Hydrogenation properties of ruthenium sulfide clusters in acidic zeolites

Catalysts of ruthenium sulfide, dispersed in a series of Y zeolites with various acidic properties, were prepared by ion exchange and subsequent sulfidation. The activities for the reactions of hydrogenation of tetralin and toluene, carried out in the presence of H2S (1.9%), vary widely according to the nature of the zeolites. Ruthenium sulfide catalysts are much more active when using acidic zeolite, HY and HYd (dealuminated), and a partially potassium-exchanged KHYd sample, than when using the KY support. The acidic properties of the sulfided RuY catalysts were determined in situ using infrared spectroscopy and the conversion of isooctane. Both methods gave similar rankings of catalyst acidity. The electronic properties of the ruthenium sulfide phase were examined by means of the infrared study of the adsorption of CO. A low-frequency shift of 15 cm(-1) was observed for CO adsorbed on RuKY by reference to CO adsorbed on all other samples. The increase in activity for the hydrogenation of aromatics is related to the electron-deficient character of the sulfide particles in the acidic zeolites as has been proposed, in the literature, for metal catalysts. A superimposed influence of the acidic sites on the adsorption of the aromatic molecule may also occur which could explain the amplitude of the effect (difference of activity between the most and less active catalysts similar to 200 times) and the variations of activity observed within the series of the acidic catalysts. (C) 1997 Academic Press.