High Atom Efficiency Research Articles

Single-Atom Catalysts in Environmental Engineering: Progress, Outlook and Challenges.

Recently, single-atom catalysts (SACs) have attracted wide attention in the field of environmental engineering. Compared with their nanoparticle counterparts, SACs possess high atomic efficiency, unique catalytic activity, and selectivity. This review summarizes recent studies on the environmental remediation applications of SACs in (1) gaseous: volatile organic compounds (VOCs) treatment, NOx reduction, CO2 reduction, and CO oxidation; (2) aqueous: Fenton-like advanced oxidation processes (AOPs), hydrodehalogenation, and nitrate/nitrite reduction. We present the treatment activities and reaction mechanisms of various SACs and propose challenges and future opportunities. We believe that this review will provide constructive inspiration and direction for future SAC research in environmental engineering.

Multicomponent Reaction-Assisted Drug Discovery: A Time- and Cost-Effective Green Approach Speeding Up Identification and Optimization of Anticancer Drugs.

Multicomponent reactions (MCRs) have emerged as a powerful strategy in synthetic organic chemistry due to their widespread applications in drug discovery and development. MCRs are flexible transformations in which three or more substrates react to form structurally complex products with high atomic efficiency. They are being increasingly appreciated as a highly exploratory and evolutionary tool by the medicinal chemistry community, opening the door to more sustainable, cost-effective and rapid synthesis of biologically active molecules. In recent years, MCR-based synthetic strategies have found extensive application in the field of drug discovery, and several anticancer drugs have been synthesized through MCRs. In this review, we present an overview of representative and recent literature examples documenting different approaches and applications of MCRs in the development of new anticancer drugs.

Single-Site SnOCu Pairs with Interfacial Electron Transfer Effect for Enhanced Electrochemical Catalysis and Sensing.

As advanced electrochemical catalysts, single-atom catalysts have made great progress in the field of catalysis and sensing due to their high atomic utilization efficiency and excellent catalytic performance. Herein, stannum-doped copper oxide (CuOSn1 ) nanosheets with single-site SnOCu pairs as active sites are synthesized as electrocatalysts for biological molecule detection. Compared with CuO-based electrochemical sensors, the CuOSn1 -based electrochemical sensors have improved detection sensitivity with a rapid electrochemical response. Theoretical calculation reveals that the single-site SnOCu pairs induced interfacial electronic transfer effect can strengthen hydroxy adsorption and thus reduce the energy barrier of the biological molecule oxidation process. As a concept application, electrochemical detection of dopamine and uric acid molecules is achieved, exhibiting satisfactory sensitivity and selectivity. This work demonstrates the advantages of single-site SnOCu pairs in electrochemical catalysis and sensing, which provides theoretical guidance for understanding the structure-activity relationship for sensitive electrochemical sensing.

High throughput screening of single atomic catalysts with optimized local structures for the electrochemical oxygen reduction by machine learning

Single atomic catalysts (SACs), especially metal-nitrogen doped carbon (M−NC) catalysts, have been extensively explored for the electrochemical oxygen reduction reaction (ORR), owing to their high activity and atomic utilization efficiency. However, there is still a lack of systematic screening and optimization of local structures surrounding active centers of SACs for ORR as the local coordination has an essential impact on their electronic structures and catalytic performance. Herein, we systematic study the ORR catalytic performance of M−NC SACs with different central metals and environmental atoms in the first and second coordination sphere by using density functional theory (DFT) calculation and machine learning (ML). The geometric and electronic informed overpotential model (GEIOM) based on random forest algorithm showed the highest accuracy, and its R2 and root mean square errors (RMSE) were 0.96 and 0.21, respectively. 30 potential high-performance catalysts were screened out by GEIOM, and the RMSE of the predicted result was only 0.12 V. This work not only helps us fast screen high-performance catalysts, but also provides a low-cost way to improve the accuracy of ML models.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

A universal strategy for green synthesis of biomass-based transition metal single-atom catalysts by simple hydrothermal and compression treatment

