铁尾矿两步法制备多级孔ZSM-5分子筛

Synthesis of a hierarchical ZSM-5 zeolite from iron-ore tailings by a two-step method

以铁尾矿为原料替代纯化学试剂,采用两步法制备含有介孔–微孔复合孔的多级孔ZSM-5分子筛.首先在介孔模板剂(CTAB)作用下合成介孔分子筛(MCM-41),然后通过固相转换法将MCM-41晶化转变为多级孔ZSM-5分子筛.采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和氮气吸附脱附测试(BET)等技术对样品进行表征.实验结果表明,由于体系中没有液态水相参与,成功避免了CTAB与微孔结构导向剂(TPABr)在水溶液中相互竞争,从而得到高结晶度的多级孔ZSM-5分子筛.因此,本文为铁尾矿制备多级孔ZSM-5提供了一种全新方法.

Iron-ore tailings(IOT) are mineral waste obtained via the iron-ore mining process.This has become a very critical issue in industrial solid waste management.The stacking of IOT occupies a large area and causes serious pollution,which can harm human life.This has become a serious matter of concern for society.IOT are usually rich in SiO2 and Al2 O3 and can be used as raw materials in producing zeolitic materials.They have substantial benefits from both economic and environmental perspectives.However,few studies have been reported on the synthesis of zeolite or zeolite-like materials using IOT.As a type of zeolite,ZSM-5 has a regular pore structure and high thermal and hydrothermal stability and is widely used in catalytic materials.However,the application of ZSM-5 is greatly limited in many catalytic reactions owing to the large molecules associated with its inherently small pore sizes(<1.5 nm).Introduction of a hierarchically porous structure into conventional ZSM-5 maintains the crystal structure,acidic active center,and high thermal and hydrothermal stability and accelerates the diffusion/transfer of large molecules and greatly reduces the formation of carbon residue.This prolongs the service life of the catalyst used,which is extremely desirable in catalysis.In this study,hierarchically porous ZSM-5 was prepared via a two-step process using IOT as a silica source instead of pure chemical reagents.First,mesoporous MCM-41 was synthesized using cetyltrimethylammonium bromide as a mesoporous template.Then,hierarchically porous ZSM-5 was fabricated by impregnating a structure-directing agent into the as-synthesized MCM-41,followed by a solid-phase conversion method to transform amorphous silica into a zeolite crystal.To evaluate the textural properties of the zeolites,the as-synthesized samples were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,and nitrogen adsorption.The results show that phase separation between the surfactant and zeolite crystals is avoided because of the absence of the liquid-water phase during the solidphase conversion.Therefore,the synthetic route presented herein provides a novel method for the synthesis of hierarchically porous ZSM-5 from IOT.