Influence of pore topology on synthesis and reactivity of Sn-modified zeolite catalysts for carbohydrate conversions

Abstract

A range of Sn-modified MWW, MFI, MOR and Beta zeolites were prepared by a post-synthetic Sn functionalization method and their catalytic properties for sugar conversions were evaluated. The focus of this work was to understand the effect of micropore dimensions and additional mesoporosity on the Sn incorporation and on the catalytic properties. The post-synthetic approach, which involves aciddealumination of the parent zeolite followed by SnCl 4 grafting, is highly efficient for the selective incorporation of lattice Sn sites in wide-pore Beta and MOR zeolites. The modification of the medium-pore MWW and MFI is impaired by the more difficult dealumination and hence the lower efficiency of the Sn incorporation. Hierarchical structuring of the zeolites allows the increase of the Sn loading in the final zeolites. The catalytic properties were assessed in the isomerization and retro-aldolization reactions of glucose and the conversion of 1,3-dihydroxyacetone to methyl lactate. The catalytic results depend strongly on the structural and topological properties of the catalysts as well as on the reactant. Glucose isomerization carried out at a relatively low temperature is mainly limited by strong adsorption of carbohydrates to the active sites. This explains why zeolite nanostructuring had little effect on the catalyst activity, which instead depends mainly on the zeolite topology and the nature of the reactive Sn centers. The influence of pore size is most pronounced for Sn-MWW and Sn-MFI zeolites which are inactive in glucose-to-fructose isomerization, but perform in the higher-temperature retro-aldolization of carbohydrates with an activity similar to that of Sn-Beta. Because of the limited accessibility of the Sn sites inside the 1D MOR pore system, Sn-MOR catalysts were only moderately active in all probe reactions considered.

ZIF-8 Metal Organic Framework for the Conversion of Glucose to Fructose and 5-Hydroxymethyl Furfural

“…Specifically, over the hydrophobic surface of ZIF-8 the competition between reactant and solvent molecules are in favour of the reactant, glucose. This is similar to the catalytic activity of Sn-Beta in glucose isomerisation [46,47]. The activity and selectivity of Sn-Beta is, in part, attributed to the hydrophobic nature of the Beta zeolite framework, which prevents the inhibition of active Sn sites by water molecules [48].…”

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

“…The difference in van der Waals stabilization of the intermediates defined by the size and shape of zeolite pores was proposed to be the key factor for glucose to fructose isomerization activity of Sn‐modified MOR, BEA, MFI and MWW. Despite similar intrinsic reactivity of the Lewis acidic framework Sn sites in these materials, their catalytic performances drastically vary . Periodic calculations showed an increased van der Waals stabilization of the bulky carbohydrate substrates and products in narrow pores of Sn‐MFI and Sn‐MWW zeolites, which limited their ability to access the catalytic lattice Sn sites …”

Exploring the Synthesis of Mesoporous Stannosilicates as Catalysts for the Conversion of Mono- and Oligosaccharides into Methyl Lactate

“…Crystals of hydrothermal Sn-Beta zeolites prepared with the use of HF as mineralizing agent have a capped bipyramidal morphology [24]. In contrast, the textural properties strictly depend on the starting H-Beta zeolite in post-treated materials [11]. SEM pictures showed that during the Sn incorporation, the small crystals of the initial H-Beta zeolite reorganized into larger round-shape crystals (Supporting Information S3.1).…”

“…PLAs represent about 10% of the raw material globally produced for bioplastics, and their production capacity is expected to grow by 50% by 2022 as a consequence of the biobased origin and biodegradability of the compounds [9]. Additional a-hydroxy esters, such as methyl vinyl glycolate (MVG) and methyl trans-2,5,6trihydroxy-3-hexenoate (THM) are formed in the sugar conversion reaction, making the process a possible source for the production of diverse polyester monomers that contains additional groups for functionalization [7,[10][11][12] ( Figure 1). Although Sn-Beta bears great potential as a catalyst for biorefineries, it has been applied only to the conversion of simple sugars, while applications to the conversion of second generation biomass components are still lacking [13].…”