Carbon-based single-atom catalysts (SACs) have attracted increasing extensive attention due to their excellent catalytic performance and high atomic utilization efficiency. Traditional porous carbon materials are not suitable supports for SACs synthesis owing to the inert surface and heteroatoms such as N and S are necessarily introduced as increased anchoring sites for single metal atoms. Herein, we reported a novel universal strategy to synthesize carbon-based transition metal (Fe, Co, Ni, Cu, and Zn) SACs by one-pot hydrothermal treatment combined with a mechanochemical method by virtue of abundant active oxygen naturally in biomass feedstock. The hydrothermal treatment resulted in relatively monodispersed metal ions within the carbonaceous matrix and compression process played a vital role in the formation and anchoring of the single atom, preventing self-aggregation during pyrolysis by confinement effect. The characterization results showed the metal atoms were atomically dispersed on carbon support in the form of M-O3C coordination and had relatively high metal contents of up to 1.15 wt%. Due to the in-situ formation, unique coordination surroundings, and high content of metal atoms, the prepared catalyst exhibited excellent reactivity performance. This work demonstrated the sustainability and economic feasibility of carbon-based SACs synthesis simultaneously by co-using natural oxygen as anchoring sites and abundant carbon as the skeleton in biomass feedstock and offered a novel approach for high-value utilization of biomass.

Dual Metal Site Fe Single Atom Catalyst with Improved Stability in Acidic Conditions

Dual atom catalysts (DACs) not only retain uniform active sites and high atomic utilization efficiency as the single atom catalysts, but the two adjacent metal sites also cooperate and play a synergistic role to achieve additional benefits. However, the relationships connecting their dual-site synergistic effects on catalytic performance are not well rationalized due to limited pairs available from experiments. Herein, Fe/M dual sites supported by nitrogen doped carbon (Fe/M-N-C whereby M from 3 d–5 d electron containing transition metals) have been screened as an oxygen reduction reaction (ORR) catalyst. The results show that the absorption strength of ORR intermediates on four nitrogen coordinated metals is weaker than the three coordinated metals, which promotes favourable ORR activities. As a result, we recommended FeIr, FeRh, FeRu and FeOs as promising ORR catalysts. Ab initio molecular dynamic (AIMD) simulations suggest Fe/M-N-C (M = Ir, Rh, Ru and Os) catalysts with encouraging structural stability at room temperature. Furthermore, it is found that the nitrogen atoms in-between metals are vulnerable sites for proton attacking, yet the protonation process demands high energy, even under O2 atmosphere, which underlines good tolerance under acidic conditions. This work provides a broad understanding of Fe based catalyst and a new direction for catalytic design.

Surface synergistic effect of sub-2 nm NiFeCr hydroxide nanodots yielding high oxygen evolution mass activities

Designing cost-effective electrocatalysts with high efficiency and stability for oxygen evolution reaction (OER) is crucial for hydrogen generation by water splitting and meta-air batteries. NiFe catalysts doped with transition-metal cations have offered an efficient approach to tuning the atomic and electronic structure, thus enhancing OER activity. However, most research focused on regulating the composition of atoms in large-sized catalysts, which remains a major challenge to achieving high atom utilization efficiency and optimal surface synergistic effect. Herein, a one-step co-precipitation method is presented to directly synthesize ultrafine NiFeCr trimetallic amorphous hydroxide nanodots (AND-NiFeCr, < 2 nm) to fully expose the atoms at the surface and near-surface region. Electronic-structure investigation revealed a strong synergistic electronic interaction between Ni, Fe, and Cr cations, which subtly tailors ternary catalysts' local atomic and electronic configuration. Due to the refined ultrafine nano- and electronic-structure modulation, the optimized AND-NiFeCr (Ni:Fe:Cr = 5:3:2) catalysts demonstrated superior OER activity with a low overpotential of 271 mV at 10 mA cm−2. Moreover, an extraordinarily high mass activity of 4926 A gMetal-1 at the overpotential of 300 mV was achieved. This work provides a novel surface synergistic effect strategy to design highly efficient NiFe-based ultrafine hydroxide OER catalysts with high atomic utilization efficiency.

