Selective dissolution of micro-spherical Ca-Mn mixed oxides for efficient propane oxidation

The improvement of catalytic efficiency is of great significance to the removal of volatile organic compounds (VOCs), a class of key air pollutants leading to ground-level ozone pollution. Herein, a series of micro-spherical Ca-Mn mixed oxides (Ca x Mn y O z ), namely CaMn 3 O 6 , Ca 2 Mn 3 O 8 and CaMnO 3 , were prepared by a two-step precipitation method, and defects were constructed on which by selective dissolution to enhance the low-temperature catalytic performance in the oxidation of propane (C 3 H 8 ) as a representative short-chain alkane VOCs. The synthesized Ca x Mn y O z oxides demonstrated drastically different response to the dissolution modification initiated by acid treatment. Specifically, after acid dissolution, while CaMn 3 O 6 and Ca 2 Mn 3 O 8 maintained largely their original structures, the perovskite-type CaMnO 3 underwent lattice rearrangement and was transformed into γ-MnO 2 -like product with only a tiny amount of Ca. In C 3 H 8 oxidation, the catalytic performance of CaMnO 3 was significantly improved after selective dissolution, as indicated by a significant decrease of T 90 , i.e. the temperature to achieve 90% C 3 H 8 conversion, from 455 °C to 240 °C. Mechanistic investigation by in-depth X-ray photoelectron spectroscopy studies revealed that selective dissolution led to higher Mn 4+ concentrations and more oxygen vacancies on the oxide surfaces, thus facilitated electron transfer and O 2 activation in C 3 H 8 oxidation reactions. This study paves a new path for the design of cost-effective oxide catalysts toward the abatement of short-chain alkane VOCs.