Structural Evolution of Mordenite-Supported Pt Clusters in Ammonia and Hydrogen Atmospheres

Unveiling the microstructural evolution of the active sites in reaction atmospheres is the basis of catalytic reaction mechanisms. Herein, the Pt clusters confined within mordenite (MOR) in ammonia and hydrogen atmospheres are investigated with both first-principles calculations and experiments. The thermodynamic states of Ptn clusters (n = 1-7) in NH3 and H2 atmospheres, both in gas phase and MOR channels, are systematically investigated using ab initio thermodynamics. Theoretical results reveal that smaller Ptn clusters remain stable in an NH3 atmosphere due to strong Pt-NH3 coordination, which promotes cluster dispersion. In contrast, H2 favors the formation of slightly larger clusters by acting as a double-edged sword: H inserts into the Pt-Pt bonds while simultaneously serving as a bridge to stabilize the cluster. Control experiments confirm that treatment with NH3 and H2 redisperses Pt clusters in MOR, with NH3 treatment exhibiting superior dispersion performance characterized by aberration-corrected scanning transmission electron microscopy.