Adsorption and Reaction of Thiophene on Graphene/Ruthenium: Experiment and Theory

The adsorption of thiophene (C4H4S) on graphene (Gr) epitaxially grown on Ru(0001) (short Gr/Ru) was studied at ultrahigh vacuum conditions by thermal desorption spectroscopy (TDS) and Auger electron spectroscopy (AES). In multimass TDS, the parent mass of C4H4S was detected but also masses which are not part of thiophene’s gas-phase fragmentation pattern. Thus, in addition to a molecular adsorption/desorption pathway, thiophene also dissociates. Multimass TDS suggests the formation of gaseous acetylene (C2H2) and thioketene (C2H2S). In addition, AES revealed adsorbed sulfur and carbon after TDS experiments, consistent with thiophene’s decomposition. Two different Gr preparations were used: one that does generate grain boundary defects and the other one does not. In both cases, vacancy defects are absent. Catalytic activity was identical on both types of samples, and sulfur-covered Gr/Ru remains catalytically active. A kinetic mechanism is proposed; kinetic parameters are determined. Complementary, first-principles density functional theory calculations confirm the crucial role of the Ru(0001) substrate in facilitating thiophene dissociation into acetylene and thioketene, as a consequence of a complex interplay between electronic and geometric effects, similar to what we observed for the dissociation of H2S on Gr/Ru [J. Vac. Sci. Technol. A 2023, 41, 062201-7].