Heteropoly Tungstate Supported on Metal Oxide Catalysts for Liquid Phase Oxidation of Benzyl Alcohol with Hydrogen Peroxide

Han Xiaoxiang,Wang Kuiwu,Hung Chin-Te,Chen Qing,Kuang Yingying,Liu Shang-Bin,Liu Li-Li,Xiong Chunhua,Tang Xiujuan

doi:10.21577/0103-5053.20170117

Abstract

A series of metal oxide supported tungstophosphoric acid catalysts were prepared by impregnation. The physicochemical and acidic properties of these materials were characterized by a variety of different analytical and spectroscopic techniques, namely Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and nuclear magnetic resonance (NMR), and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H2O2). Among them, 20 wt.% H3PW12O40/CeO2 catalyst exhibited the best oxidative activity. Further process optimization by response surface methodology (RSM) based on the Box-Behnken design model resulted in a benzyl alcohol conversion of 95.2% and a benzaldehyde yield of 94.2% with 98.9% selectivity, in good agreement with the experimental results. Kinetic studies based on an irreversible parallel reaction model led to an activation energy (Ea) of 44.73 kJ mol-1.

Highlights

Aldehydes and ketones, which are important chemical intermediates, play critical roles in chemical industries and have been extensively used in drugs, additives and spices industries.[1,2,3,4] These carbonyl compounds are normally produced by selective catalytic oxidation, which has been widely used in clean production of chemicals.[5,6,7,8,9] One of the major concerns for oxidation reaction is product selectivity, a challenge arising from the fact that most products are thermodynamically unstable
Regardless of minor variations in intensities of characteristic bands responsible for the PW polyanions, their presence in all supported HPW/CeO2 catalysts confirm that Keggin structure remains intact upon supporting varied where CA and CB represents the concentration of benzyl alcohol (BzOH) and H2O2, respectively, k’ is the rate constant, and α and β denote the reaction order of BzOH and H2O2, respectively
The satisfying catalytic performance observed for the 20HPW/CeO2 catalyst during oxidation of BzOH with H2O2 may be correlated to its acid properties, as evidenced by results obtained from 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) of adsorbed trimethylphosphine oxide (TMPO) (Figures 3 and 4) discussed above

Summary

Introduction

Aldehydes and ketones, which are important chemical intermediates, play critical roles in chemical industries and have been extensively used in drugs, additives and spices industries.[1,2,3,4] These carbonyl compounds are normally produced by selective catalytic oxidation, which has been widely used in clean production of chemicals.[5,6,7,8,9] One of the major concerns for oxidation reaction is product selectivity, a challenge arising from the fact that most products are thermodynamically unstable. Together with the ultra-strong Brønsted acidity, a synergy effect due to Brønsted-Lewis acid sites may be inferred for the satisfying catalytic performance observed for the supported HPW/CeO2 catalysts during oxidation of BzOH (vide infra).

Results

Conclusion