Effect of TiO2-Al2O3 Sol-Gel Supports on the Superficial Ni and Mo Species in Oxidized and Sulfided NiMo/TiO2-Al2O3 Catalysts: Influence on Dibenzothiophene Hydrodesulfurization

The present work presents a comparative study of NiMo catalysts supported on sol-gel TiO(2)-Al(2)O(3) mixed oxides with 5 and 95 mol% content of Al(2)O(3). The DRX and N(2) physisorption results showed that the sol-gel method allows preparation of TiO(2)-Al(2)O(3) mixed oxides possessing high superficial area and an amorphous TiO(2) structure. Results of zeta-potential showed that the net surface pH of the supports depends on their structure and composition. According to UV-Vis and Raman spectra obtained from the solids after impregnation, catalysts with high content of Al(2)O(3) showed Mo(7)O(24) 2-s and Mo(8)O(26) 4- species displaying Mo-O-Mo stretching vibration modes. On the other hand, catalysts with high content of TiO(2) showed Mo(7)O(24) 2- and Mo(8)O(26) 4- species with vibration modes corresponding to terminal Mo=O(t) bonds. Therefore, it appears that impregnation of catalysts with a pH 9 solution allows a polymerization process of MoO(4) 2- and [Ni2+4O2-] solution species to Mo(8)O(26) 4- and Mo(7)O(24) 2- species with a close interaction with [Ni2+6O2-] species. However, these species have low interaction with the support. Thus, composition of the support appears to be more important than net surface pH in order to obtain a better distribution of superficial Mo species. XPS results suggest a higher proportion of NiMoS phase on the TiO(2) rich support. The most active catalyst in the dibenzothiophene hydrodesulfurization was NiMo/TiO(2)-Al(2)O(3) with 5 mol% Al(2)O(3). This suggests that Mo(7)O(24) 2- and Mo(8)O(26) 4- in combination with [Ni2+p6O2-] species produce a better Ni/(Ni + Mo) ratio and NiMoS phase.