Role and advantages of H<inf>2</inf>S in catalytic steam reforming over nanoscale CeO<inf>2</inf>-based catalysts

Abstract

The activity of nanoscale CeO2and doped CeO2(with Gd, Y, Nb, La, and Sm) toward the steam reforming of CH4in the presence of H2S was investigated for later application as an in-stack reforming catalyst in a solid oxide fuel cell. Although H2S is commonly known as a poisonous gas for metallic-based catalysts, it was found that the presence of appropriate H2S content increases the reforming activity of these CeO2-based catalysts. According to postreaction catalyst characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed desorption, H2/H2O + H2S titration, and18O/16O isotope exchange, it was revealed that this behavior is related to the formation of various Ce-O-S phases (Ce(SO4)2, Ce2(SO4)3, and Ce2O2S) during the reaction. Our studies indicated that the formation of Ce(SO4)2promotes the oxygen storage capacity, the lattice oxygen mobility, and eventually the reforming activity, whereas the formation of Ce2O2S oppositely reduces both properties and lowers the reforming rate. © 2010 Elsevier Inc. All rights reserved.