Preparation of novel uniform mesoporous alumina catalysts by the sol–gel method

Abstract

A novel sol–gel process for preparing alumina sol is reported in this article. Ultrasound is used to prepare the alumina sol at room temperature. The study of the effect of ultrasound as a function of treatment time on the pH and the particle diameter distribution of the sol was also made. 27 Al NMR, TEM, XRD and DTA were used to detect the properties of the sol and the alumina materials. The result of 27 Al NMR shows that there existed Al 13 7+ species in the sol. The acid used not only acted as catalyst for peptizing, but also as reactant to react with aluminum hydroxide to produce the Al 13 7+ species. On the other hand, TEM results show that the morphology of the particles was spherical in the sol, but transformed to needle-like as well as spherical when calcined at 450°C. At the end, the morphology of the particles changed to spherical again at 550°C. By using this alumina sol as precursor, an alumina material with uniform mesoporous distribution was formed after calcination at 550°C without adding any templates or other organic additives. The results of this work also show that the formation of alumina with uniform mesoporous distribution is related to its crystalline phase, the morphology of the particles and the particle diameter distribution of the precursor sol.