Hydrogen activation and reactivity of ruthenium sulfide catalysts: Influence of the dispersion

In order to examine the influence of the size of particles on the catalytic properties of sulfide catalysts, a series of ruthenium sulfide based catalysts, dispersed in a KY zeolite, supported on silica or unsupported, were prepared and characterized. Such a methodology allowed us to vary the particle size in a large domain. The particle sizes were determined by HREM for RuS(2)/silica (3.6 nm) and the unsupported sample (5 nm) and by SAXS for the zeolite catalyst (1.2 nm), From these measurements, the fractions of ruthenium and sulfur present at the surface of the catalysts were deduced. The TPR patterns of the three catalysts exhibit three peaks whose relative proportions were also related to the amount of surface sulfur, An excellent agreement was observed between both kinds of determination. Then, the influence of a progressive reduction of the surface on the adsorbing and catalytic properties of the three samples was studied in the whole S/Ru range. Striking similarities were observed for the three catalysts concerning the nature of the hydrogen species and the variation of the hydrogenation activity with S/Ru. Indeed, inelastic neutron scattering revealed the presence of hydride species, as was already observed for unsupported RuS(2). The determination by TPD of the amount of hydrogen adsorbed and the measurements of catalytic activities allowed the determination of the turnover frequency for the catalysts of the present series. It appeared that these values are almost similar, which shows that the same active phase can be obtained as unsupported catalyst or highly dispersed in a zeolite. The interest of using this KY zeolite is to stabilize nanoparticles of sulfide phase inside its framework and consequently to obtain a high number of active sites. (C) 1999 Academic Press.