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[HO-EtMIm][OTf] efficiently catalyzes the dehydrative cyclization of vicinal diols under metal-free conditions, producing 1,4-dioxanes in 100% selectivity.

Perfluorinated covalent triazine frameworks (F-CTFs) have shown unique features and attractive performance in separation and catalysis. However, state-of-the-art F-CTFs synthesized via the ZnCl2 -promoted procedure have quite low fluorine contents due to C-F bond cleavage induced by chloride (a Lewis base) and the harsh conditions deployed (400-700 °C). Fabricating F-CTFs with high fluorine contents (>30 wt %) remains challenging. Herein, we present a low-temperature ionothermal approach (275 °C) to prepare F-CTFs, which is achieved via polymerization of tetrafluoroterephthalonitrile (TFPN) over the Lewis superacids, e.g., zinc triflimide [Zn(NTf2 )2 ] without side reactions. With low catalyst loading (equimolar), F-CTFs are afforded with high fluorine content (31 wt %), surface area up to 367 m2 g-1 , and micropores around 1.1 nm. The highly hydrophobic F-CTF-1 exhibits good capability to boost electroreduction of CO2 to CO, with faradaic efficiency of 95.7 % at -0.8 V and high current density (-141 mA cm-2 ) surpassing most of the metal-free electrocatalysts.

Herein, we report a CO2-mediated base catalysis approach for the activation of triple bonds in ionic liquids (ILs) with anions that can chemically capture CO2 (e.g., azolate, phenolate, and acetate), which can achieve hydration of triple bonds to carbonyl chemicals. It is discovered that the anion-complexed CO2 could abstract one proton from proton resources (e.g., IL cation) and transfer it to the CN or CC bonds via a six-membered ring transition state, thus realizing their hydration. In particular, tetrabutylphosphonium 2-hydroxypyridine shows high efficiency for hydration of nitriles and CC bond-containing compounds under a CO2 atmosphere, affording a series of carbonyl compounds in excellent yields. This catalytic protocol is simple, green, and highly efficient and opens a new way to access carbonyl compounds via triple bond hydration under mild and metal-free conditions.

The visible-light-driven photoreduction of CO2 to value-added chemicals over metal-free photocatalysts without sacrificial reagents is very interesting, but challenging. Herein, we present amide-bridged conjugated organic polymers (amide-COPs) prepared via self-condensation of amino nitriles in combination with hydrolysis, for the photoreduction of CO2 with H2O without any photosensitizers or sacrificial reagents under visible light irradiation. These catalysts can afford CO as the sole carbonaceous product without H2 generation. Especially, amide-DAMN derived from diaminomaleonitrile exhibited the highest activity for the photoreduction of CO2 to CO with a generation rate of 20.6 μmol g−1 h−1. Experiments and DFT calculations confirmed cyano/amide groups as active sites for CO2 reduction and second amine groups for H2O oxidation, and suggested that superior selectivity towards CO may be attributed to the adjacent redox sites. This work presents a new insight into designing photocatalysts for artificial photosynthesis.

Alcoholysis of propylene oxide (PO) is achieved over azolate ionic liquids (IL, e.g., 1-hydroxyethyl-3-methyl imidazolium imidazolate) at room temperature, accessing glycol ethers in high yields with excellent selectivity (e.g., >99%). Mechanism investigation indicates that cooperation of hydrogen-bonding of the anion with methanol and that of the cation with PO catalyses the reaction.

N-Methylation of amines with CO2/H2 to N-methylamines over non-noble metal catalysts is very interesting but remains challenging. Herein, we present an alcohol (e.g., ethanol) promoted strategy for the N-methylation of anilines with CO2/H2 with high efficiency under mild conditions (e.g., 125 °C), which is achieved over a cobalt catalytic system composed of Co(OAc)2·4H2O, triphos and Sn(OTf)2. This catalytic system has a broad substrate scope and is tolerant toward a wide range of anilines and N-methyl anilines, and a series of N,N-dimethyl anilines were obtained in high yields. Mechanism investigation indicates that the alcohol solvent shifts the equilibrium of CO2 hydrogenation by forming an alkyl formate, which further reacts with the amine to produce N-formamide, and Sn(OTf)2 promotes the deoxygenative hydrogenation of N-formamides to afford N-methylamines. This is the first example of the N-methylation of amines with CO2/H2 over a cobalt catalytic system, which shows comparable performance to the reported Ru catalysts and may have promising applications.

