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Migration and Growth of Silver Nanoparticles in Zeolite Socony Mobil 5 (ZSM-5) Observed by Environmental Electron Microscopy: Implications for Heterogeneous Catalysis

Silver metal nanoparticles are among the most widely studied nanoparticles. 
They are widely used heterogeneous catalysts used for many purposes such as antisepsis,hydrogenation, and carboxylation but also for the trapping of xenon in nuclear test and detection facilities. The catalytic activity and adsorption capacity of silver nanoparticles, 
which depend on their size distribution and dispersion on the support, generally decrease with time because of agglomeration of the metal into larger particles. In this study, we quantified the sintering process of silver nanoparticles supported in Zeolite Socony Mobil 5 
(ZSM-5) zeolite. It was found that 85% of the sintering process of the silver nanoparticles was driven by Ostwald ripening. We found that silver nanoparticles are trapped in porous, cavities that are meso- or macroporous defects in the zeolite. Although this phenomenon limits the amount of silver that diffuses to the zeolite external surface, it does not prevent the formation of large particles by atom migration. The presence of chloride reactants facilitates the sintering phenomenon by lowering the energy barrier. This finding provides a rational basis for the design of silver-containing zeolite-based heterogeneous catalysts.