Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO₂

Abstract

Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO. In these structures, isolated Pt atoms, Pt, remain stable through various conditions, and spectroscopic evidence suggests Pt species exist in homogeneous local environments. Comparing Pt to ∼1 nm preoxidized (Pt) and prereduced (Pt) Pt clusters on TiO, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt ≪ Pt < Pt. Pt species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Pt clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO and that Pt exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO. This approach should be generally useful for studying the behavior of supported precious metal atoms.

Maximizing the Number of Interfacial Sites in Single‐Atom Catalysts for the Highly Selective, Solvent‐Free Oxidation of Primary Alcohols

“…[13] We therefore further studied aP t 1 /CeO 2 and aP t/CeO 2 -NP catalyst with NPs of 6.5 nm ( Figure S8). [13] We therefore further studied aP t 1 /CeO 2 and aP t/CeO 2 -NP catalyst with NPs of 6.5 nm ( Figure S8).…”

Nitrogen Reduction to Ammonia on Atomic‐Scale Active Sites under Mild Conditions

“…For example, the CO molecules adsorbed on Pt SACs (Pt iso ) possess a sharp band at 2112 cm −1 with no change in frequency, width, or symmetry in the IRAS spectra. In contrast, the ones adsorbed on the pre‐oxidized Pt ox (2100–2125 cm −1 ) and pre‐reduced Pt metal (2040–2100 cm −1 ) Pt clusters show broader bands and changes in frequency and symmetry as well …”

“…b) Schematic illustration of wet impregnation for fabricating Pt 1 /TiO 2 . Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…[22d] The Pt atoms take the exact spots of the Fe atoms in the FeO x lattice and are stabilized due to the formation of PtOFe coordination. In another case, the Pt precursor (0.05 wt%) was homogeneously loaded on TiO 2 through the strong electrostatic adsorption between the surface oxygen anion and the cationic precursor [(NH 3 ) 4 Pt] +2 (Figure b), resulting in Pt iso /TiO 2 SACs …”

Ag10Ti28‐Oxo Cluster Containing Single‐Atom Silver Sites: Atomic Structure and Synergistic Electronic Properties

“…[1][2][3][4][5][6] Especially,t he recently developed single-atom catalysts are attracting tremendous interest due to their excellent activity and selectivity. [24][25][26][27][28][29] Recent developments in the molecular analogues of TiO 2 ,crystalline polyoxotitanium clusters (PTCs), provides us with wonderful opportunities to investigate the structures and reactivities of titanium oxides at the molecular level. [12,13] Moreover,d ue to the lack of atomic structures,i ti sr ather difficult to study the metal-support interaction and the functional role of the support which is crucial for the performance of such catalyst systems.…”