Organocalcium Hydride-Catalyzed Intramolecular C(sp3)–H Annulation of Functionalized 2,6-Lutidines

This work reports an intramolecular C(sp3)-H annulation of functionalized 2,6-lutidines catalyzed by an organocalcium hydride [{(DIPPnacnac)CaH(thf)}2] (DIPPnacnac = CH{(CMe)(2,6-iPr2-C6H3N)}2). This reaction constitutes a streamlined approach for producing a new family of tetrahydro-1,5-naphthyridines and hexahydropyrido[3,2-b]azocines derivatives in good to excellent yields with high atom efficiency and broad substrates scope. A calcium alkyl complex was isolated from the stoichiometric reaction between calcium hydride and the substrate through deprotonation, which was structurally characterized and confirmed as the catalytic intermediate.

Sodium-Directed Photon-Induced Assembly Strategy for Preparing Multisite Catalysts with High Atomic Utilization Efficiency.

Integrating different reaction sites offers new prospects to address the difficulties in single-atom catalysis, but the precise regulation of active sites at the atomic level remains challenging. Here, we demonstrate a sodium-directed photon-induced assembly (SPA) strategy for boosting the atomic utilization efficiency of single-atom catalysts (SACs) by constructing multifarious Au sites on TiO2 substrate. Na+ was employed as the crucial cement to direct Au single atoms onto TiO2, while the light-induced electron transfer from excited TiO2 to Au(Na+) ensembles contributed to the self-assembly formation of Au nanoclusters. The synergism between plasmonic near-field and Schottky junction enabled the cascade electron transfer for charge separation, which was further enhanced by oxygen vacancies in TiO2. Our dual-site photocatalysts exhibited a nearly 2 orders of magnitude improvement in the hydrogen evolution activity under simulated solar light, with a striking turnover frequency (TOF) value of 1533 h-1 that exceeded other Au/TiO2-based photocatalysts reported. Our SPA strategy can be easily extended to prepare a wide range of metal-coupled nanostructures with enhanced performance for diverse catalytic reactions. Thus, this study provides a well-defined platform to extend the boundaries of SACs for multisite catalysis through harnessing metal-support interactions.

Electrochemical selenium-catalyzed para-amination of N-aryloxyamides: access to polysubstituted aminophenols.

Aminophenols are a class of important compounds with various pharmacological activities such as anticancer, anti-inflammatory, antimalarial, and antibacterial activities. Herein, we introduce a mild and efficient electrochemical selenium-catalyzed strategy to synthesize polysubstituted aminophenols. High atom efficiency and transition metal-free and oxidant-free conditions are the striking features of this protocol. By merging electrochemical and organoselenium-catalyzed processes, the intramolecular rearrangement of N-aryloxyamides produces para-amination products at room temperature in a simple undivided cell.

Diastereoselective construction of carbo-bridged polyheterocycles by a three-component tandem annulation reaction.

By a hydroamination-induced tandem annulation process, we herein report a new three-component reaction for room temperature construction of carbo-bridged polyheterocycles with exclusive diastereoselectivity, which features readily available feedstocks, catalyst-free conditions, good substrate and functionality compatibility, no need for transition metal catalysts, and high step and atom efficiency. The products are formed via initial formation of 1,2-dihydro-3H-pyrazol-3-one nucleophiles from but-2-ynedioates and hydrazine followed by 2,4-difunctionalization of N-heteroarenium salts. Given that the obtained products possess structurally important tetrahydroquinoline and pyranopyrazole motifs, the developed chemistry is anticipated to be further applied to the discovery of functional molecules including biomedical ones.

Rearrangement of 2-(benzofuran-2-yl)-3-phenylpyridines via photoinduced 6π-electrocyclization.

By photoinduced 6π-electrocyclization of 2-(benzofuran-2-yl)-3-phenylpyridine derivatives 1, a method for the synthesis of trans-dihydrobenzo[f]quinolines 2, cis-dihydrobenzo[f]quinolines 3 and 8b-methyl-1,8b-dihydrobenzo[f]quinolines 4 was developed. Irradiation of 2-(benzofuran-2-yl)-3-phenylpyridine 1 in acetone-H2O (5 : 1, v/v) with a 313 nm UV lamp under an argon atmosphere at room temperature successfully yielded 2, which was further converted into 3 at elevated temperature (200 °C) in glycerol. However, irradiating 2-(3-methylbenzofuran-2-yl)-3-phenylpyridines 1 in CH2Cl2 with a 254 nm UV lamp gave 4 in good yields. The syntheses of 2, 3 and 4via the 6π-electrocyclization rearrangement of 1 not only offer high atom efficiency but also do not require transition metal catalysts or additives.

Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation.

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between -3.11 and -3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd-O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.

A new strategy for mass production of single-atom catalysts for high performance of CO2 electrochemical reduction

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, the poor yield for SACs production seriously limits the industry-relevant application. In this work, a simple but robust method was developed for the mass production of single-atom NiNC catalysts by using hydrogen-bonded organic frameworks (HOFs) as the precursors, exploiting the efficient and low-cost guar gum. Benefiting from its coordinatively unsaturated Ni-N3 configuration to afford a high catalytic activity, the as-fabricated SA-Ni/NC-900 catalyst shows excellent selectivity and activity for the electrochemical reduction of CO2 to CO with Faradaic efficiency (FE) of 95.6 %, achieving a turnover frequency (TOF) of ∼34000 h−1 at −0.8 V (vs. RHE) and highly stable performance for more than 24 h. Mass-producing a highly potent single-atom electrocatalyst paves the way for fulfilling the carbon–neutral goal through the carbon-negative CO2RR process.

Dual Pt-Ni atoms dispersed on N-doped carbon nanostructure with novel (NiPt)-N4C2 configurations for synergistic electrocatalytic hydrogen evolution reaction

Single-atom catalysts with high atomic utilization efficiency, well-defined active centers, and catalytic sites with low atomic coordination numbers are promising to boost electrocatalytic performance. Dual-atom catalysts (DACs) with neighboring heteroatoms are expected to exert the synergistic effect of the two atoms, further improving the activity. Herein, we report a PtNi-NC catalyst consisting of PtNi dual atoms anchored on a nitrogen-doped carbon substrate synthesized through atomic layer deposition. X-ray absorption spectroscopy confirms the existence of the PtNi dual atoms. The as-prepared PtNi-NC catalyst exhibits extraordinary catalytic activity, with an overpotential of 30 mV for hydrogen evolution reaction (HER) in acidic media at a current density of 10 mA cm−2, which is comparable to that of commercial 20 wt% Pt/C. Notably, PtNi-NC possesses a much higher mass activity, about 21 times, than 20 wt% Pt/C. Density functional theory calculations reveal that PtNi dual atoms generate a synergistic effect by modulating the local electronic structure and optimizing the charge distribution, contributing to optimized adsorption properties and enhanced electrocatalytic performance. This work provides a new avenue for the fabrication of DACs, revealing their potential applications in electrocatalytic HER and beyond.

Single-atom Cu catalyst in a zirconium-based metal–organic framework for biomass conversion

Single-atom catalysts (SACs) have received great interests due to their high atomic utilization efficiency and unique electronic properties of active center atom. Here we reported a single-atom catalyst, Cu@UiO-66-(COOH)2, prepared by a simple, facile, and efficient solvothermal strategy, where Cu atoms were coordinated to the defect sites of secondary building units (SBUs) in a Zr-based metal–organic framework (MOF) UiO-66-(COOH)2. The single-atom Cu@UiO-66-(COOH)2 catalyst exhibited high activity for biomass derived platform chemical levulinic acid (LA) hydrogenation to γ-valerolactone (GVL) through catalytic transfer hydrogenation (CTH) process using isopropanol (IPA) as hydrogen donor under mild reaction conditions, where 96.7% GVL yield was achieved. The site isolation and uniform distribution of single Cu atoms combined with the aid of acid sites in MOF, attributing to the excellent catalytic performance for biomass upgrading.

I2/FeCl3-Catalyzed Domino Reaction of Aurones with Enamino Esters for the Synthesis of Highly Functionalized Pyrroles.

A novel and efficient I2/FeCl3-catalyzed domino reaction of aurones with enamino esters via Michael addition, iodination, intramolecular nucleophilic substitution, and spiro ring opening processes has been developed, affording a vast variety of polysubstituted pyrroles in moderate to excellent yields. This protocol features mild reaction conditions, broad substrate scope, high atom economy and efficiency, and feasibility for large-scale synthesis. A plausible mechanism for the pyrrole synthesis is proposed.

