Lewis acidic zeolites are rapidly emerging liquid-phase Lewis acid catalysts. Nevertheless, their inefficient synthesis procedure currently prohibits greater utilization and exploitation of these promising materials. Herein, we demonstrate that SnIV-containing zeolite beta can readily be prepared both selectively and extremely rapidly by solid-state incorporation (SSI) method. Through a combination of spectroscopic (XRD, UV/Vis, X-ray absorption, magic-angle spinning NMR, and diffuse reflectance infrared Fourier transform spectroscopy) studies, we unambiguously demonstrate that site-isolated, isomorphously substituted SnIV sites dominate the Sn population up to a loading of 5 wt % Sn. These sites are identical to those found in conventionally prepared Sn-beta, and result in our SSI material exhibiting identical levels of intrinsic activity (that is, turnover frequency) despite the threefold increase in Sn loading, and the extremely rapid and benign nature of our preparation methodology. We also identify the presence of spectator sites, in the form of SnIV oligomers, at higher levels of Sn loading. The consequences of this mixed population with regards to catalysis (Meerwein–Pondorf–Verley reaction and glucose isomerization) are also identified.

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.

We investigate the continuous generation of hydrogen via the low temperature (< 110 °C), additive-free dehydrogenation of formic acid over heterogeneous Pd/C. Through a combination of kinetic (batch and continuous), spectroscopic and mechanistic studies, we develop structure-activity-lifetime relationships for this process, and in doing so reveal that a combination of pore fouling and poisoning by formate ions result in deactivation of the catalyst during continuous operation. Although these factors result in extensive deactivation in Plug Flow mode, promising results can be obtained by minimizing the steady state concentration of formic acid by operating in a Continuous Stirred Tank reactor. In doing so, continuous operation of the system without loss of activity for over 2500 turnovers is achieved, at mild conditions and in the absence of stoichiometric additives.