Oxidation of ethane on high specific surface SmCoO 3 and PrCoO 3 perovskites M. Alifanti a , G. Bueno b , V. Parvulescu c , V.I. Parvulescu a , V. Corte ´ s Corbera ´n b, * a University of Bucharest, Department of Chemical Technology and Catalysis, B-dul Regina Elisabeta 4-12, Bucharest 030016, Romania b Institute of Catalysis and Petroleumchemistry, CSIC, C. Marie Curie 2, 28049 Madrid, Spain c Romanian Academy, ‘‘I. G. Murgulescu’’ Institute of Physical Chemistry, Splaiul Independentei 202B, Bucharest 060023, Romania 1. Introduction Perovskite-type oxides are materials of permanent interest due to their tunable oxidative features as, by a proper choice of the cations and a suitable synthesis method, its oxygen content and availability may be varied, while the cubic perovskite structure is preserved. They are quite active in catalytic oxi- dation, but its use often faces the problem of relatively low surface areas, depending of the preparation method [1]. Among the number of methods reported for the synthesis of perovskites, the choice of a particular one depends mostly on the expected use for these oxides. Application of perovskites in the field of catalysis requires solids with well-developed surface area and porous system. In special, the use of rare-earth-based perovskites for catalytic combustion purposes encounters the difficulty of obtaining high surface area materials, as usually high calcination temperatures are needed for completing the formation of the perovskite structure. Hence, the preparative route plays a critical role on the physical and chemical properties of the reaction products, controlling the structure, morphology, grain size and the surface area of the obtained materials. Several alternative methods have been reported in the literature to obtain high surface area oxides at relatively low temperatures, many of them using organic compounds and precursors which are decomposed during the calcination. They include the use of precursors prepared via sol–gel [2] spray drying [3], freeze drying [4], heteronuclear complexes [4], combustion of solutions [5] or polymers [6], decomposition of citratres [7] or oxalates [8], among others. In the sol–gel method, inorganic polymers generated in a first step are further decomposed to give either simple metal oxides, mixed oxides or solid solutions of high homogeneity. This method allows a strict control of composition; at the same time a calcination temperature lower than for the other methods is needed to obtain the desired structure, thus avoiding the sintering phenomena [2]. Sol–gel procedures guarantee stoichiometry and homogeneity of cation distribution. Different complexation agents (oxalic acid [9,10], glycine [11], citric acid [12–16], etc.) have been reported for sol–gel preparation of perovskites. Ethane is the second most abundant component of natural gas (1.8–5 mol%), and one of the less reactive alkanes. Its main petro- chemical use is its conversion to ethylene via steam cracking, an energy-intensive process that gives a complex mixture of hydro- carbons. However, main uses of ethylene require a high purity raw material. The oxidative dehydrogenation (ODH) of ethane could to be a more economic alternative route, but a process for the direct Catalysis Today 143 (2009) 309–314 ARTICLE INFO Article history: Available online 26 March 2009 Keywords: Perovskites Ethane oxidation Oxidation kinetics Praseodymium cobalt oxide Samarium cobalt oxide ABSTRACT An adapted sol–gel method allowed synthesizing SmCoO 3 and PrCoO 3 oxides with high specific surface (ca. 28 m 2 g 1 ) and a relatively clean perovskite phase at 600 8C, a temperature much lower than the one required in ceramic methods. The perovskites were investigated as catalysts for the oxidation of ethane in the temperature range 300–400 8C. Both catalysts were very active: ethane was activated already at 300 8C, i.e., 100 8C below the temperatures previously reported for perovskites. The main product was CO 2 on both catalysts, but on PrCoO 3 oxidehydrogenation (ODH) to ethylene was observed already at 300 8C, with the low selectivity. Even so, this was quite unusual for simple perovskites, and for such a low temperature. TPR data showed that praseodymium decreases the reducibility of Co 3+ in the perovskite, what could explain the observed ODH, and suggest it proceeds via a Mars–van Krevelen mechanism. Kinetic study showed a similar apparent activation energy for both catalysts (ca. 80 kJ/mol), but a difference in the nature of the participating oxygen species: while on PrCoO 3 both adsorbed and lattice species contribute to the reaction, on SmCoO 3 contribution of adsorbed species is practically negligible, due to its very high oxygen lability. The results show that these simple perovskites may be promising catalysts for ethane oxidation at relatively low temperatures. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +34 915854783; fax: +34 915854760. E-mail address: vcortes@icp.csic.es (V. Corte ´ s Corbera ´ n). Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod 0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2009.02.026