FCC gasoline sulfur reduction additives: Mechanism and active sites

The interaction and reactivity of model sulfur compounds with gasoline sulfur reduction additives based on Zn-, Na-, and F-doped γ-Al2O3 have been investigated by in situ and operando infrared spectroscopy and microactivity tests. While gasoline sulfur reduction additives selectively crack tetrahydrothiophene (THT) into H2S and butadiene they are inactive toward thiophene. When blended with a fluid catalytic cracking (FCC) catalyst, gasoline sulfur reduction additives do reduce (alkyl)thiophene contents in gasoline. There is a synergy between the FCC catalyst and the gasoline sulfur reduction additive leading to sulfur reduction. Under actual FCC conditions, Al2O3-based gasoline sulfur reduction additives reduce thiophenic compounds by decomposing (alkyl)THT formed via hydrogen transfer on the FCC catalyst. A balance between acid and base properties is required for an optimum activity of the additive, suggesting that THT cracking occurs on Lewis acid–base pairs through successive E2 eliminations.