Preparation and Characterisation of Bimetallic Cobalt and Molybdenum Carbides

A series of mixed metal oxides CoxMo1−xOy have been prepared by calcination of a mechanical mixture of Co(NO3)2 and molybdenum oxide. They were carburised by temperature-programmed reactions using a C2H6/H2 gas mixture. The carburisation process was monitored with GC-MS. The catalytic performance of the resulting mixed metal carbide catalysts was evaluated for hydrodenitrogenation using pyridine as the model reactant. The oxide precursors and the catalysts have been characterized by X-ray diffraction (XRD), laser Raman spectrum, infrared spectrum, 13C solid state NMR, and scanning electron microscope (SEM). The data show that addition of cobalt to molybdenum oxide leads to both CoMoO4 and a new complex oxide phase. During the carburisation reaction, some oxides decompose and the initial cobalt oxide is first reduced to the metallic state, and this then catalyses the hydrogenolysis of ethane into methane, which further carburises molybdenum oxide. The presence of the cobalt oxide lowers the temperature required for the carburisation of pure molybdenum oxide. The Co0.2Mo0.8Cx system is a homogeneous bimetallic carbide phase, but the Co0.4Mo0.6Cx and Co0.5Mo0.5Cx systems contain impurity phases of Co metal, Co3C, and Mo2C. NMR spectra reveal that the face-centred cubic (fcc) carbide (MoC1−x) is the main phase present in the bimetallic carbide. The shape of the carbide particles become more regular as the Co content increases. Catalytic stability under hydrodenitrogenation conditions increases from Co0.2Mo0.8Cx to Co0.4Mo0.6Cx. However, when the Co content is increased to 0.5, the lifetime of the catalyst for pyridine HDN is greatly decreased and the surface symmetry of the carbide changes during the reaction.