First-principles study adsorption properties of CO2 molecule on CaO(100) surfaces

Abstract

The process of stable adsorption of CO2 molecules on CaO (100) surfaces were studied using a periodic slab model by PW91 of generalized gradient approximation (GGA) within the framework of density functional theory (DFT). The results indicated that the surface oxygen atoms (Osurf) are the most active adsorbed sites for adsorb CO2 on the CaO (100) surfaces. It is a truth universally acknowledged that the emission of carbon dioxide (CO2) leads to global warming which results in a change in the climatic conditions. Despite this, CO2 or synthetic discharge gas is produced during the burning or gasifying process of the carbon-based fuels, in particular, from the burning of fossil fuel in fossil fuel heat-engine plant which causes more than 30% of the total CO2 emissions (1). The heat-engine plants become the largest source of CO2 emission, and this has attracted significant world-wide attention. However, CO2 is also an effective carbon resource, which can meet the ever increasing demand for energy; thus, providing solution for the environmental problems. Therefore, the economical capture, transport, storage, and transformation of CO2 are highly desirable for the gradual reduction and control of anthropogenic greenhouse gas emissions. In recent years, capture and storage of CO2 by the cyclic reaction involving adsorption, carbonation, and calcination of calcium-based sorbents have attracted significant attention of the researchers world-wide (2-3). Utilizing this technology, CO2 was captured in order to shift the steam reforming equilibrium for the production of hydrogen (4), and the CO2 in dual curing coal combustion system could be attached directly to the bed (5). According to the study of the calcium-based sorbent, the absorptivity of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) (with higher theoretical absorbance) is better than other sorbents. Theoretically, 0.786 g of CO2 could be adsorbed by 1 g of CaO. CaO is commercially and readily available as it is easy to prepare (6-7) and it is cost effective. However, reports based on the theoretical research on the CO2 adsorption by CaO are limited (6, 8), and studies on its decomposition kinetics have not been reported. In this study, the process of stable adsorption of CO2 molecules on CaO surfaces was investigated by using density functional theory. The CO2 adsorption behavior on the surface of CaO was simulated by Materials studio. The adsorption was configured; and the charge, frequency, and density of the states were analyzed. Moreover, the temperature and pressure dependence reaction kinetics on the adsorption behavior were investigated to provide theoretical support for further research on CaO as adsorbent for CO2.