Reducibility of undoped and Cs-doped α-NiMoO 4 catalysts: Kinetic effects in the oxidative dehydrogenation of n-butane

Abstract

Temperature-programmed reduction (TPR) was used to study the reduction of undoped and doped α-NiMoO 4 with several Cs loads. The results contributed to clarify the mechanism of the nickel molybdate reduction by hydrogen. It was found that the reducibility of the catalysts, as inferred from the temperature of reduction onset, decreases with Cs load. The catalysts were tested for the oxidative dehydrogenation of n-butane and the activity followed the same trend recorded in the TPR experiments. It was possible to conclude that the catalytic activity is related to the reducibility of the sample while the selectivity is determined by the basicity of the surface. Kinetic studies over unpromoted and 3% Cs-promoted α-NiMoO 4 evidenced that Cs doping only affects the partial order with respect to butane, which increases for dehydrogenation products and decreases for CO and CO 2. The partial order with respect to oxygen is almost unaffected. The kinetic results were discussed based on the basicity and reducibility of the catalysts.