Sulfonic Acid and Phospho-tungstic Acid-Loaded Organosilicon Nanotubes for Efficient Catalysis of Esterification Reaction

Abstract

In this paper, we proposed the synthesis of dual-acid organosilicon nanotubes loaded with sulfonic acid (─SO₃H) and phospho-tungstic acid (HPW) named SO₃H_x-Si-NTs/HPW_y (Si-NTs = ethylene-bridged organosilicon nanotubes), by one-pot approach using P105 (EO₃₇PO₅₆EO₃₇) as a single micelle template for the first time. A variety of analytical methods were employed to characterize the composites and the optimal material SO₃H_0.3-Si-NTs/HPW_0.7, which exhibits strong Brønsted acidity, displays a hollow tubular structure with a diameter of approximately 9.1 nm. Due to the synergistic effect of ─SO₃H and HPW, SO₃H_0.3-Si-NTs/HPW_0.7 achieved a 99.3% yield of methyl oleate under the optimal reaction conditions (25/1 methanol/oleic acid molar ratio and 60 mg catalyst dosage at 120 °C for 8 h) and maintained a yield of 92.0% after five times reuse. Simultaneously, under the optimal reaction conditions (5/1 ethanol/levulinic acid molar ratio and 5 wt% catalyst dosage at 115 °C for 4 h), the yield of ethyl levulinate was 90.6%, with a yield of 83.1% after five cycles of reuse. The catalytic results indicate that SO₃H_0.3-Si-NTs/HPW_0.7 has excellent catalytic activity and stability.