Boosted Oxygen Vacancies and Lattice Oxygen Reactivity by Cobalt-Oxygen-Manganese Asymmetric Sites in Cryptomelane for Photoactivated Abatement of Volatile Organic Compounds.

Abstract

Catalytic activity is influenced by the local coordination environment. Cryptomelane-type octahedral molecular sieve (OMS-2) catalysts doped via K⁺ substitution in the tunnels rarely exhibit photoactivation effects for volatile organic compound (VOC) abatement. We incorporated Co ions into the framework of OMS-2, not by replacing K⁺ in the tunnels, thereby facilitating the formation of Co-O-Mn asymmetric sites. Engineering Co-incorporated OMS-2 efficiently promotes the generation of oxygen vacancies, the facile release of lattice oxygen, the reducibility of the catalysts, and a low formation energy of oxygen vacancies, as evidenced by experimental and theoretical results. Thus, the Co-OMS-2 catalysts exhibit excellent thermocatalytic activity for the oxidation of benzene. More importantly, Co-O-Mn asymmetric sites induce a photoactivation effect. A particularly marked enhancement of photothermocatalytic activity is observed over the Co-OMS-2 catalysts. Photoactivation further weakens the Mn-O bonds, promoting the release of lattice oxygen and increasing the concentration of oxygen vacancies. Furthermore, light irradiation induces distinct low-temperature shifts in both the H₂ consumption and O₂ release peaks relative to those observed in the dark. The reactivity of lattice oxygen is enhanced by a photoactivation effect. In situ DRIFTS provides further evidence for the synergy of Co-O-Mn asymmetric sites and photoactivation. This work proposes an effective approach to enhance photothermocatalytic VOC degradation through the rational design of asymmetric bimetallic sites.