(266f) Hydrothermal Synthesis of Zeolite with Three Dimensionally Ordered Mesoporous-Imprinted (3DOm-i) Structure
AIChE Annual Meeting
Tuesday, October 18, 2011 - 10:40am to 11:00am
Due to the intrinsic ordered micropore structures and strong acid strength, zeolites are extensively used as heterogeneous acid catalysts in crude oil refineries and petrochemical processes. However, the micropore structures and high intrinsic activities frequently lead these materials to be subject to diffusion limitations that restricts reactant accessibility to the active sites on the interior surfaces of zeolites and inhibits the full utilization of zeolite catalysts. Nanofabrication of hierarchical zeolite catalysts with mesoporosity is a proved strategy for integrating shape selectivity provided by the intrinsic micropore structures and efficient mass transport facilitated by the mesopore structures. Considerable efforts have been devoted to the synthesis of zeolite catalysts with mesoporosity. Among the various approaches, the synthesis of hierarchical zeolites by the confined synthesis in hard templates holds exciting implications in term of creating ordered mesopore structures and controlling mesopore sizes. In principle, any desired mesopore structure can be achieved by manipulating the structure of the hard template. These advantages provide the unique opportunities to design the hierarchical pore structure and quantitatively investigate the effects of mesopore structure on the catalytic performance of zeolite catalysts.
Recently, we have demonstrated how a wide range of crystal morphologies of zeolite (MFI) can be realized through the confined growth within 3-dimensionally ordered mesoporous (3DOm) carbon by steam assisted crystallization (SAC) method1. Herein, we report a general synthesis route for the confined synthesis of zeolite within 3DOm carbon template through hydrothermal (HT) synthesis method. Different from the SAC approach, most zeolites have been successfully synthesized under hydrothermal (HT) conditions. The challenge for the zeolite growth inside the 3DOm carbon during the HT synthesis is to hinder the crystal growth outside the 3DOm carbon and allow the growth inside the 3DOm carbon. In the new approach, the formation of zeolite crystal outside 3DOm carbon is reduced by controlling the crystal growth conditions. Various zeolites including zeolite BEA, LTA, FAU and LTL with three dimensionally ordered mesoporous-imprinted (3DOm-i) structure have been synthesized by this approach. The approach exhibits versatile abilities for controlling the mesopore size (5 nm to 10 nm) and structure (ordered and disordered). The success in growth of zeolite in confined space by HT synthesis could provide a versatile alternative for the nanofabrication of hierarchical zeolites and other hierarchical materials.
(1).Fan, W.; M. A. Snyder; S. Kumar; P. S. Lee; W. C. Yoo; A. V. McCormick; R. L. Penn; A. Stein; M. Tsapatsis Nat. Mater. 2008, 7, 984-991.