Performance Comparison of Molybdenum-Impregnated Sulfated Mesoporous Silica Catalysts by Spray and Wet Impregnation in Transforming Used Palm Cooking Oil into Bio-Jet Fuel

This study examined the effects of two molybdenum impregnation methods, i.e., spray and wet impregnation, on the activity and selectivity of sulfated mesoporous silica (SO4–SiO2) in producing bio-jet fuel from used palm cooking oil through an atmospheric hydrotreatment process. For the wet impregnation method, 2% (w/w) molybdenum metal from (NH4)6Mo7O24·4H2O was dissolved in 50 mL of deionized water, and 5 g of SO4–SiO2 was soaked in this solution and stirred for 24 h. In contrast, for the spray impregnation method, the same concentration of molybdenum was dissolved in 5 mL of deionized water and sprayed onto 5 g of SO4–SiO2 using a spray bottle. Surprisingly, the spray impregnation method successfully produced the Mo/SO4–SiO2 catalyst, which exhibited higher acidity, BET surface area, and thermal stability than the wet impregnation catalyst. XPS data revealed that the spray catalyst was predominantly composed of Mo(IV) species, resulting in a liquid product conversion of 63.65%. The selectivity for bio-jet fuel (first drop–450 °C) and the total bio-jet fuel yield were 84.71% and 51.29%, respectively. These results outperformed those obtained with the Mo/SO4–SiO2 wet catalyst primarily composed of Mo(VI) species. Furthermore, the second and third applications of the Mo/SO4–SiO2 spray catalyst produced promising total bio-jet fuel yields of 50.96% and 46.59%, respectively. Therefore, this catalyst, prepared using a straightforward method, shows significant potential as a candidate for the biofuel industry in the future to support a green aviation industry.