THE USE OF TIO2-AL2O3 BINARY OXIDES AS SUPPORTS FOR MO-BASED CATALYSTS IN HYDRODESULFURIZATION OF THIOPHENE AND DIBENZOTHIOPHENE

Molybdenum, cobalt-molybdenum and nickel-molybdenum catalysts were pre pared over mixed TiO2-Al2O3 oxides containing between 0 and 100% TiO2. The supports and samples were characterized in their oxidic or sulfid e state by BET, X-Ray diffraction (XRD), diffuse reflectance spectrosc opy (DRS), temperature programmed desorption of ammonia, X-Ray photo e lectron spectroscopy (XPS) and high resolution electron microscopy (HR EM). The three series of catalysts were evaluated in the hydrodesulfur ization of thiophene at atmospheric pressure and dibenzothiophene unde r 45 x 10(5) Pa. The results provided evidence for a support effect on the catalytic activities of the sulfided catalysts. For low or interm ediate TiO2 content in the support, a loss of cobalt in the Al2O3 lead s to a decrease of activity (compared to the pure Al2O3 supported samp les), but for x = TiO2/[TiO2+Al2O3] higher than 0.8, the support effec t improved the HDS activity. Moreover, the observed variations in acti vity depended on the nature of the model molecule used in the catalyti c test and/or on the experimental conditions (H-2 or H2S partial press ure). These points are discussed in relation to the mechanisms of the reactions. (C) 1997 Elsevier Science B.V.