In recent decades, the environmental protection and long-term sustainability have become the focus of attention due to the increasing pollution generated by the intense industrialization. To overcome ...these issues, environmental catalysis has increasingly been used to solve the negative impact of pollutants emission on the global environment and human health. Supported platinum-metal-group (PGM) materials are commonly utilized as the state-of-the-art catalysts to eliminate gaseous pollutants but large quantities of PGMs are required. By comparison, single-atom site catalysts (SACs) have attracted much attention in catalysis owing to their 100% atom efficiency and unique catalytic performances towards various reactions. Over the past decade, we have witnessed burgeoning interests of SACs in heterogeneous catalysis. However, to the best of our knowledge, the systematic summary and analysis of SACs in catalytic elimination of environmental pollutants has not yet been reported. In this paper, we summarize and discuss the environmental catalysis applications of SACs. Particular focus was paid to automotive and stationary emission control, including model reaction (CO oxidation, NO reduction and hydrocarbon oxidation), overall reaction (three-way catalytic and diesel oxidation reaction), elimination of volatile organic compounds (formaldehyde, benzene, and toluene), and removal/decomposition of other pollutants (Hg
0
and SO
3
). Perspectives related to further challenges, directions and design strategies of single-atom site catalysts in environmental catalysis were also provided.
Display omitted
•The up-to-date reports with respect to the chemical synthesis of SAA are overviewed.•The significance of SAA for representative electrochemical and heterogeneous catalytic reactions ...is analyzed.•The major challenges and opportunities pertaining to this cutting-edge field are suggested.
The development of low-cost, high-performance catalysts at the atomic level has become a challenging issue for large-scale applications of renewable clean energy technologies. Atomic sites catalysts, such as single atoms catalysts (SAC), single clusters catalysts (SCC), single-atom alloys (SAA), have proved their performance in various catalytic reactions due to their extremely high atom utilization efficiency, unique structure, and exceptional catalytic selectivity. A deep understanding and design of the active center of the catalyst at the atomic level has become a top priority for current research. Compared with SAC and SCC, SAA has its own uniqueness. In this review, we focused on the recent progress on the preparation methods of SAA and discussed the key factors controlling the structure of SAA. In addition, several important catalytic reactions performed over well-defined SAA are analyzed. Finally, the challenges and the perspectives of this cutting-edge field are suggested. We believe that this critical review provides a guidance for the rational design of SAA for catalytic applications.
Demonstrated here is the correlation between atomic configuration induced electronic density of single‐atom Co active sites and oxygen reduction reaction (ORR) performance by combining ...density‐functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, a MOF‐derived Co single‐atom catalyst with the optimal Co1‐N3PS active moiety incorporated in a hollow carbon polyhedron (Co1‐N3PS/HC) was designed and synthesized. Co1‐N3PS/HC exhibits outstanding alkaline ORR activity with a half‐wave potential of 0.920 V and superior ORR kinetics with record‐level kinetic current density and an ultralow Tafel slope of 31 mV dec−1, exceeding that of Pt/C and almost all non‐precious ORR electrocatalysts. In acidic media the ORR kinetics of Co1‐N3PS/HC still surpasses that of Pt/C. This work offers atomic‐level insight into the relationship between electronic density of the active site and catalytic properties, promoting rational design of efficient catalysts.
The correlation between atomic configuration induced electronic density of single‐atom Co active sites and oxygen reduction reaction (ORR) performance has been established by combining density‐functional theory calculations and electrochemical analysis. A metal–organic framework derived single‐atom Co catalyst, comprising an optimal Co1‐N3PS active moiety supported on hollow carbon polyhedron (Co1‐N3PS/HC), was synthesized, and it exhibits superior alkaline and acidic ORR performance.
Platinum (Pt)-based catalysts have been unanimously considered the most efficient catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). Unfortunately, the ...exorbitant cost of Pt hampers the widespread adoption and development of PEMFCs. Scientists have devoted tremendous efforts to achieving higher catalytic activity with less Pt usage by constructing delicate nanostructures. Substituting Pt with cheaper metals may be a feasible solution but suffers from a relatively low intrinsic activity. Recently, single-atom catalysts (SACs), which possess the highest metal utilization and excellent activity because of the minimum size of metal and unique coordination structure, are developing rapidly and have been regarded as a potential alternative to Pt-based materials. Here, we review the development of conventional Pt- and nonprecious-metal-based ORR catalysts and summarize recent achievement in SACs for the ORR. A brief perspective on the remaining challenges and future directions of SACs is also presented.
