摘要
Polyoxometalates （POMs） are useful catalysts in both redox and acid catalysis reactions since its catalytic features can be controlled at a molecular level. We investigated POM （POM = H3PW12040） on tantalum pentoxide （Ta2O5） via hydrolysis of tantalum pentachloride （TaCl5） in the presence of POM using the sol-gel method for acid catalytic reaction. All obtained amorphous materials have been characterized by inductively coupled plasma atomic emission spectroscopy （ICP-AES）, Fourier transform infrared （FT-IR） spectra, Raman scattering spectroscopy, 31P magic-angle spinning （MAS） NMR, field emission scanning electron microscopy （FESEM）, and nitrogen adsorption/desorption analysis, in order to confirm the structure integrity of the Keggin unit in as-prepared composites and investigate the morphology and surface textural property of the composites. Catalytic activity of the catalysts has been evaluated for esterification of acetic acid with ethanol as a model reaction with different catalytic reaction parameters such as POM loading, reaction time, catalyst dose, molar ratio of the reactants, etc. The conversion of ethanol reached 87.4 % and the turnover frequency （TOF） was 2.9x 103.Meanwhile, it is easy to separate and recover POM/Ta205 from the reaction system.
Polyoxometalates （POMs） are useful catalysts in both redox and acid catalysis reactions since its catalytic features can be controlled at a molecular level. We investigated POM （POM = H3PW12040） on tantalum pentoxide （Ta2O5） via hydrolysis of tantalum pentachloride （TaCl5） in the presence of POM using the sol-gel method for acid catalytic reaction. All obtained amorphous materials have been characterized by inductively coupled plasma atomic emission spectroscopy （ICP-AES）, Fourier transform infrared （FT-IR） spectra, Raman scattering spectroscopy, 31P magic-angle spinning （MAS） NMR, field emission scanning electron microscopy （FESEM）, and nitrogen adsorption/desorption analysis, in order to confirm the structure integrity of the Keggin unit in as-prepared composites and investigate the morphology and surface textural property of the composites. Catalytic activity of the catalysts has been evaluated for esterification of acetic acid with ethanol as a model reaction with different catalytic reaction parameters such as POM loading, reaction time, catalyst dose, molar ratio of the reactants, etc. The conversion of ethanol reached 87.4 % and the turnover frequency （TOF） was 2.9x 103.Meanwhile, it is easy to separate and recover POM/Ta205 from the reaction system.
基金
Funded by the National Natural Science Foundation of China(No.51002111)
the Fundamental Research Funds for the Central Universities(No.2012-IV-085)
