Enhancing CO2 Electroreduction to Methane with a Cobalt Phthalocyanine and Zinc–Nitrogen–Carbon Tandem Catalyst

Developing copper-free catalysts for CO₂ conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO₂ reduction reaction (CO₂RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc–nitrogen–carbon (Zn-N-C) tandem catalyst for CO₂RR to CH₄. This tandem catalyst shows a more than 100 times enhancement of the CH₄/CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO₂ is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH₄ over Zn-N₄ site, decoupling complicated CO₂RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N₄, which is the key to achieve the high CH₄ production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.     

Hollow Spheres of Iron Carbide Nanoparticles Encased in Graphitic Layers as Oxygen Reduction Catalysts

Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low‐temperature fuel cells. A novel type of catalysts prepared by high‐pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting of uniform iron carbide (Fe₃C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts.     

Advanced Non-metallic Catalysts for Electrochemical Nitrogen Reduction under Ambient Conditions

The electrochemical reduction of nitrogen into ammonia under ambient conditions is a potential strategy for sustainable ammonia production. At present, one of the main research directions in the field of electrochemical nitrogen fixation is to improve the current efficiency and ammonia yield by developing efficient nitrogen reduction catalysts. To optimise the selectivity and catalytic activity of nitrogen reduction catalysts more efficiently, herein, we systematically summarise the progress of research on nitrogen reduction catalysts in recent years and present some general catalyst design strategies. Considering that it is difficult for metal-based catalysts to balance the competitive reactions of nitrogen activation and hydrogen evolution, we discuss in detail the advantages and application prospects of non-metallic catalysts in electrochemical nitrogen fixation. Moreover, both the design strategy of surface or interface defects, and how this atomic-level control of functionalisation helps to promote selectivity and catalytic activity are also discussed by theoretical and experimental electrochemistry. On this basis, we also discussed the future development direction, opportunities and challenges of nitrogen reduction electrocatalysts.     

Highly Efficient CO2 Electroreduction on ZnN4‐based Single‐Atom Catalyst

The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FE_CO) up to 95 % at ?0.43 V), remarkable durability (>75 h without decay of FE_CO), and large turnover frequency (TOF, up to 9969 h^?1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N₄) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step.     

The Effect of TiO2 Catalyst on the NO Reduction by Barrier Discharge in Nitrogen

The study investigated NO reduction by N radicals produced by barrier discharge in nitrogen and the possible effect of TiO₂ catalyst on this reaction. The experiments for NO reduction were carried out at temperatures ranging from room temperature to 140 °C and at NO concentrations ranging from 200 to 800 ppm. The experimental results were described by a model which was based on six main reactions for the calculation of the NO and NO₂ concentrations. The analysis of model suggested two simple methods for the estimation of nitrogen radical production efficiency which in present study was 2 ppm/(J/L). The model also confirmed that N radicals are used very efficiently in the reduction of NO and this process can’t be improved by the catalyst. Nonetheless, experiments showed that the presence of TiO₂ catalyst improved the removal of NO. The experimental results can be explained by surface processes taking place with NO₂ with the help of other plasma produced nitrogen species.

     

Reinforced nickel catalysts for steam reforming of methane to synthesis gas

XRD, mercury porosimetry, low-temperature nitrogen adsorption and electron microscopy were used to study peculiarities of the formation of reinforced composite nickel catalysts. The catalysts were prepared by sintering powdered metallic nickel with a supported nickel catalyst (GIAP-3 or NIAP-18) applied to a reinforcing stainless steel gauze. It was found that a metal matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The NIAP-18-based catalyst exceeded the GIAP-3-based catalyst in activity toward the methane steam reforming. The NIAP-18-based catalyst was as active as the Cr₂O₃-doped NIAP-18-based catalyst, but showed a worse coke-resistance. A chromium oxide additive increased the activity of the GIAP-3-based catalyst.     

