Structural and Kinetic Insights into Interfacial Site Effects in NiMo-Catalyzed Hydrodeoxygenation of Palmitic Acid

Second-generation biodiesel is the dominant biomass-derived liquid fuel produced from nonedible natural or waste oils and fatty acids through selective oxygen removal. Here, we developed a highly selective sulfur-free NiMo/TiO2 catalyst by disentangling electronic and geometric effects to produce second-generation biodiesel via the hydrodeoxygenation of palmitic acid─one of the most common fatty acids in these feedstocks. An unprecedented hexadecane yield of 96.0% (on a mole basis) was achieved over the Ni1Mo1/TiO2 catalyst (with a Ni:Mo ratio of ∼1:1) at 300 °C and 3 MPa H2. Kinetic studies reveal that the competition between hydrodeoxygenation (C–O scission) and decarbonylation (C–C scission) of the intermediate hexadecanol is key to optimizing selectivity. Furthermore, Mo incorporation markedly lowers the apparent activation energy of hydrodeoxygenation─especially in the Ni1Mo1/TiO2 catalyst, which has the lowest Ni–Ni coordination number. Combined with catalyst characterization, these findings elucidate a Mo-induced “Ni coordination environment”-directed reaction pathway: the superb hydrodeoxygenation activity and selectivity of Ni1Mo1/TiO2 stem from its abundant NiMo interfacial sites, where Mo-induced oxygen vacancies synergize with adjacent Ni sites to facilitate the adsorption of O-containing groups and subsequent C–O bond cleavage.