

confidence: 95%

Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

Ding

Wade

et al. 1998

Ind. Eng. Chem. Res.

171

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“…Portanto este trabalho sugere que o uso de suportes redutíveis pode produzir uma inibição parcial do envenenamento por cloreto. Catalisadores com suportes mistos, onde um dos óxidos é redutível, foram muito estudados nos últimos anos [32][33][34][35][36] , sendo que esses sistemas mostram melhor atividade catalítica que os catalisadores que usam alumina pura como suporte [32][33][34] .…”

Section: Análise Por Espectroscopia De Fotoelétrons Excitados Por Raiunclassified

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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“…CeO 2 is a highly reducible oxide exhibiting oxygen storage and release properties that are important for the operation of three-way, automotive exhaust catalysts . It can also stabilize the dispersion of noble metal particles, and CeO 2 -supported vanadia is much more active for methanol synthesis than vanadia dispersed on other supports. , Since it is hard to prepare bulk CeO 2 with a high surface area, interest has arisen in dispersing ceria onto high surface area supports. While there have been numerous attempts to disperse ceria on SiO 2 or Al 2 O 3 − or to incorporate cerium atoms into the walls of mesoporous silica, − these efforts have largely led to the formation of small crystallites of CeO 2 because ceria has a strong tendency to sinter at elevated temperatures. − While there have been some reports of noncrystalline CeO 2 species grafted on SiO 2 , ,,− the deposited material has not been well characterized.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties

2011

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An investigation was performed to establish the effects of precursor composition on the structure of ceria deposited onto mesoporous silicas, MCM-41 and SBA-15. The structure of the deposited ceria was characterized by XRD, TEM, Raman and UV-visible spectroscopy, XANES, and EXAFS. Using Ce(acac) 3 as the precursor resulted in formation of 3 nm diameter ceria particles located predominantly in the mouths of the support pores. Amorphous agglomerates, but with domains of comparable size to those obtained using Ce(acac) 3 , were obtained using Ce(O i Pr) 4 . Much smaller domains and a high degree of dispersion were obtained using Ce(O t Bu) 4 as the precursor. The structure of the deposited ceria affects its reduction-reoxidation properties. Reduction and reoxidation are almost fully reversible for the nanoparticles. Only surface reduction is observed up to 723 K, whereas partial bulk reduction takes place at higher reduction temperatures. In case of the well-dispersed, layerlike Ce species on the silica surface, an extent of reduction similar to that of the nanoparticles is achievable, but upon heating the samples in 10% H 2 /He to 923 K the reduction becomes partially irreversible. The latter effect might be explained by a formation of cerium silicates that prevent the complete reoxidation of the cerium species. ' INTRODUCTIONDispersion of a transition metal oxide on a high surface area support such as Al 2 O 3 or SiO 2 makes it possible to combine the catalytic properties of the transition metal oxide with the high surface area and thermal and mechanical stability of the support. 1 Good illustrations of the manner in which the transition metal oxide is introduced onto the support and the physical properties of the deposited oxide are given for the cases of TiO x , 1-9 VO x , 5,[9][10][11][12][13][14] or MoO x 10,11,15-21 dispersed on high surface area supports. A notable consequence of this approach is the formation of catalytically active sites which are not present on either the support or the bulk transition metal oxide. For example, neither TiO 2 nor SiO 2 is active for the liquid-phase epoxidation of alkenes, but TiO 2 /SiO 2 exhibits high activity and selectivity for this reaction. 6,[22][23][24] The appearance of such novel catalytically active sites has been attributed to the formation of a twodimensional oxide overlayer whose physical properties differ from those of the corresponding bulk oxide. Dispersed transition metal oxides have also been shown to stabilize the dispersion of small metal particles and to enhance the activity of supported metal oxo species. For example, Au particles have been shown to be much more stable on TiO x /SiO 2 than on SiO 2 25 and isolated vanadate species dispersed on TiO x /SiO 2 exhibit turnover frequencies that are up to 60-fold higher than when dispersed on SiO 2 . 7 CeO 2 is a highly reducible oxide exhibiting oxygen storage and release properties that are important for the operation of threeway, automotive exhaust catalysts. 26 It can also stabilize the dispersion of n...

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Influence of the redox properties of ceria on the preparation of three-way automotive platinum—rhodium/ alumina—ceria catalysts

Cited by 39 publications

References 21 publications

Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

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

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties

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Influence of the redox properties of ceria on the preparation of three-way automotive platinum—rhodium/ alumina—ceria catalysts

Cited by 39 publications

References 21 publications

Supercritical Water Oxidation of NH3 over a MnO2/CeO2 Catalyst

Supercritical Water Oxidation of NH3 over a MnO2/CeO2 Catalyst

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

Synthesis of Different CeO2 Structures on Mesoporous Silica and Characterization of Their Reduction Properties

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Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

Supercritical Water Oxidation of NH₃ over a MnO₂/CeO₂ Catalyst

Synthesis of Different CeO₂ Structures on Mesoporous Silica and Characterization of Their Reduction Properties