Water-soluble heteropolyacid-based ionic liquids as effective catalysts for oxidation of benzyl alcohol in water with hydrogen peroxide

Abstract

A series of organic-inorganic composite catalysts were prepared by modifying tungstophosphoric acid (H3PW12O40) and propyl sulfonic acid-functionalized ionic complex. The obtained water-soluble catalysts were well characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and nuclear magnetic resonance, and investigated for their performance as homogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H2O2) in water. Among them, the [DMBPSH]H2PW12O40 catalyst exhibited the best oxidative activity with a desirable benzaldehyde (BzH) selectivity of 97.0% and an excellent BzOH conversion of 98.5%. Further kinetic studies and model analysis by response surface methodology revealed that alcohols’ oxidation reaction followed an apparent order of 2.2 with an activation energy of 36.18 kJ/mol. And the optimal reaction conditions were established as follows: BzOH/H2O2 molar ratio of 1:1.7, amount of catalyst 5.4 wt%, reaction time 3.9 h, amount of water 24 ml, and a maximum yield of BzH of 95.8%. Under optimum conditions, [DMBPSH]H2PW12O40 catalyst showed a superior catalytic efficiency and reusability due to strong acidity and excellent surface activity.

Keywords

• ionic liquid
• optimization
• oxidation
• reaction engineering
• tungstophosphoric acid