Electrocatalytic and Solar‐Driven CO2 Reduction to CO with a Molecular Manganese Catalyst Immobilized on Mesoporous TiO2

Electrocatalytic CO₂ reduction to CO was achieved with a novel Mn complex, fac‐[MnBr(4,4′‐bis(phosphonic acid)‐2,2′‐bipyridine)(CO)₃] ( MnP ), immobilized on a mesoporous TiO₂ electrode. A benchmark turnover number of 112±17 was attained with these TiO₂| MnP electrodes after 2 h electrolysis. Post‐catalysis IR spectroscopy demonstrated that the molecular structure of the MnP catalyst was retained. UV/vis spectroscopy confirmed that an active Mn–Mn dimer was formed during catalysis on the TiO₂ electrode, showing the dynamic formation of a catalytically active dimer on an electrode surface. Finally, we combined the light‐protected TiO₂| MnP cathode with a CdS‐sensitized photoanode to enable solar‐light‐driven CO₂ reduction with the light‐sensitive MnP catalyst.     

调节氧化镉-炭黑界面高效电催化CO2还原生成CO

通过调节氧化镉与炭黑之间的界面实现了高效电化学二氧化碳还原. 不同氧化镉和炭黑含量的 CdO/CB复合材料利用超声处理方法制备. 采用X射线衍射、 X射线光电子能谱和透射电子显微镜对所得复合材料进行表征, 揭示了其结构组成和形貌. 用H型电解池对CdO/CB复合材料电催化二氧化碳还原的性能进行测试发现, CdO质量分数为20%的CdO/CB 可在-1.0 V(vs. RHE)电位下获得高达92.7%的总法拉第效率, 而纯CdO在相同条件下的法拉第效率仅为69.5%. CO的法拉第效率最高可达87.4%. 进一步的对比实验和动力学研究结果表明, CdO/CB具有更高的电催化CO₂还原性能源于复合材料中氧化镉与炭黑之间的界面和高接触面积. 此外, CdO/CB可在至少10 h的二氧化碳电还原反应中保持稳定的CO法拉第效率.     

The Mutual Conversion of CO2 and CO in Dielectric Barrier Discharge (DBD)

Non-equilibrium plasma, which was engendered by dielectric barrier discharge (DBD) was used to analyze the mutual conversion between CO₂ and CO. The results showed that the conversion ratio of CO increased monotonously with the increasing voltage. But CO₂ was not so. Its conversion ratio reached maximum when the voltage was 3600 V in Ar system. It also showed that the existence of water molecules was more advanageous for the conversion of CO to CO₂ in Air system than in oxygen system, and the conversion ratio could reach 75.8% when the relative humidity was 100%. We also discussed the energy yield and energy efficiency, and the result was that high voltage and high concentration of reactant was disadvantageous for energy utilization.     

1,2-亚苯基二硫桥[FeFe]-氢化酶模拟物选择性光催化还原CO2至CO

利用基于非贵金属的分子催化剂通过光驱动催化CO2还原生成CO是将太阳能储存为化学能和缓解CO2温室效应的有效途径之一,具有重要的科学意义和潜在的应用前景.已报道的非贵金属分子催化剂,大多数对于光驱动CO2还原表现出缓慢的催化反应速率和/或对CO产物的低选择性,反应常常伴随着质子还原产氢反应,只有很少几种非贵金属分子催化剂对光催化CO2还原生成CO表现出高催化反应速率(>100 h?1)和高选择性.研究表明,双核过渡金属配合物由于分子中邻近的两个金属中心的协同催化作用,对于CO2还原生成CO的催化活性明显高于相应的单核配合物.因此,具有两个邻近的金属离子的非贵金属双核配合物有望作为CO2选择性还原的高效分子催化剂.我们最近的研究发现,具有刚性、共轭亚苯基二硫桥结构的[FeFe]-氢化酶模拟物[(μ-bdt)Fe2(CO)6](1,bdt=苯-1,2-二巯基)能够高活性、高选择性地光化学还原CO2至CO,而与其类似的模拟物[(μ-edt)Fe2(CO)6](2,edt=乙烷-1,2-巯基)则不具有光催化还原CO2活性,表明铁铁氢化酶模拟物中硫-硫桥的结构是影响模拟物的催化性能的重要结构因素之一.可见光照射1/[Ru(bpy)3]2+/BIH(BIH=1,3-二甲基-2-苯基-2,3-二氢-1H-苯并[d]-咪唑)体系4.5 h,1催化生成CO的循环数(TON)为710,在初始1 h的转化率(TOF)为7.12 min^-1,CO的选择性达到97%,内量子效率为2.8%.有趣的是,向体系中加入TEOA时可以调节1的催化选择性,光化学反应能够在CO2还原产生CO和质子还原产生H2之间进行切换.此外,采用稳态荧光和瞬态吸收光谱研究了光催化体系中的电子转移,提出可能的光催化反应机理.该研究结果揭示了刚性硫-硫桥结构的氢化酶模拟物对光化学CO2还原至CO的特殊催化活性,拓展了铁铁氢化酶模拟物的催化多功能性.     

