New Insights into the Kinetics of Structural Transformation and Hydrogenation Activity of Nano-crystalline Molybdenum Carbide

Abstract

Transformation of cubic molybdenum carbide into hexagonal β-Mo2C was found to follow the Avrami–Erofeev kinetic model with an n parameter of four indicating a slow nucleation step with a polyhedral growth of the transformed phase. The transformation not only occurred at 773 K under atmospheric H2 pressure, but also imperceptibly occurred under the employed hydrogenation reaction conditions (413 K and 70 psig of H2 pressure) when using toluene or 1-octene as reactants, not affecting the activity under the steady state. Our computational studies also revealed that both crystal structures share common atomic cluster arrangements with small differences in angles and interatomic distances. The transformation was triggered by local distortions which favored shorter and more homogeneous interatomic distances as present in the hexagonal phase. The prepared molybdenum carbide materials were selective to the hydrogenation of 1-octene under the mild hydrogenation conditions tested. Hydrogenation of 1-octene was preferential in a 50 wt% mixture of toluene and 1-octene with minimal toluene hydrogenation under the tested conditions.