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

Abstract

In this paper, CO atmosphere reduced cobalt manganate (CoMn₂O₄/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NO_x removal. CoMn₂O₄/CO shows higher activity (84%) than CoMn₂O₄/air (82%), Co₃O₄ (76%) and Mn₂O₃ (76%). Hydroxyl radicals (·OH) have been detected in the catalytic ozonation process, which has been confirmed to determine the catalytic performance of NO_x removal. Compared to Co₃O₄ and Mn₂O₃, CoMn₂O₄ exhibits more surface hydroxyl groups and oxygen vacancies, both of which are critical for the ·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 O₃ on the surface –OH and thus the production of ·OH radicals. A possible mechanism for the catalytic ozonation of NO_x was proposed.