Kinetic studies of methane steam reforming on ceria-supported Pd

Steady-state, steam-reforming rates for methane were measured on model and high-surface-area, ceria-supported Pd catalysts and compared to rates on Pd/silica between 600 and 825 K. Specific rates on Pd/ceria were higher than those on Pd/silica by a factor of 10(5) and were higher even than rates reported in the literature for Ni catalysts. Model catalysts prepared with Pt or Rh on ceria also showed very high rates, essentially identical to rates for Pd/ceria. However, catalysts prepared by addition of Pd to ceria which had been calcined to high temperatures (>1175 K) before the addition of I'd were not active. Based on these results, we suggest that steam reforming on ceria-supported catalysts occurs through a bifunctional mechanism in which oxygen from ceria reacts with dissociated methane on the precious metal. High-temperature calcination of ceria significantly changes its reducibility, so that the reaction is not enhanced.