Controlled Synthesis of a Vacancy‐Defect Single‐Atom Catalyst for Boosting CO2 Electroreduction

The reaction of precursors containing both nitrogen and oxygen atoms with Ni^II under 500 °C can generate a N/O mixing coordinated Ni‐N₃O single‐atom catalyst (SAC) in which the oxygen atom can be gradually removed under high temperature due to the weaker Ni?O interaction, resulting in a vacancy‐defect Ni‐N₃‐V SAC at Ni site under 800 °C. For the reaction of Ni^II with the precursor simply containing nitrogen atoms, only a no‐vacancy‐defect Ni‐N₄ SAC was obtained. Experimental and DFT calculations reveal that the presence of a vacancy‐defect in Ni‐N₃‐V SAC can dramatically boost the electrocatalytic activity for CO₂ reduction, with extremely high CO₂ reduction current density of 65 mA cm^?2 and high Faradaic efficiency over 90 % at ?0.9 V vs. RHE, as well as a record high turnover frequency of 1.35×10⁵ h^?1, much higher than those of Ni‐N₄ SAC, and being one of the best reported electrocatalysts for CO₂‐to‐CO conversion to date.     

制备高碳醇稀土改性Cu-Fe催化剂

在Ｃｕ－Ｆｅ系催经剂中添加稀土,利用稀土改性提高Ｃｕ－Ｆｅ系催化剂的活性,或直接利用氮氢混合气还原脂肪酸酯制备碳脂肪醇。用纯氢气作气源,添加１％的Ｓｍ２Ｏ３,高碳醇收率可提高约３％。用氮氢混合气作气源,不含稀土的Ｃｕ－Ｆｅ系催化剂活性大幅度下降,添加Ｙ、ＮＤ等可阻止其活性下降甚至提高其活性,与不含稀土的Ｃｕ－Ｆｅ系催化剂相比,添加１％的Ｎｄ２Ｏ３或１％的Ｙ２Ｏ３可分别提高碳醇收率２９％和３３％。     

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g., acetophenone, benzophenone and benzaldehyde with NaBH₄ as a reducing agent. Before the reaction, cryptand-22 was adsorbed on the sulfonic resin with ion-pairing, resin-SO₃^{? +}NH-cryptand-22. The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and the cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, the cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCl and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone with NaBH₄. Effects of solvents, pH of solutions, concentration of the catalyst, reducing agents and resin property on the reduction of ketones were investigated and discussed. The reaction mechanism of the cryptand catalyzed reduction was also studied.     

Isolated Single Iron Atoms Anchored on N-Doped Porous Carbon as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential (E_1/2) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density (J_k) of 37.83 mV cm⁻² at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species.     

Nitrogen‐Enriched Fe3O4@Carbon Nanospheres Derived from Fe3O4@3‐Aminophenol/Formaldehyde Resin Nanospheres Based on a Facile Hydrothermal Strategy: Towards a Robust Catalyst Scaffold for Platinum Nanocrystals

Robust nitrogen‐enriched Fe₃O₄@carbon nanospheres have been fabricated as a catalyst scaffold for Pt nanoparticles. In this work, core–shell Fe₃O₄@3‐aminophenol/formaldehyde (APF) nanocomposites were first synthesized by a simple hydrothermal method, and subsequently carbonized to Fe₃O₄@N‐Carbon nanospheres for in situ growth of Pt nanocrystals. Abundant amine groups were distributed uniformly onto Fe₃O₄@N‐Carbon nanospheres, which not only improved the dispersity and stability of the Pt nanocrystals, but also endowed the Pt‐based catalysts with good compatibility in organic solvents. The dense three‐dimensional cross‐linked carbon shell protects the Fe₃O₄ cores against damage from harsh chemical environments, even in aqueous HCl (up to 1.0 m ) or NaOH (up to 1.0 m ) solutions under ultrasonication for 24 hours, which indicates that it can be used as a robust catalyst scaffold. In the reduction of nitrobenzene compounds, the Fe₃O₄@N‐Carbon@Pt nanocatalysts show outstanding catalytic activity, stability, and recoverability.     

