(229c) Subnanometric Metal Clusters and Single Metal Atoms inside Zeolites

Many chemical processes rely on the use of highly dispersed metal catalysts to speed up the desired transformations. However, most metals are prone to sinter under the harsh conditions needed to overcome thermodynamic or kinetic limitations to activate unfuntionalized molecules (e.g. alkanes). Temperature and redox stress primarily trigger this instability responsible for a gradual loss of activity during the catalyst lifetime. In this work, we show how zeolites, when treated as well-defined (macro)ligands of the metal species, can impart outstanding levels of stability to keep the metal within the subnanometric size space, even under harsh reaction conditions. We discuss the different sintering mechanisms by which Pt aggregates inside zeolites when subjected to cycling H₂ and O₂, and present strategies based on metal/zeolite interactions to limit both particle coalescence and single-atom Ostwald ripening. XAFS and HAADF-STEM are combined to rigorously determine the catalytic structures, including under reactions conditions. Several interesting applications that take advantage of both the outstanding metal stability and size-selectivity effects will be presented and discussed.