Oxygen storage capacity of La 1x A 0 x BO 3 perovskites (with A 0 = Sr, Ce; B = Co, Mn)—relation with catalytic activity in the CH 4 oxidation reaction S. Royer a, * , H. Alamdari b , D. Duprez c , S. Kaliaguine a a Department of Chemical Engineering, Laval University, Sainte Foy, Que., Canada G1K 7P4 b Nanox Inc., 4975 rue Rideau, Local 100, Que., Canada G2E 5H5 c LACCO – UMR CNRS 6503, Universite ´ de Poitiers, F-86022 Poitiers Cedex, France Received 9 November 2004; received in revised form 20 December 2004; accepted 21 December 2004 Available online 27 January 2005 Abstract The aim of this work was to study the effect of cation-substitution on the reducibility of the perovskite, as well as the effect on the catalytic activity for the CH 4 oxidation reaction. Six perovskites (LaCoO 3 , LaMnO 3 , La 1x Sr x MnO 3 (x = 0.2, 0.4), and La 1x Ce x MnO 3 (x = 0.05, 0.1)) were synthesized by reactive grinding. The reducibility of the perovskite was studied by means of the oxygen storage capacity (OSC) measurement. OSC was performed at different temperatures on LaCoO 3 and LaMnO 3 , in order to elucidate the different mechanisms of reduction involved at each temperature. The substituted samples showed that reduction profile is modified at high-substitution degrees; however, no differences were observed on the OSC values (amount of most active oxygen, calculated after one pulse of CO) between the pure lanthanum sample and the substituted ones. Tested in the CH 4 oxidation reaction, the LaCoO 3 sample was found to present a little higher activity than LaMnO 3 , even if the cobalt- based sample presented a smaller specific surface area. Moreover, all the substituted samples presented very slightly higher activities than the pure LaMnO 3 solid. Because of the supposed redox oxidation mechanism (Mars-Van-Krevelen), this agrees well with the OSC results obtained for the reducibility of the manganese on these samples, by which it was observed that substitution does not clearly affect the immediate reduction of the manganese. # 2004 Published by Elsevier B.V. Keywords: Perovskite; OSC measurement; Catalytic activity in methane oxidation; Sr- and Ce-substitution effect 1. Introduction The perovskites (general formula ABO 3 ) were exten- sively studied as catalysts during the past 30 years [1–5], since some of these solids were found to compete with supported noble metals in oxidation reactions [2,6]. Generally, perovskite formation can be achieved when the tolerance factor, t t ¼ r A þr O ffiffi 2 p ðr B þr O Þ   , is in the range 0.75–1 and the A and B cations are stable in octahedral and dodecahedral environments, respectively. Under these considerations, it is possible to obtain perovskites with a wide range of different compositions. Moreover, these solids support partial substitutions and compounds with formula A 1x A 0 x B 1  y B 0 y O 3 can be obtained. However, only a minor part of the perovskite mixed oxides presents an interesting activity in oxidation reactions. Among the possible compositions, the cobalt- and manganese-based perovskites were found to be the most active. Then, systems with lanthanum in A position, and Co or Mn in position B, were the most studied for catalytic oxidation [7–10]. It was however observed that substituting La for some other rare earths (from Pr to Gd) yields a high activity [11,12]. Much more efforts were also made in order to increase activity by partial substitution of the A cation by cations of different valencies, like Sr 2+ and Ce 4+ [13–18]. These substitutions www.elsevier.com/locate/apcatb Applied Catalysis B: Environmental 58 (2005) 273–288 * Corresponding author. Tel.: +1 418 656 2708; fax: +1 418 656 3810. E-mail address: gchsro@hermes.ulaval.ca (S. Royer). 0926-3373/$ – see front matter # 2004 Published by Elsevier B.V. doi:10.1016/j.apcatb.2004.12.010