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Catalytic reduction of CO2 to high value-added chemicals is an important approach for tackling the rising CO2 concentration in the atmosphere. Recently, a range of heterogeneous and potentially low-cost single-atom catalysts (SACs) have emerged as promising candidates for the reduction of CO2. However, in comparison to conventional metal nanoparticle catalysts, SACs have long faced challenges in reactions involving multiple reactants and multiple reaction steps due to the limitation of isolated metal sites. This review presents the most recent research advances on the development of single-atom catalysis for deep reduction of CO2. Based on the approaches proposed for proton-coupled multi-electron transfer, detailed introductions and summaries were classified into three categories: 1) strengthen the metal–support interaction to achieve a synergistic catalysis; 2) rational design and regulation of the coordination environment of isolated metal atoms; 3) development of SACs with multi-atom active sites. Finally, the main challenges and future research directions in the field of SACs for CO2 reduction are proposed.

To address the ongoing rise in carbon dioxide (CO2) emissions, CO2 utilization presents a promising approach due to its ability to convert CO2 into valuable industrial products and enable carbon recycling. For this reason, a high-quality catalyst is required to ensure the effective activation and conversion of CO2. In this study, a series of dicationic pyrazolium ionic liquids (DPzILs) were first synthesized via a one-step process and employed as catalysts in the cycloaddition reaction of CO2 and epoxides, yielding cyclic carbonates. Among the synthesized DPzILs, [DMPz-6]I2 exhibited outstanding catalytic performance on diluted CO2 from simulated flue gas (60% CO2 in N2), achieving 94.1% PC yield and 100% selectivity under reaction conditions (100 °C and 10 bar CO2 pressure) without metal, co-catalyst, or solvent. The study investigated the effects of DPzILs structures, catalyst dosage, CO2 pressure, reaction temperature, and reaction time on the production of cyclic carbonates. Furthermore, [DMPz-6]I2 could be efficiently recovered and reused seven times without significant degradation of catalytic activity. It demonstrated significant adaptability to various epoxides. Structure–activity studies indicated that PO activation is synergistically facilitated by the presence of C3/C5 hydrogen from dual-pyrazolium cation rings tethered by alkyl chain lengths and a paired halide anion (I−/Br−/Cl−) in DPzILs. Finally, the reaction mechanism was investigated using FT-IR, 1H NMR, and DFT calculations.

The ent-kaurene synthase catalyses the formation of ent-kaurene through a multistep cyclization process, which is an essential step in the biosynthesis of many bioactive natural products. Channeling the key carbocation intermediates through different reaction pathways offers access to different diterpene scaffolds. Herein, we report that the F72Y mutation of the ent-kaurene synthase from Bradyrhizobium japonicum leads to the formation of tricyclic ent-rosa-5(10),15-diene and ent-pimara-8,15-diene as well as tetracyclic ent-kaurene. The combined computational and experimental studies suggest that Tyr72 serves as a general base for reshaping the catalytic function. This finding provides a promiscuous synthase for further engineering to improve its activity and selectivity, which can be used in the heterologous synthesis of ent-rosane and ent-pimarane diterpenoids.

To examine the mechanism and origin of regio- and stereo-selectivity, density functional theory calculations were employed for the Cu-catalyzed asymmetric alkene trifluoromethyl–arylation cross-coupling reaction. Theoretical studies reported that this reaction proceeded via single electron transfer, radical addition, transmetallation, one-electron oxidation, and reductive elimination. The stereoselectivity of this reaction was determined by the one-electron oxidation step. Independent gradient model calculations were employed to investigate the origin of stereoselectivity established using the chiral dioxazoline ligand. Furthermore, the substituent effects of the alkene substrate were calculated. This study aims to serve as a theoretical framework for future experimental investigations on the alkene difunctionalization cross-coupling reaction.

