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

Abstract

Unpromoted and Rb-promoted Mo2C 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 cm3 gMo–1 h–1 and H2/CO ratio of 1:1. Unpromoted Mo2C functioned as a Fischer–Tropsch catalyst producing mostly hydrocarbons at the standard conditions. Passivation of freshly synthesized Mo2C nanoparticles in 1% O2 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 Mo2C shifted the selectivity of the catalyst by inhibiting the formation of hydrocarbons while preserving the formation of alcohols. The presence of Rb with Mo2C also reduced substantially the sensitivity of the catalyst to passivation by 1% O2 compared with unpromoted Mo2C. The partial oxidation of the Mo2C nanoparticles by passivation and partial reduction by syngas was confirmed by Mo K edge X-ray ...