A Study On Synthesis,Characterization And Catalytic Performance Of Heteroatom Zeolites

Heteroatom-containing zeolites,e.g.so-called metallosilicates,expand the definition of traditional zeolites and have achieved great achievements in new applications.Among them,titanosilicates and tinsilicates attract wide attentions due to their high efficiency and production of only water as by-product under mild catalytic reaction conditions,which meets the requirements of"green chemistry".The liquid-phase epoxidation of cyclopentene（CPE）was performed in the Ti-zeolite/H₂O₂ catalytic system for the clean synthesis of cyclopentene oxide.Among all the Ti-zeolites（Ti-Beta,Ti-MOR,Ti-MCM-68,TS-1,TS-2,and Ti-MWW）investigated in the present study,Ti-MWW provided relatively lower CPE conversion of 13%due to the diffusion constrains but a higher CPO selectivity of 99.5%.The catalytic performance of Ti-MWW was significantly enhanced by piperidine（PI）treatment,as the CPE conversion and CPO selectivity increased to 97.8 and 99.9%,respectively.The structural rearrangement upon PI treatment converted the3-dimensional（3D）MWW structure to a 2D lamellar one,which enlarged the interlayer space and greatly alleviated the diffusion constrains of cyclic cyclopentene.Furthermore,the newly constructed“open site”six-coordinated Ti active sites with PI as the ligand exhibited higher catalytic activity.In addition,the extra-large pore titanosilicates with the pores larger than 12 MR showed an absolute advantage in catalyzing reactions of bulky molecular substrates.Based on the extra-large pore zeolite ECNU-24 recently studied by our group,corresponding titanosilicate Ti-ECNU-24 was obtained by liquid-phase isomorphous substitution of Ti into framework,which exhibited better catalytic performance than traditional titanosilicates in the thiophene oxidative desulfurization reaction.Sn-ECNU-24 was further obtained by introducing Sn into the framework with a method similar to liquid-phase post synthesis of Ti-ECNU-24,and it exhibited a good catalytic performance in the Baeyer-Villiger（B-V）oxidation reaction of rigid large molecules of 2-adamantanone.