Effect of delayed neutralization on the synthesis of mesoporous MCM-41 molecular sieves

We present a detailed study on the preparation of highly-ordered MCM-41 molecular sieves based on a new delayed neutralization process. Products synthesized from cationic surfactants with different carbon chain lengths (alkyltrimethylammonium salt), counterions and head groups gave almost constant wall thickness (about 1.7nm), small lattice contraction after calcination, and sharp pore size distribution. However, the structural order decreased with the decrease of the carbon chain length. Adding a proper amount of alcohols as cosurfactants would improve the XRD patterns of the surfactants with carbon chain lengths less than 14. A head group of larger size would shrink the pore size and damage somewhat the structural order of MCM-41 materials. The rate of acidification and the source of the acid did not have much effect on the XRD patterns of MCM-41, but would affect its morphology. The formation process and the nature of the MCM-41 product based on octadecyltrimethylammonium bromide (C₁₈TMAB) are dependent on the synthetic temperature.