The Carburization of Transition Metal Molybdates (MxMoO4, M = Cu, Ni or Co) and the Generation of Highly Active Metal/Carbide Catalysts for CO2 Hydrogenation

A new approach has been tested for the preparation of metal/Mo2C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to study the reduction and carburization processes of Cu3(MoO4)2(OH)2, α-NiMoO4 and CoMoO4·nH2O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo2C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu2+, Ni2+ and Co2+ cations inside each molybdate. The synthesized Cu/Mo2C, Ni/Mo2C and Co/Mo2C catalysts were highly active for the hydrogenation of CO2. The metal/Mo2C systems exhibited large variations in the selectivity towards methanol, methane and CnH2n+2 (n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C–O bonds. Cu/Mo2C displayed a high selectivity for CO and methanol production. Ni/Mo2C and Co/Mo2C were the most active catalysts for the activation and full decomposition of CO2, showing high selectivity for the production of methane (Ni case) and CnH2n+2 (n > 2) hydrocarbons (Co case).