(532au) Understanding of the Reaction Mechanism and Insight into the Multi-Step Elementary Reaction in Glycerol Oxidation Reaction in Ni, Nico, and Co Hydroxides

Although the redox centers of transition metal oxides and hydroxides are generally regarded to be the metal sites, it has been shown lately that proton and oxygen in the hydroxides play a significant role in catalytic reactions, determining their reactivity. Herein, we demonstrate the influence of proton and oxygen anion (de)intercalation processes on the elementary steps using the glycerol electroxodation reaction (GOR) as a model reaction. Density functional theory study was used to reveal the most probable structure of (001) surface of Ni, NiCo, and Co (oxy)hydroxides and the reaction mechanism of glycerol oxidation through lattice oxygen and hydrogen. Furthermore, the reaction mechanism study reveals that the rate-determining step is the second C-C bond cleavage to form formic acid from glycolic acid. As a result, NiCo (oxy)hydroxide exhibits the highest catalytic activity among the hydroxide catalysts. The density of state and crystal orbital hamilton population caculations indicate that the oxygen vacancies formed in NiCo hydroxide during glycerol oxidation reaction increase d-band filling on Co sites, thereby facilitating charge transfer from the catalyst surface to the cleaved molecules during the second C-C bond cleavage. These results further confirmed experimentally that among the activities of Ni, NiCo, and Co hydroxides in the glycerol oxidation reaction, NiCo has the highest activity and selectivity toward the production of formate. Our study will provide a better understanding of the glycerol oxidation reaction mechanism and practical guidelines for optimizing catalytic performance by highlighting the critical reaction step.