Investigation of synthesizing MCM-41/ZSM-5 composites

MCM-41/ZSM-5 composites were prepared using a dual templating method through a process of two-step crystallization. Mesoporous MCM-41 was first synthesized using the self-assembling of surfactant cetyltrimethylammonium bromide and subsequently the amorphous wall of MCM-41 was recrystallized with a structure-directing agent tetrapropylammonium bromide, which was introduced into the MCM-41 wall through a pretreatment process. A solid to solid-phase transformation mechanism was presented for the recrystallization of MCM-41 framework. Two kinds of stable MCM-41/ZSM-5 composites can be synthesized during the course of recrystallization. Crystallized mesoporous MCM-41 containing only short-range ordered ZSM-5 structure was first synthesized in the early stage of the recrystallization. With the increase of recrystallization time, some discrete micron-sized ZSM-5 crystals were produced and firmly attached to the loose aggregates of crystallized MCM-41, and another kind of MCM-41/ZSM-5 composite containing interconnected mesopore and micropore was therefore obtained. Because of improved acidity and a 2-fold pore system, both MCM-41/ZSM-5 composites are more advantageous than amorphous MCM-41 and a mechanical mixture of MCM-41 and ZSM-5 in acid catalysis.