Tandem Reduction–Reoxidation Augments the Catalytic Activity of Sn-Beta Zeolites by Redispersion and Respeciation of SnO₂ Clusters

Abstract

High dispersion of Sn in beta (β) zeolites is pivotal to obtain highly active Snβ catalysts with high productivity. However, at higher Sn loadings, Sn dispersion and the activity per Sn decrease. The present work highlights the augmentation of catalytic activity in the Baeyer-Villiger oxidation and Meerwein-Ponndorf-Verley reactions of as-synthesized Snβ catalysts with Sn loadings up to 10 wt. % by tandem reduction-reoxidation and discusses the effect in terms of Lewis Acid (LA) density, Sn dispersion, Sn speciation, and catalytic performance. To do so, non-treated, reduced and reduced-reoxidized Snβ catalysts are characterized by N2-physisorption, XRD and a multitude of spectroscopic techniques such as TPR-MS, probe FTIR, DRUV-vis, 119 Sn Mössbauer, 119 Sn MAS NMR, ICP-AES and XPS. Although not mutually exclusive, the higher catalytic activity seems to arise from different phenomena depending on the Sn loading. At lower Sn content (≤ 5 wt. %), the higher activity arises from redispersion of SnO2 clusters into smaller active Sn species whereas at higher Sn content (≥ 5 wt. %), the catalytic activity seems to improve based on respeciation of SnO2 clusters.

Lewis acid Sn-Beta catalysts for the cycloaddition of isoprene and methyl acrylate: a greener route to bio-derived monomers

“…Some of it, especially when higher loadings are aimed, ends up in formation of extra-framework SnO 2 during SSIE. 69 This SnO 2 is not only inactive in the reaction, as we have tested in control experiments, but it may also sit on the zeolite surface, possibly even blocking some of the active sites. 48 Therefore, the TON which is normalized against the total amount of metal in the zeolites decreases with increasing Sn-loading.…”

Toward Industrially Relevant Sn-BETA Zeolites: Synthesis, Activity, Stability, and Regeneration

“…Instigated by the higher mobility of Sn­(II)O that led to higher Sn dispersion, our group recently proposed a way to create highly active Snβ catalysts by pioneering a reactivation methodology based on deeper understanding of the Sn redox chemistry . By performing tandem reduction-reoxidation, the so-called “redreox” treated catalysts outperformed the air-calcined counterparts in the catalytic BVO (Figure A) and MPV reaction.…”

“…The wt % in brackets correspond to the amount of Sn present in the sample. Adapted with permission from ref . Copyright 2021 American Chemical Society.…”

Catalytic amination of lactic acid using Ru–zeolites

“…23,24 Zeolites are well known for their high thermal stability and ability to well disperse the functional metals. [25][26][27] Furthermore, ruthenium-based zeolites have been used in a variety of catalytic reactions from the epoxidation of styrene, conversion of glucose and sorbitol to glycols and ammonia synthesis. [28][29][30] Also, the activity of Ru catalysts has been documented in the direct amination of alcohols to produce primary amines.…”