CoMo/Ti-SBA-15 catalysts for dibenzothiophene desulfurization

With a view to reducing the sulfur content in diesel fuels, novel desulfurization CoMo catalysts were supported on a Ti-loaded hexagonal mesoporous SBA-15 material. The Ti-SBA-15 substrates were synthesized using triblock copolymers as structure-directing agents. Catalytic activity was assessed in the model reaction of hydrodesuffurization (HDS) of dibenzothiophene (DBT), carried out in a batch reactor at T = 623 K and with a total hydrogen pressure of 3.1 MPa. The reaction proceeds via the direct desulfurization route (main route) and the hydrogenation (HYD) pathway. The incorporation of Ti into the SBA-15 afforded catalysts that were more active than the Ti-free counterpart, due to the enhancement of the DDS route in this reaction. This difference was explained in terms of a larger number of coordinately unsaturated sites (CUS) of the metal sulfide on Ti-loaded catalysts. Under steady-state conditions, the CoMoST20 catalyst with a Si/Ti ratio of 20 was the most active among the catalysts studied. Since this catalyst exhibited both Ti4+ ions incorporated into the SBA-15 framework and separate anatase TiO2 clusters located on its surface, the activity enhancement on this sample was explained by the larger intrinsic activity of the "Co-Mo-S" phase located on these TiO2 nanoparticles. The Ti-SBA-15 supports and the CoMo/Ti-SBA-15 catalysts were studied by N-2 adsorption-desorption isotherms, XRD, TEM, FTIR of adsorbed pyridine and NO, UV-vis DRS, TPR, micro-Raman and XPS spectroscopy. (C) 2007 Elsevier B.V. All rights reserved.