Synthesis Of Zeolites Assisted By Hydroxyl Free Radicals And Thier Structural Characterization

Zeolite is a kind of microporous crystalline aluminosilicates,which is widely used as ion exchangers in detergent industry,as catalysts in petrochemical industry and as adsorbents in air separation.Zeolites are usually obtained from the raw materials in a suitable ratio crystallizing for a few hours to a few weeks.Shortening the crystallization time of this kind of material can reduce the synthesis cost and save energy at the same condition.So far,several methods have been developed to accelerate the crystallization of zeolites.Seed has been widely used to accelerate the crystallization of zeolite.Previous studies have shown that grinding seeds can produce silicon-oxygen free radicals,that is,form non-bridging oxygen hole center on the surface,which can react with water to generate hydroxyl radicals accelerating the synthesis of zeolites.The crystallization process was accelerated via hydroxyl free radicals generated from grinding seeds at 120?.Different characterization methods showed that the crystallization products for 60 hours in the presence of seed milled for 0.5 hours were similar to those for 90hours in the presence of normal seed,Through XRD,SEM,EPR,XRF and other characterizations,it is proved that both hydroxyl radical and seed accelerate the synthesis of zeolite synergistically.The introduction of hydroxyl radical reduced the amount of organic templates,made the process more green and economical,Then,the all silica version of ZSM-5?MFI?was synthesized by using the small amount of organic templates in the presence of radicalized seed under the neutral condition.It was also mentioned in this thesis that the relatively good conditions for the synthesis of ordered microporous and mesoporous composites were pre-crystallization for 12 h at 90?and re-crystallization for 24 h at 90?,high crystalline products were obtained with the molar composition of 25SiO₂:9TPAOH:480H₂O:0.05 CTAB.