Investigation of the promotion effect of metal oxides on the water-gas shift reaction activity over Pt-MO_x/CeO₂ catalysts for aqueous phase reforming

Aqueous phase reforming (APR) of methanol is a potential pathway for the effective hydrogen production under relatively mild conditions. The Pt/CeO₂ and a series of Pt-MO_x/CeO₂ (M = Fe, Cr, Mg, Mn) catalysts were prepared by sequential impregnation method and their APR reaction performances were studied. The catalyst properties including valence state of the promoters, the amount of oxygen vacancies, the metal distributions, the adsorption properties of CO and the acidity/basicity of catalysts were characterized and analyzed by XPS, XRD, TEM, CO-TPD, NH₃-TPD, CO₂-TPD, etc. It was found that the addition of MO_x weakened the Pt-CeO₂ interaction and promoted the generation of Pt^{δ +} species with lower valence state, which contribute to the C−H bond cleavage and facilitate methanol conversion. The highest hydrogen production (164.78 mmol) and relatively low CO and CH₄ selectivities were obtained over the Pt-MgO/CeO₂, while the highest CH₄ selectivity was obtained over the Pt-CrO_x/CeO₂ (2.21%). Over the Pt/CeO₂ and Pt-MO_x/CeO₂ (M = Fe, Cr, Mg, Mn) catalysts, CO₂/CH₄ ratio correlated well with the catalyst basicity, indicating that the basicity promotes the dissociation adsorption of H₂O as well as the water-gas shift (WGS) reaction activity and decreases the methanation activity.