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 catal ysts, dispersed in a KY zeolite, supported on silica or unsupported, were p repared and characterized. Such a methodology allowed us to vary the partic le size in a large domain. The particle sizes were determined by HREM for R uS2/silica (3.6 nm) and the unsupported sample (5 nm) and by SAXS for the z eolite catalyst (1.2 nm), From these measurements, the fractions of rutheni um and sulfur present at the surface of the catalysts were deduced. The TPR patterns of the three catalysts exhibit three peaks whose relative proport ions were also related to the amount of surface sulfur, An excellent agreem ent was observed between both kinds of determination. Then, the influence o f a progressive reduction of the surface on the adsorbing and catalytic pro perties 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 RuS2. The determination b y TPD of the amount of hydrogen adsorbed and the measurements of catalytic activities allowed the determination of the turnover frequency for the cata lysts of the present series. It appeared that these values are almost simil ar, which shows that the same active phase can be obtained as unsupported c atalyst or highly dispersed in a zeolite. The interest of using this KY zeo lite is to stabilize nanoparticles of sulfide phase inside its framework an d consequently to obtain a high number of active sites. (C) 1999 Academic P ress.