Study of Excited States and Electron Transfer of Semiconductor-Metal-Complex Hybrid Photocatalysts for CO2 Reduction by Using Picosecond Time-Resolved Spectroscopies

A semiconductor-metal-complex hybrid photocatalyst was previously reported for CO₂ reduction; this photocatalyst is composed of nitrogen-doped Ta₂O₅ as a semiconductor photosensitizer and a Ru complex as a CO₂ reduction catalyst, operating under visible light (>400 nm), with high selectivity for HCOOH formation of more than 75 %. The electron transfer from a photoactive semiconductor to the metal-complex catalyst is a key process for photocatalytic CO₂ reduction with hybrid photocatalysts. Herein, the excited-state dynamics of several hybrid photocatalysts are described by using time-resolved emission and infrared absorption spectroscopies to understand the mechanism of electron transfer from a semiconductor to the metal-complex catalyst. The results show that electron transfer from the semiconductor to the metal-complex catalyst does not occur directly upon photoexcitation, but that the photoexcited electron transfers to a new excited state. On the basis of the present results and previous reports, it is suggested that the excited state is a charge-transfer state located between shallow defects of the semiconductor and the metal-complex catalyst.     

Emergence of CO2 electrolyzers including supported molecular catalysts

With access to cheap, sustainable electricity, electrocatalysis is a promising technology for converting electric power into storable chemical fuels or value-added chemical compounds. This has sparked the development of electrocatalysts that need to operate at high product selectivity and high energy efficiency. Electrocatalytic alcohol oxidation, oxygen activation and nitrogen and carbon dioxide (CO₂) reduction are examples of reactions with a huge industrial potential. Notably, electrocatalytic reduction of CO₂ has recently developed as a favourable pathway to convert this greenhouse gas into value-added chemicals and fuels. Earth-abundant metals stabilized by carbon/nitrogen macrocycle ligands are well-known efficient and selective catalysts for the electrochemical reduction of CO₂ in homogeneous conditions. Recently, such catalysts have also been used in supported conditions and implemented in flow cell electrolyzers, showing promising performances. This review provides a synopsis for the evolution of CO₂ electrolyzers using molecular catalysts.     

An Enzyme‐Mimicking Single‐Atom Catalyst as an Efficient Multiple Reactive Oxygen and Nitrogen Species Scavenger for Sepsis Management

Sepsis, characterized by immoderate production of multiple reactive oxygen and nitrogen species (RONS), causes high morbidity and mortality. Despite progress made with nanozymes, efficient antioxidant therapy to eliminate these RONS remains challenging, owing largely to the specificity and low activity of exploited nanozymes. Herein, an enzyme‐mimicking single‐atom catalyst, Co/PMCS, features atomically dispersed coordinatively unsaturated active Co‐porphyrin centers, which can rapidly obliterate multiple RONS to alleviate sepsis. Co/PMCS can eliminate O₂^.? and H₂O₂ by mimicking superoxide dismutase, catalase, and glutathione peroxidase, while removing ^.OH via the oxidative‐reduction cycle, with markedly higher activity than nanozymes. It can also scavenge ^.NO through formation of a nitrosyl–metal complex. Eventually, it can reduce proinflammatory cytokine levels, protect organs from damage, and confer a distinct survival advantage to the infected sepsis mice.     

The active species of the chromium (phillips type) catalysts for the polymerization of ethylene: A unifying approach

From literature data it is concluded that the rate of the reduction, alkylation, polymer chain growth, and chain transfer reactions of three chromium(II) and one chromium(III) surface species all increase with decreasing electron density at the chromium ion. This electron density has previously been measured by the IR shift of the stretching vibration of one CO molecule terminally adsorbed on these chromium ions. It is observed that the reduction half time decreases proportional to the increasing Lewis acidity and that the rate of the polymer chain growth reaction increases exponentially for three chromium surface species with increasing CO stretching vibration. Due to the large difference of the polymer chain growth rates for the two chromium (II) species (A_d and C_d), common in the normal Phillips catalyst, both contribute almost equally to the polymer product, although the A_d species outnumbers the C_d one by more than 3 to 1.     

