Electrocatalytic processes have garnered increased attention for energy conversion and mass production because of their high efficiency and selectivity. In particular, electrocatalysts play a critical role in catalytic performance. Two-dimensional (2D) materials, which feature a large surface area with abundant active sites and tunable physicochemical properties, have been regarded as one of the most important candidates for future electrocatalysis. However, further research efforts are required to specifically optimize their catalytic performance to realize their commercialization. In this account, strategies for regulating the local electronic structures of 2D electrocatalysts, including heteroatom doping, single-atom loading, heterojunction formation, vacancy engineering, and strain engineering, are briefly summarized. Furthermore, the relationship between these strategies and the electrocatalytic performance of the developed materials is discussed. Finally, an outlook of the 2D electrocatalysts is provided.

Fischer-Tropsch synthesis to olefins (FTO) with high carbon efficiency is an important but challenging research target. Current routes for direct syngas conversion to olefins suffer from high CO2 selectivity and low olefin yields due to the inevitable water-gas shift (WGS) reaction. Herein, we report that product selectivity can be controlled by tuning the wettability of the environment around the active center through simple physical mixing of cobalt carbide (Co2C) with a hydrophobic SiO2 component. The suppressed WGS reactivity results in a greatly improved catalytic performance of Co2C, significantly decreased CO2 selectivity (from 47.8% to 16.8%), and increased olefin selectivity (by ~65%) and activity (by 30%). The local hydrophobic environment favors the rapid diffusion of water away from the Co2C active center, thus remarkably enhancing the linear adsorption of CO and suppressing the production of CO2 via WGS. This work provides a simple yet effective strategy to modulate the product selectivity and improve the carbon efficiency of the FTO process.

Supported Pt nanoparticles (NPs) are highly active catalysts for heterogeneous catalytic hydrogenation reactions; however, controlling their selectivity remains the biggest challenge toward their applicability. Herein, we propose the formation of a highly selective and stable, surface-strained Pt-based nanocatalyst via a facile and scalable thermal reduction treatment. Spherical-aberration-corrected transmission electron microscopy (SACTEM) and various spectral analytic techniques reveal a strong metal-support interaction between the Pt NPs and carbon nanotubes (CNTs) support during the annealing process. Thereafter, a fraction of carbon atoms is etched from the carbon-coated Pt NPs, inducing a compressive strain on the surface of the Pt NPs. Notably, the chemoselectivity of the surface-strained Pt/CNTs-800H catalyst (where 800 represents the heat-treatment temperature; H represents a hydrogen atmosphere) is almost completely different compared to that of its pristine counterpart. This catalyst is used for the hydrogenation reactions of a styrene and nitrobenzene mixture as well as 4-nitrostyrene. Interestingly, similar findings were observed with 5 wt% Pt/C and Pt/rGO catalysts, confirming that this treatment could be generalized. Hence, it has great potential in the design and synthesis of carbon-based catalytic materials.

Electrochemical nitrate reduction reaction (eNO3RR) has been considered as an alternative route for decentralized ammonia (NH3) synthesis. However, a major challenge is products selectivity at low overpotentials, namely, the competition between nitrite (HNO2) and ammonia. Herein, we employed a single-atom catalyst (FeN4) as model to study the competitive mechanism of NH3 and HNO2 by density functional theory calculations. It was found the optimal paths for ammonia and nitrite productions share a key intermediate (NO2*), whose adsorption structures and preference in the following conversion determines the selectivity. We have incorporated potential-dependent barriers and microkinetic modeling to understand the Faradaic efficiency at different potentials. Our results are in good agreement with the experimental trend of Faradaic efficiencies of NH3 and HNO2, which can be rationalized well by the charge transfer coefficient (β) for NO2* protonation to cisHNO2* with respect to that to HNO2. A low selectivity of ammonia production at small overpotentials can be ascribed to a kinetic issue. The electron localization function and crystal orbital Hamilton population were analyzed on the initial and transition states for NO2* protonation to cisHNO2* and HNO2. The computational mechanistic insights can help to design new catalyst for eNO3RR highly active and selective to NH3.

