Enhanced catalytic ozonation over reduced spinel CoMn2O4 for NOx removal: active site and mechanism analysis

In this paper, CO atmosphere reduced cobalt manganate (CoMn2O4/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NOx removal. CoMn2O4/CO shows higher activity (84%) than CoMn2O4/air (82%), Co3O4 (76%) and Mn2O3 (76%). Hydroxyl radicals (center dot OH) have been detected in the catalytic ozonation process, which has been confirmed to determine the catalytic performance of NOx removal. Compared to Co3O4 and Mn2O3, CoMn2O4 exhibits more surface hydroxyl groups and oxygen vacancies, both of which are critical for the center dot OH generation. More importantly, more oxygen vacancies are generated when the CoMn2O4 is calcined in the reduced atmosphere. These oxygen vacancies benefit the adsorption of sufficient H2O to yield active surface -OH on the catalyst surface, promoting the adsorption of O-3 on the surface -OH and thus the production of center dot OH radicals. A possible mechanism for the catalytic ozonation of NOx was proposed.