(638c) Catalytic Activity in Un-Doped and Rare Earth-Doped Strontium Cerates

Following Iwahara’s report in 1981 [1], acceptor-doped strontium cerates (SrCe_1-xM_xO_3-δ) have been studied as high-temperature protonic conductors (HTPCs). The substitution of Ce⁴⁺ with trivalent cations (M³⁺) leads to the formation of charge-compensating oxygen-ion vacancies (δ), which may react with gas-phase steam or oxygen leading to the incorporation of protonic or p-type electronic conductivity, respectively. Mixed protonic and electron-hole conductivity in Yb-doped SrCeO₃ enabled its application as both membrane and catalyst in an electrochemical reactor for the non-oxidative coupling of methane to form C₂-hydrocarbons [2]. However, SrCeO₃-based materials have not been studied from a purely catalytic standpoint, either as active catalysts or as supports. A significant body of work though has been carried out on oxygen-ion conducting oxides as catalysts [3]. Recent studies have also reported catalytic activity in the related class of BaCeO₃-based materials [4, 5].      

The objective of the present study was to document inherent catalytic activity in un-doped SrCeO₃, and its evolution upon doping with different trivalent, rare earth cations. Powders of the oxides were synthesized from the respective precursors using the conventional technique of solid-state reaction. Carbon monoxide oxidation and water-gas shift were selected for the investigation. The reactions were carried out between operating temperatures of 400 and 1000^oC. In addition to atmosphere and operating temperature, the choice of dopant has also been demonstrated to influence the electrochemical properties of SrCeO₃ [6]. Hence, any variation in catalytic activity observed with respect to the dopant would enable deductions regarding the dependence of reaction mechanism on the protonic and electronic conductivities in the oxides.

[1] H. Iwahara, T. Esaka, H. Uchida, N. Maeda, Solid State Ionics, 3/4 (1981) 359-363

[2] Y. Liu, X. Tan, K. Li, Ind. Eng. Chem. Res., 45 (2006) 3782-3790

[3] P. J. Gellings, H. J. M. Bouwmeester, Catal. Today, 12 (1992) 1-105

[4] A. Suresh, J. Basu, C. B. Carter, N. Sammes, B. A. Wilhite, J. Mater. Sci., 45 (2010) 3215-3227  

[5] F. W. B. Lopes, M. Arab, H. P. Macedo, C. P. de Souza, J. F. de Souza, J. R. Gavarri, Powder Technol. 219 (2012) 186-192

[6] X. Qi, Y. S. Lin, Solid State Ionics, 130 (2000) 149-156