Synthesis and Hydrodeoxygenation Activity of Carbon Supported Molybdenum Carbide and Oxycarbide CatalystsOxycarbide

Carbothermal hydrogen reduction (CHR) of ammonium heptamolybdate impregnated activated charcoal (AC) yields a mixed Mo2C/MoOxCy catalyst. As the CHR temperature increases (from 600 to 800 degrees C) the Mo2C content increases. At 675 degrees C graphite networks are generated that attach to the beta-Mo2C particles, and at >= 700 degrees C agglomeration and sintering occur, all of which decrease catalyst activity. An optimal CHR temperature of similar to 650 degrees C is identified based on the catalyst activity for the hydrodeoxygenation (HDO) of 4-methylphenol (4-MP) at 350 degrees C and 4.3 MPa H-2 and the high selectivity for direct deoxygenation (DDO: to yield toluene) versus hydrogenation (HYD: to yield cyclohexane). The Mo2C/MoOxCy catalysts have higher DDO selectivity than MoP, MoO2, or MoS2 when operated at similar conditions. The apparent activation energies for DDO (125 kJ/mol) and HYD (89 kJ/mol) are invariant among the catalysts with varying Mo2C content, but the rate per g Mo correlates with the CO uptake. The fact that the kinetics are not strong functions of the CHR reduction temperature and hence relative content of Mo2C versus MoOxCy suggests that the active site of the catalyst is a result of O adsorption and/or exchange with the catalyst during reaction, and these active sites occur on both Mo2C and MoOxCy during the HDO reaction.