Xiaonan Xu,Nana Luo,Wan-Hui Wang,Ming Bao,Jiasheng Wang
Fatty acid hydrogenation is an important method for the production of fatty alcohols. The combination of Ni and Mo has been reported to be an effective and low-cost catalyst. However, the effect of Mo doping has yet to be fully understood. Here Ni-MoOx/TiO2 catalysts were prepared via simple impregnation. and the enhancement effects of Mo doping were comprehensively revealed. First, MoOx can attract electrons from Ni, reduce the electron density of Ni to improve the intrinsic activity of Ni, and form a Niδ+-(MoOx)δ− heterojunction to induce H2 heterolytic cleavage to active hydrogen ions. Second, the reduction of MoOx generates oxygen vacancies, which can absorb C═O of the fatty acid and facilitate the reaction progression. Third, a Ni1–xMox solid solution can be formed, which can increase the hydrogen adsorption quantity and accelerate the reaction rate. Finally, the bond strength of Mo–O is found to be the most optimum that can absorb the fatty acids while releasing the alcohols so as to recover the oxygen vacancies and avoid overhydrogenation. Therefore, high activity and selectivity for the hydrogenation of carboxylic acid substrates to alcohols can be obtained. Under significantly milder conditions (155 °C, 3 MPa H2) the catalyst provided a 98% yield of lauryl alcohol from lauric acid hydrogenation with a low activation energy of 40.1 kJ/mol. This work could provide an insightful understanding about the effects of Mo doping to Ni on catalyzing hydrogenation reactions.
Selective hydrodeoxygenation is the central challenge in converting bio-derived fatty acids into fatty alcohols under mild conditions. Herein, an effective and highly selective carbon-supported NiMo catalyst (NiMo@C) was developed by the thermolysis Ni-based metal–organic frameworks (MOF) impregnated Mo species. At a low temperature of 160 °C, the stearic acid can be efficiently converted into corresponding stearic alcohols over the NiMo@C with about 97% selectivity at 100% reactant conversion, which is superior to the most reported catalysts containing noble catalysts. The excellent catalytic performance of NiMo@C catalyst was mainly attributed to the ordered arrangement of Ni in the MOF and the uniform loading of molybdenum salt, which leads to an ideal distribution of Ni and Mo after pyrolysis of the MOF. The carbon support also prevents the aggregation of metal particles, which promotes the dissociation of hydrogen and enhances the synergy between Ni and Mo sites. More importantly, the synthesized NiMo@C catalyst showed excellent reusability with no loss of activity after 15 consecutive runs due to the stability of the catalyst structure. This provides a useful and simple method for synthesizing highly efficiency and stable NiMo@C bimetallic catalysts, which can facilely and selectively hydrogenate the bio-derived fatty acids to corresponding alcohols under mild conditions.
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