Influence of Passivation on the Reactivity of Unpromoted and Rb-Promoted Mo2C Nanoparticles for CO Hydrogenation

Unpromoted and Rb-promoted Mo 2 C nanoparticles (∼1 nm in size) were synthesized on α-alumina and used for CO hydrogenation. The reaction was performed in a fixed-bed reactor system operating at 573 K and 30 bar with a gas flow rate of 24,000 cm 3 g Mo –1 h –1 and H 2 /CO ratio of 1:1. Unpromoted Mo 2 C functioned as a Fischer–Tropsch catalyst producing mostly hydrocarbons at the standard conditions. Passivation of freshly synthesized Mo 2 C nanoparticles in 1% O 2 prior to CO hydrogenation decreased the Fischer–Tropsch activity of the catalyst by about 40% compared with a nonpassivated sample. Addition of Rb promoter to Mo 2 C shifted the selectivity of the catalyst by inhibiting the formation of hydrocarbons while preserving the formation of alcohols. The presence of Rb with Mo 2 C also reduced substantially the sensitivity of the catalyst to passivation by 1% O 2 compared with unpromoted Mo 2 C. The partial oxidation of the Mo 2 C nanoparticles by passivation and partial reduction by syngas was confirmed by Mo K edge X-ray absorption spectroscopy.