Synthesis Of MWW-Type Metallosilicates And High-Silica MOR Zeolites

This dissertation focuses on the synthesis,characterizations and catalyticproperties of MWW-type metallosilicates Zr-MWW,Sn-MWW as well as thesynthesis of high-silica mordenite by dual-template method.This dissertation iscomposed of three parts.In the first part,a novel zirconosilicate with the MWW topology,Zr-MWW,washydrothermally synthesized firstly in alkaline media using hexamethyleneimine(HMD or piperidine(PI)as a structure-directing agent(SDA),boric acid as acrystallization-supporting agent and zirconium sulfate as a Zr source.The influence ofsynthetic conditions on the crystallization such as the amount of NaOH,H₃BO₃,Zr(SO₄)₂ and crystal seeds have been studied.It was shown that both NaOH andH₃BO₃ played crucial roles in the crystallization of Zr-MWW.Highly crystallineZr-MWW could be obtained at NaOH/Si ratio of 0.18 when using HMI as an SDA,and at NaOH/Si of 0.1 using PI.However,the suitable Si/B ratio was between 3 and 5for both HMI and PI.Under optimal conditions,Zr-MWW could be synthesized evenat Si/Zr ratio of 50.The XRD patterns showed that the calcination converted ofas-synthesized Zr-MWW with a two-dimensional(2D)layered structure into 3DMWW topology.The materials were thin platelets,which were similar toconventional MWW aluminosilicate.Zr-MWW had typical Lewis acid as evidencedby pyridine-adsorption IR spectroscopy.Zr-MWW was applied to Meerwein-Ponndorf-Verley(MPV)reduction of cyclohexanone with secondary alcohol as areducing agent.It showed a cyclohexanone conversion high as 99.6%,and acyclohexanol selectivity of 100%.Zr-MWW synthesized with PI showed a higheractivity,and was more active than conventional Zr-Beta for cycloootanone.In the second part,I utilized the same method for the synthesis of Zr-MWW tointroduce Sn into the framework of MWW.The synthesis conditions have beeninvetigated,such as the amount of NaOH,H₃BO₃,SnCl₄·4H₂O,and crystal seed etc.Very similar results to Zr-MWW have been obtained.Under optimal conditions,Sn-MWW could be obtained at Si/Sn ratio of 75.Nevertheless,the synthesis ofSn-MWW was more difficult than Zr-MWW,and its catalytic activity in MPVreaction was also much lower than Zr-MWW.In the third part,high-silica mordenite zeolites were synthesized hydrothermallyat 443 K for three days by dual-template method using both tetraethylammonium hydroxide(TEAOH)and hexamethyleneimine(HMI)as organic structure-directingagents.MOR were obtained at Si/Al ratio lower than 60,even at the Si/Al ratio of 60with the presence of a small amount of mineralizing agent NH₄NO₃ corresponding toNH₄NO₃/Si of 0.01.The ICP analysis indicated that the product had a Si/Al ratio of37.1,which is the highest value reported so far.The samples were characterized withseveral techniques including XRD,TG,SEM,²⁷A1 and ²⁹Si NMR MAS techniques.²⁷Al MAS NMR spectra showed that almost all Al atoms were tetrahedrallycoordinated in the framework.The effects of dual templates on the synthesis ofhigh-silica MOR were also investigated by ¹³C MAS NMR,TG/DTG and elementanalyses.It was verified that the dual templates played cooperative roles in thecrystallization of high-silica MOR.The organic species of as-synthesized MOR werecomposed of 65% TEAOH and 35% HMI.In summary,the synthesis of Zr-MWW,Sn-MWW,high-silica MOR is the mainpart of this thesis.Firstly,I succeeded in synthesizing Zr-MWW and Sn-MWW byutilizing HMI and PI as SDA for the first time.Secondly,a dual-template method hasbeen applied to the synthesis of high-silica MOR.A high-silica MOR was prepared tohave a Si/Al ratio high as 37.1,which is the highest value reported in the literature sofar.