Effect of Mn-doped CaO on NO reduction by CO in carbonation stage of calcium looping: A density functional theory study

Abstract

Calcium looping uses CaO carbonation/calcination cycles to capture CO2, which is a promising carbon capture technology for coal-fired power plants. However, after CaO absorbs CO2 to generate CaCO3, the catalytic performance of CaO for NOx reduction by CO decreases drastically. In this work, Mn-doped CaO was used to improve NO reduction by CO in carbonation of calcium looping and the mechanism of Mn-doped CaO on NO reduction by CO was determined by the density functional theory. The experimental results show that Mn doping not only improves the CO2 capture capacity of CaO, but also increases NO reduction by CO. Density functional theory calculation results show that the Mn atom provides new adsorption sites for CO and NO on CaO surface, respectively. After addition of Mn, the values of co-adsorption energy for CO and NO on CaO surface increases by 1.5 and 6.9 times in the carbonation stage, respectively. In addition, the total energy barrier for the reaction of NO reduction by CO under the catalysis of CaO in carbonation stage decreases from 11.08 to 8.66 eV due to the addition of Mn. The negative effect of the carbonation of CaO on NO removal by CO is greatly mitigated by Mn. Therefore, NO removal by CO in the presence of Mn-doped CaO is significantly improved in the carbonation stage of the calcium looping.