EFFECT OF MIXED TITANIA-ALUMINA SUPPORTS ON THE PHASE-COMPOSITION OF NIMO TIO2-AL2O3 CATALYSTS/

NiMo catalysts supported on mixed TiO2-Al2O3 oxides containing between 0 and 22 wt.-% TiO2 have been prepared and characterized by temperatu re-programmed reduction (TPR), infrared (IR) and diffuse reflectance ( DR) spectroscopy, BET and ammonia adsorption measurements. The samples have been tested in hydrodesulphurization (HDS) of thiophene. The spe ctral results show that the proportion of weakly bonded MoO42- groups is higher for NiMo/TiO2-Al2O3 catalysts compared to catalysts containe d only molybdenum. The increase in TiO2 content in the mixed supports leads to a decrease of inactive NiAl2O4 spinel. An increase of Ni2+ io ns in octahedral surroundings, included in a structure analogous to Ni TiO3 is observed. Acidity shows the nickel-molybdenum surface interact ion to be a result of the formation of a precursor of NiMoO4-like stru cture. The TPR results demonstrate that addition of titania into the s upport facilitates the Mo6+ reduction to Mo5+ and Mo4+. The influence of nickel on the molybdenum reducibility is revealed by a decrease of the temperature of reduction of the molybdenum species. The HDS activi ty of NiMo/TiO2-Al2O3 catalysts reaches a maximum at 17 wt.-% TiO2 due to formation of an active phase with an optimal composition of the ox idic precursors.