Role and advantages of H2S in catalytic steam reforming over nanoscale CeO2-based catalysts

The activity of nanoscale CeO2 and doped CeO2 (with Gd, Y, Nb, La, and Sm) toward the steam reforming of CH4 in 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, and 18O/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)2 promotes 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.