Stoichiometric Reduction of CO(2) to CO by Aluminum-Based Frustrated Lewis Pairs

Reducing frustration: The reaction of Mes(3) P(CO(2) )(AlI(3) )(2) in the presence of a CO(2) atmosphere results in the formation of Mes(3) P(CO(2) )(O(AlI(2) )(2) )(AlI(3) ) and [Mes(3) PI][AlI(4) ] (Mes=2,4,6-Me(3) C(6) H(2) ) with the evolution of CO.     

铜基电催化剂还原CO2

温室气体CO₂的大量排放给全球气候造成潜在威胁,电化学还原CO₂为有用的化工产品作为一种人为的碳循环的方式,拓展了新的利用CO₂的可能性,并且是一种很有前景的显著改善环境、促进可持续发展的方法。然而,在转化CO₂为有价值的产品过程中,最大的挑战是抑制析氢副反应的同时达不到高效率、高选择性。铜因其在电催化还原CO₂过程中优异的催化性能而得到广泛关注。本文重点介绍了近年来电催化还原CO₂的发展以及电化学转化CO₂的优缺点,介绍了CO₂RR的热力学与动力学研究并概述了Cu电极、Cu MOFs材料电极以及通过氧化、合金化、纳米化和表面修饰等方法修饰的铜电极的进展,但是电催化还原CO₂的反应机理尚不太确定。最后,讨论了未来铜基电极催化剂高效率地选择性转化CO₂会面临的挑战和可能研究的方向。     

Selective Conversion of CO2 into Isocyanate by Low‐Coordinate Iron Complexes

Discovery of the mechanisms for selective transformations of CO₂ into organic compounds is a challenge. Herein, we describe the reaction of low‐coordinate Fe silylamide complexes with CO₂ to give trimethylsilyl isocyanate and the corresponding Fe siloxide complex. Kinetic studies show that this is a two‐stage reaction, and the presence of a single equivalent of THF influences the rates of both steps. Isolation of a thermally unstable intermediate provides mechanistic insight that explains both the effect of THF in this reaction, and the way in which the reaction achieves high selectivity for isocyanate formation.     

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex

The controlled electrochemical reduction of carbon dioxide to value added chemicals is an important strategy in terms of renewable energy technologies. Therefore, the development of efficient and stable catalysts in an aqueous environment is of great importance. In this context, we focused on synthesizing and studying a molecular Mn^III‐corrole complex, which is modified on the three meso‐positions with polyethylene glycol moieties for direct and selective production of acetic acid from CO₂. Electrochemical reduction of Mn^III leads to an electroactive Mn^II species, which binds CO₂ and stabilizes the reduced intermediates. This catalyst allows to electrochemically reduce CO₂ to acetic acid in a moderate acidic aqueous medium (pH 6) with a selectivity of 63 % and a turn over frequency (TOF) of 8.25 h^?1, when immobilized on a carbon paper (CP) electrode. In terms of high selectivity towards acetate, we propose the formation and reduction of an oxalate type intermediate, stabilized at the Mn^III‐corrole center.     

Selective Photoelectrochemical Reduction of Aqueous CO2 to CO by Solvated Electrons

Reduction of CO₂ by direct one‐electron activation is extraordinarily difficult because of the ?1.9 V reduction potential of CO₂. Demonstrated herein is reduction of aqueous CO₂ to CO with greater than 90 % product selectivity by direct one‐electron reduction to CO₂^.? by solvated electrons. Illumination of inexpensive diamond substrates with UV light leads to the emission of electrons directly into water, where they form solvated electrons and induce reduction of CO₂ to CO₂^.?. Studies using diamond were supported by studies using aqueous iodide ion (I^?), a chemical source of solvated electrons. Both sources produced CO with high selectivity and minimal formation of H₂. The ability to initiate reduction reactions by emitting electrons directly into solution without surface adsorption enables new pathways which are not accessible using conventional electrochemical or photochemical processes.     

Atropisomeric Hydrogen Bonding Control for CO2 Binding and Enhancement of Electrocatalytic Reduction at Iron Porphyrins

The manipulation of the second coordination sphere for improving the electrocatalytic CO₂ reduction has led to breakthroughs with hydrogen bonding, local proton source, or electrostatic effects. We have developed two atropisomers of an iron porphyrin complex with two urea functions acting as multiple hydrogen-bonding tweezers to lock the metal-bound CO₂ in a similar fashion found in the carbon monoxide dehydrogenase (CODH) enzyme. The αα topological isomer with the two urea groups on the same side of the porphyrin provides a stronger binding affinity to tether the incoming CO₂ in comparison to the αβ disposition. However, the electrocatalytic activity of the αβ atropisomer outperforms its congener with one of the highest reported turnover frequencies at low overpotential. The strong H/D kinetic isotope effect (KIE) observed for the αα system indicates the existence of a tight water hydrogen-bonding network for proton delivery which is disrupted by addition of an acid source. The small H/D KIE for the αβ isomer and the enhanced electrocatalytic performance on addition of stronger acid indicate the free access of protons to the bound CO₂ on the opposite side of the urea arm.     

