DeterminingIdentifying and controlling the uniformity of isolated metal sites on surfaces of supports are central goals in investigations of single-site catalysts, because well-defined species provide opportunities for fundamental understanding of the surface sites for fundamental understanding and industrial applications. CO is a useful probe molecule of the surface metal sites, often reacting with them to formleading to the formation of metal gem-dicarbonyls, the infrared spectra of which provide insights into the nature of the metal sites and the metal-support interface. Metals bonded to variousto various support surface sites give broad bands in the spectra, and when narrowFull width at half maximum values characterizing the ν CO values bands are observed, they provide evidence of indicate a highthe degree of uniformity of the metal sites, because metals bonded to a set of various sites give broad bands in the spectra. Much rReecent work focused on single-site catalysts has been done withuses supports that are inherently nonuniform, giving supported metal species that are therefore leading to a non-uniform metal sites, and ultimately resulting in a lack of fundamental understanding of the chemistry. Herein we summarize new and already reported values of ν CO data characterizing supported iridium gemdicarbonyls, showing that the most nearly uniform of them are those supported on zeolites and

Single-atom catalysts (SACs) exhibit unique catalytic property and maximum atom e ciency of rare, expensive metals. A critical barrier to applications of SACs is sintering of active metal atoms under operating conditions. Anchoring metal atoms onto oxide supports via strong metal-support bonds may alleviate sintering. Such an approach, however, usually comes at a cost: stabilization results from passivation of metal sites by excessive oxygen ligation-too many open coordination sites taken up by the support, too few left for catalytic action. Furthermore, when such stabilized metal atoms are activated by reduction at elevated temperatures they become unlinked and so move and sinter, leading to loss of catalytic function. We report a new strategy, con ning atomically dispersed metal atoms onto functional oxide nanoclusters (denoted as nanoglues) that are isolated and immobilized on a robust, high-surfacearea support-so that metal atoms do not sinter under conditions of catalyst activation and/or operation.High-number-density, ultra-small and defective CeOx nanoclusters were grafted onto high-surface-area SiO2 as nanoglues to host atomically dispersed Pt. The Pt atoms remained on the CeOx nanoglue islands under both O2 and H2 environment at high temperatures. Activation of CeOx supported Pt atoms increased the turnover frequency for CO oxidation by 150 times. The exceptional stability under reductive conditions is attributed to the much stronger a nity of Pt atoms for CeOx than for SiO2-the Pt atoms can move but they are con ned to their respective nanoglue islands, preventing formation of larger Pt particles. The strategy of using functional nanoglues to con ne atomically dispersed metal atoms and simultaneously enhance catalytic performance of localized metal atoms is general and takes SACs one major step closer to practical applications as robust catalysts for a wide range of catalytic transformations Main TextThe design strategy integrates three components into the nal catalyst: 1) a robust, high-surface-area support (e.g., SiO 2 , Al 2 O 3 , etc.), 2) nanoscale functional metal oxides (e.g., CeO x , TiO x , FeO x , etc.) anchored stably onto the robust support as isolated nanoglue islands, and 3) single metal atoms (M 1 ) selectively localized to only the nanoglue islands. The nanoglue selection criteria include a) its stability in dispersed form on the support surface due to strong bonding, b) a much stronger a nity for the active metal atoms than the support, and c) interactions with the active metal that enhance activity and/or selectivity for the desired catalytic reactions. The selected nanoglue not only behaves as a "double-sided tape" but also contributes to the desired functions for the targeted catalytic reaction.We selected SiO 2 , an irreducible, inexpensive support widely used in processing industries, to demonstrate our strategy because of its high-surface-area, structural stability, and availability in various forms 14 . Because metal atoms anchor onto reducible metal oxides (e.g., CeO 2 , TiO 2 ,...

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Enveloping atomically dispersed supported iridium with the choice of ionic liquid molecular sheaths and supports controls the catalytic performance.

Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized metal accessibility and utilization. The characterization of these materials, however, remains challenging. Using atomically-dispersed Pt supported on crystalline MgO (chosen for its well-defined bonding sites for Pt) as a prototypical example, in this work, we demonstrate how systematic density functional theory calculations (for assessing all the potentially stable Pt sites) combined with automated EXAFS analysis can lead to unbiased identification of isolated, surfaceenveloped platinum cations as the catalytic species for CO oxidation. The catalyst has been characterized by atomic-resolution imaging, EXAFS, and HERFD-XANES spectroscopies; the proposed Pt site are in full agreement with experiment. This theory-guided workflow leads to rigorously determined structural models and provides a more detailed picture of the structure of the catalytically active sites than what is currently possible with conventional EXAFS analysis. As this approach is efficient and agnostic to the metal, support, and catalytic reaction, we posit that it will be of broad interest to the materials characterization and catalysis communities.