Zinc Catalyst Research Articles

Zinc (II) complex immobilized on the surface of magnetic nanoparticles modified with phenanthroline: A novel and efficient nanomagnetic reusable catalyst for cross-coupling reaction of aryl iodides with terminal aromatic alkynes

A novel and green nanomagnetic zinc catalyst were fabricated via the immobilization of zinc (II) complex on the surface of magnetic nanoparticles modified with phenanthroline (MNPs-Phen-Zn(II)). The structure of MNPs-Phen-Zn(II) nanomaterial was characterized by a series of spectroscopic techniques including FT-IR spectroscopy, SEM, TEM, EDX, XRD, VSM, and ICP-OES. The resulting zinc nanomagnetic catalyst was shown high catalytic activity for the synthesis of disubstituted alkynes via C(sp2)–C(sp) cross-coupling reactions of alkynes with aryl iodides under eco-friendly conditions. To the best of our knowledge, it is the first report on the utilization of zinc nanomagnetic catalyst for the Sonogashira type cross-coupling reaction of alkynes with aryl iodides in the absence of added Pd and Cu sources. The simple preparation of the catalyst from commercially available materials, excellent chemoselectivity, easy separation of products, and straightforward recovery and reusability of the catalyst with unaltered activity make our procedure a green and practical method.

Enriched sp2-Hybridized C Atoms toward the Tradeoff between Activity, Conductivity and Stability of Spherical Porous Metal–Nitrogen–Carbon Catalysts for Rechargeable Zinc–Air Batteries

Enriched sp²-Hybridized C Atoms toward the Tradeoff between Activity, Conductivity and Stability of Spherical Porous Metal–Nitrogen–Carbon Catalysts for Rechargeable Zinc–Air Batteries

Zinc and magnesium catalysts for the synthesis for PLA and its degradation: Clues for catalyst design

Homoleptic and heteroleptic zinc and magnesium complexes bearing phenoxy-imine pyridine ligands were synthetized and characterized. Several structural parameters such as the structure of the ancillary ligand, the nature of the metal centre and the coordination geometry were investigated for identifying design elements purposeful to improve the catalytic activity in the ring opening polymerization (ROP) of lactide and in the reverse reaction of degradation of polylactide by alcoholysis. High efficiency and control degree were reached with zinc catalysts while magnesium ones showed lower activity and a weak control degree. NMR studies demonstrated that, for the homoleptic zinc complex, an activated-monomer mechanism was active. Differently, a coordination/insertion mechanism was observed for the related homoleptic zinc complex. Significantly, the complexes that showed the best activity in the ROP of lactide revealed to be the most efficient also in the degradation reaction.

Magnetic nanoparticles supported zinc (II) complex (Fe3O4@SiO2-Imine/Thio-Zn(OAc)2): a green and efficient magnetically reusable zinc nanocatalyst for synthesis of nitriles via cyanation of aryl iodides

Herein we introduce a novel and reusable nanomagnetic copper catalyst (Fe3O4@SiO2-Imine/Thio-Zn(OAc)2) constructed by immobilizing Zn (II) complex on the surface of magnetic nanoparticles functionalized with Imine/Thio group. The structure of the as-constructed Fe3O4@SiO2-Imine/Thio-Zn(OAc)2 nanomaterial was well analyzed by a number of spectroscopic techniques including: FT-IR, SEM, TEM, EDX, XRD, VSM, AAS and ICP-OES. Experimental studies have well revealed that Fe3O4@SiO2-Imine/Thio-Zn(OAc)2 nanomaterial is an ecofriendly and efficient nanocatalyst for synthesis of synthesis of nitriles via cyanation of aryl iodides. The grafting of the zinc catalyst to the surface of magnetic nanoparticles has increased the catalytic activity of the material and also simplified catalyst recovery from the reaction mixture by an external magnet. The Fe3O4@SiO2-Imine/Thio-Zn(OAc)2 nanocatalyst was readily recovered by simple magnetic decantation and can be reused seven cycles without considerable loss in catalytic activity.

