H3PW12O40 synergized with MCM-41 for the catalytic nitration of benzene with NO2 to nitrobenzene

Developing a new environmentally friendly process for benzene nitration to nitrobenzene has been highly desirable for a long time. In this work, NO2 was used as a nitration agent to replace traditional nitric acid, and different mesoporous SiO2 and their supported heteropoly acid (salt) were employed to catalyze benzene nitration to nitrobenzene. Several typical catalysts were characterized using XRD, BET and FT-IR, and the acid amounts of the various catalysts were determined. The effects of various factors such as different catalysts, the molar ratio of benzene to NO2, reaction temperature, reaction time, HPW loading, the acid amounts of the catalyst and the reuse of the catalyst on the nitration reaction have also been systematically examined. The results indicate that the supported HPW/MCM-41 catalysts exhibit a remarkably synergistic catalytic performance on the nitration reaction of benzene to nitrobenzene. In particular, the 50% HPW/MCM-41 catalyst gives the best results with 73.4% benzene conversion and 98.8% selectivity to nitrobenzene under the optimal reaction conditions. Moreover, the mesoporous structure of MCM-41 was retained under the high loading of HPW. The possible reaction mechanism for the nitration reaction of benzene with NO2 over HPW/MCM-41 is suggested in the present work. This method provides a promising strategy for the preparation of nitro-aromatic compounds from a catalytic nitration reaction by using NO2 as the nitration reagent.