Catalytic oxidation of benzyl alcohol over MnO2: Structure-activity description and reaction mechanism

Activity evaluation of metal oxide catalysts with different crystal structures has been an important prerequisite for industrial applications. This work systematically elucidates the structure-activity relationship of α-, β-, γ- and δ-MnO2 catalysts toward the selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Exposed surfaces of MnO2 are evaluated by a combined theoretical and experimental investigation. On this basis, a catalytic activity descriptor is established considering the surface energies, formation energies of oxygen vacancies (OVs), O2 adsorption energies, and areal densities of OVs and unsaturated Mn. Inspired by this, we fabricate β-MnO2 with a high surface area and it delivers the highest BA conversion among all MnO2. Furthermore, a developed Mars-van Krevelen (MvK) mechanism is proposed to describe the BA oxidation process on the β-MnO2 (1 1 0) surface. The research paradigm opens a door to the rational design of metal oxide catalysts.