The electrochemical nitrate reduction reaction (NO3RR) to produce NH3 has become a sustainable route for contaminant removal and producing value-added chemical and/or green energy carriers simultaneously. Pd-based nanocatalysts have been attracting increasing attention thanks to their high activity, excellent stability, and potential practical applications. This review first introduces the fundamentals of the NO3RR and explains the unique advantages of using Pd-based nanocatalysts for the NO3RR. Then, it summarizes the recent progress regarding nitrate electroreduction catalyzed by Pd-based nanocatalysts, including Pd nanomaterials, Pd-based composites, Pd alloys, and atomically precise Pd-based nanoclusters. Finally, the major challenges and future perspectives are proposed.

The electrocatalytic CO2 reduction reaction to valuable fuels is a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Herein, a single-Fe-atom was introduced into the BiOCl catalyst by a facile hydrolysis method, which exhibited a greatly enhanced catalytic performance in the electrochemical CO2RR to formate, exceeding 90% hydrogenation selectivity and maintaining above 90% activity for 10 hours.

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.

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 oxygen reduction reaction (ORR) is the key half-reaction in various modern transduction devices. However, it is still hugely urgent to exploit high-efficiency and low-cost catalysts to overcome the problem of the slow dynamics for the ORR. Here, a catalyst with atomic Sn centers decorated into N-doped porous carbon, namely Sn–NC, was formulated by thermal decomposition of SnCl2 and laver in the presence of ZnCl2. Electron microscopy and X-ray absorption spectroscopy demonstrate the atomic distribution nature of Sn species in Sn–NC with a SnN4 coordination structure. Impressively, Sn–NC displays superior ORR activity in both acid and alkaline solutions with a half-wave potential of 0.98 V versus reversible hydrogen electrode (RHE) in 0.1 M KOH and 0.82 V versus RHE in 0.1 M HClO4 as well as good stability. More importantly, when employed as the cathodic active material of a Zn–air battery and fuel cell, Sn–NC shows a peak power density of 118 and 1290 mW cm−2, respectively, competitive to the commercial Pt/C catalyst. This work should be helpful for exploiting inexpensive ORR catalysts with promising potential for practical application.

Ga-based propane dehydrogenation (PDH) catalysts are explored in industry as an alternative to PtSn and CrOx-based catalysts. Yet, at present, there is only limited understanding of the structural dynamics of surface sites in Ga-based PDH catalysts. Here, we employ atomic layer deposition (ALD) to engineer a sub-monolayer of Ga species on dehydroxylated silica, which serves as a model PDH catalyst. While the ALD-grown shell contains, after calcination at 500 °C, tetra- and pentacoordinate Ga3+ sites with both Si and Ga atoms in the second coordination sphere (i.e., [4]Ga(Si/Ga) and [5]Ga(Si/Ga) sites), its exposure to ambient air leads to sub-nanometer GaxOy(OH)z clusters with [4]Ga(Ga) and [6]Ga(Ga) sites, due to the hydrolysis of the Ga–O–Si linkages by the moisture of ambient air. When calcining the material at 650 °C, the [4]Ga(Ga) and [6]Ga(Ga) sites evolve leading to a silica surface dominated by isolated tetracoordinate [4]Ga(4Si) sites, that is, [(SiO)3Ga(XOSi)] sites, where X is H or Si. Exposure of the dehydroxylated material with [4]Ga(4Si) sites to ambient air reforms the sub-nanometer GaxOy(OH)z clusters, indicating the reversibility of the Ga dispersion and agglomeration as a function of the extent of silica (de)hydroxylation. The presence of [4]Ga(4Si) sites coincides with a high performance in PDH, achieving an initial turnover frequency of ca. 12 h−1 and propene selectivity of ca. 85%, while deactivating by only 34% over 20 h of time on stream. Overall, our results highlight the dynamic nature of the dispersion and agglomeration of Ga3+ sites during the dehydroxylation (by calcination) and rehydration (ambient air exposure).

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.

Dry reforming of methane (DRM) is appealing for syngas production yet challenging due to its high reactive energy barrier and catalyst deactivation. To address the issues in traditional thermocatalytic (TC) DRM, this paper investigated DRM under photothermal synergistic catalytic (PTSC) conditions. The synthesized Ni/ZrO2 catalyst with a hollow sphere structure (sp-Ni/ZrO2) demonstrated excellent performance in suppressing metal sintering and carbon deposition. The hollow sphere structure effectively enhanced the catalyst's light absorption ability, which can broaden spectrum absorption and decrease the bandgap from 4.9 eV to 4.2 eV, and effectively enhanced the synergistic photocatalysis. Under PTSC conditions at 600 °C, the catalyst achieved CO and H2 yields of 73.4 mmol g−1 h−1 and 63.7 mmol g−1 h−1, respectively, while maintaining stability for 18 hours. The activation energies for CO2 and CH4 dissociation under PTSC are 27.2 kJ mol−1 and 32.9 kJ mol−1, significantly lower than the corresponding values of 40.0 kJ mol−1 and 44.4 kJ mol−1 under TC conditions. Besides, the turnover frequencies of CH4 and CO2 for sp-Ni/ZrO2 range from 0.35 to 1.19 s−1 and 0.47 to 1.37 s−1, respectively, which are 1.1–2.1 times higher than those in TC-DRM. This paper provides a new perspective on PTSC catalyst design and offers an innovative solution to overcome the limitations of conventional DRM reactions.

