The effect of Cu on NO reduction by char with density functional theory in carbonation stage of calcium looping

Abstract

Cu can improve NO removal efficiency of char and CO in carbonation stage of calcium looping, but the mechanism of NO reduction by char and CO in the presence of Cu has been rarely reported. In this work, the density functional theory was utilized to investigate the effect of Cu on NO reduction by both char and CO in carbonation stage of calcium looping for CO2 capture. Density of state result proves that Cu decreases the possibility of char deactivation and retains stable promoting effect for NO reduction. Adsorption energies and structural parameters were used to determine adsorption sites of reactant molecules (CO, NO and O2) and Cu atom on the basic configuration of zigzag graphite structure with six benzene rings. Adsorption energies of reactant molecules on char surface in the presence of Cu follow the order: CO < NO < O2. Cu decreases energy barriers for NO reduction by char, NO reduction by CO and CO oxidation by O2 from 31.73, 61.31, 113.86 kcal/mol to 19.99, 12.51, −11.68 kcal/mol, respectively. Accordingly, Gibbs free energies reduce from 1.14, −7.69, −66.02 kcal/mol to −39.95, −9.21, −68.10 kcal/mol, respectively. Therefore, Cu significantly promotes NO reduction by both char and CO as well as CO oxidization by O2. Furthermore, char has more significant effects on the reduction of NO than CO in the presence of Cu. Thus, the effect of Cu on reaction paths is determined.