Single-atom metal catalysts (SAMCs) have high catalytic activity, but mass production of SAMCs with high metal loading remains challenging. In this work, a two-step and one-pot strategy is presente...

N-formylation of amines with CO2/H2 is a green route to access N-formamides, which has been explored extensively in recent years. In this article, a heterogeneously catalytic system, “Ru/C+[Bmim][OAc]” was designed to catalyze the N-formylation of amines including primary, secondary and aryl amines under mild conditions, which afforded a series of N-formamides in good to excellent yields at 100 °C and 8 MPa (CO2:H2=3:5) without any additives. Detailed study indicates that [Bmim][OAc] plays multiple roles in the reaction process with activating amines through H-bonding interaction and modifying the Ru nanoparticles to improve their activities.

N-heterocyclic compounds are important chemicals, and their reductive synthesis using H2 under mild conditions is attractive but challenging. Herein, we report chemoselective hydrogenation of 2-nitroacylbenzenes to 2,1-benzisoxazoles under ambient conditions for the first time, wihch is achieved over cellulose-derived carbon (c-C) supported Pt nanocatalyst (Pt/c-C), and a series of 2,1-benzisoxazoles can be obtained in excellent yields. Pt/c-C also shows high performance for ambient reductive amination of levulinic acid with H2, accessing various pyrrolidones in excellent yields. The systematic studies indicated that the c-C support played multiple roles in catalysis with enhancing electron density of the Pt nanoparticles and activating reactant molecules. Especially, the O-containing groups on the c-C surface provided the c-C support with both acid and base features, thus endowing Pt/c-C with high performances. This work provides an accessible and highly efficient catalyst for reductive synthesis of N-heterocycles using H2 under ambient conditions, which may have promising applications.

The fabrication of catalysts that can activate CO2 under ambient conditions is very interesting but challenging. Metal–organic hybrids (MOHs) have promising applications in catalysis, and their fabrication from renewable resources is very attractive. Herein, we report a simple protocol to fabricate metal–organic hybrids (MOHs) from chitosan, phytic acid and ZnCl2, obtaining mesoporous MOH-Zn possessing –OH, –NH2, and –PO4 groups. The resulting MOH-Zn shows excellent activity for CO2 activation and enables the cyclization of epoxides with CO2 to proceed under ambient conditions, affording a high turnover frequency of 7.8 h−1. The high performance of MOH-Zn originates from the synergistic effects among multi-functional sites in the catalysts.

A cobalt-based catalytic system composed of Co(BF4)2·6H2O and ligand P(CH2CH2PPh2)3 was developed for hydrogenation of levulinic acid to γ-valerolactone (GVL), which showed high efficiency for this...

Developing high-performance catalysts for water splitting via renewable electricity is of great significance for the clean production of hydrogen. This work reports rational design and controllable fabrication of metal oxide hybrid catalyst CoNiFe2O5·2CuO with unique biphasic microstructures for electrochemical water splitting. Benefited from the presence of CuO nanoparticles as the second phase, more defects and active sites were formed around the interfaces of CoNiFe2O5 and CuO, which led to excellent performances for electrocatalytic water splitting. In particular, the catalyst exhibited outstanding activity for hydrogen evolution reaction with a small overpotential of 30 mV to reach a current density of 10 mA cm-2 and showed a higher turnover frequency (0.3 s-1) than commercial catalyst Pt/C (0.1 s-1) under an overpotential of 50 mV. Moreover, it also displayed good activity for oxygen evolution reaction with an overpotential of 264 mV at 10 mA cm-2. Using CoNiFe2O5·2CuO as the catalyst for electrode pair to construct a cell, a very low cell voltage of 1.53 V is enough to achieve overall water splitting at 10 mA cm-2 in 1 M KOH electrolyte, and the cell could maintain the stable performance at 10 mA cm-2 within 100 h. The as-prepared metal oxide hybrids with biphasic microstructures may have promising application potentials in water splitting.

