Simultaneous NO/CO2 removal performance using Ce-doped CaO in calcium looping process: Experimental and DFT studies.

In carbonation stage of calcium looping process, NO could be reduced by CO using CaO as a catalyst, allowing simultaneous CO 2 and NO removal. However, to achieve efficient NO removal, the required CO/NO molar ratio in the carbonator is very high (up to 30:1), which leads to lots of unreacted CO in the exhaust gas. In this work, to maintain high efficiency of NO removal at low CO concentration in carbonator, Ce-doped CaO was employed to simultaneously enhance NO and CO 2 removal performance. The effects of Ce-doped CaO on simultaneous CO 2 and NO removal in bubbling fluidized bed reactor were investigated during the carbonation stage of calcium looping process. When the molar ratio of CO/NO is about 3.57:1, Ce-doped CaO obtains an 83% CO 2 capture efficiency and a 97% NO removal efficiency in 20 cycles in chemical reaction controlling stage. The average CO concentration in exhaust gas of Ce-CaO was reduced by 79% at the same NO removal efficiency as Mn-doped CaO. The presence of Ce³⁺ makes the charge imbalance of the material, resulting in more charge transfer from the Ce-CaO surface to the molecules. The density functional theory reveals that Ce doping reduces the energy barriers of the conversion of NO to N 2 and the CO 2 adsorption, promoting the simultaneous NO/CO 2 removal in carbonation stage. Therefore, under a low molar ratio of CO/NO in carbonation stage of calcium looping, Ce considerably improves the simultaneous CO 2 and NO removal action of CO and CaO. [Display omitted] • Ce markedly catalyzes NO and CO 2 removal in carbonation stage of calcium looping. • NO/CO 2 removal efficiencies reach 97% and 83% at low CO concentration, respectively. • CO concentration in exhaust gas using Ce-doped CaO decreases significantly. • Effect of Ce-doped CaO on NO and CO 2 removal in calcium looping is studied by DFT. • Ce reduces the energy barriers of NO and CO 2 removal on CaO from 8.97 to 7.12 eV. [ABSTRACT FROM AUTHOR]