Determination of the catalytically active oxidation Lewis acid sites in Sn-beta zeolites, and their optimisation by the combination of theoretical and experimental studies

Metalloenzyme-like catalyzed isomerizations of sugars by Lewis acid zeolites

“…Framework Sn can exist in two different states, octahedral or tetrahedral, depending if is hexacoordinated or tetracoordinated. Also, Boronat et al (18) Fig. 2.…”

State of the art of Lewis acid-containing zeolites: lessons from fine chemistry to new biomass transformation processes

“…DFT calculations, IR spectroscopy and catalytic tests confirm that the most active site is the partially hydrolyzed tin framework center for the selective Baeyer-Villiger oxidation of cyclic ketones to form the corresponding lactones. 24 The concentration of both tin centers in the catalyst can be easily tuned during the calcination process (dry or wet atmosphere), and interestingly, a linear correlation can be observed between the initial rate for the oxidation of cyclic ketones and the amount of partially-hydrolyzed tin centers in the catalyst. 24 Multisite reaction mechanisms Once the partially-open tin center has been elucidated as the catalytic site for the SnBeta material, the reaction mechanisms for the Baeyer-Villiger oxidation and MPV reduction have been studied by combining molecular mechanics and quantumchemical calculations.…”

“…24 The concentration of both tin centers in the catalyst can be easily tuned during the calcination process (dry or wet atmosphere), and interestingly, a linear correlation can be observed between the initial rate for the oxidation of cyclic ketones and the amount of partially-hydrolyzed tin centers in the catalyst. 24 Multisite reaction mechanisms Once the partially-open tin center has been elucidated as the catalytic site for the SnBeta material, the reaction mechanisms for the Baeyer-Villiger oxidation and MPV reduction have been studied by combining molecular mechanics and quantumchemical calculations. 25 In the case of the Baeyer-Villiger oxidation, it was found that the catalytic active site is formed by two centers.…”

Mechanochemically assisted hydrothermal synthesis of Sn-substituted MFI-type silicates

“…Notably, the absorption band at approximately 260 nm that is attributed to octahedral Sn 4+ spaces is not observed for the calcined Sn-S MC . On the other hand, the band at 240–250 nm is still in debate, however, penta-coordinated Sn species [30,31], extra-framework Sn species [17], and small tin oxide particles [30,32] have been assigned to the peaks at around 240–250 nm. These results strongly support the idea that Sn 4+ ions were introduced into the Sn-MFI framework as tetrahedrally coordinated states.…”

“…As exhibited in Figure 9, all the samples show an absorption at approximately 2309 cm −1 , which is attributable to C ≡ N stretching of CD 3 CN molecules adsorbed on the Sn-site of Sn-S MC and Sn-S HT in the framework. Montejo-Valencia et al reported that an Sn-doped BEA zeolite has ‘closed’ and ‘open’ Sn sites with Sn(OSi) 4 and Sn(OSi) 3 (OH) structures, respectively [30,35]. The absorbance peaks of CD 3 CN on the ‘closed Sn’ and the ‘open Sn’ sites are at 2309 cm −1 and 2317 cm −1 , respectively.…”