Density functional theory study on the microscopic mechanism of NO2 adsorption and reduction by potassium-doped biochar: the key role of the active sites

Abstract Biochar is a porous carbon material that can effectively remove NO x from flue gas. The influence of K element and active sites on the microscopic mechanism of NO 2 gas adsorption and reduction reaction remains elusive. Through density functional theory (DFT), two NO 2 molecules are selected on reasonable biochar models to calculate the reaction pathway. The reaction pathways involve the sequential adsorption of two NO 2 molecules at different active sites for reduction reaction, and desorption of two NO molecules and one CO 2 molecule. Through the energy barrier difference of the reaction path and interaction region indicator (IRI) analysis of important molecular structures, it was found that K atom promotes the adsorption reduction reaction in three reaction processes: the breakage of N–O bond, the desorption of NO molecule, and the dissociation of CO 2 molecule. Based on the different numbers of active sites in the four reactant models, it can be concluded that the promotion range of the K atom for the adsorption and reduction process of NO 2 molecules is 0.6157 nm. Thermodynamic and kinetic analyses indicate that the addition of K enhances the upper limit and the maximum reaction rate of the reaction pathways. This study provides certain theoretical guidance for preparing biochar to regulate NO 2 emissions. Graphical Abstract