Silanols in zeolite catalysis: from defects to designable functionality

Zeolite silanols were long treated mainly as structural defects, but recent catalytic studies show that specific silanol populations can also function as catalytically relevant sites or local environments. This review develops a structure-microenvironment-reactivity framework that connects the construction, chemical regulation, and cross-validated characterization of silanol populations with catalytic function. We discuss how silanol motif, location, accessibility, hydrogen-bond topology, chemical state, and evolution under working conditions determine three major roles: oxygen-donor anchoring and working-state evolution of mono- and multimetallic species; confined mild Brønsted acidity generated by cooperative hydrogen-bonded ensembles; and hydrogen-bond-mediated control of adsorption, reactant enrichment, solvent organization, and reacting-state stabilization. We further examine how silanol-derived metal interfaces affect durability, redispersion, regeneration, and active-site identity under catalytic conditions. Finally, we outline priorities for descriptor standardization, operando and correlative characterization, controlled perturbation, and scalable construction of targeted silanol populations. Treating silanols as designable catalytic functionalities rather than a single defect variable provides a basis for predictive zeolite catalyst design.