Desulfurization reactions of methanethiol on defect CeO₂ surfaces

Methanethiol (CH₃SH) is a volatile organic compound that poses a high health risk and causes corrosion to equipment in petroleum refineries. The removal of the sulfur content in mercaptans using potent catalysts assumes a fundamental importance from industrial and environmental perspectives. Motivated by experimental studies involving stand-alone cerium oxide (CeO₂) catalysts, we have deployed a defect CeO₂ surface with an oxygen vacancy (CeO₂(1 1 1)_V_o) to explore the decomposition chemistry of methanethiol based on first principle density functional theory (DFT) calculations. The study presents potential formation pathways for the major experimentally reported compounds, namely, CH₄, H₂S, CO, CO₂, CH₃SCH₃, and COS. Initial uptake of CH₃SH takes place via either C-S or S-H bond fissions through modest activation barriers. In initial decomposition pathways, V_o spots represent strong acidic sites, and thus facilitating rupture of C-S and S-H fissions. Formation of CO takes place through a series of H transfer reactions that commence from the CH₂* adduct. Adjacent HS* and HO*sites undergo a hydrogen diffusion reaction to ultimately produce H₂S rather than water. Several investigated reactions lead to the filling of the vacant oxygen sites with S atoms leading to the generation of CeO_2-xS_y phases. The latter exhibits a neat-metallic character. Through the occurrence of both Eley-Rideal and Langmuir-Hinshelwood-type mechanisms, CeO_2-xS_y phases maintain catalytic activity. Findings herein provide a detail atomistic understanding of the desulfurization capacity of stand-alone ceria surfaces.