Revealing\nthe Effects of Mo Doping to Ni on Catalyzing\nHydrogenation of Fatty Acids to Fatty Alcohols

Fatty\nacid hydrogenation is an important method for the production\nof fatty alcohols. The combination of Ni and Mo has been reported\nto be an effective and low-cost catalyst. However, the effect of Mo\ndoping has yet to be fully understood. Here Ni-MoO<sub><i>x</i></sub>/TiO<sub>2</sub> catalysts were prepared via simple impregnation.\nand the enhancement effects of Mo doping were comprehensively revealed.\nFirst, MoO<sub><i>x</i></sub> can attract electrons from\nNi, reduce the electron density of Ni to improve the intrinsic activity\nof Ni, and form a Ni<sup>δ+</sup>-(MoO<sub><i>x</i></sub>)<sup>δ−</sup> heterojunction to induce H<sub>2</sub> heterolytic cleavage to active hydrogen ions. Second, the\nreduction of MoO<sub><i>x</i></sub> generates oxygen vacancies,\nwhich can absorb CO of the fatty acid and facilitate the reaction\nprogression. Third, a Ni<sub>1–<i>x</i></sub>Mo<sub><i>x</i></sub> solid solution can be formed, which can\nincrease the hydrogen adsorption quantity and accelerate the reaction\nrate. Finally, the bond strength of Mo–O is found to be the\nmost optimum that can absorb the fatty acids while releasing the alcohols\nso as to recover the oxygen vacancies and avoid overhydrogenation.\nTherefore, high activity and selectivity for the hydrogenation of\ncarboxylic acid substrates to alcohols can be obtained. Under significantly\nmilder conditions (155 °C, 3 MPa H<sub>2</sub>) the catalyst\nprovided a 98% yield of lauryl alcohol from lauric acid hydrogenation\nwith a low activation energy of 40.1 kJ/mol. This work could provide\nan insightful understanding about the effects of Mo doping to Ni on\ncatalyzing hydrogenation reactions.