Modified NiFe-layered double hydroxide (NiFe LDH) materials with a high oxygen evolution reaction (OER) performance make it possible to replace noble metal catalysts for widespread applications. Herein, we prepare a layered carbon dot (CD) composite catalyst (denoted as NiFe LDH@CDs) by a one-step coprecipitation method without heating or hydrothermal treatment. Due to the numerous functional groups of CDs, there were strong electron interactions between the two components. The CDs promoted rapid charge transfers and accelerated OER kinetics. Moreover, through binding with the CDs, the NiFe LDH@CDs formed a heterojunction structure, which could efficiently suppress photoelectron–hole recombination. Based on the beneficial factors, the Tafel slope of NiFe LDH@CDs-200 was 44.77 mV dec−1, which further decreased to 38.44 mV dec−1 under light even with a low content of CDs.

The thermal activation of nanoclusters on a support material can enhance their activity and selectivity in heterogeneous catalysis. However, their evolution upon thermal activation remains challenging to study due to their small size. Herein, we probe the speciation and structural evolution of trigonal [Pd3(μ-Cl)(μ-PPh2)2(PPh3)3]Cl nanoclusters on carbon supports upon thermal activation at different temperatures via the combination of in situ differential Pair Distribution Function (dPDF) analyses, Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and X-ray Absorption Spectroscopy (XAS). EXAFS and dPDF measurements show that upon activation at 150 °C, the phosphine ligands were removed from the nanocluster surface. Upon further heating the nanoclusters, a transformation from Pd nanoclusters towards Pd nanoparticles occurred, as evidenced by an increase in the Pd–Pd coordination number. XPS, XANES, and EXAFS measurements also show the formation of PdO starting at 250 °C. The speciation and structural evolution of Pd nanoclusters during the thermal treatment has direct effects on the catalytic potential of the nanoclusters in terms of activity and selectivity. Nanoclusters activated at 150 °C (with the smallest Pd–Pd contribution and no phosphines present) were found to be extremely selective for the partial hydrogenation of 3-hexyn-1-ol to trans-3-hexen-1-ol. In Suzuki–Miyaura cross-coupling reactions, the Pd nanoclusters activated at 150 °C were the most active catalytic system. Three-phase studies suggests that the presence of surface ligands on the surface of nanoclusters reduces the strong-metal surface interaction between metal and support, which causes excessive leaching of Pd in reaction solvent during the reaction.

The selective hydrogenation of phenylacetylene to styrene, instead of ethylbenzene, holds significant importance in the polymer industry. However, existing heterogeneous catalysts face the challenge of achieving exceptional activity while maintaining high selectivity. Herein, we introduce a novel intermetallic PdCu3 catalyst supported on defective nanodiamond–graphene (ND@G), showcasing not only high selectivity (95%) but also remarkable activity (turnover frequency: 2940 h−1, 6 times higher than that of the commercial Lindlar catalyst). Experimental results and DFT calculations reveal that the exceptional selectivity of the catalyst originates from the unique intermetallic structure of PdCu3 with abundant isolated Pd sites on its surface, which favors the rapid desorption of styrene. Simultaneously, the high activity is attributed to the electron transfer from ND@G to PdCu3, facilitating the reduction in the energy barrier of the rate-determining step for styrene formation.

M–N–C materials derived from zeolitic imidazolium frameworks have exhibited remarkable efficacy as carriers for catalyzing glycerol carbonylation reactions, attributable to their meticulously modifiable pore size architecture, elevated catalytic selectivity, and commendable stability. In this study, we accomplished the successful integration of Cu2+ ions into the growth kinetics of ZIF-8 through a facile hydrothermal method. Subsequently, the resulting Cu–NC material was calcinated at 950 °C in a nitrogen atmosphere. This derived material served as an optimal substrate for the deposition of palladium nanoparticles, yielding the Pd/Cu–NC catalyst. The catalytic potential of this catalyst was evidenced by its superior efficiency in driving the glycerol carbonate synthesis from glycerol, surpassing the performance of the NC carrier in isolation. Impressively, a 98.3% yield and 99.7% selectivity were achieved within a mere 2-hour reaction span, conducted at 140 °C and 4 MPa. Employing density functional theory simulations, we delved into the intricate mechanisms governing carbonyl formation and ring closure during the oxidative carbonylation of glycerol. The strategic introduction of metallic copper during the initial phase of the transition state prominently underscored the robust interaction between copper and palladium. This interaction engendered a harmonized and systematically orchestrated charge distribution encircling the metallic palladium, thereby facilitating a more stable trajectory for ring formation processes.

