Unveiling the role of local temperature gradients in individual zeolites containing metal active sites

Abstract

The spatial distribution of active sites governs the behavior of solid catalysts, yet how it shapes local temperature gradients and thereby affects catalytic performance remains poorly understood. Here, using the industrially important propane dehydrogenation (PDH) over CoOx confined in silicalite-1 (S-1) zeolites as a model system, we show that catalytic activity and stability are enhanced when CoOx is peripherally confined near the crystal surface (CoOx@S-1-M), rather than uniformly distributed throughout the zeolite (CoOx@S-1-U), which differs from conventional catalyst design strategies that emphasize uniform active-site dispersion for stability. To uncover the origin of this behavior, we probe the local temperatures of CoOx clusters by developing in situ high-resolution microscopic Raman thermometry. CoOx@S-1-U exhibits a pronounced core-to-edge thermal gradient, with the temperature difference exceeding 17 °C, whereas CoOx@S-1-M maintains a much more uniform temperature distribution, with the difference limited to 8 °C. CoOx@S-1-M also exhibits higher propane conversion and stability, consistent with this thermal behavior. Mechanistic analysis reveals that the smaller temperature drop at CoOx clusters in CoOx@S-1-M enhances propylene desorption and suppresses side reactions and coke formation, deviating from the commonly accepted view that higher temperatures generally promote coke growth. These findings establish a direct link between active-site spatial location and catalytic performance through microscale temperature gradients at active clusters, providing a new perspective for the rational design of supported metal catalysts.