Synthesis of MCM-48 mesoporous molecular sieve with thermal and hydrothermal stability with the aid of promoter anions

MCM-48 mesoporous molecular sieve with thermal and hydrothermal stability can be conveniently prepared within only 24 h with the aid of promoter anions SO42-, NO3- or Cl- (referred as P). The influences of the P/Si ratio and OH-/Si ratio to the formation of MCM-48 were investigated here, where the P/Si and OH-/Si ranges were set between 0-0.3 and 0.45-0.55, respectively. The suitable P/Si range for the formation of MCM-48 mainly depends on the hydration energy of the promoter anion, which follows the order of SO42- > Cl- > NO3-. The lower the hydration energy is, the wider the P/Si range is. Moreover, the P/Si range also varies with the OH-/Si, which is wider when the OH-/Si is lower. The thermal and hydrothermal stability of MCM-48 can be considerably improved by directly adding promoter anions to the synthesis gel. The results show SO42- is the most effective promoter for the improvement of structure stability due to its extremely high hydration energy, which is followed by NO3- and Cl- successively. Each promoter added to the synthesis gel has an optimum P/Si ratio for the improvement of the stability since overmuch addition of promoters obstructs the electronic interaction between anion silicates and cation surfactants, leading to the formation of poor ordered MCM-48 materials. (c) 2006 Elsevier Inc. All rights reserved.