Insights into methane to syngas on stoichiometric and defect Ce2(SO4)3 crystal surface

Abstract

We present a first principles study using periodic density functional theory on the reaction between Ce2(SO4)3 oxygen carrier and CH4 during chemical looping partial oxidation. The (001) surface has an appropriate bond strength and oxygen vacancy (Ov) formation energy (Evac). Further analysis shows that CH4 has a weak adsorption performance on (001) surface, while CHx (x = 0–3) radicals have a strong electron density overlap. The lattice oxygen atoms tend to leave the crystal surface during adsorption process, which is conducive to the syngas formation. Compared with (102) surface, (001) surface has a lower dehydrogenation and syngas formation energy barrier. CH3 → CH2 + H serves as the rate-determining step on (102) surface, while on (001) surface is CH2 → CH + H (TS3). Ov effects are emphasized through the comparison of (102), (001) and Ov (001) surface. The corresponding energetic results show that the Ov facilitates the adsorption and dehydrogenation process. But when the Ov concentration is larger than 1.96%, increasing the Ov concentration does not continue to reduce the energy barrier of TS3. In summary, (001) surface has a better reaction performance, and Ov play a critical role in both adsorption and dehydrogenation process.