Circumventing the scaling relationship on bimetallic monolayer electrocatalysts for selective CO2 reduction

Electrochemical conversion of CO₂ into value-added chemicals continues to draw interest in renewable energy applications. Although many metal catalysts are active in the CO₂ reduction reaction (CO₂RR), their reactivity and selectivity are nonetheless hindered by the competing hydrogen evolution reaction (HER). The competition of the HER and CO₂RR stems from the energy scaling relationship between their reaction intermediates. Herein, we predict that bimetallic monolayer electrocatalysts (BMEs) – a monolayer of transition metals on top of extended metal substrates – could produce dual-functional active sites that circumvent the scaling relationship between the adsorption energies of HER and CO₂RR intermediates. The antibonding interaction between the adsorbed H and the metal substrate is revealed to be responsible for circumventing the scaling relationship. Based on extensive density functional theory (DFT) calculations, we identify 11 BMEs which are highly active and selective toward the formation of formic acid with a much suppressed HER. The H–substrate antibonding interaction also leads to superior CO₂RR performance on monolayer-coated penta-twinned nanowires.

Dual-functional active sites are designed to circumvent the scaling relationship between the HER and CO₂RR on bimetallic monolayer electrocatalysts.     

Organic molecules involved in Cu-based electrocatalysts for selective CO2 reduction to C2+ products

Electrocatalytic carbon dioxide (CO₂) reduction reaction (CO₂RR) is a promising process to mitigate the environmental issues caused by CO₂, as well as to produce valuable multicarbon (C₂₊) products. Significant progresses have been made to explore highly efficient Cu-based electrocatalysts for CO₂RR in recent years. Adding organic molecules into electrocatalytic systems can tune the CO₂ interaction with the electrocatalysts for CO₂RR, therefore, the final C₂₊ products, which are not solely achieved by inorganic modification. In this review, we will summarize the recent progress of the organic molecules participation in CO₂ electroreduction to C₂₊ products on Cu-based electrocatalysts. The applied organic molecules are reviewed based on the heteroatoms (N and S), with the emphasis on their roles in activity and selectivity toward C₂₊ products. A perspective on the application of organic molecules for efficient and selective CO₂RR has been provided.     

New technology for selective catalytic oxidation of ammonia to nitrogen

The selective catalytic oxidation (SCO) of ammonia to N₂ was studied by using a series of noble metal-V₂O₅-WO₃ catalysts supported on titania-silica (TS) prepared by coprecipitation method. In the V₂O₅-WO₃ catalyst system, the use of TS as a support was very effective to enhance catalytic activity compared with TiO₂ or SiO₂ alone. The addition of a slight amount of Pd and Ir to V₂O₅-WO₃/TS catalyst caused also remarkable enhancement of the catalytic activity without decreasing the selectivity to N₂. The present catalysts provide remarkably high catalytic performance for SCO of ammonia to N₂ under the practical reaction conditions for an industrial application.     

Pt monolayer electrocatalysts for O2 reduction: PdCo/C substrate-induced activity in alkaline media

We measured the activity of electrocatalysts, comprising Pt monolayers deposited on PdCo/C substrates with several Pd/Co atomic ratios, in the oxygen reduction reaction in alkaline solutions. The PdCo/C substrates have a core-shell structure wherein the Pd atoms are segregated at the particle’s surface. The electrochemical measurements were carried out using an ultrathin film rotating disk-ring electrode. Electrocatalytic activity for the O₂ reduction evaluated from the Tafel plots or mass activities was higher for Pt monolayers on PdCo/C compared to Pt/C for all atomic Pd/Co ratios we used. We ascribed the enhanced activity of these Pt monolayers to a lowering of the bond strength of oxygenated intermediates on Pt atoms facilitated by changes in the 5d-band reactivity of Pt. Density functional theory calculations also revealed a decline in the strength of PtOH adsorption due to electronic interaction between the Pt and Pd atoms. We demonstrated that very active O₂ reduction electrocatalysts can be devised containing only a monolayer Pt and a very small amount of Pd alloyed with Co in the substrate. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24, 2007.     

Controlled location of S vacancies in MoS2 nanosheets for high-performance hydrogenation of CO2 to methanol

<正>Introduction In a joint co ntribution amo ng many Chinese research Institutes,a recent paper published on Nature Catalysis reported the use of sulfur vacancy-rich MoS₂ as a novel catalyst for the hydrogenation of CO₂ to methanol [1].     

