Morphology and Atomic-Scale Structure of MoS2 Nanoclusters Synthesized with Different Sulfiding Agents

We use scanning tunneling microscopy to investigate the morphology and atomic-scale edge structure of MoS2 nanoclusters synthesized on a gold single crystal as a model system for hydrodesulfurization catalysts using three different sulfur sources for sulfiding. Crystalline and triangularly shaped MoS2 nanoclusters are predominantly produced from sulfiding with H2S, dimethyl disulfide (DMDS) and dimethyl sulfide (DMS), but the detailed dispersion, stacking and distribution of active edge sites is sensitive to the selection of the sulfiding agent. The main effect of varying the sulfiding agent seems to be related to the variation in the reactivity of the sulfur, i.e. changes in the sulfur chemical potential. H2S and DMDS both yield fully sulfided edge structures, but lower sulfur content is obtained on the edges of MoS2 sulfided with DMS reflected by Mo-edges terminated by sulfur monomers. The present model studies demonstrate that MoS2 morphology and hereby also the dispersion, type and amounts of active edge sites can be manipulated by control of sulfiding conditions and choice of sulfiding agent. The findings are in line with previous reports on activity variations on technical catalysts which have undergone different sulfidation procedures.