The Effect of Alkaline Treatment to the Structure of ZSM5 Zeolites

Hierarchical zeolites combining micro- and mesoporosity were prepared using desilication method in alkaline solution of NaOH 0.2 M on two types of ZSM5: ”template free” commercial ZSM5 (Si/Al 8.62) and ‘templated’ as-synthesized ZSM5 (Si/Al 25). The powder X-ray diffraction patterns revealed that crystallinity and short-range order in the alkaline treated zeolites were virtually unchanged compared to both of the parent zeolites. The surface measurement on the ”template free” ZSM5 zeolites showed that the surface area was reduced by 2.33%, but the adsorption isotherm can be categorized into Type IV which is typical of for mesoporous material, supported by the change in mesopore volume, and the BJH pore size distribution (from 10 to 18 nm). On the other hand, the surface area of the alkaline treated as-synthesized ZSM5 was increased by 8.25%, but its isotherm adsorption curve falls into Type I for microporous structure. The mesopore volume was increased by 26%, from 0.037 cm3/g to 0.046 cm3/g, with the intrinsic zeolite properties were mainly preserved. Based on these results, it can be concluded that the existence of organic template plays an important role in preserving the zeolitic structure during the alkaline treatment.