| Molybdenum carbides have been proposed as substitutes for traditional MoS2-based hydrodesulfurization (HDS) catalysts. However, questions remain regarding the fundamental surface chemistry associated with the HDS of organosulfur molecules on carbided and sulfided molybdenum surfaces.; To investigate the suitability of Mo2C for HDS applications, the interaction of thiols with model catalyst surfaces was examined by utilizing carbon-modified Mo(110) single crystals. Specifically, the reaction of ethanethiol and 1,2-edianedithiol was studied on the clean Mo(110), defective p(4 x 4)-C/Mo(110), and p(4 x 4)-C/Mo(110) surfaces using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED).; The reaction of ethanethiol on the clean Mo(110) surface yielded ethane and ethylene as products. Relative to clean Mo(110) surfaces, ethanethiol TPD experiments performed on carbided Mo(110) surfaces showed no significant differences in reactivity (conversion), selectivity, or reaction pathways.; 1,2-Ethanedithiol TPD experiments conducted on the clean Mo(110), defective p(4 x 4)-C/Mo(110), and p(4 x 4)-C/Mo(110) surfaces produced similar reaction products. However, significant changes in selectivity and reaction pathways were observed on the carbided Mo(110) surfaces. On the clean Mo(110) surface, 1,2-ethanedithiol decomposed to acetylene, ethylene, vinyl thiol, and ethanethiol. Vinyl thiol was absent from the product distribution associated with TPD experiments on the defective p(4 x 4)C/Mo(110) surface, which yielded acetylene, ethylene, and ethanethiol as products. The reaction of 1,2-ethanedithiol on the pristine p(4 x 4)-C/Mo(110) surface resulted in complete desulfurization and produced only acetylene and ethylene.; The addition of one sulfhydryl (SH) functional group to ethanethiol results in a change in surface chemistry on both clean and carbided Mo(110) surfaces. Due to the presence of two sulfhydryl groups, 1,2-ethanedithiol forms multiply bonded species on both clean and carbided Mo(110) surfaces, which further decompose to hydrocarbon products. Overall, the presence of surface carbon does not appear to effect thiol surface chemistry unless multiple sulfhydryl groups are present in the reactant.; Ethanethiol and 1,2-ethanedithiol TPD experiments were also performed on clean and carbided Mo(110) surfaces with adsorbed sulfur. As sulfur coverage (thetaS) increases, both the clean and carbon-modified surfaces become progressively less reactive towards thiols. Sulfur is thought to bond to adsorption sites and block the formation of the thiolate surface intermediate, resulting in decreased surface reactivity. |