ConspectusMetal-free catalysis is a promising protocol to access chemicals without metal contamination. Ionic liquids (ILs) that are entirely composed of organic cations and inorganic/organic anions have emerged as promising alternatives to molecular solvents and metal catalysts due to their unique properties such as structural tunability, the coexistence of multiple interactions among ions (e.g., electrostatic interaction, hydrogen bonding, van de Waals forces, acid/base interactions, hydrophilic/hydrophobic interactions, etc.), unique affinity for a wide range of chemicals, good chemical and thermal stability, and quite low volatility. ILs have shown potential applications in various chemical processes.In this Account, we systematically described our most recent work on IL-catalyzed approaches under metal-free conditions. The first section presents the IL-catalyzed strategies toward the transformation of CO2 to value-added chemicals, focusing on the CO2-reactive IL-catalyzed CO2 transformation to various heterocycles and the IL-catalyzed reductive transformation of CO2 to chemicals. In these approaches, we designed task-specific ILs that are able to chemically capture and activate CO2 via forming anion-based carbonate/carbamate or cation-based carboxylate/carbamate intermediates, thus further accomplishing its transformation to a series of heterocycles including quinazoline-2,4(1H,3H)-diones, cyclic carbonates, 2-oxazolidinones, oxazolones, and benzimidazolones under metal-free conditions. For the IL-catalyzed approaches to reducing CO2 with hydrosilanes to chemicals, we employed ILs capable of activating the Si-H bond in hydrosilanes and the N-H bond in amine substrates via H-bonding, thus achieving the reductive transformation of CO2 to formamides, benzimidazoles, and benzothiazoles via cooperative catalysis. The second section describes our finding on the IL-catalyzed hydration of the C≡C bond in propargylic alcohols. Azolate anion-based ILs that can chemically capture CO2 via the formation of carbamates could serve as robust nucleophiles to attack the C≡C bond in propargylic alcohols and then efficiently catalyze the hydration of propargylic alcohols to produce α-hydroxy ketones with the assistance of atmospheric CO2 gas under metal-free conditions. The third section unveils the cooperative catalysis strategy of hydrogen bond donors and acceptors of ILs for chemical reactions. In the hydrogen-bonding catalysis protocols, cations of the ILs act as H-bond donors and anions, as acceptors, forming H-bonds with the reactant molecules, respectively, in opposite ways, which can cooperatively catalyze the ring-closing C-O/C-O bond metathesis reactions of aliphatic diethers to O-heterocycles, the dehydrative etherification of alcohols to ethers, and direct oxidative esterification of alcohols to esters. We believe that these IL-catalyzed metal-free processes and strategies display promising practical applications, and their commercialization would bring great benefits to the production of the as-afforded value-added chemicals.

A novel high-throughput array analytical platform based on derived β-cyclodextrin supramolecular imprinted polymer (SMIP) fibers was constructed to achieve selective enrichment and removal of parabens. SMIP fiber arrays have abundant imprinting sites and introduce the host–guest inclusion effect of the derived β-cyclodextrin, which is beneficial to significantly improve the adsorption ability of fiber for parabens. Upon combination with HPLC, a specific and sensitive recognition method was developed with a low limit of detection (0.003–0.02 µg/L, S/N = 3) for parabens analysis in environmental water. This method has a good linearity (R > 0.9994) in the linear range of 0.01–200 µg/L. The proposed SMIP fiber array with high-throughput adsorption capacity has great potential in monitoring water pollution, which also provides a reliable reference for the analysis of more categories of pharmaceutical and personal care product pollutants.

