Low temperature synthesis of cubic molybdenum carbide catalysts via pressure induced crystallographic orientation of MoO3 precursor
Direct conversion of MoO3 to cubic molybdenum carbides by temperature-programmed reaction (TPR) with a reacting gas mixture of H2/toluene has been studied at 673 K. We report for the first time that the MoO3 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 MoO3 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 MoO2 structures. Molybdenum carbides produced were found to be active for the low temperature hydrogenation of toluene.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (256 K)Download as PowerPoint slideHighlights► Conversion of MoO3 to α-Mo2C at 673 K was achieved. ► Preferred orientation of MoO3 facilitates the carburization. ► MoO2 formation is disfavored when MoO3 is preferentially oriented by pressure. ► XRD simulations suggests the formation of Mo vacancies in the α-Mo2C. ► α-Mo2C is active for the low temperature hydrogenation of toluene.
Journal: Applied Catalysis A: General - Volume 400, Issues 1–2, 30 June 2011, Pages 221–229