ZIF-67-derived hierarchical hollow Co3O4@CoMn2O4 nanocages for efficient catalytic oxidation of formaldehyde at low temperature

Abstract

Low-temperature HCHO oxidation over transition-metal oxide catalysts is still a ‘‘hot potato”. Herein, hierarchical hollow Co3O4@CoMn2O4 nanocages (Co3O4@CoMn2O4-NCs) were designed and prepared by using ZIF-67 nanocubes (ZIF-67-NCs) engaged self-templated method. Compared with single-compositional Co3O4-NCs and solid CoMn2O4-NPs, the as-prepared Co3O4@CoMn2O4-NCs exhibited much superb HCHO oxidation performance, achieving 90% HCHO conversion at 107°C. The characterization results manifested that the special hierarchical hollow structure of Co3O4@CoMn2O4-NCs facilitated the exposure of active sites and the generation of oxygen vacancies, thereby endowing them with higher O2 activation ability and richer reactive oxygen species (ROS). In-situ DRIFTS results suggested that richer reactive oxygen species (ROS) of hierarchical hollow Co3O4@CoMn2O4-NCs boosted the oxidation of formate species, which was the rate-determining step for HCHO oxidation. Meanwhile, the interaction of cobalt and manganese species of Co3O4@CoMn2O4-NCs enhanced their low-temperature reducibility. Eventually, benefiting from the dual merits of structure and composition, Co3O4@CoMn2O4-NCs manifested much better HCHO oxidation performance. This work demonstrates that metal-organic frameworks (MOFs)-derived mixed-metal oxides with hierarchical hollow structure possess promising application perspective for low-temperature HCHO oxidation.