Catalytic decomposition of benzothiophenic and dibenzothiophenic sulfones over MgO-based catalysts

Bulk and supported MgO based catalysts with weight loadings from 3 to 30 wt% were prepared by wet impregnation (WI) and sol-gel (SG) methods and tested for sulfone decomposition to sulfur-free hydrocarbon in real and surrogate liquid hydrocarbon fuels. The catalysts were characterized by BET analysis, XRD measurements,CO2-chemisorption and XPS. Among bulk MgO, MgO/Al2O3 (WI) and MgO/SiO2 (WI) catalysts, activity for sulfone decomposition was greatly influenced by crystallite size of MgO. Increasing calcination temperature increased MgO crystallite size which adversely affected catalytic activity. 30MgO/SiO2 (WI) showed the highest activity for decomposition of sulfones both in real jet and diesel fuels. The effect of temperature on decomposition of benzothiophenic and dibenzothiophenic sulfones over 30MgO/SiO2 (WI) was examined from 320 to 450 degrees C using (pre-oxidized) JP-5 jet fuel and BP-325 diesel fuel to elucidate the difference in decomposition activity of two and three ring sulfones. At 450 degrees C, about 77% of the dibenzothiophenic sulfones in BP-325 diesel fuel were decomposed over 30MgO/SiO2 catalysts. Benzothiophenic sulfones were more active for decomposition and about 97% of the sulfones in JP-5jet fuel were decomposed at 400 degrees C. In contrast to bulk MgO, MgO/Al2O3 (WI) and MgO/SiO2(WI) catalysts; MgO/TiO2 (WI) and MgO/SiO2 (SG) promoted undesired conversion of sulfones back to sulfur compounds by oxygen removal. The difference in selectivity was attributed to the effect of support and synthesis procedure potentially resulting in catalyst with different surface properties. Model compounds decomposition of dibenzothiophenic sulfone and 3-methyl benzothiophene sulfone were also studied to evaluate the potential pathway from sulfones to sulfur-free hydrocarbons. (C) 2013 Elsevier B.V. All rights reserved.