Single-Atom Catalysts Recent Advances in
Since the concept of single-atom catalysis was jointly proposed by Academician Tao Zhang from Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Professor Jun Li from Tsinghua University and Professor Jingyue Liu from Arizona State University in 2011, single-atom catalysts have become a high-speed dynamic and fast-developing field in recent years. Single-atom catalysts achieve atomic scale homogeneity of catalytic sites and show the advantages of homogeneous catalysts with high atom utilization, high activity and selectivity. In addition, single-atom catalysts have multiphase characteristics such as easy separation, recyclability and good stability, which combine the advantages of both homogeneous and multiphase catalysts and are regarded as an important bridge between homogeneous and multiphase catalysts. Therefore, the establishment of feasible synthesis strategies for the preparation of high-performance catalysts, in-depth understanding of the active site structure and catalytic mechanism, and the development of practical catalysts with industrial value are the important research directions for single-atom catalysts at present.
1. Adv. Mater: Dynamic reconfiguration between copper monoatoms and clusters during electrocatalytic urea synthesis
The synthesis of this catalyst was carried out with an average urea yield of 52.84 mmol h-1 gcat-1 at an applied potential of -1.6 V versus RHE. XAS spectra showed the remodeling of copper monoatoms (Cu1) to clusters (Cu4) during electrolysis, and this electrochemically reconfigured Cu4 clusters are the real active sites for electrocatalytic urea. The favorable carbon and nitrogen coupling reactions and urea formation on Cu4 were verified using SR-FTIR and DFT calculations. When the applied potential is switched to an open-circuit potential, the clusters are dynamically and reversibly transformed to a single-atom configuration, which endows the catalyst with excellent structural and electrochemical stability. The related research results were published as “Dynamic Reconstitution Between Copper Single atoms and Clusters for Electrocatalytic Urea synthesis” in Advanced Materials
Associate researcher An Xiaoqiang of academician Qu Jiuhui’s team at the Center for Water Quality and Water Ecology, Tsinghua University, in collaboration with Prof. Tang Junwang of the Department of Chemical Engineering and Prof. Liu Limin of Beihang University, has proposed a new strategy for sodium-assisted photoinduced assembly (SPA). Through the special interaction between sodium ions and gold atoms on the carrier surface to form stable pairs of atoms free from the titanium oxide surface, and at the same time driving the adjacent gold atoms to migrate and aggregate into clusters with the help of light field, the produced two-site synergistic catalysts show two orders of magnitude higher catalytic efficiency in the reaction of photolysis of water to produce hydrogen, which is a good example for the “bottom-up” construction of single-atom/gold catalysts at the atomic scale. “The catalytic efficiency of the produced two-site synergistic catalysts in hydrogen production from photolyzed water was enhanced by two orders of magnitude, which provides a new idea for the construction of single-atom/nanocluster synergistic multi-point catalysts on the atomic scale from the bottom up. The results were published in the Journal, “Sodium-Directed Photon-Induced Assembly Strategy for Preparing Multisite Catalysts with High Atomic Utilization Efficiency”. “The results were published in the Journal of the American Chemical Society.
The team of Prof. Ifan E. L. Stephens, Department of Materials, Royal School of Mines, Imperial College London, in conjunction with the team of Prof. Maria-Magdalena Titirici, Department of Chemical Engineering, describes a simple method for the preparation of porous N-aminopyrimidines (NAPs) by using Mg2+ salts as the active site templates and porosity agents and another organic precursor, 2,4,6-triamino-pyrimidine (TAP ) porous N-doped carbon hosts were prepared and then used for Fe coordination, resulting in the preparation of FeNC materials with record high FeNx electrochemical utilization. Unlike Fe (which forms nitrides and carbides upon pyrolysis), Mg2+ is a Lewis acidic metal cation that forms Nx groups and creates pores.TAP interacts efficiently with water molecules of hydrated Mg2+ salts and melts upon pyrolysis, resulting in effective polymerization and uniform distribution of Mg throughout the material.Fe was then ligated in a high-surface-area nitrogen-doped carbon (~ 3295 m2 g-1) in low-temperature wet impregnation to produce highly available FeNx active sites. The researchers conducted an in-depth study of the polymerization pathways and growth of the prepared materials by thermogravimetric analysis, mass spectrometry, solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy.
