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

Abstract

The activity of nanoscale CeO 2 and doped CeO 2 (with Gd, Y, Nb, La, and Sm) toward the steam reforming of CH 4 in the presence of H 2S was investigated for later application as an in-stack reforming catalyst in a solid oxide fuel cell. Although H 2S is commonly known as a poisonous gas for metallic-based catalysts, it was found that the presence of appropriate H 2S content increases the reforming activity of these CeO 2-based catalysts. According to postreaction catalyst characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed desorption, H 2/H 2O + H 2S titration, and 18O/ 16O isotope exchange, it was revealed that this behavior is related to the formation of various Ce–O–S phases (Ce(SO 4) 2, Ce 2(SO 4) 3, and Ce 2O 2S) during the reaction. Our studies indicated that the formation of Ce(SO 4) 2 promotes the oxygen storage capacity, the lattice oxygen mobility, and eventually the reforming activity, whereas the formation of Ce 2O 2S oppositely reduces both properties and lowers the reforming rate.