Journal of Catalysis 253 (2008) 37–49 www.elsevier.com/locate/jcat Surface reconstruction of supported Pd on LaCoO 3 : Consequences on the catalytic properties in the decomposition of N 2 O J.P. Dacquin, C. Dujardin, P. Granger ∗ Université des Sciences et Technologies de Lille, Unité de Catalyse et de Chimie du Solide, Equipe Catalyse Hétérogène, UMR CNRS 8181, Bâtiment C3, 59655 – Villeneuve d’Ascq Cedex, France Received 20 July 2007; revised 11 October 2007; accepted 29 October 2007 Abstract This study deals with the catalytic decomposition of N 2 O over noble metal based catalysts. The deposition of palladium on reducible supports such as LaCoO 3 leads to higher activity from temperature-programmed experiments in comparison with conventional supports such as alumina. Such a different catalytic behaviour cannot be completely explained by changes in the metal dispersion but also by the extent of the metal/support interaction. Interestingly, successive reductive (250 ◦ C in H 2 ) and oxidative thermal treatments in the reactant mixture at high temperature enhance the conversion of N 2 O particularly on perovskite support. Additional surface characterisations show a re-dispersion and the stabilisation of palladium species in unusual oxidation states which would originate a rate enhancement in the decomposition of N 2 O.  2007 Elsevier Inc. All rights reserved. Keywords: Greenhouse gas; Nitrous oxide; N 2 O catalytic decomposition; Perovskite; Noble metals; X-ray photoelectron spectroscopy; Surface reconstruction 1. Introduction Potential catalytic applications for perovskite materials ABO 3 have been previously reviewed [1]. Those materials can be attractive due to lower costs and flexibility of their compo- sition since they can tolerate significant substitution and non- stoichiometry. The main drawback is usually related to their low specific surface area despite significant developments in the preparation procedures for obtaining solids exhibiting ho- mogeneous compositions and high specific surface areas [2,3]. Also, those materials can be profitably used as support. The deposition of active phases, such as noble metals, may consid- erably enhance the overall activity due to cooperative effects between noble metals and the support. In this latter case, re- markable catalytic performances were obtained in the course of the reduction of NO by hydrogen in O 2 excess on 0.1 wt% Pt/ La 0.7 Sr 0.2 Ce 0.1 FeO 3 with significant rate and selectivity en- hancement towards the transformation of NO into nitrogen below 200 ◦ C [4,5]. It was found that this rate enhancement * Corresponding author. Fax: +33 3 20 43 65 61. E-mail address: pascal.granger@univ-lille1.fr (P. Granger). may depend on the extent of metal/support interaction, i.e. on the metal dispersion, with the creation of highly active sites at the metal/support interface. Recently, Uenishi et al. [6] in- vestigated the redox behaviour of palladium at start up in the perovskite-type structure LaFe 0.95 Pd 0.05 O 3 with Pd homoge- neously distributed in the solid according to a sol–gel route for the catalyst synthesis. They also reported an interesting cat- alytic behaviour due to their self-regenerative function under cycling conditions with typical successive reductive and ox- idative atmospheres. Under reductive conditions, isolated Pd species stabilised in the perovskite structure with unusual ox- idation state +III and/or +IV segregated out onto the surface from the B-site at relatively low temperature then the nano- sized Pd 0 particles re-oxidise under net oxidising conditions into Pd 2+ at 200–300 ◦ C. Successive formation of a solid so- lution occurs with an increase in temperature. Unfortunately, such reversible properties have been characterised essentially on highly-loaded Pd catalysts. Actually, a particular attention is paid towards the reduction of noble metal contents in the catalyst formulation or the development of alternative non- noble metal catalysts. According to those objectives, the use of sol–gel methods could not be a powerful procedure for op- timising the surface concentration of noble metals particularly 0021-9517/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2007.10.023