Desulfurization reactions of methanethiol on defect CeO2 surfaces

Abstract

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(111)_Vo) 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, Vo 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 CeO2-xSy phases. The latter exhibits a neat-metallic character. Through the occurrence of both Eley-Rideal and Langmuir-Hinshelwood-type mechanisms, CeO2-xSy phases maintain catalytic activity. Findings herein provide a detail atomistic understanding of the desulfurization capacity of stand-alone ceria surfaces.