Promoted methane activation on doped ceria via occupation of Pr(4f) states

Steam reforming of the methane stream obtained from biomass gasification is a potential route for sustainable syngas (CO + H2) and hydrogen production. The rate-limiting step for the reactions involved in methane steam reforming (MSR) is thought to be CH4 activation. Praseodymium-doped ceria-based catalysts, with easily reducible Pr cations and high oxygen storage capacity, could be attractive for MSR. In this work, we performed density functional theory (DFT) calculations to examine the activity of a low Pr-doped CeO2(1 1 1) surface for methane reforming. The results show a significant lowering (0.48 eV) of the energy barrier for methane activation via homolytic H3CH bond cleavage. This can be mainly explained by the easy occupation of Pr(4f) gap states by electrons transferred from adsorbed hydrogen species. The promotion of methane activation upon Pr doping of ceria was corroborated with methane temperature-programed reduction (CH4-TPR) experiments conducted in both Ce0.95Pr0.05O2 and CeO2 samples.