Development of new catalysts for deep hydrodesulfurization of gas oil

TiO₂–Al₂O₃ composite supports have been prepared by chemical vapor deposition (CVD) over γ-Al₂O₃ substrate, using TiCl₄ as the precursor. High dispersion of TiO₂ overlayer on the surface of Al₂O₃ has been obtained, and no cluster formation has been detected. The catalytic behavior of Mo supported on Al₂O₃, TiO₂ and TiO₂–Al₂O₃ composite has been investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the Mo catalysts supported on TiO₂–Al₂O₃ composite, in particular for the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) is much higher than that of conversion obtained over Mo catalyst supported on Al₂O₃. The ratio of the corresponding cyclohexylbenzenes/biphenyls is increased over Mo catalyst supported on TiO₂–Al₂O₃ composite support. This means that the reaction rate of prehydrogenation of an aromatic ring rather than the rate of hydrogenolysis of C–S bond cleavage is accelerated for the HDS of DBT derivatives. The Mo/TiO₂–Al₂O₃ catalyst leads to higher catalytic performance for deep HDS of gas oil.     

Chemothermal pulverization: Crushing titanate crystals to obtain nanosized powders via high-temperature treatment

In this study, we investigated chemothermal pulverization (CTP) phenomena that are induced in titanate single crystals and ceramics by high-temperature treatment at approximately 1000℃ under reactive gas containing ammonia and oxygen and cause these materials to break down into nanosized powders. Structural characterization revealed that there were many nanosized voids formed in titanates during heat treatment for CTP, and subsequent analysis revealed that these voids were filled with nitrogen gas. These results indicated that CTP consisted of four steps: the in-diffusion of nitride ions from the surface to titanates, the deposition of nitrogen molecules (gas) inside the titanate crystals instead of nitride formation, the growth of voids by further nitrogen transport from the surface to voids, and, finally, the breakdown of the walls between voids to form nanopowders. Furthermore, we discussed the exact mechanism of CTP phenomena by examining the effect of doping into titanates on the progress of CTP and by conducting theoretical calculations for the simulation of nitrogen impurities in titanate lattices.