Structure and Catalytic Performance of H3PW12O40/SiO2 Prepared by Several Methods

Silica-supported H3PW12O40 catalysts were prepared by the impregnation method, sol-gel technique, and sol-gel technique using ionic liquids as the template, respectively, to solve the problems of H3PW12O40 such as low surface area, difficult separation, and reuse. The catalysts were characterized by means of Fourier transform infrared spectroscopy, X-ray diffraction, N2 adsorption, and NH3 temperature-programmed desorption. Their catalytic performance for the nitration of benzene was evaluated. The results revealed that H3PW12O40 in all the catalyst samples kept its Keggin structure. The specific surface area of the H3PW12O40/SiO2 catalyst prepared by the impregnation method was 475.2 m2/g, and the yield of benzene over it decreased from 82.4% to 70.7% after 4 runs. The specific surface area of the H3PW12O40/SiO2 catalyst prepared by the sol-gel technique was 498.6 m2/g, and the nitration of benzene over it decreased from 85.1% to 79.6% after 4 runs. The H3PW12O40/SiO2 catalyst prepared by the sol-gel technique using [emim]BF4 as the template had mesoporous structure and a specific surface area of 558.5 m2/g, and the nitration of benzene over this catalyst decreased from 84.7% to 79.9% after 4 runs. The three H3PW12O40/SiO2 catalyst samples showed higher stability and activity in the nitration of benzene.