Direct hydrogenation of CO2 to C2+ hydrocarbons is very interesting, but achieving this transformation below 200 °C is challenging and seldom reported. Herein, a homogeneous catalytic system was developed composed of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6 ]), Pd(PtBu3 )2 , FeCl2 , and the ligand 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) for hydrogenation of CO2 under mild conditions, which resulted in C2 -C4 hydrocarbons in selectivities up to 98.3 C-mol % at 180 °C. The combination of [BMIm][PF6 ]) with Xantphos endowed the Pd-Fe catalysts with the ability of activating CO2 and H2 simultaneously via [HPd(PtBu3 )(BMIm-COO)(BMIm)(PF6 )Fe]+ species, thus catalyzing the formation of C2 -C4 hydrocarbons through CO2 hydrogenation. In addition, this catalytic system is stable and recyclable, which may have promising applications.

Photoreduction of carbon dioxide to chemicals or fuels is very interesting from the viewpoint of green chemistry. Herein, we report the photoreduction of CO2 catalyzed by a metal-free photocatalyst...

The electrochemical CO2 reduction (ECR) into fuels and feedstocks enables the storage of intermittent renewable electricity and, ultimately, a net reduction of greenhouse gas emissions, which therefore have been paid much attention. In this article, the advances on ECR in the past 3 years are reviewed with focus on the developments of electrolytes, electrocatalysts, and new strategies for ECR.

Catalytic experiments were performed to investigate the hydrogenation of o-cresol to 2-methylcyclohexanol on a platinum catalyst in water. It has been observed experimentally both here and in prior studies that intermediate ketones desorb from the catalyst surface in the vapor phase or in hydrocarbon solvents, but they are not observed when reactions are carried out in the aqueous phase. Density functional theory was employed to explore the atomic-scale mechanism of o-cresol hydrogenation at the water/Pt(111) interface. Here, we show that water plays a dual role of accelerating the rate of hydrogenation of these ketones by shuttling hydrogen from the surface while also decreasing the rate of desorption of the less polar ketone intermediate from the catalyst surface. These two effects, when combined, explain the lack of observation of these ketone intermediates when this hydrogenation reaction is carried out in the aqueous phase.

Production of methanol from electrochemical reduction of carbon dioxide is very attractive. However, achieving high Faradaic efficiency with high current density using facile prepared catalysts remains to be a challenge. Herein we report that copper selenide nanocatalysts have outstanding performance for electrochemical reduction of carbon dioxide to methanol, and the current density can be as high as 41.5 mA cm−2 with a Faradaic efficiency of 77.6% at a low overpotential of 285 mV. The copper and selenium in the catalysts cooperate very well for the formation of methanol. The current density is higher than those reported up to date with very high Faradaic efficiency for producing methanol. As far as we know, this is the first work for electrochemical reduction of carbon dioxide using copper selenide as the catalyst., While the conversion of CO2 to valuable, storable chemicals is attractive, there are few inexpensive and abundant catalysts that are also active and selective for liquid fuels. Here, the authors study copper selenide as a high-performing and efficient electrocatalyst for CO2 conversion to methanol.

Synthesis of renewable acetic acid from CO2 and lignin was effectively achieved over an ionic liquid (e.g., [BMIm][Cl])-based catalytic system containing Ru–Rh bimetal catalyst (Ru3(CO)12 and RhI3) and LiI. As far as we know, this is the first initiative to produce acetic acid from lignin and CO2.

A Rose bengal-functionalized porous organic polymer (RB-POP) was prepared with a specific surface area of up to 562 m2 g−1. In the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, RB-POP supported Ag(0) nanoparticles exhibited excellent performance for catalyzing cyclization of propargyl alcohols with CO2 at 30 °C, achieving a TOF of 5000 h−1, the highest value among the reported ones.

