BEA、MOR、MFI及其二元共生沸石的介孔改性

Mesopore modification of zeolites BEA,MOR,MFI and relevant binary intergrowths

用晶种诱导法合成二元共生沸石β(BEA)-丝光(MOR)(w(MOR)=50%)和ZSM-5(MFI)-MOR(w(MOR)=58%)。用碱酸处理法对商业BEA、MOR、MFI及共生沸石进行介孔改性。采用XRD、N_2吸附-脱附、ICP-AES、TEM、SEM/EDX等技术研究改性沸石的晶体结构和织构介孔性质。借助纯硅BEA,MOR,MFI的骨架密度、孔道拓扑和生成焓数据,考察脱硅选择性、介孔性质与沸石骨架结构和热力学稳定性的关系。实验结果表明,系列改性沸石具有较高的介孔率和结晶度保留率;改性沸石的介孔面积及介孔体积由大至小依次为BEA(t),BEA-MOR(t),MFI-MOR(t),MFI(t),MOR(t)。骨架密度和热力学稳定性降低导致脱硅选择性降低和介孔面积效率提高。

Binary zeolite intergrowths, namely β-zeolite（BEA）-mordenite（MOR）（w（MOR） 50%） and ZSM-5 zeolite（MFI）-MOR（w（MOR） 58%）, were synthesized by the seed-induced growth method. The two intergrowths and commercial zeolites with the BEA, MOR and MFI structures were modified through combined alkaline-acid treatments to form mesopores. The crystal structure and mesoporosity of the modified zeolites were investigated by means of XRD, N2 adsorption- desorption, SEM, TEM and ICP-AES. Both of the desilication selectivity and the mesoporosity were correlated with the framework structures and the thermodynamic stability of the initial zeolites based on the framework density, pore channel topology and formation enthalpy of the pure silica zeolites. The results showed that, the modified zeolites were provided with significant mesoporosity and crystallinity preservation, and both the mesoporous specific surface area and the mesoporous volume were in order of BEA（t）〉BEA-MOR（t）〉MFI-MOR（t）〉MFI（t）〉MOR（t）. The decrease in the framework density and the thermodynamic stability led to the decrease of the desilication selectivity but the increase of the efficiency of the mesoporous specific surface area.