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Abstract: Supported molybdenum-sulfide nanoparticles are known catalysts for petroleum hydrodesulfurization as well as for electrochemical hydrogen evolution. In this study, we investigate molybdenum-sulfide nanoparticles supported on Au(111) using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), aiming to correlate spectroscopically determined chemical states with atomically resolved nanostructure. The results of this study allow us to conclude the following: (1) the XPS results from our model system are in good agreement with previously published results on supported MoS2 for industrial applications, validating in part the fidelity of the model system; (2) STM reveals that catalytically active, crystalline MoS2 nanoparticles exhibiting the well-known metallic edge state are only present after a post-deposition annealing step in the synthesis procedure, without which the particles exhibit amorphous shapes and incomplete sulfidation; and (3) the sulfided nanoparticles are found to be stable in air at room temperature. [Copyright &y& Elsevier]

Abstract: The scanning tunneling microscopy and temperature programmed oxidation methods were used to study the catalytic oxidation of graphite by mass-selected Ru nanoparticles. Channeling by the nanoparticles was observed on the unsputtered HOPG basal surface at temperatures above 750°C in 10−6 mbar . ion bombardment was used to create layers of disordered carbon of various depths on the HOPG surface. The channel propagation rate in the disordered carbon layer was found to increase for larger nanoparticles. The depth of the interface between the disordered carbon layer and the graphite determined whether the nanoparticles etched paths parallel or perpendicular to the surface. The gasification onset temperature depended on the degree of graphitisation of the surface, with more heavily sputtered surfaces undergoing gasification at much lower temperatures than the unsputtered surface. [ABSTRACT FROM AUTHOR]

Abstract: Scanning tunneling microscopy was used to compare the morphologies of Ru nanoparticles deposited onto highly-oriented graphite surfaces using two different physical vapour deposition methods; (1) pre-formed mass-selected Ru nanoparticles with diameters between 2nm and 15nm were soft-landed onto HOPG surfaces using a gas-aggregation source and (2) nanoparticles were formed by e-beam evaporation of Ru films onto HOPG. The particles generated by the gas-aggregation source are round in shape with evidence of facets resolved on the larger particles. Annealing these nanoparticles when they are supported on unsputtered HOPG resulted in the sintering of smaller nanoparticles, while larger particles remained immobile. Nanoparticles deposited onto sputtered HOPG surfaces were found to be stable against sintering when annealed. The size and shape of nanoparticles deposited by e-beam evaporation depend to a large extent on the state of the graphite support and the temperature. Ru deposition onto unsputtered HOPG is characterised by bimodal growth with large flat particles formed on the substrate terraces and smaller diameter particles aligned along the substrate steps. Evaporation onto sputtered HOPG results in the formation of 2nm round particles with a narrow size distribution. Finally, thermal deposition onto both sputtered and unsputtered HOPG at 660°C results in larger particles showing a flat Ru(0001) top facet. [Copyright &y& Elsevier]