Sustainability and Polyesters: Beyond Metals and Monomers to Function and Fate.

ConspectusPoor waste management and unchecked consumption underpin our current paradigm of plastics use, which is demonstrably unsustainable in the long term. Nonetheless, the utility and versatility of plastics suggest that the notion of a plastic-free society is also unsustainable. Responses to this conundrum are increasing, and among these are research efforts focused on the development of more sustainable plastics. This Account, written by trained chemists, reflects an academic research journey culminating in an appreciation of the importance of improving and enabling the overarching systems that plastics exist within. Our primary initial focus was on catalyst development because catalysts are key drivers of sustainability by improving the efficiency and ease of polymerization. Metal catalysts ranging in ligand structure and the incorporated metal(s) were developed for the preparation of traditional polyesters such as poly(lactic acid) and polycaprolactone. The central themes in these works were stereocontrol (tacticity), efficiency (polymerization rate), and versatility (monomer scope). Alongside insights gained by systematically varying catalyst structure came impressive results gained through collaboration, including the remarkably high activity of novel heterometallic zinc catalysts toward various cyclic esters.This catalysis work was complemented by and slowly transitioned to a focus on polymer functionality and monomer design. Several fundamental studies focus on polymer topology, specifically star-shaped polyesters, tuned arm number, length, and tacticity. These reports feature emphases on the end of life (solvolysis) and physical properties of polymers, which were increasingly important themes as work shifted toward new methods of incorporating functionality in polymers produced by ring-opening polymerization. Three key highlights demonstrate this shift: the first two rely upon the exploitation of olefin metathesis (cross- and ring-closing) to functionalize polyesters or polyethers, and the third involves the manipulation of ring-opening polymerization equilibrium to enable selective monomer recovery from a polyester. Our foundational work on 1,3-dioxolan-4-one (DOX) monomers is then discussed because this emerging class of molecules offers a distinct synthetic pathway toward functional polyesters, both conventional and novel. With this DOX framework, polyesters that are usually challenging to synthesize (e.g., poly(mandelic acid)) are accessible because polymerization is driven by the concomitant, controlled extrusion of small molecules (acetone or formaldehyde).After these polyester-focused highlights, the foundation of our ongoing work is presented, namely, that polymer sustainability must be viewed from a systems-level perspective, including economic and social components alongside the environmental considerations. Material design must be driven by practice, and we have to involve key players in academia, industry, and government in a concerted effort to enable positive and robust change. The key goal is to develop sustainable systems that retain plastics in their highest value state for as long as possible by designing materials and products for a particular (and assured) end-of-life fate, whether that be reuse, recycling, (bio)degradation, or energy recovery.

Selection of oxygen reduction catalysts for secondary tri-electrode zinc\u2013air batteries

Oxygen reduction reaction (ORR) electrocatalysts, which are highly efficient, low-cost, yet durable, are important for secondary Zn–air cell applications. ORR activities of single and mixed metal oxide and carbon electrocatalysts were studied using rotating disc electrode (RDE) measurements, Tafel slope and Koutecky–Levich plots. It was found that MnOx combined with XC-72R demonstrated high ORR activity and good stability—up to 100 mA cm−2. The performance of the selected ORR electrode and a previously optimised oxygen evolution reaction (OER) electrode was thereafter tested in a custom-built secondary Zn–air cell in a tri-electrode configuration, and the effects of current density, electrolyte molarity, temperature, and oxygen purity on the performance of the ORR and OER electrode were investigated. Finally, the durability of the secondary Zn–air system was assessed, demonstrating energy efficiencies of 58–61% at 20 mA cm−2 over 40 h in 4 M NaOH + 0.3 M ZnO at 333 K.

