Sulfur-resistant and regenerable Ni/Co spinel-based catalysts for methane dry reforming

Oxide-supported metal catalysts were prepared by thermal impregnation of highly crystalline and highly-faceted starting spinels of the form (M 0.75 Mg 0.25 )Al 2 O 4 , where M = Ni, Co, or Cu and mixtures thereof. In situ reduction at 900 °C extracts the transition metals from the oxide, and the resulting catalysts contain metal crystallites with particle sizes of ~100 nm and exceedingly low dispersion, but show high activity for dry reforming of methane with turnover frequencies as large as 3.9 at 850 °C. The Ni 0.375 Cu 0.375 Mg 0.25 Al 2 O 4 catalyst shows stable methane conversion out to 12 hours on stream without performance-degrading coking. For the Ni/Co catalysts, the reforming activity and sulfur tolerance are both functions of the Ni/Co ratio and the synthesis temperature of the starting spinel, with Ni 0.375 Co 0.375 Mg 0.25 Al 2 O 4 synthesized at 1500 °C displaying fast reaction kinetics even in the presence of 20 ppm H 2 S. High reforming activity is attributed to long linear lengths of high-perfection facet edges and corners on the metal crystallites. Sulfur tolerance appears to be improved by a combination of the oxygen storage capacity of the defective spinel support and its faceting that provides additional reaction sites for activation of CO 2 . High-perfection Ni/Co spinel microcrystalline catalysts with extensive faceting show high turnover frequencies in methane dry reforming and good sulfur tolerance.