Magnetic core-shell composites are readily accessed by encapsulating Fe3O4 nanoparticles with NHC-M (M = Ir, Pd) coordination assemblies, which function as solid molecular catalysts and exhibit enhanced catalytic activity compared to the corresponding bis-NHC-Ir molecules in both hydrogenation and dehydrogenation reactions related to CO2. A record turnover number (TON: 1.69 × 106) was achieved in the hydrogenation of CO2 to formic acid. In addition, robust solid catalysts can be magnetically recovered and reused for more than 11 runs without obvious loss in activity and selectivity for the dehydrogenation of ammonium formate, even at 10–6 mmol level catalyst loadings.

The light penetration effect will weaken the driving force of charge separation from phase to surface by the built-in electric field of nanoscale photocatalysts, like low-dimensional materials. Therefore, in this study, a novel nanoscale lamination catalyst design method was proposed using a polymeric carbon nitride (PCN)-nano polyhedral SrTiO3 core-shell structure catalyst (PCN-SrTiO3). The results showed that the nanoscale lamination effect could be generated by the formation of the N–Sr bond, which could regulate the built-in electric field of the PCN simultaneously. Moreover, detailed characterization indicated that the N–Sr bond, which facilitates the generation of N vacancies in PCN, could act as a novel channel for charge transfer. Both surface and interior core N-deficient PCN have been discovered, resulting in more positive and negative VB positions, respectively. Synchronously, the light absorption ability of the PCN-SrTiO3 samples increased. Consequently, the enhanced photocatalytic overall water splitting could be ascribed to the synergism of the built-in electric field regulation caused by the N-Sr formation-induced nanoscale lamination effect, which was favorable for energy flow adaption on the spatiotemporal scale.

Ir nanoparticles (NPs) were synthesized via a colloidal method using tetradecyltrimethyl ammonium bromide (TTAB) as the ligand, and the supported Ir/BN catalysts were employed for selective hydrogenation of crotonaldehyde (CRAL). It was found that by proper thermal treatments, the TTAB-capped Ir NPs were very active and selective for the reaction. The Ir/BN catalyst calcined at 300 °C with surface TTAB residue gave a quasi-steady state turnover frequency (TOF) for crotyl alcohol (CROL) formation of 0.02 s−1 and a CROL selectivity of 94.4%, while that calcined at 500 °C with clean surface gave a TOF of 0.004 s−1 and a CROL selectivity of 56.2%. The Ir-TTAB interface was essential for the enhanced performance. In-situ IR spectra along with kinetic investigation revealed that TTAB improved CRAL adsorption and strengthened C=O adsorption, which accounted for high activity and selectivity. However, high coverage of TTAB on the Ir surface suppressed the H2 adsorption and consequently lowered the activity. Thus the findings provided useful information on the design of efficient catalysts for selective hydrogenation.

Singe-atom catalysts (SACs), as heterogeneous catalysts, have attracted increasing attention in recent years owing to their numerous advantages in the field of electrocatalysis, such as a high atom-utilization rate and unique structural characteristics. In this review, we introduce various preparation methods for obtaining SACs based on top-down and bottom-up synthesis strategies and the corresponding research progress made in recent years. We also focus on the electrocatalytic applications of SACs containing noble metals (Pt, Pd, Ir, etc.) and non-noble metals (Fe, Cu, Co, etc.) in the oxygen evolution reaction, hydrogen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction. Finally, the future challenges and prospects of monatomic catalysts are also discussed.

Iron-catalyzed carbonylation reactions are highly desirable in our sustainability-advocating chemical community because of its low cost, abundance, and potential for distinct and complementary reactivity patterns. Meanwhile, alkyl bromides as well as low nucleophilic amides and indoles are considered to be particularly challenge substrates for carbonylation reactions. Herein, we report an iron-catalyzed carbonylative coupling of unactivated alkyl halides with amines, amides, and indoles to assemble amide structural units, affording various amides, imides and N-acyl indoles with excellent yields and unprecedented functional group compatibility. Remarkably, our approach also represents the example on Fe-catalyzed aminocarbonylation of alkyl halides. Our preliminary mechanistic studies suggest that the reaction pathway is substrate dependent: the carbonylation proceeds via a radical pathway when alkyl iodides were used; while a two-electron transfer (TET) process occurred when alkyl bromides served as the electrophiles.