Display omitted
Proton-exchange membrane fuel cells (PEMFCs) are now of great interest because of zero emission and high efficiency. Current PEMFCs require an unaffordable amount of Pt-based catalysts to overcome the sluggish kinetics of the oxygen reduction reation (ORR) on cathodes, hampering the widespread adoption of PEMFCs. Tremendous efforts have been devoted to achieving higher catalytic activity with less Pt usage by nanoscale engineering. Substituting Pt with cheaper metals may be also a feasible solution but suffers from low intrinsic activity. Recently, single-atom catalysts (SACs), which possess the highest metal utilization and excellent activity because of the minimum size of metal and unique coordination structure, have been regarded as potential alternatives. Here, we review the development of Pt- and nonprecious-metal-based ORR nanocatalysts and summarize recent achievements in SACs for the ORR. At last, a brief perspective on the remaining challenges and future directions of SACs for the ORR is presented.
Proton-exchange membrane fuel cells (PEMFCs) are considered the ideal devices for direct chemical-to-electrical energy conversion but suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) on cathodes. For an overview of the recent progress in this field, this review introduces the mechanism and electrochemical evaluation of the ORR, elaborates on the development of conventional Pt- and nonprecious-metal-based catalysts for the ORR, summarizes recent achievements in the ORR, and presents the remaining challenges as well as future directions of single-atom catalysts.
The performance and the cost of electrocatalysts play the two most vital roles in the development and application of energy conversion technologies. Single-atom catalysts (SACs) are recently emerging ...as a new frontier in catalysis science. With maximum atom-utilization efficiency and unique properties, SACs exhibit great potential for enabling reasonable use of metal resources and achieving atomic economy. However, fabricating SACs and maintaining the metal centers as atomically dispersed sites under synthesis and catalysis conditions are challenging. Here, we highlight and summarize recent advances in wet-chemistry synthetic methods for SACs with special emphasis on how to achieve the stabilization of single metal atoms against migration and agglomeration. Moreover, we summarize and discuss the electrochemical applications of SACs with a focus on the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and CO2 reduction reaction (CO2RR). At last, the current issues and the prospects for the development of this field are discussed.
Display omitted
The development of synthetic strategies plays a fundamental role in advancing catalysis science and practical application of single-atom catalysts (SACs). Owing to the high surface energy of single atoms, achieving the atomic dispersion of mononuclear metal precursors and stabilizing the as-formed single atoms against migration and agglomeration are key aspects in the synthesis of SACs. Several innovative synthetic strategies for SACs are summarized and highlighted through discussion of recent advances in the synthesis of SACs via wet-chemistry approaches.
Furthermore, the great potential of SACs in electrochemical applications, with special emphasis on key clean energy conversion reactions including the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and CO2 reduction reaction (CO2RR), are presented and discussed. Further research on single-atom catalysis should focus on understanding the structure-performance relationship and catalytic mechanism at the atomic scale by employing SACs as model systems with the aid of theoretical calculation and in situ characterization technologies to achieve an atomic-economic green catalytic process.
Developing single-atom catalysts (SACs) plays a fundamental role in advancing catalysis science and practical application. Owing to high surface energy, fabricating SACs remains a great challenge. In this review, we not only summarize recent advances on wet-chemistry methods and discuss the key points for the synthesis of SACs, but also highlight the potential applications of SACs for clean energy conversion reactions.
Various metal-based electrocatalysts from nanocrystals, to clusters and single-atoms, have been well-discovered towards high-efficient power devices and electrocatalytic conversion. To accelerate ...energy transformation materials discovery, developing high-throughput DFT calculations and machine-learning techniques is of great necessity. This review comprehensively outlines the latest progress of theory-guided design of advanced energy transformation materials. Especially, we focus on the study of single atoms in various power devices, such as fuel cell (oxygen reduction reaction, ORR; acid oxidation reaction; alcohol oxidation reaction), and other reactions for energy-related electrocatalytic conversion of small molecules, such as H2O2 evolution reactions (2e− ORR), water splitting (H2 evolution reaction/O2 evolution reaction, HER/OER), N2 reduction reaction (NRR), and CO2 reduction reactions (CO2RR). Firstly, the electronic structure, interaction mechanism, and reaction activation path are discussed to provide an overall blueprint in electrocatalysis and batteries mentioned above. Thereafter, the experimental synthesis strategies, structural recognition, and electrocatalytic performance for the advanced energy transformation materials are figured out. Finally, some viewpoints into the current issues and future design concept of the advanced energy transformation materials are provided.