The hydrogenation of CO2 enables the production of high-value fuels and chemicals, contributing to a sustainable and environment-friendly energy transition. Currently, for the CO2 hydrogenation to methanol reaction, either increasing the CO2 conversion or improving the methanol selectivity while maintaining high CO2 conversion is challenging. Herein, a new catalyst loaded with Cu nanoparticles (NPs) dispersed on amorphous MoOx with Li2CO3 as a promoter (denoted as Li–Cu/MoOx) was constructed via an in situ dispersion and alkali metal-promotion stepwise regulation strategy. At 260 °C and 5 MPa, the as-designed catalyst exhibited a satisfactory catalytic performance with a CO2 conversion of 13.4% and a methanol selectivity of 88.8%. The methanol selectivity of the Li–Cu/MoOx catalyst is higher than that of all the Cu-based catalysts reported in the literature to date under the conditions of CO2 conversion >10% and reaction pressure <8 MPa in a fixed-bed reactor. Furthermore, the Li–Cu/MoOx catalyst showed an excellent thermal stability. It was found that the in situ dispersion step enabled a high dispersion of Cu NPs and the production of the amorphous MoOx support, resulting in the formation of more Cu–support interfaces, which increased the number of active sites in the catalyst. The high methanol selectivity was attributed to an alkali metal-promotion step, which increased the Mo4+ content in MoOx, leading to a change in the types of active sites. In addition, the strong metal–support interaction (SMSI) in the catalyst was responsible for the high thermal stability. This strategy also has potential for designing other highly efficient catalysts.

Zeolites with defects can be combined with appropriate synthetic protocols to beneficially stabilise metallic clusters and nanoparticles (NPs). In this work, highly dispersed Ni NPs were prepared on a defect-rich dealuminated beta (deAl-beta) zeolite through strong electrostatic adsorption (SEA) synthesis, which enabled strong interactions between the electronegative deAl-beta and cationic metal ammine complexes (e.g., Ni(NH3)62+) via the framework silanol nests. Ni NPs with diameters of 1.9 ± 0.2 nm were formed after SEA and reduction in H2 at 500 °C and showed good activity in CO2 methanation (i.e., specific reaction rate of 3.92 × 10−4 mol s−1 gNi−1 and methane selectivity of 99.8% at 400 °C under GHSV of 30 000 mL g−1 h−1). The mechanism of the SEA synthetic process was elucidated by ex situ XAFS, in situ DRIFTS, and DFT. XAFS of the as-prepared Ni catalysts (i.e., unreduced) indicates that SEA leads to the exchange of anions in Ni precursors (e.g., Cl− and NO3−) to form Ni(OH)2, while in situ DRIFTS of catalyst reduction shows a significant decrease in the signal of IR bands assigned to the silanol nests (at ∼960 cm−1), which could be ascribed to the strong interaction between Ni(OH)2 and silanol nests via SEA. DFT calculations show that metallic complexes bind more strongly to charged defect sites compared to neutral silanol nest defects (up to 150 kJ mol−1), confirming the enhanced interaction between metallic complexes and zeolitic supports under SEA synthesis conditions. The results provide new opportunities for preparing highly dispersed metal catalysts using defect-rich zeolitic carriers for catalysis.

Sulfur-containing organic molecules such as sulfones are prevalent in pharmaceuticals and agrochemicals. Herein, we report the first transition-metal-free process for in situ denitrogenation of tosylhydrazones to produce a diverse array of aryl alkyl sulfones. We have used phenalenyl-based odd alternant hydrocarbon as a photoredox catalyst for denitrogenation of tosylhydrazones, where the phenalenyl acts as a potent oxidant to form a sulfinate radical intermediate from a sulfinate anion. We performed radical trapping, in situ electron paramagnetic resonance (EPR), and fluorescence quenching studies to elucidate the plausible mechanism. This method shows wide functional-group tolerance, with applications in late-stage modification of various natural products with good to high yields. The protocol provides an easy method for the synthesis of sulfones.