Gasification of hydrolysis lignin with CO2 in the presence of Fe and Co compounds

The effect of the nature of the metal (Fe and Co) deposited on the surface of hydrolysis lignin, as well as the metal content (1, 3, 5 and 7 wt%), on the process of dry catalytic lignin reforming has been studied. The use of the catalyst led to a twofold increase in the conversion of carbon dioxide at temperatures of 500–800 °C, while both metals showed similar activity. The maximum specific catalytic effect is achieved when supporting 7 wt% of active metals.     

Highly Efficient,Selective, and Stable CO2 Electroreduction on a Hexagonal Zn Catalyst

Electrocatalytic CO₂ conversion into fuel is a prospective strategy for the sustainable energy production. However, still many parts of the catalyst such as low catalytic activity, selectivity, and stability are challenging. Herein, a hierarchical hexagonal Zn catalyst showed highly efficient and, more importantly, stable performance as an electrocatalyst for selectively producing CO. Moreover, we found that its high selectivity for CO is attributed to morphology. In electrochemical analysis, Zn (101) facet is favorable to CO formation whereas Zn (002) facet favors the H₂ evolution during CO₂ electrolysis. Indeed, DFT calculations showed that (101) facet lowers a reduction potential for CO₂ to CO by more effectively stabilizing a ^.COOH intermediate than (002) facet. This further suggests that tuning the crystal structure to control (101)/(002) facet ratio of Zn can be considered as a key design principle to achieve a desirable product from Zn catalyst.     

Asymmetric Push–Pull Type Co(II) Porphyrin for Enhanced Electrocatalytic CO2 Reduction Activity

Molecular electrocatalysts for electrochemical carbon dioxide (CO₂) reduction has received more attention both by scientists and engineers, owing to their well-defined structure and tunable electronic property. Metal complexes via coordination with many π-conjugated ligands exhibit the unique electrocatalytic CO₂ reduction performance. The symmetric electronic structure of this metal complex may play an important role in the CO₂ reduction. In this work, two novel dimethoxy substituted asymmetric and cross-symmetric Co(II) porphyrin (PorCo) have been prepared as the model electrocatalyst for CO₂ reduction. Owing to the electron donor effect of methoxy group, the intramolecular charge transfer of these push–pull type molecules facilitates the electron mobility. As electrocatalysts at −0.7 V vs. reversible hydrogen electrode (RHE), asymmetric methoxy-substituted Co(II) porphyrin shows the higher CO₂-to-CO Faradaic efficiency (FE_CO) of ~95 % and turnover frequency (TOF) of 2880 h⁻¹ than those of control materials, due to its push–pull type electronic structure. The density functional theory (DFT) calculation further confirms that methoxy group could ready to decrease to energy level for formation *COOH, leading to high CO₂ reduction performance. This work opens a novel path to the design of molecular catalysts for boosting electrocatalytic CO₂ reduction.     

A Highly Active N‐Heterocyclic Carbene Manganese(I) Complex for Selective Electrocatalytic CO2 Reduction to CO

We report here the first purely organometallic fac‐[Mn^I(CO)₃(bis‐^MeNHC)Br] complex with unprecedented activity for the selective electrocatalytic reduction of CO₂ to CO, exceeding 100 turnovers with excellent faradaic yields (η_CO≈95 %) in anhydrous CH₃CN. Under the same conditions, a maximum turnover frequency (TOF_max) of 2100 s^?1 was measured by cyclic voltammetry, which clearly exceeds the values reported for other manganese‐based catalysts. Moreover, the addition of water leads to the highest TOF_max value (ca. 320 000 s^?1) ever reported for a manganese‐based catalyst. A Mn^I tetracarbonyl intermediate was detected under catalytic conditions for the first time.     

Selective CO2 adsorption by a triazacyclononane-bridged microporous metal-organic framework

Metal-organic frameworks constructed by self-assembly of metal ions and organic linkers have recently been of great interest in the preparation of porous hybrid materials with a wide variety of functions. Despite much research in this area and the large choice of building blocks used to fine-tune pore size and structure, it remains a challenge to synthesise frameworks composed of polyamines to tailor the porosity and adsorption properties for CO(2). Herein, we describe a rigid and microporous three-dimensional metal-organic framework with the formula [Zn(2)(L)(H(2)O)]Cl (L=1,4,7-tris(4-carboxybenzyl)-1,4,7-triazacyclononane) synthesised in a one-pot solvothermal reaction between zinc ions and a flexible cyclic polyaminocarboxylate. We have demonstrated, for the first time, that a porous rigid framework can be obtained by starting from a flexible amine building block. Sorption measurements revealed that the material exhibited a high surface area (135 m(2) g(-1)) and was the best compromise between capacity and selectivity for CO(2) over CO, CH(4), N(2) and O(2); as such it is a promising new selective adsorbent for CO(2) capture.