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First principles study of low miller index RuS<inf>2</inf> surfaces in hydrotreating conditions

Abstract:

Density functional theory (DFT) calculations combined with surface thermodynamic arguments and the Gibbs-Curie-Wulff equilibrium morphology formalism have been employed to explore the effect of the reaction conditions, temperature (T), and gas-phase partial pressures (p H2 and p H2S) on the stability of low Miller index ruthenium sulfide (RuS 2) surfaces. The calculated thermodynamic surface stabilities and the resulting equilibrium morphology models suggest that unsupported RuS 2 nanoparticles in HDS conditions are like to a polyhedron with six, eight, and twelve (100), (111), and (102) faces, respectively. The area of these faces covers about 40%, 37%, and 23% of the total particle, respectively. The atomic basins of the outermost individual atoms of the exposed surfaces were determined using the quantum theory of atoms in molecules methodology. Direct visualization of these basins has shown that a hole just at the middle of the outermost sulfur basins provides access to uncovered metal sites. Analysis of the electrostatic potential mapped onto a selected electron density isocontour (0.001 au) on the exposed surface reveals a very high potential reactivity of these holes toward electrodonating reagents. Consequently, the high attraction between these uncovered sites and S atoms coming from reagent polluting molecules makes these kinds of particles quite active for HDS catalysis. © 2009 American Chemical Society.