Modulating Propane Dehydrogenation over Silicalite-1-Encapsulated CoO <sub> <i>x</i> </sub> Catalysts via Surface Silanol Engineering for Surface Barrier Control
Shaojia Song, Xiaoming Ma, Luyuan Yang, Linfeng Zhang, Jia Guo, Zhen Zhao, Riguang Zhang, Jian Liu, Weiyu Song, Chunming Xu
Abstract
Zeolite-encapsulated metal catalysts offer significant potential by stabilizing subnanometric metal clusters within confined micropores; however, diffusion limitations arising from structural defects often hinder accessibility to active sites and catalytic performance. This study addresses silanol-induced diffusion limitations in zeolite-encapsulated CoO x catalysts using a tetraethyl orthosilicate (TEOS)-mediated surface-silanol-healing strategy. Temperature-programmed experiments, in situ spectroscopy, and theoretical studies collectively demonstrate that TEOS treatment reduces surface silanol groups, thereby weakening van der Waals and hydrogen-bonding interactions between propane and silanol nests, while simultaneously expanding external pore entrances. These two factors mitigate propane trapping and enhance accessibility to the encapsulated cobalt sites. Additionally, X-ray absorption spectroscopy and theoretical studies reveal that the elimination of surface silanol groups leads to electron-deficient cobalt sites, which lower the activation barrier of propane C–H bond cleavage. In propane dehydrogenation (PDH) reactions, the combined diffusion and electronic enhancements enable the TEOS-modified CoO x -S1–0.3 catalyst to achieve a propylene production rate of 86.6 mmol·g cat –1 ·h –1 at 600 °C under a pure propane feed, representing a 1.6-fold improvement over the parent CoO x -S1 and rivaling state-of-the-art Co-based PDH catalysts. This work provides fundamental insights into silanol-mediated molecular diffusion and electronic effects in catalysis.