Abstract
Steam reforming of methanol, CH3OH + H2O → 3H2 + CO2, was carried out over Cu/ZnO and various supported group 8–10 metal catalysts. Over Cu/ZnO catalysts prepared by a coprecipitation method, the steam reforming of methanol occurs with high selectivity regardless of composition of the catalyst and structure of the precursor (aurichalcite, malachite, hydrozincite or their mixture). The Cu/ZnO catalysts prepared from the aurichalcite precursor are more active than those prepared from other precursors.
By contrast, over supported group 8–10 metal catalysts, such as supported Pd, Pt, Co, Ni, Rh, Ir and Ru catalysts, hydrogen and carbon monoxide are predominantly produced by decomposition of methanol, CH3OH → 2H2 + CO. The selectivity for the steam reforming is lower than those over Cu/ZnO catalysts. However, the selectivity for the steam reforming is markedly improved upon the previous reduction of Pd/ZnO, Pd/Ga2O3, and Pd/In2O3 at higher temperatures. Upon addition of Zn to the supported Pd catalysts, the selectivity for the steam reforming and the rate of hydrogen formation are markedly increased. Over Zn modified Pd/CeO2 catalyst, the selectivity attains to 99.0%, being comparable to Cu/ZnO catalysts. Combined results with temperature programmed reduction, XRD, XPS and AES measurements revealed that PdZn alloy was formed by the previous reduction of Pd/ZnO or Zn modified Pd/CeO2 catalyst. Catalytic functions of Pd are greatly modified upon the formation of PdZn alloys.
