The stability of Sn-Beta for the continuous upgrading of hexoses is improved dramatically upon the addition of small amounts of water to the methanol/sugar reaction feed, despite water itself being an unfavourable solvent. Herein, the molecular level origin of this effect is investigated. Spectroscopic studies of the catalytic materials pre-, post-and during operation, with operando UV-Vis, 119 Sn CPMG MAS NMR, DRIFTS-MS, TGA, TPD/O-MS and porosimetry, are coupled to additional kinetic studies, to generate detailed structure-activity-lifetime relationships. In doing so, we find that the addition of water influences two particular processesfouling and active site modification. However, mitigating the second is the most crucial role of water. Indeed, in the absence of water, the loss of Sn-OH and Si-OH sites occurs. Notably, these changes in active site hydration correlate to deactivation and reactivation of the system. The consequences of these findings, both for mechanistic understanding of the system in addition to the design of alternative regeneration methods, are also discussed.

The stability of Sn-beta for the continuous upgrading of sugars is enhanced dramatically by small amounts of water.

The stability, activity and selectivity of various Sn-Beta catalysts are investigated to identify how the composition of the catalyst, in addition to its method of preparation, impact its ability to continuously isomerise glucose to fructose. Increasing the Sn loading in post-synthetically prepared catalysts leads to a decrease of both activity and stability. Accordingly, materials containing dilute amounts of Sn appear to be most suitable for continuous operation. Furthermore, the method of preparation has a profound impact on the overall performance of the catalyst. In fact, preparation of Sn-Beta by hydrothermal synthesis results in improvements of both activity and stability, with respect to the post-synthetic preparation of an otherwise-analogous material. The improved resistance of hydrothermal Sn-Beta is attributed, through a combination of operando UV-Vis, TPD-MS and vapour adsorption isotherms, to its greater resistance to deactivation by methanol (the reaction solvent). Complementary 119 Sn CPMG MAS NMR experiments also indicate the presence of different Sn sites in the hydrothermal material, which, alongside the presence of a less adsorptive siliceous matrix, may be intrinsically less prone to solvent interaction than those present in post-synthetic Sn-Beta.

Sn-Beta has emerged as a state-of-the-art catalyst for a range of sustainable chemical transformations. Conventionally prepared by bottom-up hydrothermal synthesis methods, recent research has demonstrated the efficiency of several top-down...

Minimizing catalyst deactivation and developing regeneration protocols are critical challenges in the area of biomass upgrading. Herein, we investigate the regeneration of Sn-containing zeolites for the continuous conversion of glucose. In doing so, we reveal that permanent changes to the properties of the catalyst occur following continuous operation and regeneration, resulting in surprising improvements to performance during subsequent operational cycles. Through a combination of characterization (119Sn CPMG MAS NMR, DRIFTS, and vapor sorption) and kinetic methodologies, we reveal that improved performance arises from restructuring of the catalyst, which causes the active-site environment to become more accessible, more hydrophobic, more reactive, and more stable. Based on these findings, we demonstrate how these positive changes can be emulated without resorting to extended operation, by optimizing pretreatment of the catalyst prior to reaction. This process, termed preactivation, involves treatment of the fresh catalyst in a flow of methanol at 110 °C for 0.5 h, prior to its heat treatment at 550 °C in air for 3 h. This relatively rapid procedure allows substantial improvements to catalyst activity and stability to be achieved in a permanent fashion prior to the first operational cycle.