Fluoride-free Hydrothermal Synthesis And Catalytic Properties Of BEA* And CHA-type Metallosilicates

Isomorphous introduction of a small fraction of tin?IV?and titanium?IV?in the tetrahedral sites of zeolitic frameworks provides materials with excellent catalytic properties for Baeyer-Villiger oxidation of ketone and partial oxidation reactions with hydrogen peroxide?H₂O₂?,respectively.In this thesis,Sn-Beta and Ti-CHA zeolite were directly synthesized in fluoride-free medium via a hydrothermal method,and their catalytic performance was also evaluated.Instead of using toxic fluoride to hydrothermally synthesize Sn-Beta catalyst ending up with low Sn content,or approaching high Sn-containing Beta zeolite synthesized via post-synthesis strategy?e.g.,chemical vapor deposition employing tin?IV?chloride vapor?,high Sn-containing BEA*-type zeolite can be directly synthesized without addition of fluoride via a hydrothermal conversion method with the assistance of N-cyclohexyl-N,N-dimethylcyclohexanaminium hydroxide?M₂Cy₂NOH?as OSAD and seed crystals.To the best of our knowledge,the highest isolated Sn content?Si/Sn molar ratio of 39?of this synthesized Sn-Beta zeolite results in more efficient Lewis acid sites in comparison with previous conventional hydrothermally synthesized ones.The synthesized Sn-Beta zeolites showed higher catalytic performance for the Baeyer-Villiger oxidation of 2-adamantanone and isomerization-esterification of dihydroxyacetone?DHA?than conventional Sn-Beta-F synthesized in fluoride medium,which is mainly ascribed to its high Sn incorporation in BEA*-type framework and outstanding diffusion properties profiting from its extraordinary morphology that the synthesized Sn-Beta zeolite consists of more discrete and smaller crystal domains in comparison to conventional Sn-Beta-F.Ti-containing chabazite?Ti-CHA?zeolite with various Si/Ti ratio and smaller crystal size were hydrothermally prepared with assistance of boric acid?H₃BO₃?and seed crystal?B-CHA?in absence of fluoride by optimizing the H₃BO₃/SiO₂ and H₂O/SiO₂ ratios of initial gel.Post-treatments were applied to perfect the coordination state of Ti species in Ti-CHA,which exhibited considerably higher catalytic activity in the epoxidation of ethelene than Ti-CHA-F synthesized in fluoride medium.