THE INFLUENCE OF METAL-SUPPORT INTERACTIONS ON THE ACCURATE DETERMINATION OF RU DISPERSION FOR RU/TIO2

Titania-supported Ru catalysts have been characterized by TEM,H-1 NMR, and H-2 chemisorption to determine the metal particle size, the fraction of the metal surface available for H-2 chemisorption, and the H-2 adsorption capacity of the catalyst, as functions of the reduction temperature. TEM micrographs show that as the reduction temperature rises from 573 to 773 K, the average particle size of Ru remains the same but the surface of the particles is covered to an increasing extent by an amorphous layer of titania. Quantitative estimates of the fraction of the Ru particle surface available for H-2 chemisorption were obtained by H-1 NMR. The NMR spectra also show that a fraction of the adsorbed H-2 spills over onto the support and that as a consequence measurements of total H-2 chemisorption overestimate the number of Ru sites available for H-2 adsorption. The implications of these results for the correct calculation of Ru dispersion and the determination of turnover frequencies for reactions carried out over Ru/TiO2 are discussed. (C) 1994 Academic Press, Inc.