Effects of structural differences between γ-MnO2 and γ-Mn2O3 catalysts on CO oxidation: different active oxygen species and carbonate species using operando TPR-DRIFTS-MS

Abstract

Reactive oxygen species and carbonates on the catalyst surface are key species in the process of CO oxidation. However, the essential relationship between reactive oxygen species production, carbonate desorption and catalytic activity under real conditions remains unclear. In this paper, γ-MnO₂ and γ-Mn₂O₃ catalysts are prepared by an aerosol method, and operando TPR-DRIFTS-MS is used as the main characterization method. γ-MnO₂ has the best CO oxidation activity (90 °C) and redox capacity due to its surface defects (oxygen vacancies) and more surface oxygen adsorption. Operando TPR-DRIFTS-MS results show that MnO plays a major role at low temperature. MnO also facilitates the formation of v_as(CO₃²⁻) or v_s(OCO), and decomposition at low temperatures is a decisive step in CO oxidation. In addition, the existence of oxygen vacancies is conducive to promoting the dissociation and activation of O₂. The above conclusions reveal the relationship between surface carbonates (surface oxygen species) and catalyst activity, and provide a theoretical basis for regulating the microstructure of Mn-based catalysts.