A safe and selective method for reduction of 2-nitrophenylacetic acid systems to N-aryl hydroxamic acids using continuous flow hydrogenation

The cyclic hydroxamic acid functional group is critical to the biological activity of numerous natural products and drug candidates. Efficient, reliable, and green synthetic methods to produce cyclic hydroxamic acids are needed. Herein, flow hydrogenation has been explored as a novel approach toward achieving the selective partial reduction of 2-nitrophenylacetic acid to 1-hydroxyindolin-2-one. The bidentate ligand, 1,10-phenanthroline, has been identified as a unique inhibitor for modulating product selectivity in this Pt/C-catalyzed process. Under the newly optimized reaction conditions, the targeted hydroxamic acid is produced with high selectivity (49:1) over the lactam by-product. The scope of the reaction is demonstrated for a variety of 2-nitrophenylacetic acid derivatives.     

Electrolysis of solid MoS2 in molten CaCl2 for Mo extraction without CO2 emission

Sintered (300 °C) porous pellets of MoS₂ were electrolysed to elemental S and Mo in molten CaCl₂ (800–900 °C) under argon at 1.0–3.0 V for 1–20 h. On a graphite anode, the product was primarily S (but traces of CS₂ could not yet be excluded by this work) and evaporated from the molten salt, allowing the electrolysis to continue. It then condensed to solid at the lower temperature regions of the system. The anode remained intact after repeated uses. The MoS₂ pellet was highly conducting at high temperatures and could be fast electro-reduced to fine Mo powders (0.1–1.0 μm) in which the S content could be below 1000 ppm. No reduction occurred at voltages below 0.5 V. Partial reduction was seen at 0.5–0.7 V, and converted MoS₂ to a mixture of MoS₂ and Mo₃S₄, or Mo₃S₄ and Mo with the Mo content increasing with the voltage. Cyclic voltammetry of the MoS₂ powder in a Mo-cavity electrode, together with the electrolysis results, revealed the reduction mechanism to include two steps: MoS₂ to Mo₃S₄ at −0.28 V (potential vs. Ag/AgCl), and then to Mo at −0.43 V.     

Electrochemical reduction of nitrogen to ammonia: Progress,challenges and future outlook

Ammonia is an important chemical used in the production of fertilizers. The electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia has emerged to be a potential alternative approach. Here, we provide a short opinion of the current progress and challenges of nitrogen reduction reaction from the recent literature. Different types of electrocatalysts with their performances and design principles are briefly outlined. However, most of the electrocatalysts showed unsatisfactory catalytic performance for NRR because of various factors, such as the competing side reactions and the large thermodynamic energy barrier. Hence, the concept of conducting NRR should be re-evaluated. We provide our opinion on the future possible outlook on how to improve the NRR performance. Alternative external energy input should be coupled with the electrochemical reduction of nitrogen to help with the activation of nitrogen to ammonia. Some possible energy input could be the use of cold plasma and surface plasmon resonance.     

ZnO-ZrO2固溶体催化剂上CO2高选择性加氢制甲醇

CO2引起的气候变化已引起全世界的关注,但同时CO2也是一种可持续的碳资源.将CO2转化为高附加值的燃料或化学品不仅可以解决CO2的问题,还可变废为宝得到有用的化学品.CO2加氢制甲醇是实现这一过程的理想选择之一,因为甲醇不仅是很好的燃料,还可转化得到烯烃、芳烃等高附加值化学品,需要强调的是整个过程所需的氢气是利用太阳能等可再生能源通过光催化、光电催化或电解水制氢得到.使用煤或天然气经合成气用CuZnOAl2O3催化剂合成甲醇已工业化50年左右,甲醇选择性可达99%,但该催化剂应用于CO2加氢制甲醇时,较强的逆水煤气变换副反应致使甲醇选择性只有60%左右,另外,反应生成的水会加速Cu基催化剂的失活.因此,开发新型高选择性催化体系显得尤为必要,世界上很多科学家展开了新型催化剂的研发,如Cu/ZnO/ZrO2,Pd/ZnO,"georgeite"Cu,Cu(Au)/CeOx/TiO2,Ni-Ga,MnOx/Co3O4催化剂等,但这几类催化剂体系上甲醇选择性都不超过60%,CO2加氢制甲醇选择性低的问题一直没有解决.近期,中国科学院大连化学物理研究所李灿院士课题组开发了一种不同于传统金属催化剂的双金属固溶体氧化物催化剂ZnO-ZrO2,在近似工业条件下(5.0 MPa,24000 mL/(g h),H2/CO2=3/1~4/1,320~315oC),当CO2单程转化率超过10%时,甲醇选择性仍保持在90%左右,是目前同类研究中综合水平最好的结果.研究表明,该催化剂的固溶体结构特征提供了双活性中心反应位点,Zn和Zr,其中H2和CO2分别在Zn位和原子相邻的Zr位上活化,在CO2加氢过程中表现出了协同作用,从而可高选择性地生成甲醇.原位红外-质谱同位素实验及DFT理论计算结果表明,表面HCOO*和H3CO*是反应主要的活性中间物种.该催化剂反应连续运行500 h无失活现象,还具有极好的耐烧结稳定性和一定的抗硫能力,表现出了良好的工业应用前景.传统甲醇合成Cu基催化剂要求原料气含硫低于0.5 ppm,而该催化剂的抗硫能力无疑可使原料气净化成本大大降低,在工业应用方面表现出潜在的优势.     