A Zinc(II) Catalyst for the Synthesis of Cyclic Carbonates and Cyclic Carbamates from Carbon Dioxide

A Zinc(II) Catalyst for the Synthesis of Cyclic Carbonates and Cyclic Carbamates from Carbon Dioxide

Nature of the Active Sites of Copper Zinc Catalysts for Carbon Dioxide Electroreduction

AbstractThe electrochemical CO2 reduction (CO2ER) to multi‐carbon chemical feedstocks over Cu‐based catalysts is of considerable attraction but suffers with the ambiguous nature of active sites, which hinder the rational design of catalysts and large‐scale industrialization. This paper describes a large‐scale simulation to obtain realistic CuZn nanoparticle models and the atom‐level structure of active sites for C2+ products on CuZn catalysts in CO2ER, combining neural network based global optimization and density functional theory calculations. Upon analyzing over 2000 surface sites through high throughput tests based on NN potential, two kinds of active sites are identified, balanced Cu−Zn sites and Zn‐heavy Cu−Zn sites, both facilitating C−C coupling, which are verified by subsequent calculational and experimental investigations. This work provides a paradigm for the design of high‐performance Cu‐based catalysts and may offer a general strategy to identify accurately the atomic structures of active sites in complex catalytic systems.

Nature of the Active Sites of Copper Zinc Catalysts for Carbon Dioxide Electroreduction.

The electrochemical CO2 reduction (CO2 ER) to multi-carbon chemical feedstocks over Cu-based catalysts is of considerable attraction but suffers with the ambiguous nature of active sites, which hinder the rational design of catalysts and large-scale industrialization. This paper describes a large-scale simulation to obtain realistic CuZn nanoparticle models and the atom-level structure of active sites for C2+ products on CuZn catalysts in CO2 ER, combining neural network based global optimization and density functional theory calculations. Upon analyzing over 2000 surface sites through high throughput tests based on NN potential, two kinds of active sites are identified, balanced Cu-Zn sites and Zn-heavy Cu-Zn sites, both facilitating C-C coupling, which are verified by subsequent calculational and experimental investigations. This work provides a paradigm for the design of high-performance Cu-based catalysts and may offer a general strategy to identify accurately the atomic structures of active sites in complex catalytic systems.

Fatty-acid-derived ester-urethane macromonomers synthesized using bismuth and zinc catalysts

Photocurable materials that can be delivered as liquids and rapidly (within seconds) cured in situ using UV light are gaining increased interest in advanced minimally invasive procedures. The aim of this work was to synthesize and characterize fatty-acid-derived ester-urethane telechelic (methacrylate) macromonomers, suitable for photopolymerization. The commonly used dibutyltin dilaurate catalyst was replaced with bismuth neodecanoate, bismuth tris(2-ethylhexanoate), and zinc (II) acetyloacetonate as less-toxic alternative catalysts. Additionally, ethyl acetate was used as a “green” solvent. The progress of the two-step synthesis was monitored with infrared spectroscopy. The chemical structure and molecular weight of the obtained viscous materials was characterized with nuclear magnetic resonance spectroscopy and gel permeation chromatography. Photocrosslinking of the macromonomers into elastomeric films was achieved using 150 s per spot of UV light (20 mW/cm2) exposure. Mechanical tensile testing of the films indicated their elasticity up to 120% and low modulus typical for soft and elastomeric materials. Finally, in vitro cytotoxicity tests showed high cell viability for the case of materials synthesized using bismuth and zinc catalysts. Overall, our results indicate that bismuth and zinc catalysts are excellent alternatives to organotin compounds in the synthesis of photocurable methacrylate ester-urethanes with improved environmental and safety profile, and for potential biomedical applications.

Reversible On/Off Switching of Lactide Cyclopolymerization with a Redox-Active Formazanate Ligand.

Redox-switching of a formazanate zinc catalyst in ring-opening polymerization (ROP) of lactide is described. Using a redox-active ligand bound to an inert metal ion (Zn2+) allows modulation of the catalytic activity by reversible reduction/oxidation chemistry at a purely organic fragment. A combination of kinetic and spectroscopic studies, together with mass spectrometry of the catalysis mixture, provides insight in the nature of the active species and the initiation of lactide ring-opening polymerization. The mechanistic data highlight the key role of the redox-active ligand and provide a rationale for the formation of cyclic polymer.