Display omitted
In this study, we explored expression and functions of circular RNA LPAR3 (circLPAR3) in esophageal squamous cell carcinoma (ESCC). The differential expression of circular RNAs (circRNAs) in 10 ESCC ...and corresponding paracarcinoma tissues was analyzed through circRNA microarray, then the candidate circRNAs were detected and verified through quantitative RT‐PCR, and a novel circRNA was screened, which was circLPAR3. Circular RNA LPAR3 showed apparently high expression in ESCC tissues and cells, which was closely correlated with the clinical stage and lymph node metastasis of ESCC patients. Circular RNA LPAR3 was mainly located in the cytoplasm of ESCC cells, which was more stable than the baseline gene. Circular RNA LPAR3 upregulated MET gene expression through sponge adsorption of microRNA (miR)‐198, activated the RAS/MAPK and the PI3K/Akt pathways, and promoted ESCC cell migration, invasion, and metastasis in vivo and in vitro. However, it had no effect on ESCC cell proliferation. Circular RNA LPAR3 can regulate the miR‐198‐MET signal axis to promote the migration, invasion, and metastasis of esophageal cancer cells, which can thereby serve as a potential diagnostic and therapeutic target of esophageal cancer.
In esophageal squamous cell carcinoma (ESCC), high circular RNA LPAR3 expression is positively correlated with lymph node metastasis and advanced tumor TNM stage. Circular RNA LPAR3 serves as a sponge of microRNA‐198 to regulate MET expression, thus promoting ESCC cell migration, invasion, and metastasis.
Hollow nanomaterials have attracted a broad interest in multidisciplinary research due to their unique structure and preeminent properties. Owing to the high specific surface area, well‐defined ...active site, delimited void space, and tunable mass transfer rate, hollow nanostructures can serve as excellent catalysts, supports, and reactors for a variety of catalytic applications, including photocatalysis, electrocatalysis, heterogeneous catalysis, homogeneous catalysis, etc. Based on state‐of‐the‐art synthetic methods and characterization techniques, researchers focus on the purposeful functionalization of hollow nanomaterials for catalytic mechanism studies and intricate catalytic reactions. Herein, an overview of current reports with respect to the catalysis of functionalized hollow nanomaterials is given, and they are classified into five types of versatile strategies with a top‐down perspective, including textual and composition modification, encapsulation, multishelled construction, anchored single atomic site, and surface molecular engineering. In the detailed case studies, the design and construction of hierarchical hollow catalysts are discussed. Moreover, since hollow structure offers more than two types of spatial‐delimited sites, complicated catalytic reactions are elaborated. In summary, functionalized hollow nanomaterials provide an ideal model for the rational design and development of efficient catalysts.
Functionalization of hollow nanomaterials provides a versatile way for the rational design of hierarchical catalysts so as to achieve superior catalytic efficiency for a variety of catalytic applications, particularly for intricate reactions. Five types of functionalization strategies, i.e., geometric and composition modification, encapsulation, multishell construction, anchored single atomic sites, and surface molecular engineering, are overviewed and elaborated.
The development of low‐cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable ...isolated single‐atom Fe/N‐doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half‐wave potential (E1/2) of 0.900 V, which outperformed commercial Pt/C and most non‐precious‐metal catalysts reported to date. Besides exceptionally high kinetic current density (Jk) of 37.83 mV cm−2 at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species.
Together alone: Anchored on N‐doped porous carbon via a cage‐encapsulated precursor pyrolysis strategy, isolated single iron atoms exhibit excellent oxygen reduction reaction (ORR) performance, good methanol tolerance, and outstanding stability. Control experiments and theoretical calculations demonstrate that the ORR performance results from the atomically dispersed iron.
The solar‐driven photocatalytic reduction of CO2 (CO2RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO2 emissions. However, low catalytic efficiency and poor ...selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO2RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er1/CN‐NT) with a tunable dispersion density of single atoms. Er1/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO2RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO2RR.
A catalyst with a high density of rare‐earth single Er atoms supported on a carbon nitride nanotube (HD‐Er1/CN‐NT) is synthesized by an atom‐confinement and coordination strategy (ACC). Experimental results and DFT calculations reveal that the single Er atoms play a key role in the photocatalytic CO2 reduction reaction in a pure‐water system. The ACC strategy also extends to the synthesis of other rare‐earth single‐atom catalysts.
PDF
