Low temperature synthesis of cubic molybdenum carbide catalysts via pressure induced crystallographic orientation of MoO 3 precursor

Abstract

Direct conversion of MoO 3 to cubic molybdenum carbides by temperature-programmed reaction (TPR) with a reacting gas mixture of H 2/toluene has been studied at 673 K. We report for the first time that the MoO 3 precursor is able to produce a cubic molybdenum carbide phase which seems to have molybdenum vacancies in the cubic structure and such vacancies affect the experimental intensity ratio of the signals (1 1 1) and (2 0 0) of the X-ray powder diffraction patterns of the prepared material, this observation is backed up by simulation of the X-ray powder diffraction patterns of the defective structure and also because of the lower unit cell size of the material prepared (0.4097 ± 0.0005 nm). It is possible to increase the degree of conversion of the MoO 3 to the cubic carbide phase by pressing at 379 bar the original precursor inducing preferred orientations of the crystallographic planes (0 2 0), (0 4 0) and (0 6 0) which facilitate the carburization of the oxide by precluding the formation of MoO 2 structures. Molybdenum carbides produced were found to be active for the low temperature hydrogenation of toluene.