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The catalyst for diesel ultra-deep desulfurization is selected on the basis of several factors, including feedstock composition, liquid hourly space velocity, and operation pressure. Owing to their specific processing purposes, different catalyst systems, such as straight distillation, coking distillation, blends of straight distillation, and secondary processing oil, are applied for various feeds because of their considerable difference in terms of sulfur content, nitrogen content, aromatics constitute, and cetane number. This study aims to determine the most appropriate catalyst and grading scheme by evaluating the deep desulfurization efficiency of different schemes when processing various feeds. The results showed that the W-Mo-Ni/Mo-Co catalyst stacking is the most effective among various schemes because of the following reasons: (1) loading W-Mo-Ni catalyst on the upper bed of reactor not only benefits the saturation of polyaromatics even in the middle or at the end of the run but also provides low nitrogen feed for the bottom bed; (2) loading Mo-Co type catalyst with alkyl transfer performance in the bottom bed at high temperature reaction zone facilitates alkyl transfer reaction and mitigates the effect of thermodynamic equilibrium limitations in the middle and at the end of the run, consequently improving the HDS efficiency under high temperatures. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

It is usually difficult to remove dibenzothiophenes from diesel fuels by oxidation with molecular oxygen as an oxidant. In the study, tungsten oxide was supported on magnetic mesoporous silica by calcination to form a magnetically separable catalyst for oxidative desulfurization of diesel fuel. By tuning different calcining temperatures, the catalyst calcined at 500 °C showed a high catalytic activity with molecular oxygen as the oxidant. Under optimal reaction conditions, the sulfur removal of DBT reached 99.9% at 120 °C after 8 h. Furthermore, the removals of 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene could also get up to 98.2% and 92.3% under the same conditions. The reaction mechanism was explored by selective quenching experiments and FT-IR spectra. [ABSTRACT FROM AUTHOR]