Density Functional Theory Investigation on the Adsorption Reduction of No2 on the Biochar Surface: The Effect of Potassium

Abstract

With the purpose of providing theoretical guidance to assist in regulating NOx emissions, a thorough understanding of the catalytic mechanism of NO2 adsorption reduction on the surface of the carbon material under the impact of K in biochar can be of significance. Through density functional theory (DFT) calculations, two reaction routes including various zigzag and armchair edge biochar models are identified, indicating the changes in the structure of intermediates and the influence mechanism of the K presence. Mayer bond order analysis and wave function analysis is used to investigate a new discovery that the formation process of the pentagon–heptagon reconstruction at zigzag edges (zz-57 edges structure) and the desorption process of CO from the seven-membered ring with an oxygen atom. According to calculation results, the K catalyzes the process in three ways: facilitating the disconnection of N–O bond, the desorption of NO, and the CO2 dissociation, and brings about a decrease in the highest energy barrier for the NO2 reaction path on two char edge models by 48.04% and 39.85%. Thermodynamic and kinetic analysis indicates that the addition of K enhances the upper limit and the maximum reaction rate of the reaction path.

Keywords: Potassium (K), NO2 adsorption reduction, CO desorption, the zz-57 edges structure, Density functional theory (DFT), biochar