New understanding and simple approach to synthesize highly hydrothermally stable and ordered mesoporous materials

Highly ordered mesoporous materials with extremely high hydrothermal stability have been successfully synthesized by a novel and facile approach. Our method is built on the understanding that the hydrothermal treatment process plays an important role in the synthesis of mesoporous materials. It is proposed that in order to use high temperature hydrothermal treatment to increase the inorganic framework cross-linkage, an important requirement is that the organic surfactants must be retained as much as possible to maintain the preformed organic - inorganic composite mesostructure against framework shrinkage during the hydrothermal treatment process. This requirement can be achieved by enhancing the surfactant - silanol interaction at the organic - inorganic interface through adjusting the hydrothermal treatment pH and adding acetic acid (HAc) during the synthesis. When a high temperature (∼200 °C) hydrothermal treatment is employed, ordered mesoporous materials can only be obtained in a hydrothermal treatment pH range of 1-3. When the hydrothermal treatment pH is near the isoelectric point of silica, the highest silanol density on silica walls can entrap the largest amount of surfactants within pores, resulting in highly ordered mesostructured materials. Moreover, the disadvantage of the hydrothermal treatment under strong acidic conditions widely adopted in the literature has been revealed. Compared to previous reports, our approach is simple and does not involve environmentally unfriendly or expensive agents, thus is easy to be scaled up for industrial applications. Most strikingly, the highly ordered mesostructure of aluminosilicate synthesized by our approach can be maintained after steam treatment at 800 °C for 5 h with only a 4.9% decrease in the Brunauer - Emmett - Teller surface area. Our achievements have added new contributions to understanding the preparation of highly ordered and highly stable mesoporous materials, which sheds light on the practical applications of this new family of porous materials in the petroleum and petrochemical industry.