Sub-stoichiometric Molybdenum Sulfide Phases with Catalytically Active Basal Planes.

Molybdenum sulfide (MoS2) is widely recognized for its catalytic activities where the edges of the crystals turn over reactions. Generating sulfur defects on the basal plane of MoS2 can improve its catalytic activity, but generally there is a lack of model system for understanding metal-centered catalysis on the basal planes. Here, we synthesized a new phase of sub-stoichiometric molybdenum sulfide (s-MoSx) on sulfur-enriched copper substrate. The basal plane of s-MoSx contains chemically reactive Mo-rich sites that can undergo dynamic dissociative adsorption/desorption processes with molecular hydrogen, thus demonstrating its usefulness for hydrogen-transfer catalysis. In addition, scanning tunneling microscopy was used to monitor surface-directed Ullmann coupling of 2,8-dibromo-dibenzothiophene (DBDBT) molecules on s-MoSx nanosheets, where the four-fold symmetric surface sites on s-MoSx direct C-C coupling to form cyclic tetramers with high selectivity.