The reduction of CO2 with amines and H2 generally produces N-formylated or N-methylated compounds over different catalysts. Herein, we report the selective synthesis of formamides, 1,2-bis(N-heterocyclic)ethanes, and methylamines, which is achieved over an ionic liquid (IL, e.g., 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIm][BF4])–Pd/C catalytic system. By simply varying the reaction temperature, formamides and methylamines can be selectively produced, respectively, in high yields. Interestingly, 1,2-bis(N-heterocyclic)ethanes can also be obtained via the McMurry reaction of the formed formamide coupled with subsequent hydrogenation. It was found that [BMIm][BF4] can react with formamide to form a [BMIm]+–formamide adduct; thus combined with Pd/C it can catalyze McMurry coupling of formamide in the presence of H2 to afford 1,2-bis(N-heterocyclic)ethane. Moreover, Pd/C–[BMIm][BF4] can further catalyze the hydrogenolysis of 1,2-bis(N-heterocyclic)ethane to access methylamine. [BMIm][BF4]–Pd/C was tolerant to a wide substrate scope, giving the corresponding formamides, 1,2-bis(N-heterocyclic)ethanes or methylamines in moderate to high yields. This work develops a new route to produce N-methylamine and opens the way to produce 1,2-bis(N-heterocyclic)ethane from cyclic amine as well.

The CO2-involved synthesis of chemicals is of great significance from the green and sustainable chemistry viewpoint. Herein, we report a non-noble metal catalytic system composed of CoF2, CsF and P(CH2CH2PPh2)3 (denoted as PP3) for the synthesis of N-containing heterocycles from ortho-substituted anilines and CO2/H2. Mechanism investigation indicates that [Co(PP3)H(CO2)]+ is a catalytically active intermediate under working conditions; and CsF plays important roles in activating ortho-substituted anilines via hydrogen bond interactions, thus promoting the formation of the final products. This catalytic system is highly efficient, and allows a wide scope of ortho-substituted anilines, together with excellent functional group tolerance, affording various N-containing heterocycles in good to excellent yields.

The solar energy-driven photoreduction of CO2 with H2O to hydrocarbon fuels is an interesting but challenging topic. Herein, we report porous nitrogen-deficient carbon nitride nanotubes with tunable nitrogen vacancies (NCN-T) for visible-light-driven photoreduction of CO2 to CO in the absence of any cocatalyst and sacrificial reagent. The NCN-T series were prepared via the thermal etching approach, which showed a specific surface area of up to 207 m2 g−1 and a CO2 uptake capacity of 4.06 wt%. It was indicated that the nitrogen vacancies in NCN-T not only promoted the utilization of visible-light by extending the spectral response range, but also served as centres for capturing photoexcited electrons, hence, efficiently inhibiting the recombination of radiative electron–hole pairs. As a consequence, the NCN-T catalysts achieved the highest CO formation rate of 43.9 μmol g−1 h−1, which was >9 times higher than that obtained over the bulk counterpart.

Herein, a novel route to synthesize unsymmetrically N,N-disubstituted formamides is reported, which is achieved via reductive coupling of primary amine and aldehyde with CO2/H2 over a cobalt-based catalytic system composed of CoF2, P(CH2CH2PPh2)3 and K2CO3. The mechanism investigation indicates that a secondary amine is formed via hydrogenation of the imine originated from aldehyde and primary amine, which further reacts with HCOOH generated from CO2 hydrogenation, resulting in the formation of NNFA finally.

Bimetallic nanomaterials, which exhibit a combination of the properties associated with two different metals, have enabled innovative applications in nanoscience and nanotechnology. Here, we introduce the fabrication of dendritic Au/Ag bimetallic nanostructures for surface-enhanced Raman scattering (SERS) and catalytic applications. The dendritic Au/Ag bimetallic nanostructures were prepared by combining the electrochemical deposition and replacement reaction. The formation of Au nanoparticle shell on the surface of Ag dendrites greatly improves the stability of dendritic nanostructures, followed by a significant SERS enhancement. In addition, these dendritic Au/Ag bimetallic nanostructures are extremely efficient in degrading 4-nitrophenol (4-NP) compared with the initial dendritic Ag nanostructures. These experimental results indicate the great potential of the dendritic Au/Ag bimetallic nanostructures for the development of excellent SERS substrate and highly efficient catalysts.

