Supported Molybdenum Carbide and Nitride Catalysts for Carbon Dioxide Hydrogenation
Marwa Abou Hamdan, Abdallah Nassereddine, Ruben Checa, Mohamad Jahjah, Catherine Pinel, L. Piccolo, Noémie Perret
Abstract
Catalysts based on molybdenum carbide or nitride nanoparticles (2-5 nm) supported on titania were prepared by wet-impregnation followed by a thermal treatment under alkane (methane or ethane)/hydrogen or nitrogen/hydrogen mixture, respectively. The samples were characterized by elemental analysis, volumetric adsorption of nitrogen, X-ray diffraction, and transmission electron microscopy. They were evaluated for the hydrogenation of CO2 in the 2-3 MPa and 200-300 °C ranges with a gas-phase flow fixed bed reactor. CO, methane, methanol, and ethane (in fraction-decreasing order) were formed on carbides, whereas CO, methanol, and methane were formed on nitrides. The carbide and nitride phase stoichiometries were tuned by varying the preparation conditions, leading to C/Mo and N/Mo atomic ratios of 0.2-1.8 and 0.5-0.7, respectively. The carbide activity increased for lower carburizing alkane concentration and temperature, i.e. lower C/Mo ratio. Enhanced carbide performances were obtained with pure anatase titania as compared to P25 (anatase/rutile) titania or zirconia as support, with a methanol selectivity up to 11% at 250 °C. The nitride catalysts appeared less active but reached a methanol selectivity of 16% at 250 °C.