Preparation, Characterization And Selective Oxidation Properties Of Al-Free Sn-Beta

Metallosilicates that contain isolated transition metal ions in the framework of high-silica zeolites have received intensive attentions. Sn-Beta zeolites as good Lewis acid catalysts opened up great applications especially for developing green oxidation processes. Thus, developing new methods of preparing Sn-Beta zeolites and studying their catalytic properties are of important meanings.In this paper we prepared successfully Sn-Beta zeolites using traditional fluoride method and gas-solid reaction (Atom-Planting Method). We characterised the physicochemical properties of resultant Sn-Beta zeolites and the incorporation mechanism of Sn ions by various techniques. Their catalytic performance was explored in Baeyer-Villiger oxidation of ketones with hydrogen peroxide. The results of characterization indicated Sn-Beta zeolites (Sn-Beta-PS) prepared by postsynthesis had higher Sn loadings and smaller crystal sizes. The Sn species inserted into the framework occupied predominately the tetrahedral coordination sites and showed better Lewis acid sites. Nanosized Sn-Beta-PS was superior to Sn-Beta-F in the selective oxidation of 2-adamantanone with hydrogen peroxide. This paper consists of four parts.Section 1 Al-Free Sn-Beta-F synthesized by fluoride method proceduresSn-Beta-F zeolites were synthesized directly in a fluoride system using SnCl4·5H2O as a Sn source and with the addition of dealuminated Beta zeolite as seeds. The crystallization was carried out in a Teflon-lined stainless steel autoclave under static conditions at 413 K for 10～40 days. To realize a full crystallization, it was necessary to prolong the heating time at high Si/Sn ratios of 200～120. By series of characterization techniques such as XRD, SEM, ICP, FT-IR, we found Sn-Beta-F samples had high purity, uniformitarian appearance and micro-sized particles. The Sn species were inserted into the framework predominately as the tetrahedral coordination sites.Section 2 Al-Free nanosized Sn-Beta-PS zeolites postsynthesized through the solid-gas reaction We carried out the postsynthesis of Sn-Beta (Sn-Beta-PS) using from highly dealuminated Beta zeolite (almost free of Al) and SnCl4 vapor. The preparation strategy consists of two steps, that is, dealumination and post-incorporation of Sn species into the defect sites. The isolated Sn species exhibited Lewis acidity useful for the Baeyer-Villiger oxidation of ketones.Section 3 Characterization of nanosized Sn-Beta-PS zeolites and the study of Sn incorporation mechanismThe physicochemical properties and the incorporation mechanism of Sn ions of resultant Sn-Beta-PS were characterized by various techniques such as XRD, SEM, UV-Vis, FT-IR,29Si MAS NMR,119Sn MAS NMR and so on.Section 4 Investigation of catalytic properties of Al-free Sn-Beta zeolitesThe catalytic properties of Sn-Beta were investigated in the Baeyer-Villiger oxidation of 2-adamantanone with hydrogen peroxide. The catalytic performance of nanosized Sn-Beta-PS zeolites was compared with the micrometer-sized Sn-Beta-F. Sn-Beta-PS was superior to Sn-Beta-F in the selective oxidation of 2-adamantanone with hydrogen peroxide.