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Titolo:
The role of Pd precursors in the oxidation of carbon monoxide over Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts
Autore:
Monteiro, RS; Dieguez, LC; Schmal, M;
Indirizzi:
COPPE, PEQ, NUCAT, BR-21945970 Rio De Janeiro, Brazil COPPE Rio De Janeiro Brazil BR-21945970 BC1945970 Rio De Janeiro, Brazil Univ Fed Rio de Janeiro, Escola Quim, BR-21945970 Rio De Janeiro, Brazil Univ Fed Rio de Janeiro Rio De Janeiro Brazil BR-21945970 BCeiro, Brazil
Titolo Testata:
CATALYSIS TODAY
fascicolo: 1, volume: 65, anno: 2001,
pagine: 77 - 89
SICI:
0920-5861(20010201)65:1<77:TROPPI>2.0.ZU;2-U
Fonte:
ISI
Lingua:
ENG
Soggetto:
LOW-TEMPERATURE ACTIVITY; PALLADIUM ALUMINA CATALYSTS; METAL-SUPPORT INTERACTION; CO OXIDATION; PROGRAMMED REDUCTION; CERIA; ADSORPTION; OXYGEN; HYDROGEN; SPECTROSCOPY;
Keywords:
unsteady-state oxidation of CO; palladium; cerium oxide; Pd-Ce interaction; Pd precursors;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
47
Recensione:
Indirizzi per estratti:
Indirizzo: Schmal, M COPPE, PEQ, NUCAT, Caixa Postal 68502, BR-21945970 Rio De Janeiro, Brazil COPPE Caixa Postal 68502 Rio De Janeiro Brazil BR-21945970 BCil
Citazione:
R.S. Monteiro et al., "The role of Pd precursors in the oxidation of carbon monoxide over Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts", CATAL TODAY, 65(1), 2001, pp. 77-89

Abstract

The role of palladium precursors (e.g. chloride - PdCl2; acetylacetonate -Pd(acac)(2); nitrate - Pd(NO3)(2)) in the catalytic properties of Pd/Al2O3and Pd/CeO2/Al2O3 catalysts toward CO oxidation was herein investigated. The characterization techniques used for mapping the Pd sites were H-2 and CO chemisorption, infrared spectroscopy (FTIR) of CO adsorbed, and temperature-programmed desorption (TPD). Unsteady-state CO oxidation was carried outby temperature-programmed surface reaction (TPSR). The nature of palladiumprecursors and their interaction with CeO2 affected the metallic dispersion and the site morphologies. Highly dispersed metal particles (d > 50%) were obtained by using palladium chloride and acetylacetonate precursors on Pd/Al2O3 catalysts. Pd(1 0 0) and Pd(1 1 1) were the major palladium crystallite orientations in these samples, but a larger amount of low coordination sites located on Pd(1 0 0) faces was observed for the ex-chloride sample. These sites accounted for the oxidation of CO at very low temperatures on Pd-CI catalyst. In the presence of ceria, the Pd dispersion was a function ofthe way in which each Pd precursors interacted with CeO2. A two-fold decrease of dispersion was obtained to ex-chloride sample, while a two-fold increase to ex-nitrate and the same dispersion to ex-acetylacetonate samples were otherwise observed. The metallic redispersion may be the result of the occupancy of ceria oxygen vacancies by the palladium crystallites. Ultimately, the interaction with ceria redispersed Pd crystallites in a more organized bi-dimensional structure with the predominance of(1 1 1) orientation. Due to the transient conditions of the reaction, ceria did not promote, as expected, the oxidation of CO. Ceria reduced species (Ce3+) were not able to help CO oxidize at lower temperatures due to lack of oxygen into its lattice. Thus, the highest rates for CO oxidation were only observed at higher temperatures for the Pd/CeO2/Al2O3 catalysts, a result of a combination of strong competition for oxygen molecules, which have replenished the ceria lattice, and the low activity of Pd(1 1 1) sites. (C) 2001 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 30/09/20 alle ore 02:37:40