Doping carbon materials with heteroatoms is an effective strategy to improve the catalytic performance of carbon materials through charge redistribution. Furthermore, heteroatom-doped carbon materials have been proven to be unstable and can be completely removed from the electrode via the electrochemical oxygen evolution reaction (OER). However, since S has a electronegativity similar to that of C, the behavior of S-doped carbon materials under OER conditions might differ and thus deserves special attention. In this study, we investigated the structural evolution of S-doped carbon materials during the alkaline OER. It was observed that the S-doped graphite flake (S-GP) underwent oxidization. Notably, only partial S dopants dissolved in the form of sulfates, resulting in the emergence of new forms of S- and O-containing groups on the electrode. The results from well-designed experiments demonstrated that despite remaining on the electrode, the S-containing groups had no effect on the OER activity, and the high OER activity was attributed to the derived benzoquinone moiety. The dissolved sulfates further promoted OER activity when S-doped carbon materials were used as substrates for the Ni(OH)2 anode. Our work reveals the real activity origin of S-doped materials towards OER, motivating researchers to reconsider the catalytic mechanism of the S-doped carbon materials and their supported composites for other reactions.

The most promising method to eliminate CO2 is to find large-scale and value-added applications of CO2 as a carbon resource. However, the utilization of CO2 as feedstock for basic chemicals has long been a great challenge owing to its high thermodynamic stability. Herein, we report the coupling conversion of CO2 with light alkanes over the HZSM-5 zeolite with much higher aromatic selectivity than light alkanes as the only reactant. A CO2 conversion of 17.5% and n-butane conversion of 100% with aromatic selectivity of 80% could be achieved by the coupling reaction at the CO2 to n-butane ratio of 0.475, in which CO2 not only acted as an agent for balancing hydrogen in the reaction but also partly (~25%) incorporated into the aromatic products. Methyl-substituted lactones (MLTOs) and methyl-substituted cycloalkenones (MCEOs) were identified as key intermediates during the coupling reaction. 13C isotope labeling experiments, 13C solid-state NMR, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory (DFT)calculations revealed that CO2 could react with carbonium ions generated from alkane cracking to form MLTOs, which could further get converted into MCEOs, thus generating aromatic compounds. This coupling reaction provides guidance for the direct utilization of CO2 to produce value-added chemicals with the simultaneous transformation of light alkanes.

Carbon-based catalysts are potential substitutes for noble-metal catalysts in the oxygen reduction reaction (ORR) owing to their excellent electrical conductivities and chemical stabilities. To rationally design and accelerate the identification of highly efficient carbon-based ORR catalysts, improving the design of the active sites and microstructures is necessary. In this review, strategies for improving the intrinsic performances, activities, stabilities, and anti-poisoning properties of catalysts are analyzed. As a critical component of the microstructure, the porous structures of catalysts significantly affect their distributions of active sites and levels of mass transfer, which are also extensively analyzed. Finally, based on the formation of active sites and the fabrication of porous structures, conclusions and perspectives regarding the future development of highly efficient carbon-based electrocatalysts are provided.

Visible-light-driven photocatalytic hydrogen evolution reaction (HER) over a semiconductor provides an effective avenue to produce renewable clean energy and alleviate energy and environmental crises. However, the HER efficiency is still limited by the sluggish electron transfer process. Herein, a highly active covalent organic framework (COF) was constructed from the unusual benzimidazole monomer in a microwave-assisted solvothermal pathway. With single-atom Pt sites as cocatalyst, the catalyst exhibited an HER rate up to 115 mmol g–1 h–1 and a high turnover frequency of 4475.1 h–1 under visible-light irradiation. The above performance relied on the combination of benzimidazole moieties and COF framework, which, on the one hand, stabilized photogenerated electrons to prolong the electron lifetime, and on the other hand provided a strong host-guest interaction that resulted in the creation of single-atom Pt sites and the acceleration of the electron-transfer to the active sites for proton reduction. This work demonstrates the perspective of electron stabilization and interfacial charge transfer avenue construction in the HER process, which can be reached by a molecular-level design of COF-based organic semiconductors by using structural and functional diverse asymmetric building blocks.

