Oxidative desulfurization of diesel fuel by mesoporous phosphotungstic acid/SiO2: the effect of preparation methods on catalytic performance

Two kinds of mesoporous phosphotungstic acid/SiO2 (HPW/SiO2) have been synthesized by amino-functionalized (AF) method and evaporation-induced self-assembly (EISA) method, and their catalytic performance was investigated for deep oxidative desulfurization of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in diesel oil. Various analysis techniques such as XRD, TEM, N-2 adsorption/desorption isotherms, FT-IR and P-31 MAS NMR spectra have been used to investigate the pore structure and chemical properties of the resultant catalysts. The structural and spectroscopic analysis indicates both catalysts have a highly ordered 2D hexagonal mesostructure. HPW/SiO2-EISA can maintain the Keggin structure of HPW molecules and has a high BET surface area (403 m(2)/g). But in the AF method, the mesostructure of SBA-15 are partially blocked after the introduction of HPW molecules, and the Keggin structure of HPW molecules has been damaged. The catalytic performance results also show that HPW/SiO2-EISA exhibits higher catalytic activity and stability compared to HPW/SiO2-AF. As for HPW/SiO2-EISA, the conversions of DBT, 4,6-DMDBT and BT are found to be 99.6, 97.6, 94.8 %, respectively. It shows a good maintenance of activity even after the 7th cycle of use. While corresponding conversions by using HPW/SiO2-AF are found to be 90.2, 89.1 and 87.6 %, and the DBT conversion decreases to 75.7 % after the 5th cycle of use.