New Understanding and Simple Approach to Synthesize Highly Hydrothermally Stable and Ordered Mesoporous Materials

Abstract

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.

Hierarchical Mesoporous Zeolites: Direct Self‐Assembly Synthesis in a Conventional Surfactant Solution by Kinetic Control over the Zeolite Seed Formation

“…To solve this problem, Zhu et al proposed a new strategy to prepare hierarchical zeolites, which used CTAB coupled with tert-butyl alcohol (TBA) and 1,3,5-trimethylbenzene (TMB) as a cosolvent and additive, respectively, enhancing the stability of the surfactant micelles. [24] This coincided with the strong interactions required between zeolite precursors and templates.…”

Improved hydrothermal stability and acidic properties of ordered mesoporous SBA-15 analogs assembled from nanosized ZSM-5 precursors

“…It has been reported that the acidity of the synthesis solution is a decisive factor for not only the mesoporous regularity but also the successful incorporation of aluminum into the SBA-15 framework [31][32][33]. In this work, therefore, such effects of hydrothermal treatment pH (htt-pH) in the preparation of SBA-15 analogs from ZSM-5 nanoseeds at high temperature were investigated systematically.…”

Synthesis and characteristics of SBA-15 with thick pore wall and high hydrothermal stability

“…These approaches contain the past-treatment with organosilane [9,10], pH adjusting [11], increasing hydrothermal treatment temperature [12,13], removing surface Si-OH groups by silylation and F-ions [14,15], addition of crystal seed precursors [16,17], doping heteroatoms [18,19], and addition of inorganic salts [20,21]. These methods have played an important role in improving hydrothermal stability of mesoporous materials.…”