Titanium-modified MCM-41 molecular sieves as efficient supports to increase the hydrogenation abilities of NiMoS and CoMoS catalysts

Abstract

Ti modified MCM-41-supported NiMo and CoMo catalysts and their respective Ti free reference catalysts were prepared, characterized, and tested for the hydrodesulfurization reactions. The samples were synthesized by well-known procedures, such as liquid crystal templating and successive impregnation method for the supports and catalysts, respectively. Ti precursor was directly incorporated into the micellar solution before adding the silica precursor at different molar Si/Ti ratios (x=75 and 50). Fourier transform infrared spectroscopy, solid-state 29Si-nuclear magnetic resonance, small- and wide-angle X-ray diffraction, and nitrogen physisorption were used as characterization techniques. Four sulfided catalysts were also characterized by high-resolution transmission electron microscopy. The catalysts showed important increases in the reaction rates during both thiophene and dibenzothiophene hydrodesulfurization when the support was structurally modified with Ti-atoms. The samples supported on Ti-MCM-41(75) presented a higher activity than those supported on Ti-MCM-41(50), and they were superior to their respective Si-MCM-41-supported NiMoS and CoMoS catalysts, even NiMoTiM75 and CoMoTiM75 catalysts presented better performance compared to the conventional NiMo/Al2O3 and CoMo/Al2O3 catalysts in the DBT hydrodesulfurization. Ti incorporation also enhanced the selectivities to the hydrogenated products, which could be beneficial to destabilize refractory S-containing molecules.