Production of n-butyl levulinate over modified KIT-6 catalysts: comparison of the activity of KIT-SO3H and Al-KIT-6 catalysts

The catalytic activity of propylsulfonic acid-functionalized mesoporous silica (KIT-SO3H) was compared to the performance of alumina-incorporated KIT-6 (Al-KIT-6) in the esterification reaction of the biomass-derived levulinic acid with n-butanol. The catalysts were prepared by functionalization of the silica support with propylsulfonic acid (Pr-SO3H) by post-synthesis grafting using 3-mercaptopropyltrimethoxysilane as a propyl-thiol precursor followed by oxidation. In addition, Al-KIT-6 was synthesized according to in situ synthesis. Catalysts were characterized using various techniques such as XRD, nitrogen adsorption/desorption, SEM, TGA, ICP-OES, FT-IR and elemental analysis. It is evident that increases in catalyst loading, butyl alcohol-to-levulinic acid ratio and reaction temperature significantly enhance the butyl levulinate yield. The reusability and stability of catalysts were evaluated, and it was found that while esterification reaction by KIT-SO3H compound catalyzed under milder conditions, the stability of Al-KIT-6 catalyst was better.