Significant enhancement of VOCs conversion by facile mechanochemistry coupled MnO2 modified fly ash: Mechanism and application

Abstract

In this work, the modification of fly ash with mechanochemical coupled MnO2 was presented by balling milling to enhance its activity for volatile organic compounds (VOCs) oxidation. This simple processing significantly improved the toluene conversion, from 5% (untreated fly ash) to over 90% with the carbon balance efficiency over 94%. Microscopic characterization showed that ball milling increased the specific surface area of fly ash and the dispersion of MnO2 into the fly ash, both favoring the adsorption and oxidation of toluene. In addition, a two-stage reaction mechanism is proposed for the oxidation of toluene at the surface of modified fly ash. Based on the analysis of the valence state and reduction ability of MnO2, the reduction of MnO2 dominates the first stage to generate Mn2O3, which further oxidizes adsorbed toluene in the second stage. Furthermore, the outlet of the selective catalytic reduction (SCR) system was determined as the best location for injection of the modification fly ash for suitable temperature (around 300 °C). The results demonstrated the great potential of the MnO2-modified fly ash as a low-cost, highly active, and fully up-scalable material for VOCs conversion. More importantly, the simplicity and environmental-friendly nature of the presented modification is highly compatible with the fly ash injection system in coal-fired power plants.