Adsorption and Reaction Mechanism of Inert Carriers (Al2O3 and TiO2) Loaded with Fe2O3 in Chemical Looping Gasification Based on Density Functional Theory

In the chemical looping gasification (CLG) process, support material is used to improve the mechanical strength and thermal stability of the oxygen carrier (OC). The presence of a support material can affect the properties and performance of the OC, which influences the synthesis gas generation pathways. In this work, the density functional theory calculations were applied to investigate the reaction mechanisms and syngas formation during CLG, while Fe2O3 is used with support Al2O3 or TiO2 as oxygen material. Adsorption and reaction pathways of C atom and main constituents in syngas (CO, H-2, and H2O) on the surface of the composite carrier were studied. The reaction pathway and energy transformation regarding oxidation of C atom and CO on the composite carrier's surface were calculated and evaluated. The results indicate that CO desorption and COO* formation on the Fe2O3/Al2O3 surface were the rate-limiting steps that affect the conversion of C and CO under the studied conditions. In addition, the coadsorption of H2O and CO on composite carrier's surfaces and possible reaction pathways of them were assessed to compare performance of the two studied composite carriers. The results indicate that formation of the carboxyl intermediate is the dominant pathway during coadsorption of H2O and CO and further conversion on the Fe2O3/Al2O3 surface. On the other hand, formation of the formate as an intermediate on surface composite carrier Fe2O3/TiO2 was easier and more direct because of its highest energy barrier, which is only 2.01 eV. Therefore, Fe2O3/Al2O3 can enhance particle adsorption and capture, while Fe2O3/TiO2 was more suitable for improving water-gas shift reaction performance. These results are essential to the design and optimization of cost-effective composite materials for enhancing performance and sustainability in chemical looping processes.