Functional CeOx nanoglues for robust atomically dispersed catalysts

Abstract

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 ,...

Nested Metal Catalysts: Metal Atoms and Clusters Stabilized by Confinement with Accessibility on Supports

“…A next logical step in the development of this field emerged from insights about how to isolate and stabilize highly dispersed noble metals in metal oxide nests on supports . The synthesis is shown schematically in Figure ; a key idea was to bond platinum in salt precursors selectively to nests of isolated cerium oxide (CeO x ) and not to the silica support on which the nests were formed.…”

Geometric and Electronic Effects in Hydrogenation Reactions

“…Recently, metal oxide nanoparticles such as TiO 2 , Cr 2 O 3 , and CeO x were used to disperse and stabilize multielemental alloy nanoparticles or even atomically dispersed catalysts with a similar concept. 256,257 Single atom or the alloy catalyst is another typer of thriving catalyst, making full of the spatial confinement effect to disperse and stabilize the active metal species. Yet, we will not discuss it in detail here, since there have been many reviews to sort and classify it.…”

“…Besides the above direct spatial confinement effect by physical obstacle, energy-based spatial confinement provides us with another option. , As shown in Figure d, reducible metal oxide NPs dispersed on inert supports will induce a dense array of energy potential wells, which can further trap the metal active sites from agglomeration. , In addition, one can continue to apply the direct spatial confinement effect to further tune the active sites, such as the targeted passivation strategy as illustrated in Figure d. Recently, metal oxide nanoparticles such as TiO 2 , Cr 2 O 3 , and CeO x were used to disperse and stabilize multielemental alloy nanoparticles or even atomically dispersed catalysts with a similar concept. , …”

Theoretical insight into the relevance between the oxidation states of CeO2 supported Pt4+/2+/1+/0/2− and their HER performance

“…[4][5][6] A very recent study found that Pt single-atoms anchored to functional CeO x nanoglues could remain dispersed in both oxidizing and reducing environments at high temperatures. 7 As is well known, the catalytic activity of Pt/CeO 2 is affected by multiple factors, such as the size and loading of Pt, and the surface facets and morphology of CeO 2 . [8][9][10][11][12][13] Remarkably, the importance of OSs present in CeO 2 supported Pt catalysts has been gradually discovered in determining the catalytic activity for the HER.…”