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      Atomic (single, double, and triple atoms) catalysis: frontiers, opportunities, and challenges

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          Abstract

          SACs, DACs, and TACs, heterogeneous catalysts with the advantages of homogeneous catalysts, are ideal models for exploring catalytic mechanisms and further designing catalysts.

          Abstract

          The atomic dispersing of metal atoms supported on an optimal substrate exhibits an ideal strategy for maximizing metal utilization for catalysis, which is particularly significant for exploiting new catalysts with low cost and high catalytic efficiency. The dramatic development of atomic metal catalysts, including single atom catalysts (SACs), double atoms catalysts (DACs), and triple atoms catalysts (TACs), has spawned two remarkable platforms: (1) bridging homogeneous catalysts and heterogeneous catalysts; (2) linking theoretical calculations and experimental results. In this review, recent syntheses, characterizations, and applications of SACs, DACs, and TACs are highlighted through a focus on various applied substrates. We extensively discuss the synthetic strategies of successfully achieving SACs, DACs, and TACs. Moreover, the opportunities and challenges in developing SACs, DACs, and TACs are pointed out, together with the prospects for the development of atomic catalysis.

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          Most cited references156

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          Single-atom catalysis of CO oxidation using Pt1/FeOx.

          Platinum-based heterogeneous catalysts are critical to many important commercial chemical processes, but their efficiency is extremely low on a per metal atom basis, because only the surface active-site atoms are used. Catalysts with single-atom dispersions are thus highly desirable to maximize atom efficiency, but making them is challenging. Here we report the synthesis of a single-atom catalyst that consists of only isolated single Pt atoms anchored to the surfaces of iron oxide nanocrystallites. This single-atom catalyst has extremely high atom efficiency and shows excellent stability and high activity for both CO oxidation and preferential oxidation of CO in H2. Density functional theory calculations show that the high catalytic activity correlates with the partially vacant 5d orbitals of the positively charged, high-valent Pt atoms, which help to reduce both the CO adsorption energy and the activation barriers for CO oxidation.
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            Heterogeneous single-atom catalysis

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              Single-atom catalysts: a new frontier in heterogeneous catalysis.

              Supported metal nanostructures are the most widely used type of heterogeneous catalyst in industrial processes. The size of metal particles is a key factor in determining the performance of such catalysts. In particular, because low-coordinated metal atoms often function as the catalytically active sites, the specific activity per metal atom usually increases with decreasing size of the metal particles. However, the surface free energy of metals increases significantly with decreasing particle size, promoting aggregation of small clusters. Using an appropriate support material that strongly interacts with the metal species prevents this aggregation, creating stable, finely dispersed metal clusters with a high catalytic activity, an approach industry has used for a long time. Nevertheless, practical supported metal catalysts are inhomogeneous and usually consist of a mixture of sizes from nanoparticles to subnanometer clusters. Such heterogeneity not only reduces the metal atom efficiency but also frequently leads to undesired side reactions. It also makes it extremely difficult, if not impossible, to uniquely identify and control the active sites of interest. The ultimate small-size limit for metal particles is the single-atom catalyst (SAC), which contains isolated metal atoms singly dispersed on supports. SACs maximize the efficiency of metal atom use, which is particularly important for supported noble metal catalysts. Moreover, with well-defined and uniform single-atom dispersion, SACs offer great potential for achieving high activity and selectivity. In this Account, we highlight recent advances in preparation, characterization, and catalytic performance of SACs, with a focus on single atoms anchored to metal oxides, metal surfaces, and graphene. We discuss experimental and theoretical studies for a variety of reactions, including oxidation, water gas shift, and hydrogenation. We describe advances in understanding the spatial arrangements and electronic properties of single atoms, as well as their interactions with the support. Single metal atoms on support surfaces provide a unique opportunity to tune active sites and optimize the activity, selectivity, and stability of heterogeneous catalysts, offering the potential for applications in a variety of industrial chemical reactions.
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                Author and article information

                Contributors
                Journal
                JMCAET
                Journal of Materials Chemistry A
                J. Mater. Chem. A
                Royal Society of Chemistry (RSC)
                2050-7488
                2050-7496
                February 19 2019
                2019
                : 7
                : 8
                : 3492-3515
                Affiliations
                [1 ]Key Laboratory of Automobile Materials
                [2 ]Ministry of Education
                [3 ]School of Materials Science and Engineering
                [4 ]Jilin University
                [5 ]Changchun 130022
                Article
                10.1039/C8TA11416A
                469b487c-c117-48ea-9f04-f95753b9f84e
                © 2019

                http://rsc.li/journals-terms-of-use

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