Chiral unprotected 3-amino-2-quinolinone and 2-quinolinone-based cyclic amino acids have been recognized as important scaffolds in the structures of various drugs and bioactive molecules. However, a direct asymmetric method for the synthesis of these structures remains elusive. In this study, we report a Pd(0)-catalyzed enantioselective sequential decarboxylative allylation/desymmetrization protocol. Various vinyl benzoxazinanones can be used as substrates to react with unprotected amino esters, affording enantioenriched 2-quinolinone-based cyclic amino acids with high enantioselectivities (up to 96% ee) and good diastereoselectivities (up to 15:1 dr). Moreover, the products could be successfully transformed to chiral 3-amino-2-quinolinone derivatives after treatment with aqueous HCl. Mechanistic studies revealed that the double-hydrogen-bond-directing effect between the enolate (2-aminomalonate) and π-allyl Pd(II) complex plays an important role in the control of regioselectivity, and the steric hindrance between tert-butyl group on the ligand and allyl group on the substrate is responsible for the high enantioselectivity.

To address the over-emission of CO2, the construction of new heterojunction materials is a promising approach for the photoelectrocatalytic (PEC) conversion of CO2 into valuable chemicals. Herein, a series of heterojunctions of TiO2/TiN nanotube arrays were designed and fabricated by anodic oxidation of titanium plates, followed by in situ partial oxidation to form heterojunctions. The surface of the heterojunction with nitrogen instead of oxygen contained more active Ti3+ species, and the oxygen vacancies were able to harvest solar light and showed excellent performance in the PEC reduction of CO2. As a porous material, the TiO2/TiN nanotube supports good adsorption of CO2 as well as a confined space favoring C–C coupling. Operando Fourier transform infrared (FTIR) analysis revealed that the active species *COOH? and *CHO were the major intermediates. Density functional theory (DFT) calculations revealed that the highly active hydrogen atoms could attach to the surface of the heterojunction to form Ti–H species with Ti3+, and the existence of nitrogen atoms could promote the migration of lattice oxygen to form new oxygen vacancies, which is conducive to the adsorption and coupling of CO2 and intermediates. The vibration frequency of Ti–H predicted by DFT calculations matches well with the operando FTIR observations. The PEC cell of Pd/R-TiO2/TiN-30|SCE|BiVO4 efficiently produced carbon-based chemicals at a rate of 115.9 μmol L−1 h−1 cm−2 with high selectivity for C2 products. The total efficiency of the PEC cell approached 6.0%, exceeding that of the plant cell by 0.4%. Isotopic labeling experiments of 13CO2 and H218O verified the elemental source and inferred the reaction pathway via highly active hydrogen.

Semiconductor photocatalysis is a new sustainable development technology that has demonstrated remarkable potential in the fields of energy-production and environmental-protection. However, a single photocatalyst usually does not possess both strong redox and fast charge-separation properties, greatly limiting photocatalysis efficiency. Heterojunction photocatalysts can perfectly solve this problem by providing multiple reactive sites and fast charge separation and migration, elevating photocatalytic efficiency to a new higher level. Metal sulfides are a family of compounds composed of metals and sulfur (e.g., CdS, CuS, MoS2, In2S3, ZnIn2S4, and ZnxCd1–xS) that are preferred choices for heterojunction photocatalysts due to their narrow bandgaps, broad visible-light absorption ranges, and convenient preparation methods. This review article introduces the characteristics of metal sulfides, summarizes methods for their synthesis, and discusses various types of metal-sulfide-based heterojunctions. The use of such photocatalysts in energy and environmental-remediation applications is subsequently discussed. In addition, the roles of charge separation and transfer in heterojunction photocatalysts are demonstrated using in-situ characterization techniques. Finally, we discuss some application prospects and challenges concerning metal-sulfide-based heterojunction photocatalysts.

