Aerobic epoxidation of limonene using cobalt substituted mesoporous SBA-16 Part 1: Optimization via Response Surface Methodology (RSM)

Abstract

Cobalt substituted mesoporous SBA-16 catalysts, made by post grafting technique using directly cobalt acetylacetonate as the precursor was prepared. High loading of cobalt finely dispersed on SBA-16 silica was obtained. The Co/SBA-16 catalysts exhibited high conversion and selectivity in epoxidation of limonene towards limonene epoxides with molecular oxygen as the most desirable oxidant and isobutyraldehyde as co-reagent under very mild conditions in the presence of the green solvent ethylacetate. A variety of characterization techniques such as nitrogen physisorption, XRD, DR-UV–vis, XPS, TEM indicates that the proposed impregnation procedure is a highly tunable and reproducible strategy to disperse transition metals in mesoporous silica materials. The unique pore structure of Co/SBA-16 catalysts could be beneficial for the epoxidation of bulky alkene molecules. The reaction conditions were systematically investigated using a statistical experimental design. Repeated catalytic tests showed no remarkable difference in the activity of fresh and recycled catalysts over three process cycles.