Sulphuric acid-functionalized siliceous zirconia as an efficient and reusable catalyst for the synthesis of glycerol triacetate

In the present study, a sulphated siliceous zirconia catalyst (SSZ-550) has been prepared and characterized by XRD and FTIR analysis to indicate the incorporation of sulphate group over the matrix. X-ray photoelectron spectroscopy also revealed that sulphur group was incorporated over the matrix to impart the Bronsted acidity to the catalyst which is vital for the acetylation activity. To optimize the reaction parameters, viz. reagent molar ratios (3-12; glycerol/acetic acid), catalyst amount (1-5 wt%; catalyst/glycerol), reaction duration (20-50 min) and reaction temperature (30-100 degrees C) have been varied to obtain the optimum catalyst activity for the maximum glycerol triacetate yield. Finally, under the optimized reaction parameters of 9:1 glycerol/acetic acid molar ratio, 3 wt% catalyst, 80 degrees C reaction temperature and 40 min of reaction duration, a 93% glycerol triacetate yield was obtained. The catalyst was recovered from the reaction mixture and reused during six consecutive reaction runs while retaining 50% glycerol triacetate selectivity in the last cycle. A plausible mechanism suggests the heterogeneous catalyst-assisted protonation of carbonyl group of acetic acid to initiate the stepwise esterification of the hydroxyl groups of glycerol.