Catalytic oxidative desulfurization mechanism in Lewis–Brønsted complex acid

• Lewis acid is the core of complex acid system, catalyzing the sulfur oxidation.
• Lewis acid improves the Brønsted acidity of system and the dissolution of oxidant.
• Thiophenic compound is oxidized not only at S-atom but also at unsaturated bond.
• Catalysis of complex acid for ODS against olefins is controllable.

Lewis–Brønsted complex acid, such as BF3, SnCl4, FeCl3, or ZnCl2-CH3COOH, can enhance thiophenic compound oxidation using solid oxidants. The catalytic oxidative mechanism was studied here. For the catalysis of the complex acid system, Lewis acid was the core, improving the Brønsted acidity of the system, promoting the dissolution of oxidant in the system, and finally catalyzing the oxidation of sulfur in the oil. For the oxidation of thiophenic compound, dibenzothiophene (DBT) was oxidized to its sulfone, but benzothiophene (BT) and thiophene (T) were oxidized to some unidentified products besides the sulfones or sulfoxides. These unidentified products originated from the oxidation of unsaturated bonds on thiophenic compounds. The electronic property of unsaturated bonds, which included bond order and π orbital occupancy, was used to explain the reactivity of unsaturated bonds on those compounds. On the basis of mechanism obtained, the catalysis for the oxidation of sulfur against olefins was controlled.

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