The Role of Undercoordinated Sites on Zinc Electrodes for CO2 Reduction to CO

AbstractThe electrochemical CO2 reduction reaction (CO2RR) using renewable energies is a promising route toward global carbon neutrality. Recently, the use of copper catalysts and CO feedstocks, instead of CO2, has been shown to enhance the selectivity toward multicarbon products, leading to increased efforts in developing tandem electrocatalytic systems. State‐of‐the‐art CO2‐to‐CO electrocatalysts are mainly based on noble metals such as silver and gold. Earth‐abundant zinc, in contrast, displays poorer selectivity and activity. Herein, the use of porous dendritic oxidederived zinc (OD‐Zn) catalysts for CO2RR is reported. These catalysts can reduce CO2 to CO with a maximum Faradaic efficiency of 86% at −0.95 V versus reversible hydrogen electrode (RHE) and partial current density of −266 mA cm–2 at −1.00 V vs RHE. OD‐Zn is further found to have a higher amount of undercoordinated sites and exhibits higher CO2RR activity and CO selectivity than electrodeposited Zn metal. While oxygen vacancies have been previously implicated as active sites, detailed experiments and density functional theory calculations show that Zn sites with a high degree of undercoordination provide even higher activity, in view of their nearly optimal *COOH adsorption energies. These findings showcase Zn‐Oderived particles with plentiful undercoordinated sites as cost‐effective electrocatalysts for CO production.

Oxygen-Terminated Nb2CO2 MXene with Interfacial Self-Assembled COF as a Bifunctional Catalyst for Durable Zinc-Air Batteries.

The desirable air cathode in Zn-air batteries (ZABs) that can effectively balance oxygen evolution and oxygen reduction reactions not only needs to adjust the electronic structure of the catalyst but also needs a unique physical structure to cope with the complex gas-liquid environment. In this work, first-principles calculations were carried out to prove that oxygen-terminated Nb2CO2 MXene played an active role in enhancing the sluggish reaction of oxygen intermediates. Nb2CO2 MXene could also stimulate the spatial accumulation of discharge products, which was beneficial to improve the stability of secondary ZABs. Molecular dynamics simulation was used to show that the confinement effect of COF could effectively regulate the concentration of O2 on the surface of Nb2CO2@COF, which was conducive to an efficient and durable reaction. COF-LZU1 was self-assembled on the interface of Nb2CO2 MXene (Nb2CO2@COF) for the first time. The Nb2CO2@COF electrode had excellent OER/ORR overpotentials with the potential difference (ΔE) of 0.79 V. When applied to the configuration of ZABs, Nb2CO2@COF showed a power density of 75 mW cm-2 and favorable long-term charge/discharge stability, so it could be used as a potential candidate cathode for noble-metal-based catalysts. This idea of combining MXenes and COFs sheds some light on the design of ZABs.

Nitrogen-Doped Carbon-Incarcerated Zinc Electrodes as Heterogeneous Catalysts for Electrochemical Allylation of Carbonyl Compounds.

Electrochemical allylation reactions of carbonyl compounds using cathodes prepared from nitrogen-doped carbon (NDC)-incarcerated zinc catalysts have been developed. A range of aldehydes and ketones afforded the desired allylic alcohols in high yields with <10 mol % zinc leaching, and the heterogeneous nature of the active species was suggested. Compared with bulk zinc electrodes, NDC-stabilized zinc nanoparticle species were compatible with a broader range of heteroaromatic substrates and enabled the use of an undivided cell.

Hierarchical leaf-shaped Ni@Zn bimetallic catalyst with high stability and selectivity for borohydride oxidation

The bimetallic nickel zinc catalyst (Ni@Zn) with hierarchical morphology has been fabricated successfully by an ultrafast and simple synthesis strategy. Unique hierarchical morphology of the catalyst composes of honeycomb arrays, which are formed by Ni shell/Zn core leaves. This Ni@Zn possesses excellent catalytic activity, stability, and selectivity towards borohydride oxidation reaction (BOR). Moreover, a direct borohydride fuel cell (DBFC) with the Ni@Zn/C anode delivers a peak power density of 180.3 mW cm−2 at 298 K. The outstanding performances originate from the increase of electroactive surface area, enhancement of reactants adsorption, and the inhibition of Ni oxidation, which are attributed to its unique hierarchical structure and the introduction of Zn. This study may provide important inspiration for developing efficient noble-metal-free catalysts for DBFC.

