Influence mechanism of inert carrier on the anti-carbon deposition effect of nickel-based oxygen carrier in chemical looping methane reforming process

Abstract

In this paper, density functional theory (DFT) calculations are applied to investigate the reaction mechanism of syngas production by chemical looping reforming of methane on NiO-based surfaces. The work mainly focused on the basic reaction steps, including the catalytic dehydrogenation of CH4, the generation of H2 and H2O, and the formation of CO. The mechanism of formation and removal of carbon deposits is analyzed emphatically. Firstly, it is found that NiO fragments are very stably attached on the surface of ZrO2 and Al2O3 and carriers. For the methane dehydrogenation step, it is shown that CH4 → CH3 + H is the rate-limiting step on both surfaces. Moreover, the calculation results showed that the formation of CO and H2O molecules was also more favorable on the surface of NiO/Al2O3, indicating that the Al-Ni structure owns better lattice oxygen transferring ability. For the key step of the H2 molecule generation, the surface of NiO/ZrO2 shows better reaction performance and lower activation energy. The NiO fragments loaded on the surface of Al2O3 is able to exhibit better anti-carbon properties, indicating that the introduction of Al2O3 can well enhance the cyclic stability of oxygen carriers.