Effects of Alkali‐Metal Ions and Counter Ions in Sn‐Beta‐Catalyzed Carbohydrate Conversion

• Published in: ChemSusChem 2018-04, Vol.11 (7), p.1198-1203
• Main Authors: Elliot, Samuel G., Tolborg, Søren, Madsen, Robert, Taarning, Esben, Meier, Sebastian
• Format: Article
• Language: English
• Subjects: Alkali metals; Anion exchanging; Breakage; Carbohydrates; Catalytic converters; Cation exchanging; Conversion; Dehydration; esters; heterogeneous catalysis; Ions; kinetics; Metal ions; Reaction control; Substrates; zeolites
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201702413

Alkali‐metal ions have recently been shown to strongly influence the catalytic behavior of stannosilicates in the conversion of carbohydrates. An effect of having alkali‐metal ions present is a pronounced increase in selectivity towards methyl lactate. Mechanistic details of this effect have remained obscure and are herein addressed experimentally through kinetic experiments and isotope tracking. The presence of alkali‐metal ions has a differential effect in competing reaction pathways and promotes the rate of carbon–carbon bond breakage of carbohydrate substrates, but decreases the rates of competing dehydration pathways. Further addition of alkali‐metal ions inhibits the activity of Sn‐Beta in all major reaction pathways. The alkali‐metal effects on product distribution and on the rate of product formation are similar, thus pointing to a kinetic reaction control and to irreversible reaction steps in the main pathways. Additionally, an effect of the accompanying basic anions is shown, supposedly facilitating the cation exchange and eliciting a different concentration‐dependent effect to that of neutral alkali‐metal salts. Time for a promotion: Catalyst modifiers have an outstanding impact on the practicality and profitability of catalytic processes. Alkali‐metal ions, for instance, influence the catalytic properties of silicate‐based materials such as zeolites in carbohydrate conversion towards handpicked products. The functional role of catalyst modifiers in promoting and poisoning reaction pathways is probed.