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

Abstract

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.