Silver nanoparticles, supported on porous zeolites, have important applications in catalysis, as well as, in the capture of radioactive iodine. The functionality of these systems is strongly dependent on the structure and distribution of the Ag particles within the zeolite. Accordingly, a comprehensive understanding of the Ag particle formation is key to controlling the structure and reactivity. Both thermal dehydration of water adsorbed within the zeolite pores and chemical reduction can contribute to Ag-particle formation in Ag-exchanged zeolites. Absorbed water and pore surface functionality (e.g. hydroxyl groups), affects silver cation mobility and, thus, has potential to impact cluster and particle growth kinetics. Thermal dehydration during the high temperature reduction reaction and/or changes to the pore surface, may affect cation mobility in the partially reduced material. Understanding the evolving structure of the clusters and nanoparticles, how this is coupled to desorption of molecular species and changes to surface functionality, and how these can impact reduction and particle growth, is of prime importance in controlling these processes. By probing a single sample within a single in-situ sample environment, inconsistencies that may arise from separate experiments (e.g., environments, procedures, etc.) can be avoided. Herein, we combine simultaneous PDF and DRIFTS measurements with XANES data to study the role of water and surface hydroxyl groups in Ag particle formation in Zeolite A (LTA). Experiments were undertaken at elevated temperature in reducing atmosphere, as typical of a solid-gas reaction for industrial catalyst preparation. Furthermore, molecular dynamics calculations on Ag nanocluster formation inside the zeolite pores, with and without water molecules, are used to support the structure prediction of the nanoparticles.

In situ PDF/DRIFTS Study of the role of water in Ag particle formation in zeolites

ACS Spring Meeting 2021

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