CsPbBr3 holds promise as a visible light photocatalyst, but its instability in oxygen-rich and polar solvent environments poses a significant challenge for practical utilization. This study demonstrates the effectiveness of orthorhombic CsPbBr3 nanocrystals (NCs) synthesized from dibromoisocyanuric acid. These NCs exhibit high efficiency as heterogeneous visible light photocatalysts (450–470 nm, 5 mol%) in a template-free aerobic thio/seleno etherification reaction involving 1,3,5-trimethoxybenzene, employing diaryl sulfides and diaryl selenides in acetonitrile (ε ∼ 37.5). A novel surface treatment approach is proposed, utilizing electron-rich 1,3,5-trimethoxybenzene as a reactant to stabilize CsPbBr3 NCs in situ and address stability challenges in polar solvents and open-air environments. Additionally, among the four systems, the bromide-enriched orthorhombic CsPbBr3 NCs exhibit markedly enhanced photocatalytic efficiency and stability compared to the cubic systems. The orthorhombic CsPbBr3 NCs, with prolonged excited state lifetime, promote efficient electron transfer, leading to the generation of superoxide radical anions from the conduction band. These findings highlight the potential of perovskite nanocrystals and provide insights into their applications as visible light photocatalysts in organic transformations.

Replicating the enzymatic surface microenvironment in vitro is challenging, but constructing an analogous model could facilitate our understanding of surface effects and aid in developing an efficient bioinspired catalytic system. In this study, we generate five unique Cu2O morphologies: cubic (c-Cu2O), octahedral (o-Cu2O), rhombododecahedral (r-Cu2O), cuboctahedral (co-Cu2O), and spherical (s-Cu2O) with an average edge length between 0.59 and 0.61 μm. By precisely controlling crystal growth on distinct surface planes, with surface energies in the order γ{100} < γ{111} < γ{110}, we achieve a wide spectrum of shape variations during the evolution of these structures. The variations in surface morphology are a consequence of differences in the exposure of low-index facets, such as {100}, {111}, and {110}, leading to varying numbers of unsaturated copper sites at the surface. The peroxidase-like activity was investigated by altering the Cu2O surface structures in the reduction of H2O2 using chromogenic substrates like TMB/ABTS. The activity catalyzed by various Cu2O surfaces (r-Cu2O, o-Cu2O, and c-Cu2O) followed the typical Michaelis–Menten kinetics, with Km values ranging from 0.096 to 0.120 mM for TMB and 1.57 to 2.90 mM for H2O2 as substrates, respectively. Compared to native peroxidase enzymes (with Km values of 0.434 mM for TMB and 3.70 mM for H2O2 under identical conditions), these Cu2O catalysts exhibited a higher affinity. In general, the reactivity order observed was as follows: co-Cu2O ≈ r-Cu2O > o-Cu2O > c-Cu2O > s-Cu2O. Mechanistically, the H2O2 reduction on the surface produces hydroxyl radicals that undergo H-abstraction from TMB, where the latter was found to be the rate-determining step. Both kinetic and DFT studies have unveiled that the heightened reactivity of r-Cu2O can be attributed to its higher proportion of {110} planes, which contain a higher number of dangling (unsaturated) Cu atoms that facilitate H2O2 decomposition. Additionally, they exhibit sufficiently low energy barriers (TS2: 0.70 eV) that enable OH radicals to efficiently oxidize TMB molecules compared to other morphologies.

