Silanol Networks Control Methanol Reactivity in Nano‐ and Micron‐sized Silicalite‐1

The catalytic activity of silanol groups in zeolites has long been overlooked because of their much lower acidity compared to Brønsted acid sites. Here, we demonstrate their non-negligible catalytic role in methanol conversion using pure silica MFI zeolite (Silicalite-1). Two silicalite-1 samples with different crystal sizes, micron-sized (Sil1_micro) and nano-sized (Sil1_nano), were synthesized and investigated by in situ and operando FTIR spectroscopy using probe molecules (carbon monoxide, pyridine, and methanol). multivariate-curve regression by alternating least squares was applied to elucidate the influence of the silanol hydrogen-bonding network on catalytic reactivity. Distinct acid-base behaviors were identified: isolated and weakly hydrogen-bonded silanols are active at low temperatures, whereas strongly hydrogen-bonded silanols become catalytically relevant at higher temperatures. Methanol adsorption studies reveal a unique bidentate coordination mode in Sil1_nano, associated with weakly hydrogen-bonded geminal silanols, which promotes the formation of reactive intermediates and dual coke species. In contrast, Sil1_micro, characterized by a higher fraction of strongly hydrogen-bonded silanols, exhibits a different methanol reactivity pattern. These results demonstrate that silanol groups are active functional entities rather than passive defects, capable of driving methanol reforming-like transformations and steering coke formation pathways.