Synthesis of aluminium triflate-grafted MCM-41 as a water-tolerant acid catalyst for the ketalization of glycerol with acetone

An aluminium triflate covalently grafted over MCM-41 (Al(TF)-MS catalyst) was synthesized by a novel route, aiming to generate enhanced surface acidity as compared to aluminosilicates and water-tolerant mesoporous solid acid catalysts for reactions producing water as a co-product. The synthesis strategy involves an equimolar reaction of triflic acid and aluminium isopropoxide, followed by treatment with MCM-41. The direct treatment of triflic acid with Al-grafted MCM-41 (Al-MCM-41) was also attempted to synthesize silica-supported aluminium triflate. The MCM-41-supported aluminium triflate and triflic acid were synthesized as standard samples for comparison. The catalytic potentials of the samples were studied for the ketalization of glycerol with acetone into solketal. The TGA and Al-27 MAS NMR studies revealed the formation of aluminium triflate species on the silica surface in the Al(TF)-MS sample. The covalent grafting of the aluminium triflate species in the Al(TF)-MS sample was confirmed from catalysis and reusability tests, showing the stability of the aluminium triflate species against hydrolysis by water produced during the reaction. The solvent-free and selective conversion of glycerol to solketal at room temperature and the simple reusability of spent catalyst without any regeneration are some attractive features of Al(TF)-MS, making it a suitable catalyst for solketal synthesis.