A graphical abstract is available for this content

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.

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.

In this study, we show that the hydrodehalogenation of reductively inert aryl halides is facilitated by the heteroleptic Ir(III) complex [Ir(dF(CF3)ppy)2(dtbbpy)]+ (1) in the presence of N-(tert-butoxycarbonyl)-proline and cesium carbonate under irradiation with blue light. We observed in situ modification of 1 to yield intact (Ir-int) and degraded (Ir-deg) complexes. Ir-int complexes are formed through the functionalization of both the C^N and N^N ligands with α-amino radicals, formed via single-electron-oxidation of cesium carboxylate salt (N-Boc-Pro-OCs) derived from N-(tert-butoxycarbonyl)-proline by the photoexcited Ir complex. In this functionalization, electron-withdrawing fluorine atoms on the dF(CF3)ppy ligands are substituted. The destabilization of the HOMO of the structurally modified Ir-int results in a bathochromic shift of both the excited triplet state absorption and phosphorescence bands when compared to pristine 1. In the presence of excess N-Boc-Pro-OCs, the free Ir-int undergo rapid quenching via excited-state charge-transfer complex formation. The Ir-int˙−, after radical ion separation, are responsible for the hydrodehalogenation reaction of aryl halides.

Thioether metathesis has been noted as a complementary thioether synthesis methodology with cross-coupling reactions, which can be applied to late-stage diversification. However, despite its utility, versatile direct C–S/C–S cross-metathesis of thioethers has not been previously reported. Herein, direct catalytic metathesis of various thioethers was enabled by Pd acetate and tricyclohexylphosphine precursors with no additives, affording unsymmetrical thioethers. Detailed characterization and control experiments confirmed that Pd(0) nanocluster homogeneous catalysts formed in situ are the actual active species enabling this versatile direct transformation. This work will pave the way for novel organic molecular transformations driven by metal nanocluster catalysts.

The hydrogenation of amides is an important but highly challenging reaction, which usually is applied under drastic conditions (temperature >160 °C). Here, we report a heterogeneous Pt–MoOx/TiO2 catalyst for amide and imide hydrogenation under milder conditions. The catalytic reactivity is proposed to originate from the synergistic effect between surface active species. Pt promotes formation of partially reduced MoOx that is responsible for CO activation, and MoOx-modified Pt can more efficiently generate surface species from gas-phase H2. This catalyst system enables the selective hydrogenation of several 2° and 3° amides as well as imides.

A graphical abstract is available for this content

The first page of this article is displayed as the abstract.

Acid/base catalysis plays a pivotal role in the synthesis of versatile chemicals, in which acidic/basic molecules are widely employed as highly effective catalysts. However, challenges associated with the recyclability of these homogeneous catalysts and the complexity of purification procedures impose limitations on their practical applications. Heterogeneous solid catalysts are emerging as viable alternatives to traditional acid/base catalysts. Among these, ceria (CeO2), with the coexistence of surface acidic and basic sites, has demonstrated significant potential for acid/base catalysis. Herein, the present review provides a comprehensive overview of fundamental acid/base reactions catalyzed by CeO2, including the dehydration and hydrolysis processes, the transformation of CO2 to dimethyl carbonate (DMC), the hydrogenation of unsaturated groups, etc. In particular, the reaction mechanism is discussed in conjunction with an analysis of the acidic/basic sites on CeO2. Additionally, various strategies to modulate the acid/base properties are outlined on CeO2-based catalysts, with which the enhanced catalytic activity and selectivity are realized.

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.

Here we designed and synthesized a NN–CoII bidentate complex and efficiently used it for general and expedient amination of alcohols under benign, solventless conditions. Both primary (including unactivated aliphatic) alcohols and sterically hindered secondary alcohols exhibited very good reactivity and provided diverse amines with good substrate scope (88 examples; up to 95% yields) and excellent functional group tolerance (methoxy, thiomethoxy, phenoxy, trifluoromethyl, amino, alcoholic and halides including bromo and iodo groups). Furthermore, a sequential bis-N-alkylation of diamines was also demonstrated. It was observed that the pyrazole moiety in the ligand backbone plays a crucial role in the amination reaction. Very interestingly, the reusability of the present homogeneous cobalt catalyst was successfully demonstrated.