Post-synthetic preparation of Sn-, Ti- and Zr-beta: a facile route to water tolerant, highly active Lewis acidic zeolites

Abstract

A two-step procedure for the post-synthetic preparation of Lewis acidic Sn-, Zr- and Ti-zeolite β is reported. Dealumination of a commercially available Al-β zeolite leads to the formation of highly siliceous material containing silanol nests, which can be filled in a second step via the solid-state ion-exchange or impregnation of an appropriate metal precursor. Spectroscopic studies indicate that each metal is subsequently coordinated within the zeolite framework, and that little or no bulk oxides are formed--despite the high metal loadings. The synthesised catalysts demonstrate excellent activity for the isomerisation of glyceraldehyde to dihydroxyacetone, a key model reaction for the upgrading of bio-renewable feedstocks, and the epoxidation of bulky olefins.

Lewis Acid Zeolites for Biomass Conversion: Perspectives and Challenges on Reactivity, Synthesis, and Stability

“…In particular, the type of metal salt used as a precursor in hydrothermal syntheses heavily influences the framework content and catalytic activity of the final product (79,80). Recently, many groups have reported dry-gel or postsynthetic methods for metal incorporation in zeolite Beta (21,81,82). These methods can often incorporate a higher metal content into the zeolite framework compared with the hydrothermal method, leading to higher yields normalized by total catalyst mass for certain reactions, but usually have lower TOFs when normalized by metal content at loadings above 3-5% (83-85).…”

“…For BV oxidations, the carbonyl group is first activated by the metal center and then forms a Criegee intermediate with H 2 O 2 , implying that the Lewis acid character of Sn is better suited for activating the carbonyl group, making the carbon more prone to attack by the peroxide. Similarly, Sn-containing zeolites tend to show higher activity for reactions involving the initial activation of carbonyl compounds, such as the isomerization of glucose to fructose (20), isomerization of glyceraldehyde to dihydroxyacetone (DHA) (21), and C-C coupling between DHA and formaldehyde (22), when compared to Ti-containing zeolites. However, for the Meerwein-Ponndorf-Verley (MPV) reduction using alcohol hydrogen donors via a six-membered ring transition state where both reactants are bound to the metal center, Zrand Hf-Beta show either higher or similar activity to that of Sn-Beta, whereas Ti-Beta shows drastically lower activity (23,24).…”

With Open Arms: Open Sites of ZrBEA Zeolite Facilitate Selective Synthesis of Butadiene from Ethanol

“…[2] A more recent example is a ZrBEA, which contains Zr(IV) sites introduced in the β-zeolite framework. [3] The uniform distribution of isolated Zr Lewis acid sites, in combination with unique porous structure of the material, results in an unrivalled catalytic performance in a number of industrially important processes, [4][5][6][7][8][9][10] including the synthesis of butadiene from ethanol. [8] The latter reaction is very important for the diversification of the industrial routes of synthesis of butadiene, which is an important monomer for the production of rubbers and elastomers.…”

Zeolite Catalysis for Biomass Conversion

“…Solid-state ion exchange [ 100 ], in which Sn(OAc) 2 is physically ground with dealuminated BEA zeolite and subsequently calcined, is a promising method to introduce large amounts of active sites into the framework. A similar approach has been reported for Zr(OEt) 4 [ 101 ]. Also chemical vapor deposition using an appropriate, i.e.…”