New NiMo catalysts supported on Al-containing SBA-16 for 4,6-DMDBT hydrodesulfurization: Effect of the alumination method

A series of Al-containing mesoporous molecular sieves SBA-16 was prepared by synthetic and post-synthetic methods using different Al sources. NiMo catalysts supported on Al-SBA-16 were prepared and tested in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS) reaction. The synthesized solids were characterized by N2 physisorption, XRD, ammonia TPD, Py FT-IR, 27Al MAS–NMR, temperature programmed reduction, chemical analysis and HRTEM. It was found that the characteristics of the Al-SBA-16-supports strongly depend on the used Al source and the method selected for Al incorporation into the SBA structure. Post-synthetic alumination of SBA-16 by reacting with AlCl3 or Al(i-PrO)3 has a number of advantages in comparison with the incorporation of Al by grafting with NaAlO2 or direct synthesis, among them, (i) a good control of Al content in the sample; (ii) little influence on the mesoporous structure of the parent SBA-16; (iii) creation of Brönsted acid sites; and (iv) stronger interaction with deposited Ni and Mo species providing them better dispersion. NiMo catalysts supported on Al-SBA-16, which were prepared by grafting with AlCl3 or Al(i-PrO)3, show high activity in 4,6-DMDBT HDS; this can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of these catalysts, namely, to the participation of both types of sites, coordinatively unsaturated sites (CUS) of NiMoS active phase and Brönsted acid sites of the support, in the catalytic transformations of 4,6-DMDBT.