Ni-Bi-Mo/Al2O3 Metal-Oxide Catalysts for CO2-Mediated Oxidative Dehydrogenation of n-Butane into Buta-1,3-diene: Mutual Influence of Components

Ni-Bi-Mo/Al₂O₃ metal-oxide systems are prepared by co-impregnation of γ-Al₂O₃ with water-soluble salts of Ni, Bi, and Mo and are investigated as catalysts for CO₂-mediated oxidative dehydrogenation of n-butane into buta-1,3-diene. The structure, morphology, reducibility, re-oxidizing ability, and acid-base properties of the metal-oxide systems have been studied using XRD, SEM-EDX, low-temperature (-196℃) N₂ ad(de)sorption, Raman spectroscopy, TPR, TPRO, and TPD-NH₃/CO₂ techniques. TPSR-MS measurements with pre-adsorbed n-butane and butenes have been conducted to assess the possibilities of the individual stages of n-butane dehydrogenation on the sample’s surface. The adsorption and activation of alkanes on the surface are proposed to be the rate-determining steps of the process. Lewis acid-base pair sites of weak and medium strength, formed with the participation of nickel and molybdenum, are suggested to promote the dehydrogenation reaction. The dehydrogenation of n-butane into mono- and di-olefins is significantly enhanced by the active sites formed with the participation of nickel. The addition of molybdenum to the catalyst composition results in the formation of active oxygen-containing sites that can abstract hydrogen from the alkene molecule. The higher rate of buta-1,3-diene formation achieved on the Ni-Mo/Al₂O₃ catalyst results from the synergistic effect of nickel- and molybdenum-containing active sites.