Synthesis of nanocrystalline molybdenum carbide materials and their characterization

Abstract

A convenient and practical method for the preparation of precursors to form molybdenum carbide materials using solutions of ammonium heptamolybdate and sucrose is presented. Depending on the temperature-programmed reaction protocol employed [i.e., low temperature and long times (523K for 24h, 598K for 24h and 673K for 72h) or high temperature and short times (1073K for 30min)], the C/Mo ratio of the precursors (i.e., 6.3, 3.6, 2.0, 1.0 and 0.6) and the presence or not of H2, it is possible to produce nanocrystalline molybdenum carbide materials with the cubic or hexagonal phases. The two prepared phases of molybdenum carbide showed activity for the hydrogenation of toluene at 423K to selectively produce methyl-cyclohexane. In the tested conditions, the hexagonal molybdenum carbide phase showed an initial higher activity but the deactivation of the catalyst was more pronounced than in the cubic molybdenum carbide catalyst.