Preparation And Characterization Of Mesoporous Mordenite

Mordenite (MOR), with high Si/Al ratio, high hydrothermal stability and strong acidity, is widely used in the chemical industry, especially in alkylation and isomerization processes. Besides its wide applications, however, mass transfer limitations of molecules in the micropores of MOR are available, leading to some problems associated with low catalytic activity and easy deactivation.The adsorption and diffusion of hydrocarbon molecules in MOR crystals are of great importance. However, most of the conducted work has been performed on commercial MOR samples having very small crystal sizes (<0.2μm). The fine zeolite crystals have a large exterior surface. The adsorption on the exterior surface consequently interferes with the accurate determination of the adsorption and diffusion of probe molecules inside zeolite micropores.In this thesis, based on the tailored synthesis of MOR with different crystal sizes, the adsorption and diffusion of n-butane as probe in of the synthesized MOR crystals have been systematically investigated. Additionally, mesoporous MOR has been prepared by post-treatment to improve its mass transfer properties. The main results are summarized as follows:1) MOR crystals have been hydrothermally synthesized using silicic acid powder as the silica source. The effects of the premixed time of the silicic acid powder with NaOH solution and the crystallization time on the crystal size of the synthesized MOR were systematically investigated. Additionally, the study was conducted on the adsorption and diffusion of n-butane as probe in the synthesized mordenite (MOR) crystals with a uniform size of about 8μm. The results show that the uptake of n-butane in the parent Na-MOR zeolite is extremely slow. However, the uptake can be significantly improved after the parent Na-MOR zeolite transferred into its H-form. However, after the H-MOR zeolite transferred into its Na-form, the uptake of n-butane is almost the same as that in the parent Na-MOR. Therefore, it is concluded that the Na species remaining in the synthesized MOR channels could cause the blockage of MOR micropores, resulting in the strong mass-transfer limitations.2) Nanocrystalline MOR crystals were synthesized hydrothermally using colloid silica as the silica source and the synthesized crystals were characterized by XRD and SEM techniques. The effects of several synthetic parameters, such as alkalinity in the synthesis solution, the crystallization temperature and time, addition of seeded MOR crystals on the size of the synthesized MOR crystals were systematically investigated. Rod-like nanosized MOR crystals (ca.400 nm×200 nm) to aggregate to form particles have been successfully synthesized by optimizing the alkalinity in the synthesis solution, crystallization temperature and time, and addition of seeded MOR crystals. After the alkali-treatment, mesopores were introduced into the obtained MOR crystals.