铁氮掺杂对石墨烯担载铂催化剂氧还原反应活性的影响

高氧还原活性担载铂催化剂的研发是加快质子交换膜燃料电池商业化进程的主要手段之一。以石墨烯为碳源,1,10-菲啰啉为氮源,FeCl3为铁源,用浸渍法制备铁氮掺杂石墨烯(Fe/N-G)载体,并通过乙二醇还原法获得PtFe/N-G催化剂,探究铁氮原子的引入对石墨烯担载铂催化剂氧还原反应催化活性的影响。采用X射线衍射、比表面积和孔径分布测试、X射线光电子能谱等表征手段对载体及催化剂结构进行表征,使用电化学方法对载体和催化剂的氧还原反应活性进行测试。结果表明,PtFe/N-G催化剂的氧还原反应起始电位及半波电位分别为0.96 V、0.83 V,优于相同Pt担载量的商业20%Pt/C催化剂。铁氮掺杂后,石墨烯载体具有较大的孔径更有利于氧还原反应过程中生成物与反应物的传递,PtFe/N-G催化剂中存在吡啶氮和Fe-N型氮与铂纳米颗粒的协同催化,以及铂纳米颗粒与铁氮掺杂石墨烯载体间的相互作用,是PtFe/N-G催化剂具有优异的氧还原催化活性的可能原因。     

Defect Engineering Metal‐Free Polymeric Carbon Nitride Electrocatalyst for Effective Nitrogen Fixation under Ambient Conditions

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions provides an intriguing picture for the conversion of N₂ into NH₃. However, electrocatalytic NRR mainly relies on metal‐based catalysts, and it remains a grand challenge in enabling effective N₂ activation on metal‐free catalysts. Here we report a defect engineering strategy to realize effective NRR performance (NH₃ yield: 8.09 μg h^?1 mg^?1_cat., Faradaic efficiency: 11.59 %) on metal‐free polymeric carbon nitride (PCN) catalyst. Illustrated by density functional theory calculations, dinitrogen molecule can be chemisorbed on as‐engineered nitrogen vacancies of PCN through constructing a dinuclear end‐on bound structure for spatial electron transfer. Furthermore, the N?N bond length of adsorbed N₂ increases dramatically, which corresponds to “strong activation” system to reduce N₂ into NH₃. This work also highlights the significance of defect engineering for improving electrocatalysts with weak N₂ adsorption and activation ability.     

Synergistic Effect of Boron Nitride and Carbon Domains in Boron Carbide Nitride Nanotube Supported Single-Atom Catalysts for Efficient Nitrogen Fixation

Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N₂ adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH₃ production by carbon-based single-atom electrocatalysts under ambient conditions.     

Effect of supercritical CO2 on bulk hydrogenation of nitrile butadiene rubber catalyzed by RhCl(PPh3)3

The effect of supercritical (SC) CO₂ on the bulk hydrogenation of NBR entrapped with the catalyst (RhCl(PPh₃)₃) was investigated under various reaction times, reaction temperatures, hydrogen pressures and loadings of the catalyst and the thicknesses of the polymer films. CO₂ helps in improving the transport behaviour of catalyst in polymer matrices, as well as helping to move catalyst into or out of the polymer. A method for the measurement of the dissolution extent or the apparent solubility of the Rh based catalyst in SC-CO₂ was developed. It is found that high temperatures and high SC-CO₂ densities would enhance the apparent solubility. Cosolvents, such as acetone, are also found to increase the apparent solubility. Details on the hydrogenation process are also presented.     

Electrocatalytically Active Fe‐(O‐C2)4 Single‐Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single‐atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single‐atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single‐atom electrocatalyst supported on low‐cost, nitrogen‐free lignocellulose‐derived carbon. The extended X‐ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe‐(O‐C₂)₄ coordination configuration. Density functional theory calculations identify Fe‐(O‐C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h^?1 mg_cat.^?1 (5350 μg h^?1 mg_Fe^?1) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h^?1 mg_cat.^?1 (51 283 μg h^?1 mg_Fe^?1) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.