Density Functional Theory Study On The Reaction Of Three Types Of Oxygen Carrier With CO In Chemical-Looping Combustion System

Chemical-looping combustion is a novel combustion technology. There has been an increasing interest in using chemical-looping combustion (CLC) as a promising technology in the clean use of energy. CLC can not only increase the thermal efficiency in power generation stations, but also exhibits inherent advantages for CO2 separation, which is attractive for minimizing emissions of greenhouse gas. Oxygen carrier is the medium for transferring the oxygen to fuel in CLC, so the physical and chemical properties of oxygen carrier along with the reaction mechanism between fuel and oxygen carrier is very important. Density functional theory (DFT) calculations were used to investigate the reaction between fuel gas and oxygen carrier in the fuel reactor in this paper. CO was chose for the fuel gas, while Fe2O3, CuO and Mn3O4 were chose for the oxygen carrier model. It is found that when CO approaches to the surface of these three oxygen carriers, it bonds to metal atom strongly, which is due to the strong hybridization between the 2p orbital of C atom and the 3d orbital of metal atom. The mechanism of CO oxidation in the absence of O2 on the oxygen carrier can be concluded like this:At first, CO reacts with the lattice oxygen of oxygen carrier, then a bidentate carbonate species is produced by forming a new C-O bond, which is the key process in this oxidation reaction. Finally, the bidentate carbonate species across a reaction barrier to dissociate from the surface with generating a CO2. So oxygen is transferred from oxygen carrier to CO successfully. These investigations can not only help people to understand the microscopic mechanism of the oxidation of CO in fuel reactor, but also promote the fundamental understanding and applying of oxygen carrier.