Synthesis And Catalytic Properties Of Hierarchically Porous Zeolite FER

Zeolite is a crystalline silicon aluminum material with regular multi-dimensional microporous channels.Zeolite is widely used in the fields of adsorption,separation and catalysis due to its special pore structure.Traditional microporous FER zeolite with narrow pores channels limits the diffusion of substrates or products.In order to overcome the problem of carbon deposition leading to deactivation of FER catalyst in large molecules involved reactions,it is necessary to maintain its micropores while introducing mesopores or macropores to improve the diffusion limit in zeolite pores.Therefore,preparing hierarchical ferrierite zeolite can not only retain the stability and perfect shape selectivity of its micropores,but also increase the excellent diffusion performance brought by mesopores.In this paper,hierarchical channel FER zeolite was prepared by single template method and seed-assisted single template method,in order to increase the surface area of zeolite,improve the mass transfer and reduce diffusion limits.Two parts of research work were carried out.The first part is the FER zeolite aggregates with hierarchical porosity by single template n-BA method.By adjusting the proportion of substance in the initial gel,mesoporous-macroporous rich stacked nanosheets were successfully prepared.The prepared nanosheet-structured ferrierite aggregates present regular layered accumulation,with clear surface and sharp corners.The crystal sizes of FER samples range from 200 nm to 2μm and the lamellar nanosheets with thickness of less than 50nm.The synthesis method with simple operation,cheap raw materials,low crystallization temperature and short crystallization time,which shows excellent catalytic effect in catalytic low-density polyethylene（LDPE）cracking.In the second part,hierarchical porosity FER zeolite was synthesized by seed-assisted single template protocols.Pyrrolidine（Pyr）was used as the OSDA.Hierarchical zeolite FER nano-sheet was added as the crystal seed to induce amorphous silicon aluminum species grow on the surface of the crystal seed.The effects of template type,dosage,crystal seed dosage on the crystallinity,morphology and the textual properties of the synthesized FER zeolite were systematically investigated.With the increase of seed dosage,the morphology of FER zeolite changed from thick and tightly packed to thin and loosely stacked.The surface area(S_ext)and mesoporous volume(V_meso)of the FER zeolite reached 137 m²/g and 0.17cm³/g,respectively.This demonstrated that the seed addition is instrumental in the formation of abundant mesopores.The temperature for the 50%conversion(T₅₀)of the prepared FER zeolite was as low as 343.6℃on cracking LDPE.