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The relatively low microbial loading, low extracellular electron transfer efficiency, and poor electrocatalytic activity at the anode interface of microbial fuel cells limit their power generation efficiency. Based on this, using the high electrochemical specific surface area, high porosity, facile loading, and flexible support of electrospinning as well as the superior energy storage capability of MnO2, we successfully constructed two distinct morphologies of carbon nanofiber-loaded manganese dioxide electrocatalysts. The effects of carbon nanofiber-loaded nanoflower-shaped (CNF@MnO2-S) and nanorod-shaped (CNF@MnO2-R) manganese dioxide on the electrochemical performance of the anode, microbial fuel cell power generation and pollutant purification performance were comprehensively investigated. The impact of the two electrocatalysts on the anode biofilm was analyzed, revealing the mechanism for improving the performance of microbial fuel cells. The results show that compared to pure carbon cloth and carbon nanofiber-modified carbon cloth, the CNF@MnO2-R modified carbon cloth anode exhibits the best power generation performance. An outstanding performance improvement of about 27.9% highest output voltage (0.645 V), 27.9% maximum output power (821.549 mW m−2), 1.5 times and 2 times higher specific capacitance (5.93 mF cm−2), and 31.9% higher chemical oxygen demand (COD) removal rate (84.35%) were achieved, compared to that of the pure carbon cloth anode. The performance improvement can be mainly attributed to the rough surface, high porosity, and excellent electrocatalytic performance of CNF@MnO2-R. It not only increases the electrochemical specific surface area and bio-affinity at the anode interface but also promotes microbial adhesion and reproduction and regulates the electron transfer and information exchange process between the biofilm and the anode, thereby enhancing the power generation performance and organic matter removal rate of microbial fuel cells.

Amides are ubiquitous in natural and synthetic compounds, and amidation is by far the most prevalent reaction in medicinal chemistry. In addition, atom-economical procedures for the direct amidation of esters or acids with amines are in high demand. Encouraged by the abundance and low toxicity of iron compounds, we envisaged that a new iron-catalyzed protocol for the acylation of amines with both esters and carboxylic acids could be designed if the iron catalyst was combined with dioxygen. Several experiments were carried out in order to define the iron source and to evaluate the effect of molecular oxygen, additives and different reaction media. A number of substrates were then reacted under optimized conditions, and experimental studies (kinetic, radical trapping and electron paramagnetic resonance experiments) were conducted to shed light on the reaction mechanism. As a result, a new use for dioxygen as an inducer of the direct amidation between amines and carboxylic acids or esters has been found. Thus, an earth-abundant first-row metal catalyst (Fe(acac)3) at low loading combined with pivalic acid and molecular oxygen at atmospheric pressure triggers the reaction in a biodegradable greener solvent such as diethyl carbonate. More than 65 high-yielding examples prove the generality of the procedure, which also resulted to be scalable. In addition, insight into the mechanism behind this reaction taking place under oxygenated conditions is provided as well as an explanation for the results obtained in the absence of dioxygen.

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Natural biological materials display a large number of sophisticated nanostructures that are difficult to acquire even using the most technologically advanced synthetic methodologies. Since the hierarchical porosity and structure of a catalyst including photocatalysts are becoming increasingly important in the design of catalysts, the potential of biological components of nanoscale dimension for the synthesis of catalysts with novel types of heterostructure and improved activities is being actively explored. This review summarizes the recent advances in the synthesis of nano/microstructures using biotemplates obtained from various types of plants such as Hydrilla, cyanobacteria, reeds (Phragmites communis), leaves, tobacco, and rubber latex. In addition, the applications of synthesized materials in photocatalytic hydrogen production, photocatalytic reduction of Cr(VI), photodegradation of organic pollutants, and catalytic selective oxidation of tetralin, limonene, and cyclohexane have been highlighted. The key issues to improve the catalytic efficiency during the biotemplating procedure are discussed. More importantly, outlooks towards these emerging synthetic approaches have been presented from the perspective of practical application and future challenges are proposed.

Aminoalcohols are an easily available, highly diverse, and inexpensive class of ligands with numerous applications in biological and technological contexts of metal–ligand mediated processes. Among them, 2-pyridonates exhibit especially intriguing stereoelectronic features that have enabled a versatile coordination chemistry. Learning from the natural role model of [Fe]-hydrogenase, 3d-transition metal complexes with pyridonate ligands have recently been developed for powerful catalytic transformations. This review illustrates the general properties of pyridonate ligands and their key roles in 3d transition metal catalysts.