Cytochrome P450s are versatile catalysts for biosynthesis applications. In the P450 catalytic cycle, two electrons are required to reduce the heme iron and activate the subsequent reductions through proposed electron transfer pathways (eTPs), which often represent the rate-limiting step in reactions. Herein, the P450 BM3 from Bacillus megaterium was engineered for improved catalytic performance by redesigning proposed eTPs. By introducing aromatic amino acids on eTPs of P450 BM3, the “best” variant P2H02 (A399Y/Q403F) showed 13.9-fold improved catalytic efficiency (kcat/KM = 913.5 L mol−1 s−1) compared with P450 BM3 WT (kcat/KM = 65.8 L mol−1 s−1). Molecular dynamics simulations and electron hopping pathways analysis revealed that aromatic amino acid substitutions bridging the cofactor flavin mononucleotide and heme iron could increase electron transfer rates and improve catalytic performance. Moreover, the introduction of tyrosines showed positive effects on catalytic efficiency by potentially protecting P450 from oxidative damage. In essence, engineering of eTPs by aromatic amino acid substitutions represents a powerful approach to design catalytically efficient P450s (such as CYP116B3) and could be expanded to other oxidoreductases relying on long-range electron transfer pathways.

Although the concept of click chemistry was proposed more than twenty years ago, the research progress of click chemistry has emerged with great vitality, and this year's Nobel Prize in chemistry has once again highlighted the importance of the field of click chemistry. Click chemistry is a reaction in which a variety of molecules are quickly and reliably synthesized by piecing together small units. In particular, it emphasizes the development of new combinatorial chemistry methods based on the synthesis of carbon-heteroatomic bonds and the simple and efficient acquisition of molecular diversity through these reactions. Based on the superior reaction characteristics of click chemistry, click chemistry methods for production are advancing toward precision, simplicity, and high returns, especially in producing polymer materials and some bright biomedical applications. Here, we describe the development logic of typical click reactions with different substrates and catalysts. The latest technologies of click chemistry in the structure control and functional properties of polymers, as well as in the field of biomedicine and its expanding applications, are discussed. Finally, we identify the challenges of click chemistry in reaction mechanisms and engineering applications, and suggest potential future development directions in the future.

Vinylene-linked covalent organic frameworks (COFs) are promising photocatalysts owing to their fully conjugated skeletons that facilitate charge carrier mobility. Constructing donor-acceptor (D-A) architectures could further enhance photoinduced charge generation and transport, thus promoting photocatalysis. Therefore, three D-A-type vinylene-linked COFs were fabricated via Knoevenagel polymerization for efficient photocatalysis. By varying the donor moieties from phenyl to 2,5-dimethylbenzene and 3,3’-dimethyl-1,1’-biphenyl in the skeletons, the light-harvesting, optical-bandgap, and charge-transfer properties of the COFs were precisely regulated. All three COFs exhibited attractive photocatalytic hydrogen evolution rates (HERs) upon visible-light irradiation, especially that fabricated using 2,4,6-trimethyl-1,3,5-triazine (TM) and 3,3’-dimethyl[1,1’-biphenyl]-4,4’-dicarboxaldehyde (DMA, TM-DMA-COF). TM-DMA-COF exhibited the strongest D-A interactions, excellent charge-carrier separation and transfer kinetics, and a reduced energy barrier for H2 formation. Thus, it afforded the highest HER of 4300 µmol h−1 gcat−1, surpassing those of most state-of-the-art COF photocatalysts. This study provides a simple and effective protocol for modulating the photocatalytic activities of COFs at the molecular level and an interesting insight into the relationship between structural design and photocatalytic performance.

Formaldehyde (HCHO), generating from hydrogen transfer (HT) of reactant, is significant for autocatalysis initiation and deactivation in methanol-to-olefins (MTO), but hitherto, its evolution throughout the reaction has not been thoroughly revealed. Herein, by the established colorimetric analysis method, HCHO in the MTO and dimethyl ether (DME)-to-olefins (DTO) reactions over SAPO-34 was in situ quantitatively monitored, where HCHO was detected in slight and conspicuous amounts at initial and deactivation stages with semi-conversion, also when co-fed with water or high-pressure H2. We reveal the weak HT ability of DME relative to methanol, which enables prominent olefins-based cycle and suppresses reactant-induced HT and deactivation in DTO (which is critical for MTO). A complete dynamic reaction network is disclosed, constituting two simultaneous and interplaying pathways: the main reactions for olefin generation as the open-line and HT reactions as the hidden-line. Especially, co-feeding high-pressure H2 with DME capacitating a long-term and highly efficient operation of DTO by modulating the dynamic reaction network to a more moderate autocatalysis evolution, has great potential in industry application.