Catalytic C₂H₂ synthesis via low temperature CO hydrogenation on defect-rich 2D-MoS₂ and 2D-MoS₂ decorated with Mo clusters

Rational design of novel catalytic materials used to synthesize storable fuels via the CO hydrogenation reaction has recently received considerable attention. In this work, defect poor and defect rich 2D-MoS₂ as well as 2D-MoS₂ decorated with Mo clusters are employed as catalysts for the generation of acetylene (C₂H₂) via the CO hydrogenation reaction. Temperature programmed desorption is used to study the interaction of CO and H₂ molecules with the MoS₂ surface as well as the formation of reaction products. The experiments indicate the presence of four CO adsorption sites below room temperature and a competitive adsorption between the CO and H₂ molecules. The investigations show that CO hydrogenation is not possible on defect poor MoS₂ at low temperatures. However, on defect rich 2D-MoS₂, small amounts of C₂H₂ are produced, which desorb from the surface at temperatures between 170 K and 250 K. A similar C₂H₂ signal is detected from defect poor 2D-MoS₂ decorated with Mo clusters, which indicates that low coordinated Mo atoms on 2D-MoS₂ are responsible for the formation of C₂H₂. Density functional theory investigations are performed to explore possible adsorption sites of CO and understand the formation mechanism of C₂H₂ on MoS₂ and Mo₇/MoS₂. The theoretical investigation indicates a strong binding of C₂H₂ on the Mo sites of MoS₂ preventing the direct desorption of C₂H₂ at low temperatures as observed experimentally. Instead, the theoretical results suggest that the experimental data are consistent with a mechanism in which CHO radical dimers lead to the formation of C₂H₂ that presents an exothermic desorption.