(586b) Pt Single-Atom Formation and Nano-Clustering Triggered By Dynamic Surface Reconstructions of an Oxide Support

Here, on the basis of density functional theory (DFT) free energy calculations, we investigate the role of dynamic surface atomic reconstructions on Pt atomization (beginning from a bulk-like Pt sample). Surface atomic reconstruction is a phenomenon in which the surface stoichiometry or atomic arrangement differ from those of the bulk material to minimize its free energy. Here, we extend the idea of atomic reconstructions of an oxide support (spinel MgAl₂O₄) to find thermodynamically favorable arrangements for supported Pt atoms which can be in the form of bulk-like macroscopic particles, small (sub-)nano-clusters or even single-atoms. We find that the dynamic surface reconstructions of the support which is a function of temperature and chemical potential of surrounding gases, can drive the Pt atomization or clustering. Also, the presence of the Pt atoms expands the types of possible atomic reconstructions of the support. For example, we demonstrate how small few-atoms Pt nuclei can trigger local atomic reconstructions, strongly anchor themselves to the ionic support, and avoid further agglomeration. It turns out by engineering the right temperature and gas environment one can drive single-atom or sub-nanoclusters formation in a reversible manner.

In addition to the thermodynamics of different Pt phases, electronic structure analyses are used to understand the fundamental surface chemistry that drives such surface reconstructions. Furthermore, we study the chemistry of the Pt single-sites and their reactivity toward both closed-shell (e.g., H₂O and CO) and open-shell groups (e.g., O and OH), and show how and why these values are sensitive to the exact environment of the Pt atoms. Poisoning by both CO and H₂O bonding will also be discussed. Our work, has implications not only on design paradigms for maximal or even atomic dispersion of transition metals, but also in understanding the basic chemistry of the single-atom catalyst (SAC) systems.