The researchers confirmed the atomic dispersion of Fe by scanning transmission electron microscopy and energy-dispersive X-rays, while the structure of the active sites was elucidated by X-ray absorption spectroscopy, electron paramagnetic resonance, and low-temperature Mussburger spectroscopy, with the major FeNx site formed by axial ligand pentacoordination. In acidic media, the researchers evaluated the performance of the catalysts for O2 reduction using rotating disk electrode measurements and found that the catalytic system could be made to achieve high site density, low conversion frequency and high utilization from in situ nitrite stripping. Finally, density functional theory was used to assess the effect of axial ligands on the O2 reduction activity of model FeN4 pyridine and pyrrole sites, and the researchers observed a significant change in the OH binding energy and activity of the different axial ligands as compared to the normal FeN4 sites.
The research results were published in the top international journal Advanced Materials under the title “FeNC Oxygen Reduction Electrocatalyst with High Utilisation Penta-coordinated sites”. Materials.
Professor Wei Chen’s team at the National University of Singapore has developed a photoelectrochemical method to selectively oxidize glucose to high-value-added gluconic acid by using single-atom Pt anchored to an array of defective TiO2 nanorods as a photoanode. The defect structure induced by oxygen vacancies can modulate both the charge carrier dynamics and energy band structure. By optimizing the oxygen vacancies, the defective TiO2 photoanodes show great charge separation ability and significantly enhanced selectivity and yield of C6 products. In this work, defected TiO2 with monatomic Pt achieved a glucose oxidation photocurrent density of 1.91 mA cm-2 at 0.6 V, resulting in a gluconic acid yield of 84.3% under simulated sunlight irradiation. The paper was published in the prestigious journal Nature Communications under the title “Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2”. The paper was published in the well-known journal Nature Communications, and Tian Zhuangliu was the first author and corresponding author of the paper.
Prof. Junwang Tang of University College London, UK, in association with researcher Aiqin Wang of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences (DICP, CAS), has proposed a highly selective catalyst consisting of nickel single atoms confined to the surface of titanium dioxide for the conversion of glycerol into the high-value product hydroxyacetaldehyde. Driven by light, the catalyst reacted under ambient conditions using air as a green oxidant. The optimized catalyst showed more than 60% selectivity for hydroxyacetaldehyde with a yield of 1058 μmol-gCat-1-h-1 and a conversion number nearly three times higher than that of NiOx nanoparticle-modified TiO2 photocatalyst. Different physicochemical characterizations reveal the unique functionality of single-atom nickel, which significantly promotes oxygen adsorption, acts as an electron trap, and accelerates the generation of superoxide radicals, thus enhancing the selectivity for hydroxyacetaldehyde. The related research results have been published in the prestigious journal Ad Hoc Research Center under the title “Highly selective transformation of biomass derivatives to valuable chemicals by single-atom photocatalyst Ni/TiO2 “The research results have been published in the well-known journal Adv. Mater.
6. Resolving the effect of peripheral N on Ru single-atom catalytic center for efficient propane dehydrogenation
A highly stable propane dehydrogenation catalyst based on Ru single-atom (Ru1/NC) on nitrogen-doped carbon has been developed. the conversion frequency of Ru1/NC is at least three times higher than the flip frequency of Ru nanoparticles. Experimental and density functional theory studies revealed the important role of nitrogen around the Ru1 center. The inner N layer stabilized the atomically dispersed Ru and inhibited propane cleavage, whereas the outer N layer promoted the electron accumulation in the Ru1 center, which led to significant charge repulsion between Ru1 and propylene and facilitated its desorption. At the monatomic Ru site, the combined effect of the inner and outer N layers contributes to the high efficiency of Ru1/NC. The research results were published in the international journal Nature Catalysis under the title “Peripheral-nitrogen effects on the Ru1 center for highly efficient propane dehydrogenation”. Catalysis
7. Nature: Hydrogen-substituted graphyne-assisted ultrafast spark synthesis of substable nanomaterials
Professor Yi Cui of Stanford University has developed an ultrafast high-temperature platform using hydrogen-substituted graphyne aerogel (HGDY), a two-dimensional sp/sp2 co-hybridized carbon network that provides high-density sites for substable nanomaterials. The authors designed hydrogen-substituted graphyne-assisted ultrafast spark synthesis (GAUSS) to achieve a temperature of 1640 K in 40 ms. By combining aluminum nanoparticles and oxidants, GAUSS reached a remarkable temperature of 3286 K in only 8 ms, with a heating rate of >105 K s-1. A platform including a monatomic, high-entropy alloy and a high entropy oxides as a library of substable nanomaterials. Electrochemical measurements and density functional theory show that the single-atom catalysts synthesized on the GAUSS platform promote the lithium-sulfur conversion kinetics of all-solid-state lithium-sulfur batteries. The related research work was published under the title “Hydrogen-substituted graphdiyne-assisted ultrafast sparking synthesis of metastable nanomaterials” in the top international journal Nature Nanotechnology. The related work was published in Nature Nanotechnology, a leading international journal.
