Marina Kustova

Hierarchical zeolites: progress on synthesis and characterization of mesoporous zeolite single crystal catalysts

Abstract Recently, a new family of crystalline zeolitic materials was reported, the so-called mesoporous zeolite single crystals featuring individual zeolite single crystals with an additional noncrystalline mesopore system interconnected with the usual micropore system of the zeolite, resulting in a hierarchical pore size distribution. In this work, the preparation of mesoporous ZSM-12 single crystal catalysts using a new improved procedure for directly introducing carbon in the reaction mixture is reported. The microwave heating technique is also applied for the synthesis of mesoporous silicalite-1 single crystals using this direct introduction of carbon into the reaction mixture. All samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (NH 3 -TPD), and N 2 adsorption measurements. Additionally, the results of diffusion of n -hexadecane in conventional and mesoporous zeolites are presented. Isomerization and cracking of n- hexadecane was chosen as model test reaction for these materials. All results support that mesoporous zeolites are superior catalysts due to improved mass transport. Importantly, the mesoporous zeolites show significant improved resistance to poisoning by carbon formation.

Synthesis and characterization of mesoporous ZSM-5 core-shell particles for improved catalytic properties

Abstract HZSM-5 is a unique catalyst for the conversion of methanol, dimethyl ether and other oxygenates into gasoline. During this process, catalyst deactivation by coking requires frequent regeneration and the improvement of catalyst life time is one of the challenges in catalyst development. In this study, a series of mesoporous samples consisting of a ZSM-5 core and a silicalite shell have been synthesized and characterized by XRD, N2-sorption, IR spectroscopy and electron microscopy techniques. Additionally, desilicated conventional and mesoporous ZSM-5-type samples were investigated. All samples were tested in the MTG reaction, and the results showed that both the shell-coated and the desilicated zeolites are significantly more resistant to coke formation. These results are ascribed to the effect of the removal of structural defects rather than to an improvement of the diffusion properties due to the formation of mesopores.