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

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• 作者：Haiyan Wang ; Shida Liu ; Kevin J. Smith
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：July 21, 2016
• 年：2016
• 卷：30
• 期：7
• 页码：6039-6049
• 全文大小：634K
• 年卷期：0
• ISSN：1520-5029

文摘

Carbothermal hydrogen reduction (CHR) of ammonium heptamolybdate impregnated activated charcoal (AC) yields a mixed Mo₂C/MoO_xC_y catalyst. As the CHR temperature increases (from 600 to 800 °C) the Mo₂C content increases. At 675 °C graphite networks are generated that attach to the β-Mo₂C particles, and at ≥700 °C agglomeration and sintering occur, all of which decrease catalyst activity. An optimal CHR temperature of ∼650 °C is identified based on the catalyst activity for the hydrodeoxygenation (HDO) of 4-methylphenol (4-MP) at 350 °C and 4.3 MPa H₂ and the high selectivity for direct deoxygenation (DDO: to yield toluene) versus hydrogenation (HYD: to yield cyclohexane). The Mo₂C/MoO_xC_y 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 MoO_xC_y 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 MoO_xC_y during the HDO reaction.