DFT study on effect of ZnO on CO2 adsorption performance of CaO adsorbents

ZnO-doped CaO adsorbents were prepared by extrusion molding method, and the CO2 adsorption performance of ZnO-doped CaO adsorbents was investigated. Based on density functional theory(DFT), the surface models of CaO(0 0 1) and Zn-CaO(0 0 1) were established, and the conformation, adsorption energy, state density and differential electron density of CO2 adsorption for the two materials were calculated. The mechanism of the effect of ZnO doping on the CO2 adsorption performance of CaO was revealed at the microscopic atomic level by comparing the calculated results of the materials before and after modification. The results show that with the increase of ZnO addition from 1% to 5%, the CO2 adsorption performance of CaO increases. When ZnO is added to 3%, the carbonation conversions of ZnO/CaO adsorbent in the first and fifth cycles are 0.86 and 0.76, respectively. After the addition of ZnO, the adsorption energy of CO2 decreases from −1.184 eV to −1.947 eV, and there are more formants between Zn atom and O atom than those between Ca atom and O atom. On the surface of Zn-CaO(0 0 1), a high density three-atom electron orbital resonance peak of Zn atom, C atom and O atom appears at −6.06 eV. It indicates that doping ZnO improves the stability of CaO structure and results in more charge transfer between Zn atoms, O atoms and C atoms. The charge transfer between Zn atom and O atom improves the reactivity of O atom and makes O atom easier to bond with C atom. As a result, CO2 is adsorbed on ZnO/CaO surface as CO23-. Therefore, ZnO improves the CO2 adsorption performance of CaO and it is an ideal additive.density and differential electron density of CO2 adsorption for the two materials were calculated. The mechanism of the effect of ZnO doping on the CO2 adsorption performance of CaO was revealed at the microscopic atomic level by comparing the calculated results of the materials before and after modification. The results show that with the increase of ZnO addition from 1% to 5%, the CO2 adsorption performance of CaO increases. When ZnO is added to 3%, the carbonation conversions of ZnO/CaO adsorbent in the first and fifth cycles are 0.86 and 0.76, respectively. After the addition of ZnO, the adsorption energy of CO2 decreases from −1.184 eV to −1.947 eV, and there are more formants between Zn atom and O atom than those between Ca atom and O atom. On the surface of Zn-CaO(0 0 1), a high density three-atom electron orbital resonance peak of Zn atom, C atom and O atom appears at −6.06 eV. It indicates that doping ZnO improves the stability of CaO structure and results in more charge transfer between Zn atoms, O atoms and C atoms. The charge transfer between Zn atom and O atom improves the reactivity of O atom and makes O atom easier to bond with C atom. As a result, CO2 is adsorbed on ZnO/CaO surface as CO23-. Therefore, ZnO improves the CO2 adsorption performance of CaO and it is an ideal additive. © 2022 Central South University of Technology. All rights reserved.