A Unified and Desymmetric Approach to Chiral Tertiary Alkyl Halides.

Enantioenriched tertiary alkyl halides are prevalent in bioactive molecules and can serve as versatile synthetic intermediates to construct complex structures. While conventional access to these motifs often hinges on stereoselective carbon-halogen or carbon-carbon bond formation reactions, desymmetric approaches using halogenated and prochiral tetrasubstituted carbons are largely elusive in comparison. Here, we report that a suite of dinuclear zinc catalysts with a prolinol- or pipecolinol-derived tetradentate ligand can reductively desymmetrize a large collection of easily available halomalonic esters to α-halo-β-hydroxyesters. These polyfunctionalized tertiary alkyl fluorides, chlorides, and bromides proved to be useful intermediates toward fluorinated drug analogs and polyhalogenated monoterpenes. The facile intramolecular epoxidation of the chiral chloride and bromide products has also enabled expeditious access to natural products containing tertiary alcohol motifs.

Coordinated Co-NC/CoFe dual active centre embedded three-dimensional ordered macroporous framework as bifunctional catalyst for efficient and stable zinc–air batteries

Developing efficient and stable multifunctional electrocatalyst is very important for zinc–air batteries in practical. Herein, semiconductive spinel CuFe2O4 supported Co–N co-doped carbon (Co-NC) and CoFe alloy nanoparticles were proposed. In this strategy, the three-dimensional ordered macroporous CuFe2O4 support provides rich channels for mass transmission, revealling good corrosion-resistance and durability at the same time. ZIF-67 derived Co-NC decoration improves the conductivity of the catalyst. Further, the uniformly distributed Co-NC and CoFe nanoparticles (C/CF) dramatically promote the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance. Accordingly, C/CF@CuFe2O4 catalyst shows remarkable bifunctional electrocatalytic activity, with an ORR half-wave potential of 0.86 V, and an OER over-potential of 0.46 V at 10 mA cm−2. The zinc–air battery using this catalyst exhibits a power density of 95.5 mW cm−2 and a durable cyclability for over 170 h at a current density of 10 mA cm−2, which implies a great potential in practical application.

Surface oxygenation induced strong interaction between Pd catalyst and functional support for zinc–air batteries

The surface oxygenated PdNiMnO-PF was used as a bifunctional catalyst for zinc–air batteries.

Hydroboration of CO2 catalyzed by heteroscorpionate zwitterionic zinc and magnesium hydride complexes.

The heteroscorpionate zinc hydride complex LZnH 2, (L = (MePz)2CP(Ph)2NPh, MePz = 3,5-dimethylpyrazolyl), its formate complex 3, and magnesium hydride complex LMgH 5 with the same ligand were synthesized and detected for the catalytic hydroboration reaction of CO2. With BH3·SMe2 as the reductant, zinc-based hydride complex 2 and formate complex 3 show a similar capability of hydroboration of CO2, featuring excellent reactivity and selectivity. The conversion of BH3·SMe2 reached 84%, the highest TON of 252 compared to other zinc catalysts was achieved at room temperature and borate ester products at reduction levels of CH3OH were obtained. Magnesium-based hydride complex 5 showed inferior activity for the hydroboration reduction of CO2.

A sustainable approach for the synthesis of recyclable cyclic CO2-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO2 and epoxides have attracted much attention since they can enable CO2-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO2-based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe)2, 1) to rapidly copolymerize meso-CHO and CO2 into poly(cyclohexene carbonate) (PCHC) with an unprecedentedly cyclic structure. Moreover, in the presence of trace amounts of water, a heterogeneous multi-nuclear zinc catalyst ((BDI-(ZnMe2·xH2O))n, 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to meso-CHO and CO2. This strategy not only achieves the first case of cyclic CO2-based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO2-based polycarbonates.