Nanofabrication, Molecular Modeling And Structure-Properties Relationship Study Of Micro-mesoporous Molecular Sieve

The micropore structures and high intrinsic activities frequently make zeolites subject to diffusion limitations that, for example, restrict reactant accessibility to the active sites on the interior surfaces of zeolites and inhibit the full utilization of zeolite catalysts, while the ordered mesoporous molecular sieves suffer from the poor hydrothermal stability due to their amorphous frameworks, which restricts their applications in refineries and petrochemical processes. Due to that, the nanofabrication of hierarchical zeolites with micro- and mesoporosity is a proven strategy for integrating shape selectivity (provided by the intrinsic micropore structures) and efficient mass transfer (facilitated by the mesopore structures).In this paper, three different approaches have been employed to synthesis a series of micro-mesoporous zeolites, including confined synthesis in hard templates, assembly of zeolite nanocrystals, and soft template methods. Moreover, molecular simulation technology has been used for structure exploration and structure-property relationship study of micro-mesoporous zeolites.Three-dimensionally ordered mesoporous-imprinted (3DOm-i) zeolites with LTA, MFI, BEA, FAU, and LTL topologies have been synthesized within the confined space of 3DOm carbon by conventional hydrothermal treatment. The mesoporosity can be easily tuned by varying the mesopore size of 3DOm carbon and mesoporous structure of the carbon template, and a wide range of crystal morphologies can be achieved by varying the nucleation and crystal growth rate. Moreover, zeolite suspensions of monodisperse nanocrystals with size range and uniformity have been obtained by disassembly of 3DOm-i zeolites, and further used in the fabrication of zeolite/Au and zeolite/zeolite nanocomposite catalysts.Steam-assisted crystallization treatment has been used for the confined synthesis of lamellar MFI zeolite spheres with hollow structures, and the treatment process demonstrated here has also provided a feasible approach for the morphology control of lamellar MFI zeolites.Micro-mesoporous zeolite ZSM-5-MCM-41 has been synthesized via assembly of zeolite nanocrystals on ordered mesoporous molecular sieve by microwave treatment. A structure model of ZSM-5-MCM-41 in atomicscale has been established for the first time and further used to investigate the adsorption properties of ZSM-5-MCM-41.Micro-mesoporous zeolite SBA-15 has been synthesized by soft template methods with P123 as the structure directing agent. An optimized structure model by Anneal Dynamics method has been built and used to demonstrate the effects of micropores located in the intrawall positions of SBA-15 on the adsorption properties of SBA-15Mesoscopic Dynamics (MesoDyn) method has been employed to simulate the aggregation behavior of triblock copolymer P123, and further explore the structure formation mechanism and analyze the feasibility of accurately adjusting the pore size of SBA-15. Moreover, the effects of charge matching interactions between surfactants and silicate species on mesophase morphologies of SBA-15 have been further discussed.Overall, the nanofabrication of hierarchical zeolites with micro- and mesoporosity will provide a possibility for quantitatively studying the mass-transfer limitation of porous materials on the adsorptive and catalytic process and may provide building blocks for the synthesis of zeolite thin-films and other nanomaterials, and the structure modeling of micro-mesoporous zeolite will demonstrate a proven strategy for the structure exploration and structure-property relationship investigation, while the formation mechanism study by molecular simulation will provided a theoretical basis for accurately adjusting the pore structure of micro-mesoporous zeolite.