Metal–Support Interfaces in Pt1/γ-Al2O3 Single Atom Catalysts with Atomic-Level Precision

Abstract

Single atom catalysts (SACs) appear as a promising class of materials featuring isolated metal atoms anchored to supports, where the advantages of heterogeneous catalysis are combined with a maximized noble metal atom usage. In SACs, each metal atom is fully exposed to the support surface; it is therefore critical to elucidate the nature of the metal–support interface to identify the active species and design tailored, more efficient materials. Among SACs, Pt1/γ-Al2O3, active toward CO oxidation and isomerization of olefins, represents a prototypical system. However, the chemical complexity and poor crystallinity of γ-Al2O3 hinders an atomistic description via conventional techniques (XAS, TEM) only. Here, we report the study, via multinuclear solid-state NMR and DFT modeling, of a series of Pt SACs on γ-Al2O3 supports, prepared by surface organometallic chemistry followed by calcination. This approach clarifies the coordination environment of Pt1/γ-Al2O3, revealing that highly oxidized Pt atoms are preferentially anchored by undercoordinated Al sites at the (110)b-(100) edge. The Pt atoms have a distorted square planar or square pyramidal environment and are stabilized through [4–6]Al–O–Pt and [4]Al–OH–Pt linkages. Pyridine absorption studies reveal the presence of Brønsted acidic sites, assigned to [4]Al–OH–Pt edge moieties, through DFT modeling. The findings establish morphological features of γ-Al2O3 supports needed to stabilize SACs and provide a roadmap for building accurate SAC–support models using NMR and DFT.