The mechanism of interaction between CH4and oxygen carrier surface was studied using density functional theory (DFT) calculations. The adsorption energy of CH4on Fe2O3surface Fe bridge site is the highest, indicating Fe bridge site adsorption is the most stable, and O top site follows. The CH4-Fe2O3surface reaction path was inferred as: (1) the generation of hydroxyl radical, (2) the interaction between hydroxyl radical and CH4with its intermediates in chain, and (3) the generation of H2O and CO2through oxidation. The research will provide guidance for the interaction mechanism between CH4and oxygen carrier surface and the optimization of CLC macroscopic reaction kinetics.

This paper focuses on theoretical research of Co-doped Fe-based oxygen carrier for CO oxidation in chemical-looping combustion (CLC) system. Density functional theory (DFT) calculations were carried out to study of interaction between CO molecules and CoO/Fe2O3cluster, it is found that dissociation of O atom through breaking of Fe-O bonds in the Fe2O3system is the key step for CO oxidation reaction, and Low-fold O atoms in Fe2O3system could more readily dissociate from external surface. Moreover, the presence of CoO in Fe2O3could decrease activation energy and reaction energy of CO/Co-Fe2O3system, hence the reaction between CO and Fe2O3is promoted.

The reaction of Cu-based oxygen carrier with CO during chemical looping combustion was studies using density functional theory (DFT) calculations in this paper. It was found that CO2is formed after CO chemically adsorbed onto CuO surface and it exhibits strong localization properties. Energy barrier with regard to the overall reaction is 1.947 eV with overall reaction energy of-3.686 eV, indicating the overall reaction is an exothermic process. As can be figured out from the geometries of the stable structures, after the physical adsorption of CO on CuO surface, 1.947 eV is needed to jump to the transition state, and the nearest distance between CO and the surface is 1.542 Å with bond angle of 155.381°, C-O bond has stretched to 1.151 Å from 1.147 Å. With further interaction between CO and CuO surface, nearly linear structure O-C-O group is formed with bond angle of 179.177° and almost symmetric C-O bond distance, which was thought to be the formation of CO2.

Chemical-looping combustion (CLC) has been proposed as an efficient and clean technology that could contribute to achieve carbon dioxide capture with negligible cost. The technology uses a metal oxide as oxygen carrier that indirectly transfer oxygen from air to fuels to oxidize the fuels. CuFe2O4 was prepared as a novel oxygen carrier to decrease the cost of raw material and increase the reactivity of iron-based oxygen carrier. The structure of the prepared oxygen carrier was characterized by scanning electron microscope (SEM) and an X-ray diffractometer (XRD). The reaction of CuFe2O4 with coal was tested in a thermogravimetric analyzer (TGA). Results showed that the pyrolysis of coal under CO2 was more complete than that under N2, and the final conversion of CuFe2O4 during CLC of coal reached 66.6%. SEM images and BET surface area of the fresh and the used oxygen carrier show little agglomeration during the process.

Co-doped Fe2O3 oxygen carriers reacted with CO were investigated in order to study the temperature effect on the redox characterization.Co-Fe2O3 were characterized with X-ray diffraction (XRD), BET and transmission electron microscope (TEM), which showed that the surface structure was regular, and the polymorph was stable. The TG (Thermo Gravimetric Analyzer) analysis indicted that, rational doping Co could enhance the reactivity of iron-base oxygen carrier reacted with CO under different conditions. Oxygen carrier with Fe: Co molar ratio of 1:0.1 had best reactivity. With the temperature increased, the reduction degree became deeper and the complete conversion time shortened. The reduction reaction Co0.1Fe oxygen carrier with CO was carried out step by step, and the entire process was divided into three stages, namely 344.7-391.0, 414.7-472.5 and 607.6-681.5°C.