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Issue 10, 2011
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In situ Raman and in situXRD analysis of PdO reduction and Pd° oxidation supported on γ-Al2O3catalyst under different atmospheres

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Abstract

Reduction of Pd° and decomposition of palladium oxide supported on γ-alumina were studied at atmospheric pressure under different atmospheres (H2, CH4, He) over a 4 wt% Pd/Al2O3 catalyst (mean palladium particle size: 5 nm with 50% of small particles of size below 5 nm). During temperature programmed tests (reduction, decomposition and oxidation) the crystal domain behaviour of the PdO/Pd° phase was evaluated by in situRaman spectroscopy and in situXRD analysis. Under H2/N2, the reduction of small PdO particles (<5 nm) occurs at room temperature, whereas reduction of larger particles (>5 nm) starts at 100 °C and is achieved at 150 °C. Subsequent oxidation in O2/N2 leads to reoxidation of small crystal domain at ambient temperature while oxidation of large particles starts at 300 °C. Under CH4/N2, the small particle reduction occurs between 240 and 250 °C while large particle reduction is fast and occurs between 280 and 290 °C. Subsequent reoxidation of the catalyst reduced in CH4/N2 shows that small and large particle oxidation of Pd° starts also at 300 °C. Under He, no small particle decomposition is observed probably due to strong interactions between particles and support whereas large particle reduction occurs between 700 and 750 °C. After thermal decomposition under He, the oxidation starts at 300 °C. Thus, the reduction phenomenon (small and large crystal domain) depends on the nature of the reducing agent (H2, CH4, He). However, whatever the reduction or decomposition treatment or the crystal domain, Pd° oxidation starts at 300 °C and is completed only at temperatures higher than 550 °C. Under lean conditions, with or without water, the palladium consists of reduced sites of palladium (Pd°, Pdδ+ with δ < 2 or PdOx with x < 1) randomly distributed on palladium particles.

Graphical abstract: In situ Raman and in situXRD analysis of PdO reduction and Pd° oxidation supported on γ-Al2O3 catalyst under different atmospheres

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Article information


Submitted
27 Jul 2010
Accepted
14 Dec 2010
First published
31 Jan 2011

Phys. Chem. Chem. Phys., 2011,13, 4607-4613
Article type
Paper

In situ Raman and in situXRD analysis of PdO reduction and Pd° oxidation supported on γ-Al2O3 catalyst under different atmospheres

A. Baylet, P. Marécot, D. Duprez, P. Castellazzi, G. Groppi and P. Forzatti, Phys. Chem. Chem. Phys., 2011, 13, 4607 DOI: 10.1039/C0CP01331E

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