Kinetics of CO hydrogenation over Ni-Mo/Al2O3 catalysts with and without K promotion

The effect of K promotion on the CO hydrogenation activity and C-2-C-4 hydrocarbons selectivity of the 15 wt % Ni-10 wt % Mo/Al2O3 catalyst was investigated in the 498-548 K range using unpromoted and 1-3 wt % K-promoted samples. CO2 methanation tests at 523 K were used as a probe to confirm activity trends. Intrinsic kinetic data were obtained in the initial rate region on both unpromoted and 1 wt % K-promoted Ni-Mo catalysts. K promotion of the bimetallic Ni-Mo catalyst decreases both the activity and the specific activity of the Ni sites while increasing the C-2-C-3 olefin-to-paraffin ratio. The surface carbide mechanism with dissociative adsorption of hydrogen as the rate-limiting step gives the most plausible kinetic model among the models tested for both Ni-Mo and Ni-Mo-K catalysts.