Direct assessment of confinement effect in zeolite-encapsulated subnanometric metal species

Abstract

Subnanometric metal species confined inside the microporous channels/cavities of zeolites have been demonstrated as stable and efficient catalysts. The confinement interaction between the metal species and zeolite framework has been proposed to play the key role for stabilization, though the confinement interaction is elusive to be identified and measured. By combining theoretical calculations, imaging simulation and experimental measurements based on the scanning transmission electron microscopy-integrated differential phase contrast imaging technique, we have studied the location and coordination environment of isolated iridium atoms and clusters confined in zeolite. The image analysis results indicate that the local strain is intimately related to the strength of metal-zeolite interaction and a good correlation is found between the zeolite deformation energy, the charge state of the iridium species and the local absolute strain. The direct observation of confinement with subnanometric metal species encapsulated in zeolites provides insights to understand their structural features and catalytic consequences. Zeolite-encapsulated metal nanoparticles have important catalytic properties, but their effect on the zeolite local structure has been difficult to characterize. Here the authors, using DFT calculations and scanning transmission electron microscopy, characterize the local strain due to confinement effects in metal-zeolite catalysts. ; This work has been supported by the Spanish government through the "Severo Ochoa Program" (SEV-2016-0683) (A.C. and M.B.) and PID2020-112590GB-C21 (M.B.). High-resolution STEM measurements were performed at DME-UCA node of ICTS ELECMI in Cadiz University with financial support from FEDER/MINECO (MAT2017-87579-R (J.J.C.), PID2020-113006-RB-I00 (J.J.C.) and PID2019-110018GA-I00 (M.L.-H.)). The computations were performed on the Tirant III cluster of the Servei d'Informatica of the University of Valencia. The supports from Tsinghua University (L.L.) are also acknowledged.