Preparation and characterisation of bimetallic cobalt and molybdenum carbides

A series of mixed metal oxides CoMo1-xOy have been prepared by calcination of a mechanical mixture of Co(NO3)(2) and molybdenum oxide. They were carbu rised by temperature-programmed reactions using a C2H6/H-2 gas mixture. The carburisation process was monitored with GC-MS. The catalytic performance of the resulting mixed metal carbide catalysts was evaluated for hydrodenit rogenation using pyridine as the model reactant. The oxide precursors and t he catalysts have been characterized by X-ray diffraction (XRD), laser Rama n spectrum, infrared spectrum, C-13 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 carburisati on reaction, some oxides decompose and the initial cobalt oxide is first re duced to the metallic state, and this then catalyses the hydrogenolysis of ethane into methane, which further carburises molybdenum oxide. The presenc e of the cobalt oxide lowers the temperature required for the carburisation of pure molybdenum oxide. The Co0.2Mo0.8Cx system is a homogeneous bimetal lic carbide phase, but the Co0.4Mo0.6Cx and Co0.5Mo0.5Cx systems contain im purity 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 bimet allic carbide. The shape of the carbide particles become more regular as th e Co content increases. Catalytic stability under hydrodenitrogenation cond itions increases from Co0.2Mo0.8Cx, to Co0.4Mo0.6Cx. However, when the Co c ontent is increased to 0.5, the lifetime of the catalyst for pyridine HDN i s greatly decreased and the surface symmetry of the carbide changes during the reaction. (C) 2001 Academic Press.