Factors affecting the intergrowth morphology of hierarchical ZSM-11 microspheres

Key words:  intergrowth morphology  ZSM-11  hierarchical  factors

Abstract:

The hierarchical ZSM-11 microspheres with intergrowth morphology have been synthesized by using tetrabutylammonium bromide (TBABr) as the single template via a two-stage temperature-varying crystallization route. The effects of silica source, aluminum source, SiO₂/Al₂O_3ratio, alkali cations and the organic templates on the formation of intergrowth morphology were investigated. It is found that the silica sources, aluminum sources and the alkali cations mainly influence the rate of nucleation and the crystal growth via the depolymerization-polymerization rate, which affects the crystallization kinetics and the grain size of the final product. And there is no significant influence on the intergrowth morphology. Compared with silica source (silica gel microsphere), using liquid silica source (water glass and silica sol), can obtain smaller sized zeolite microspheres. It is favorable to get smaller crystals in a short period when using aluminiumisopropoxide as aluminum source compared with inorganic aluminum source. Besides, it is found the existence of K⁺ could suppress the fast formation of small crystals relative to the Li⁺ and Na⁺. The formation of the intergrowth morphology of the crystal product is affected directly by the template types, in which the existence of tetrabutylammonium cation is a key factor. It is also found that the intergrowth morphology becomes less evident with the decline of the Al amount in the system. And the presence of Al is one of the necessary factors for this intergrowth morphology.