Synergy of Platinum Single Atoms and Platinum Atomic Clusters on Sulfur-Doped Titanium Nitride Nanotubes for Enhanced Hydrogen Evolution Reaction.

Highly dispersed Pt, such as Pt single atoms and atomic clusters, has great potential in the electrocatalytic hydrogen evolution reaction (HER) due to the high atomic efficiency and unique electronic configuration. Rationally regrating the electronic structure of Pt catalysts is desirable for promoting the HER performance. Herein, a 3D self-supported monolithic electrode consisting of Pt single atoms (PtSAs ) and Pt atomic clusters (PtACs ) anchored on sulfur-doped titanium nitride nanotubes (S-TiN NTs) encapsulated in polyaniline (PANI) on Ti mesh (PANI@Pt/S-TiN NTs/Ti) via a facile electrochemical strategy for efficient HER is designed and synthesized. Contributed by the unique structure and composition and the synergy of PtSAs , PtACs and S-TiN NTs, the PANI@Pt/S-TiN NTs/Ti electrode exhibits ultrahigh HER activities with only 12, 25 and 39mV overpotentials at -10mA cm-2 in acidic, alkaline and neutral media, respectively, and can maintain a stable performance for 25h. Impressively, the mass activities are respectively up to 26.1, 22.4, and 17.7 times as that of Pt/C/CC electrode. Theoretical calculation results show that the synergistic effect of PtSAs , PtACs , and S-TiN NTs can optimize the electronic structure of Pt and generate multiple active sites with a thermodynamically favorable hydrogen adsorption free energy (ΔGH* ), thereby resulting in an enhanced HER activity.

New frontiers in heterogeneous Hg0 oxidation by O2 over catalytic single-Fe site on boron-vacancy of h-BN: A density functional theory study

The single-atom catalysts (SACs) have shown tremendous potential in heterogeneous catalytic process, because of their high atomic utilization efficiency and controllable characteristic of various active sites. The accurate structure design at atomic scale of SACs brings new opportunities and challenges for the cost-effective Hg0 oxidation and the study in molecularly catalytic mechanism by the oxidant of O2. Herein, a series of single transition metal atom doped (Mn, Fe, Co, Ni, Cu and Zn) on h-BN vacancy (M/V-BN) were well designed and the interaction behaviours were further investigated via Density Functional Theory (DFT) method. The mercury oxidation profiles and mechanism in the existence of O2 had been clarified on the optimized single atom catalytic site. The results show that the six kinds of TM atoms can exist stably on the surface of boron-vacancy (VB-BN) monolayer and have the potential to activate the new two-dimensional material (h-BN) with high surface reactivity. Among them, the most stable configuration Fe/VB-BN exhibited the best affinity to Hg0 with an adsorption energy of -1.697 eV, and the Fe-Hg bond was the shortest of 2.747 Å. The covalent interaction of Fe-Hg bond is demonstrated by the overlaps between Fe d-orbitals and Hg p-orbital. The chemisorption mechanism dominates the adsorption processes of different mercury species (Hg0, HgO, HgCl, HgBr and HgS), with the adsorption energy ranging from -1.2 to -4.2 eV. The Hg0 oxidation over Fe/VB-BN by O2 mainly follows the Eley-Rideal mechanism, and undergoes three key steps, i.e., O2 molecule dissociation, formation of O-Hg-O structure and desorption of oxidized Hg products. O2 was firstly adsorbed on the unsaturated Fe site and strongly activated by the metal center, which contributes to the high Hg0 catalyst oxidation activity. The generation of O-Hg-O structure is the public stage of mercury products desorption. The rate-determining step of Hg0 catalytic oxidation was dependent on Hg2O2 cluster desorption with an energy of 2.91 eV, which was much smaller than the desorption barrier of traditional catalysts. As a whole, the outcomes demonstrate that Fe/VB-BN catalyst is one promising candidate for catalytic oxidation of Hg0 by O2, which enables cleaner coalfired power plant operations.