Solar-driven reduction of CO2 into renewable carbon forms is considered as an alternative approach to address global warming and the energy crisis but suffers from low efficiency of the photocatalysts. Herein, a direct Z-Scheme SnS2 /sulfur-bridged covalent triazine frameworks (S-CTFs) photocatalyst (denoted as SnS2 /S-CTFs) was developed, which could efficiently adsorb CO2 owing to the CO2 -philic feature of S-CTFs and promote separation of photoinduced electron-hole pairs. Under visible-light irradiation, SnS2 /S-CTFs exhibited excellent performance for CO2 photoreduction, yielding CO and CH4 with evolution rates of 123.6 and 43.4 μmol g-1 h-1 , respectively, much better than the most catalysts reported to date. This inorganic/organic hybrid with direct Z-Scheme structure for visible-light-driven CO2 photoreduction provides new insights for designing photocatalysts with high efficiency for solar-to-fuel conversion.

O-heterocycles have wide applications, and their efficient and green synthesis is very interesting. Herein, we report hydrogen-bonding catalyzed ring-closing metathesis of aliphatic ethers to O-heterocycles over ionic liquid (IL) catalyst under metal- and solvent-free conditions. The IL 1-butylsulfonate-3-methylimidazolium trifluoromethanesulfonate ([SO3 H-BMIm][OTf]) is discovered to show outstanding performance, better than the reported catalysts. An interface effect plays an important role in mediating the reaction rate due to the immiscibility between the products and the IL catalyst, and the products can be spontaneously separated. NMR analysis and DFT calculation suggest that a pair of cation and anion of [SO3 H-BMIm][OTf] could form three strong H-bonds with an ether molecule, which catalyze the ether transformation via a cyclic oxonium intermediate. A series of O-heterocycles including tetrahydrofurans, tetrahydropyrans, morpholines and dioxane can be obtained from their corresponding ethers in excellent yields (e.g., >99 %). This work opens an efficient and metal-free way to produce O-heterocycles from aliphatic ethers.

The reductive formylation of aryl iodides/bromides to aryl aldehydes using CO2/H2 is presented for the first time. It was realized over a catalytic system composed of RhI3 or RhI3/Pd(dppp)Cl2 (dppp = 1,3-bis(diphenyphosphino)propane) and PPh3 in the presence of Ac2O/Et3N at 100 °C, affording aromatic aldehydes in good to excellent yields, together with good functional-group tolerance and broad substrate scope. The reaction proceeds through three cascade steps, involving HCOOH formation, CO release, and formylation of aryl halides.

Solar-energy-driven photoreduction of CO2 to hydrocarbon fuels is an interesting and challenging topic, which generally requires photocatalysts with the capability to capture and photoreduce CO2 simultaneously. Herein, we demonstrate that a N,O,P-containing covalent organic polymer (NOP-COP) prepared via condensation of hexachlorocyclotriphosphazene with barbituric acid can capture CO2 and further photocatalyze its reduction to CH4 under visible-light irradiation. The characterization information indicates that the incorporation of phosphorus in the skeleton of NOP-COP promoted the absorption of visible light and improved the lifetime of the photoinduced carriers. As a result, NOP-COP exhibited enhanced efficiency for photoreduction of CO2 compared with the N,O-containing polymer, affording CH4 as the sole carbonaceous product with a rate of 22.5 μmol gcat–1 h–1 and selectivity over 90%. This work provides insight into designing and fabricating polymeric photocatalysts for CO2 photoreduction to fuels.

