B ENVIRONMENTAL ELSEVIER Applied Catalysis B: Environmental 14 (1997) 85-95 Oxidation of carbon monoxide, propene, propane and methane over a Pd/A1203 catalyst. Effect of the chemical state of Pd T. Maillet, C. Solleau, Jacques Barbier Jr., Daniel Duprez* Laboratoire de Catalyse en Chink Organique, URA CNRS 350, 40 av. du Recteur Pineau, 86022 Poitiers Cedex, France Received 24 November 1996; received in revised form 20 January 1997; accepted 26 January 1997 Abstract A 1 wt.-% Pd/y-A120j catalyst was prepared (38% dispersion) and sintered under a flow of 3 vol.% O2 in N2 at 900°C (9% dispersion). The temperature-programmed oxidation of CO, C3H6, C3Hs and CH, in substoichiometry of 02 was carried out on the fresh and, in some cases, on the sintered catalyst. The chemical state of palladium in the sintered catalyst was determined by XRD after interruption of the reaction at different temperatures. The temperatures at which a 20% conversion was obtained on the fresh pre-oxidised catalyst were: CO, 210°C < CjH6, 260°C < C3Hs, 300°C < C&, 335°C corresponding to an activity (in mmol h-’ g-l) at 300°C of: CO, 403 > C3H6, 66 > C3Hs, 15.3 > CH4, 7.9. Pre-reduction did not change the catalyst activity in CO and in C3H6 oxidation while it decreased the activity by a factor 2.4 for C3Hs and 3.2 for CH4. Except for a definite decrease of activity, the above conclusions remained valid for the sintered catalyst. XRD measurements showed that PdO initially present in the pre-oxidised sample was reduced before the oxidation of CO (< 180°C) and C3H6 (< 210°C) started, which explains why both pre-oxidised and pre-reduced samples had the same activity. In the case of C3Hs, the reduction occurred during the reaction and led to a temporary decrease of activity. For CO and C3Hs, the Pd” structure was clearly identified while a new structure PdOE (0 < < < 1) was formed with C3H6. This compound has the cfc structure of Pd” with a higher lattice parameter (3.990 A instead of 3.889 A in Pd”). 0 1997 Elsevier Science B.V. Keywords: Carbon monoxide oxidation; Methane oxidation; Palladium; Palladium oxide; Propane oxidation; Propene oxidation 1. Introduction We previously investigated the behaviour of a 1 wt.-% Pd/y-A1203 catalyst in propane oxidation [ 1). Temperature-programmed reactions of C3Hs with *Corresponding author. Tel.: +33 5 49453998; fax: +33 5 49453499. 02 were carried out with different stoichiometric ratios S(S = [02]/5[C3Hs]). This ratio corresponds to the parameter defined by Schlatter [2] when there is no NO in the reactant mixture. As already observed with supported Pt and/or Rh catalysts [3-51, the conversion profiles of C3Hs for the reaction carried out in substoichiometry of 02 (S < 1) showed two discrete domains of conversion: oxidation 0926-860x/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO926-3373(97)00014-3