An Efficient and Recyclable Sn-Based Phosphotungstic Acid with Tunable Brønsted/Lewis Acidity for Selective Oxidation of Benzyl Alcohol

A series of metal ion (M = Sn2+, Fe3+, Ni2+, Co2+, Ag+, Cu2+) exchanged tungstophosphoric acid (H3PW12O40; TPA) catalysts with tunable Bronsted/Lewis acidity were synthesized and exploited for the oxidation benzyl alcohol (BzOH) to benzaldehyde (BzH) using hydrogen peroxide (H2O2) as oxidant. The structure these M-TPA composite salts was also characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analyses (TGA) solid-state 31P nuclear magnetic resonance (NMR) probe molecule method. Among M-TPAs, Sn1/2H2PW12O40 catalyst, which presented strong Bronsted acidity, synergistic effect pseudo-liquid characteristic property, exhibited excellent catalytic activity durability 98.2% BzH selectivity 95.1% yield. optimal conditions BzOH optimized response surface methodology (RSM) follows: n(BzOH)/n(H2O2) 1:1.25, catalyst amount 5.5 wt.% BzOH, water 17 mL, 3.3 h reaction time, temperature 393 K. Moreover, further kinetic study confirmed that order 2.64 activation energy 21.75 kJ mol-1.