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We report a single atom Rh1/CeO2 catalyst prepared by the high temperature (800 °C) atom trapping (AT) method which is stable under both oxidative and reductive conditions. Infrared spectroscopic and electron microscopy characterization revealed the presence of exclusively ionic Rh species. These ionic Rh species are stable even under reducing conditions (CO at 300 °C) due to the strong interaction between Rh and CeO2 achieved by the AT method, leading to high and reproducible CO oxidation activity regardless of whether the catalyst is reduced or oxidized. In contrast, ionic Rh species in catalysts synthesized by a conventional impregnation approach (e. g., calcined at 350 °C) can be readily reduced to form Rh nanoclusters/nanoparticles, which are easily oxidized under oxidative conditions, leading to loss of catalytic performance. The single atom Rh1/CeO2 catalysts synthesized by the AT method do not exhibit changes during redox cycling hence are promising catalysts for emission control where redox cycling is encountered, and severe oxidation (fuel cut) leads to loss of performance. [ABSTRACT FROM AUTHOR]

Single-atom catalysts1 make exceptionally efficient use of expensive noble metals and can bring out unique properties1–3. However, applications are usually compromised by limited catalyst stability, which is due to sintering3,4. Although sintering can be suppressed by anchoring the metal atoms to oxide supports1,5,6, strong metal–oxygen interactions often leave too few metal sites available for reactant binding and catalysis6,7, and when exposed to reducing conditions at sufficiently high temperatures, even oxide-anchored single-atom catalysts eventually sinter4,8,9. Here we show that the beneficial effects of anchoring can be enhanced by confining the atomically dispersed metal atoms on oxide nanoclusters or ‘nanoglues’, which themselves are dispersed and immobilized on a robust, high-surface-area support. We demonstrate the strategy by grafting isolated and defective CeOx nanoglue islands onto high-surface-area SiO2; the nanoglue islands then each host on average one Pt atom. We find that the Pt atoms remain dispersed under both oxidizing and reducing environments at high temperatures, and that the activated catalyst exhibits markedly increased activity for CO oxidation. We attribute the improved stability under reducing conditions to the support structure and the much stronger affinity of Pt atoms for CeOx than for SiO2, which ensures the Pt atoms can move but remain confined to their respective nanoglue islands. The strategy of using functional nanoglues to confine atomically dispersed metals and simultaneously enhance their reactivity is general, and we anticipate that it will take single-atom catalysts a step closer to practical applications.Nanometre-sized ‘nanoglue’ islands of CeOx on high-surface-area SiO2 are shown to suppress sintering and confine on average one Pt atom per island, leading to stable single-atom catalysts under oxidizing and reducing environments. [ABSTRACT FROM AUTHOR]

A single‐atom Pt1/CeO2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt2+ in a highly symmetric square‐planar Pt1O4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt2+ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt1/CeO2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO2 to generate Pt single atoms in an asymmetric Pt1O4 configuration. Owing to this unique coordination, Pt1δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt1/CeO2_TS catalyst was retained under oxidizing conditions. [ABSTRACT FROM AUTHOR]

In this work, we compare the CO oxidation performance of Pt single atom catalysts (SACs) prepared via two methods: (1) conventional wet chemical synthesis (strong electrostatic adsorption–SEA) with calcination at 350 °C in air; and (2) high temperature vapor phase synthesis (atom trapping–AT) with calcination in air at 800 °C leading to ionic Pt being trapped on the CeO2 in a thermally stable form. As-synthesized, both SACs are inactive for low temperature (<150 °C) CO oxidation. After treatment in CO at 275 °C, both catalysts show enhanced reactivity. Despite similar Pt metal particle size, the AT catalyst is significantly more active, with onset of CO oxidation near room temperature. A combination of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and CO temperature-programmed reduction (CO-TPR) shows that the high reactivity at low temperatures can be related to the improved reducibility of lattice oxygen on the CeO2 support. While single-atom catalysts (SACs) have attracted a lot of interest, the nature of the active sites in SACs remains elusive. Here the authors elucidate that depositing single atoms via high temperature synthesis leads to improved reducibility of lattice oxygen on CeO2 yielding low temperature reactivity of Pt catalysts in CO oxidation. [ABSTRACT FROM AUTHOR]

A single-atom Pt 1 /CeO 2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over-stabilization of Pt 2+ in a highly symmetric square-planar Pt 1 O 4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt 2+ by thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO 2 to generate Pt single atoms in an asymmetric Pt 1 O 4 configuration. Owing to this unique coordination, Pt 1 δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance. CO oxidation reactivity on the Pt 1 /CeO 2 &#95;TS catalyst was retained under oxidizing conditions., (© 2021 Wiley-VCH GmbH.)