CO2 incorporation into C–H bonds is an important and interesting topic. Herein a sequential protocol for C(sp)–H carboxylation by employing a metal-free C–H activation/catalytic silylation reaction in conjunction with KO t Bu-mediated carboxylation with CO2 was established, in which KO t Bu catalyzes silylation of terminal alkynes to form alkynylsilanes at low temperature, and simultaneously mediates carboxylation of the alkynesilanes with atmospheric CO2. Importantly, the carboxylation further promotes the silylation, which makes the whole reaction proceed very rapidly. Moreover, this methodology is simple and scalable, which is characterized by short reaction time, wide substrate scope, excellent functional-group tolerance and mild reaction conditions, affording a range of corresponding propiolic acid products in excellent yields in most cases. In addition, it also allows for a convenient 13C-labeling through the use of 13CO2.

The synthesis of chemicals from biomass-derived compounds is an interesting and challenging topic. In this work, using the lignin-derived 2-phenoxyacetophenones as the feedstock we present a novel approach for the synthesis of benzanilides via the reaction of 2-phenoxyacetophenones with anilines catalyzed by CuCl2 in DMSO at 120 °C under an air atmosphere. This approach has wide scope for 2-phenoxyacetophenones and anilines, and various benzanilides accompanied by the corresponding phenols could be obtained in high yields via changing the 2-phenoxyacetophenones and anilines. The reaction mechanism study indicated that the oxidative cleavage of the C–C bond in 2-phenoxyacetophenones and the formation of a C–N bond occurred simultaneously in the reaction process, resulting in the formation of benzanilides together with phenols.

We developed a route to prepare nanoporous Cu/Ni oxide composites. It was discovered that the Cu/Ni oxide composites were very efficient electrocatalysts for CO2 reduction to formate in aqueous electrolytes. The excellent performance resulted mainly from the porous structure, synergistic effect of the two oxides, and low charge transfer resistance.

A mesoporous imine-functionalized organic polymer (Imine-POP) was prepared based on the reaction of an aryl ammonium salt with an aromatic aldehyde in water without any catalyst and template. The Pd coordinated Imine-POP exhibited high catalytic activity for the N-formylation of amines with CO2/H2 at 100 °C, affording a series of formamides in high yields.

We report the synthesis of nanostructured Fe3S4 from deep eutectic solvents via a one-step solvothermal method. The as-obtained Fe3S4 catalyst was capable of electrochemically reducing N2 to NH3 under ambient conditions, and exhibits a high NH3 yield (75.4 μg h−1 mg−1cat.) and faradaic efficiency (6.45%) at −0.4 V vs. a reversible hydrogen electrode.

The CO2-involved synthesis of chemicals is of great significance from a green and sustainable point of view. Herein, we present an efficient Co-based catalytic system composed of a commercially available Co salt, the tetradentate phosphine ligand P-(CH2CH2PPh2)3, and a base, denoted as [Co]/PP3/base, for the synthesis of formamides via the formylation of amines with CO2/H2. It was indicated that the selectivity of products (i.e., formamide or methylamine) could be tuned to some extent via changing the solvent and the base. Using ethanol as the solvent, the Co(ClO4)2·6H2O/PP3/K2CO3 system showed high activity for the production of formamides, affording product yields of 82–95%, together with its broad substrate scope. Exploration of the reaction mechanism indicated that formamide was formed with HCOOH as the intermediate, while the methylamine byproduct was produced with HCHO as the intermediate via the hydrogenolysis of dialkylaminomethane.

Using sodium borohydride (NaBH4) as the reducing reagent, the reductive fomylation of amines with CO2 was realized at 100 °C under catalyst-free conditions, and a series of formylated products were obtained in excellent yields. The reaction mechanism investigation demonstrated that NaBH4 could react with CO2 to form intermediate, which further reacted with amines, producing the formylated compounds. It was indicated that three hydrogen atoms from NaBH4 could involve in the reductive formylation, and therefore only 0.5 equiv. NaBH4 relative to the substrate was enough for getting high product yields. In addition, NaBH4 was also very efficient for the reductive cyclization of o-phenylenediamine with CO2 to synthesize benzimidazoles. NaBH4 as an efficient reducing reagent for the CO2-involed reductive reactions may have promising applications.

