MFI型金属硅酸盐合成、介孔改性与骨架原子脱除行为

采用无机原料合成高硅沸石ZSM-5、FeMFI、TS-1和超高硅SH-ZSM-5(摩尔比Si/Al=402.4),通过骨架Si、金属原子(M=Al、Fe、Ti)抽提对系列H-MFI沸石进行介孔改性.借助XRD、FT-IR、UV-vis、77 K N2吸附-脱附和SEM/EDX技术,研究沸石晶体结构、金属原子嵌入率、介孔率及骨架Si、M脱除行为.结果表明,与前体相比改性沸石Si/M摩尔比降低,高选择性脱硅沸石具有多级微、介孔结构和较高织构介孔率.引入附加介孔使BET比表面积和总孔体积显著增加.同构沸石介孔形成受骨架电荷密度、嵌入金属原子种类、晶体形貌与尺度等因素的影响.骨架原子脱除效率按ZSM-5、FeMFI、TS-1次序递减.聚集态TS-1、SH-ZSM-5因过度脱硅导致相对产率和介孔生成效率下降.

Synthesis,Mesopore Modification and Framework Atoms Removal of Diverse Metallosilicates with MFI Structure

High-silica metallosilicates with MFI structure , viz.ZSM-5, FeMFI, TS-1 and super high-silica ZSM-5 ( SH-ZSM-5 , mloe ratio Si/Al=402 .4 ) , were synthesized using inorganic raw materials . Mesoporous modification was performed on such protonic zeolites by extracting Si and metallic heteroatom ( M =Al, Fe or Ti ) from framework. The crystal structure , metallic incorporation fraction and mesoporosity were investigated by XRD , FT-IR, UV-vis, N2 adsorption-desorption at 77 K, and SEM/EDX to probe the behavior of framework desilication and demetalation .It is concluded that Si/M molar ratios for the modified zeolites appeared to decrease compared with those of individual precursors , whilst the highly selective desilication observed on isomorphous heterosilicates was shown to facilitate the formation of hierarchically micro-and mesoporous structures with significant textural mesoporosity .The introduction of mesopores in zeolite crystals led to dramatic increases both in of BET surface area and in total micro-and mesopore volume .However , the formation of mesostructure in MFI framework could be affected by different factors ,e.g.the charge density in zeolite framework , the variety of incorporated metal atoms, the changes in crystal morphology and size .The removal efficiency of framework T-atoms was observed typically to descend in the sequence of ZSM-5, FeMFI and TS-1, whereas the relative weight yield and T-atoms removal efficiency decreased for TS-1 and SH-ZSM-5 crystals occurring in aggregation state due to their immoderate desilication .