Experimental and density functional theory investigation of the NO reduction mechanism by semichars preheated in Ar and CO2/Ar atmospheres

Abstract

• Semichar preheated in CO 2 /Ar expressed higher NO initial reduction temperature. • Inert pretreatment was beneficial to arising the NO reduction index of semichar. • Occupation of active sites by oxygen atoms mildly inhibited the adsorption of NO. • Evolutionary pathways of C(O) in semichar affected the NO reduction reactivity. • The NO reduction pathways could be regulated by the preheating atmospheres. The extensive utilization of coal-based solid fuels in thermal power plants has led to massive emissions of greenhouse gases (GHG) and gaseous pollutants, resulting in serious environmental issues. In this study, the NO reduction reactivity of semichars preheated in Ar and Ar/CO 2 atmospheres was investigated via temperature-programmed reduction (TPR) experiments. Based on the TPR-DTPR method, the NO initial temperature, the maximum NO reduction rate, and the NO reduction indices of different semichars were determined. Compared with CO 2 /Ar pretreatment, the inert pretreatment enhanced the NO reduction index of the semichar. The CO 2 /Ar pretreatment was beneficial for decreasing the total Raman area and the ratio of I (Gr+VL+Vr) /I D due to the preferential consumption of high-reactivity structures and the condensation of aromatic ring structures. Furthermore, the detrimental effect of CO 2 /Ar treatment on semichar reactivity was relevant to the volumetric fraction, exerting an extraordinary correspondence with R r . Density functional theory (DFT) was employed further to analyse the NO reduction mechanisms by semichars derived from Ar and CO 2 /Ar atmospheres. For the inert pretreatment, the NO reduction pathways consisted of two pathways ( path 1 and path 2 ). Path 1 was supported by thermodynamics and dynamics. The energy barrier of the rate-determining step was 280.53 kJ/mol. Owing to the difference in the evolutionary pathways of C(O) on the semichar surface, the reaction between NO and the semichars derived from the CO 2 /Ar atmospheres could be summarized as two pathways ( path 3 and path 4 ). Path 3 was identified as the better method, and the energy barrier of the rate-determining step was 285.39 kJ/mol. The slightly adverse effects of CO 2 /Ar pretreatment on NO heterogeneous reduction were determined by coupling the experimental and theoretical methods, providing new insights into nitrogen migration and transformation mechanisms.