Task-specific ionic liquids (ILs) have shown promising applications in catalysis. Herein we present lactate-based IL (e.g., 1-butyl-3-methylimidazolium lactate, [BMIm][Lac]) catalyzed reductive amination/cyclization of keto acids using triethoxysilane as a reducing agent, which provides a metal-free route to synthesis of lactams under mild conditions, even at room temperature. [BMIm][Lac] combined with (EtO)3SiH afforded a series of five- and six-membered lactams in good to excellent yields at 80 °C within 1 h, showing comparable performance to the best metal-based catalyst reported to date. The mechanism investigation indicated that the ILs (e.g., [BMIm][Lac]) served as a multifunctional catalyst, which could activate hydrosilanes and simultaneously catalyzed the cyclization of LA with amines.

The methylation of amines using methanol is a promising route to synthesize N-methylamines, and the development of cheap and efficient catalytic system for this reaction is of great significance. Herein, we reported a cobalt (Co)-based catalytic system, which was in situ formed from commercially available Co precursor and a tetradentate phosphine ligand P(CH2CH2PPh2)3 combined with K3PO4. This catalystic system was very effective for the selective production of dimethylated products from aliphatic amines and monomethylated ones from aromatic amines. The reaction mechanism was further investigated by control and isotope labelling experiments.

Pt/SiO2-Al2O3 (Pt/SA) is commonly used as diesel oxidation catalysts (DOC) in industry, but it could be seriously deactivated caused by H2O at long-term high temperature. In this paper, the inhibition mechanism of water on Pt/SA for NO oxidation was studied. The fresh Pt/SA (Pt/SA-F) was treated in an air flow with/without 10% H2O at 700 °C for 10 h to obtain the hydrothermally/thermally aged catalysts named as Pt/SA-HA and -A, respectively. NO oxidation tests showed that Pt/SA-HA had lower activity than Pt/SA-A. A series of characterizations proved H2O didn’t affected Pt states and support structure as they were similar over two aged catalyst. 1H NMR and In-situ DRIFTS testified that water deactivation was a result of the acidity loss of catalysts, which inhibited the decomposition and desorption of reaction intermediate, finally resulting in bad NO oxidation activity.

A highly efficient Co-based catalytic system, composed of a commercially available Co salt, a tetradentate phosphine ligand P(CH2CH2PPh2)3(PP3), and a base (denoted as [Co]/PP3/base), is developed for the methylation of C(sp3)–H and C(sp2)-H bonds using methanol as a methylating reagent. The Co(BF4)2·6H2O/PP3/K2CO3 catalytic system showed high catalytic activity for the methylation of C–H bonds in aryl alkyl ketones, aryl acetonitriles, and indoles, with wide substrate scope and good functional group tolerance, and methyl-substituted products were obtained in good to excellent yields at 100 °C. This cheap, readily available, and highly efficient Co-based catalytic system may have promising applications in methylation reaction using methanol.

A series of tetrabutylphosphonium ([Bu4P]+)-based ionic liquids (ILs) with multiple-site for CO2 capture and activation in their anions are reported, which could efficiently catalyze the cyclization reaction of propargylic alcohols with CO2 at ambient conditions. Especially, the IL, [Bu4P]3[2,4-OPym-5-Ac], which has three interaction sites for attracting CO2 together with a pKa1 value of 9.13, exhibited the best performance, affording a series of α-alkylidene cyclic carbonates in moderate to good yields. The mechanism exploration demonstrated that IL served as a bifunctional catalyst with anion simultaneously activat-ing CO2 via multiple-site cooperative interactions and the C≡C triple bond in propargylic alcohol via inductive effect, thus resulting in the production of α-alkylidene cyclic carbonates..

Herein we present a simple, metal-free and versatile route to synthesize unsymmetrically N,N-disubstituted formamides (NNFAs) from CO2, primary amine and aldehyde promoted by ionic liquid (1-butyl-3-methylimidazolium chloride) at room temperature. This approach features wide scopes of amines and aldehydes, and various unsymmetrical NNFAs could be obtained in good to excellent yields. The ionic liquid can be reused at least five runs without obvious activity loss.