The Synthesis Of Sn/Ti-containing Zeolites And Their Catalytic Performance

Heteroatom-containing zeolites not only have excellent acid-base and redox catalytic properties,but also have the structural properties of conventional molecular sieves,which are promising for industrial applications.Heteroatom-containing zeolites are obtained by replacing the skeleton aluminium or skeleton silicon with metal cation homocrystals in the skeleton of conventional silica-aluminium zeolites.Therefore,in order to increase the metal content in the skeleton of Heteroatom-containing zeolites,improve the efficiency of synthesis,reduce environmental pollution,reduce diffusion resistance and improve mass transfer properties.In this paper,a series of heteroatomic molecular sieve catalysts were innovatively designed and efficiently synthesized using Sn/Ti heteroatom-containing zeolites,and the synthesis mechanism and adsorption catalytic properties were investigated in depth in three parts.In the first part,plentiful heteroatom-containing zeolites as versatile redox catalysts have been successfully postsynthesized via the top-down methodology,where the starting aluminosilicate zeolites are normally expected to be highly dealuminated to maximize the amounts of silanol nests and occasionally to evade the detrimental effect of framework Al ions on the catalytic performance.Herein,our proposed dealumination-controlled strategy for the synthesis of hierarchical Ti–Y zeolite breaks through this concept.Framework-substituted Ti and tri-coordinated Al species were afforded from the interaction of Ti ions with dealumination-derived silanol nests and from the process of acid treatment,respectively.Structure–function relationships revealed that Lewis acid sites were the catalytically active centres of Ti–Y zeolite in oxidative desulfurization with hydrogen peroxide as the oxidant,which came from the cooperative effect of dual active sites containing framework-substituted Ti and tri-coordinated Al species.The amounts of Lewis acid sites demonstrated a volcanic-type trend as the acid-treatment time increases.The reusability,regeneration ability,deactivation mechanism were also systematically investigated in oxidative desulfurization.Thus the Ti–Y zeolite catalyst was also effective for Baeyer–Villiger oxidation of 2-adamantanone.The present work offers potential applications for the preparation of other FAU-type zeolites containing heteroatoms with Lewis acid properties.Solvent-free and low-template synthesis of zeolite materials is the future direction of zeolite production,which meets the requirements of green chemistry.Ti-Beta zeolite with opened channel systems of the 3-dimensional 12-membered ring is a promising industrial catalyst in the field of selective oxidations.Herein,nanosized Ti-Beta zeolites were successfully synthesized via interzeolite transformation of siliceous MOR zeolite using sample and commercially available tetraethylammonium hydroxide（TEAOH）as organic structure-directing agents under solvent-free and low-template-content（TEAOH/Si O₂=0.2）conditions within a short crystallization time.The crystallization mechanism and Ti coordinated state were thoroughly investigated by numerous characterization techniques.It was found that the hydrothermal synthesis of Ti-Beta-M zeolites obeyed a liquid crystallization mechanism,during which pre-dissolution of the silicon source MOR zeolite was a critical step in achieving successful crystallization.Ti⁴⁺ions mainly existed in the form of tetrahedrally coordinated states in zeolite framework.Thus Ti-Beta zeolites showed remarkable activity and reusability during the oxidative desulfurization of fuel oil.Moreover,the deactivated mechanism and regenerated method were also studied in detail.This work provides new guidance for solvent-free and low template content synthesis of metallosilicate zeolites.The present work is intended to clarify the application of the synthetic chemical environment to the zeolite interzeolite transformation process through the hydrothermal synthesis of Sn-Beta zeolites from silica-based FAU-type zeolites,to establish universal rules for the synthesis of Sn-Si heteroatomic zeolites by interzeolite transformation,and to investigate the key factors determining the crystallisation process and mechanism.Characterising the grain size,structure,micro-mesoporous properties,Sn coordination state,surface hydrophilic properties of Sn-Beta zeolites synthesised under different conditions and exploring the fallout and micro-chemical environment of Sn species.Traditional Sn-Beta zeolite is amorphous material as a silicon source for direct synthesis,and this work is to develop highly dealuminated FAU zeolite as silicon source synthesis by intergranular transformation,there is a big difference between two kinds of preparation system,presents the crystallization time is short,without seed,the characteristics of the nanometer grain.The Sn-Beta zeolite prepared as Lewis acid catalyst showed excellent catalytic performance in the glucose isomerization reaction.Under the reaction condition of 120℃,the Sn-Beta zeolite catalyst showed 89.1%glucose conversion and 40.8%fructose selectivity,which was superior to the Sn-Beta molecular sieve catalyst prepared by the post-treatment method and the traditional fluorine system method.