稀土La掺杂ZSM-5／MCM-41介微孔复合分子筛的合成与表征

Synthesis and Characterization of ZSM-5/MCM-41 Meso/Microporous Composite Molecular Sieve Incorporated by Lanthanum

以CTMABr、TPABr为介、微孔模板剂,Na2SiO3为硅源,Al2(SO4)3为铝源,La2O3的H2SO4溶液为La供体,在水热条件下,通过La离子导入、预置晶种、二步晶化等手段,首次合成出La杂原子ZSM-5/MCM-41复合分子筛.XRD、N2吸附脱附结果表明,样品共存ZSM-5和MCM-41两种物相,两种结构、孔径在介、微孔范围都有分布,且La可取代分子筛骨架的少量Si.SEM照片显示,样品晶粒局部聚集成不规则的团块,构成团块的颗粒大小不一但结合紧密,与ZSM-5、MCM-41形貌明显不同.IR曲线中不存在La2O3的特征吸收谱,样品特征骨架振动峰向高波位移的现象,以及样品微分热失重峰向高温方向偏移,加之DTA曲线肩峰的出现进一步说明La杂原子ZSM-5/MCM-41复合分子筛的合成.

A ZSM-5/MCM-41 meso/microporous composite molecular sieve incorporated by lanthanum, noted as La-ZSM-5/ MCM-41, was first synthesized under hydrothermal condition using sodium silicate （Na2SiO3） and aluminium sulphate （Al2 （SO4） 3 ） as Si and Al sources, sulfurate solution of lanthanum oxide （ La2 O3 ） as La supply and cetyltrimethyammonium bromide （CTMABr） and tetrepropylammonium bromide （TPABr） as mesoporous and microporous templates. There are several main procedures performed during the synthetic process, involving the introduction of rare earth La, the addition of ZSM-5 seed crystal and the two-step crystallization. The composite was characterized by means of XRD, N2 adsorption, SEM, IR, TG-DTG and DTA. The results of XRD and N2 adsorption measurement indicate that the synthetic sample possesses a composite phase containing mesoporous MCM-41 structure and microporous ZSM-5 structure, a dual pore structure whose pore size distribution lies respectively in mesoporous and microporous region, and rare earth La can replace Si existing in the framework of the composite sample. SEM micrograph of La-ZSM-5/MCM-41 sample shows the nonuniform agglomerates assembled by many spherical particles of different sizes closely combined with each other, which differ greatly in the morphology from pure ZSM-5 and MCM-41 molecular sieves. Moreover, the characteristic absorbing bands of La2O3 cannot be seen in La-ZSM-5/MCM-41 sample＇s IR spectra. In comparison with that of ZSM-5/MCM-41 composite, La-ZSM-5/ MCM-41 sample＇s main IR vibrational peaks vary to low wavenumber and its weight loss peaks also shift to high temperature as well as a new and light exothermic peak appears in its DTA curve. All these phenomena demonstrate the replacement between Si in the framework of ZSM-5/MCM-41 composite and rare earth La, and prove the successful synthesis of ZSM-5/ MCM-41 composite molecular sieve incorporated by rare earth La.