(Pentamethylcyclopentadienyl)(polypyridyl) rhodium and iridium complexes as electrocatalysts for the reduction of protons to dihydrogen and the hydrogenation of organics

The ability of [(η⁵-C₅Me₅)M^III(L)Cl]⁺ complexes (M = Rh and Ir. L = 2,2′-bipyridine and 1, 10-phenanthroline) to act as electrocatalysts for the hydrogenation of unsaturated organic substrates has been examined in homogeneous acetonitrile solution, using formic acid as a proton source, as well as in aqueous electrolytes with electrodes modified by oxidative electropolymerization of pyrrole-substituted Rh(III) and Ir(III) complexes. The hydrogenation process involves the formation of an electrogenerated hydrido complex, followed by the insertion of the substrate in the metal-hydride bond. It appears that rhodium complexes are better catalysts than the iridium ones, and that their immobilization onto an electrode surface decreases their catalytic activity.     

Novel ultrasonic-modified MnOx/TiO2 for low-temperature selective catalytic reduction (SCR) of NO with ammonia

A novel ultrasonic-modified MnO(x)/TiO(2) catalyst was prepared and compared with two different kinds of MnO(x)/TiO(2) catalysts in the process of low-temperature selective catalytic reduction of NO with NH(3). The physicochemical properties of the catalysts were studied by using various characterization techniques, such as Brunauer-Emmett-Teller (BET) surface measurement, X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ultrasonic-modified process introduced ultrasound in the solution impregnation step of traditional impregnation method for MnO(x)/TiO(2) catalyst preparation. In this study, ultrasonic process significantly improved the dispersion behavior and surface acid property of manganese oxide on TiO(2) as well as the catalytic activity, especially at temperature below 120°C. The NO conversion could reach 90% at 100°C. For the novel ultrasonic-modified catalyst, the combination analysis of XRD and HRTEM confirmed that manganese oxide was in a highly dispersed state and Ti and Mn had strong interaction. Furthermore, in situ FT-IR studies revealed that there were significant amounts of Lewis acidity and high Mn atom concentration on the surface of the novel catalysts.     

Preparation of trimetallic electrocatalysts by one-step co-electrodeposition and efficient CO2 reduction to ethylene

Use of multi-metallic catalysts to enhance reactions is an interesting research area, which has attracted much attention. In this work, we carried out the first work to prepare trimetallic electrocatalysts by a one-step co-electrodeposition process. A series of Cu–X–Y (X and Y denote different metals) catalysts were fabricated using this method. It was found that Cu₁₀La₁Cs₁ (the content ratio of Cu²⁺, La³⁺, and Cs⁺ in the electrolyte is 10 : 1 : 1 in the deposition process), which had an elemental composition of Cu₁₀La_0.16Cs_0.14 in the catalyst, formed a composite structure on three dimensional (3D) carbon paper (CP), which showed outstanding performance for CO₂ electroreduction reaction (CO₂RR) to produce ethylene (C₂H₄). The faradaic efficiency (FE) of C₂H₄ could reach 56.9% with a current density of 37.4 mA cm⁻² in an H-type cell, and the partial current density of C₂H₄ was among the highest ones up to date, including those over the catalysts consisting of Cu and noble metals. Moreover, the FE of C₂₊ products (C₂H₄, ethanol, and propanol) over the Cu₁₀La₁Cs₁ catalyst in a flow cell reached 70.5% with a high current density of 486 mA cm⁻². Experimental and theoretical studies suggested that the doping of La and Cs into Cu could efficiently enhance the reaction efficiency via a combination of different effects, such as defects, change of electronic structure, and enhanced charge transfer rate. This work provides a simple method to prepare multi-metallic catalysts and demonstrates a successful example for highly efficient CO₂RR using non-noble metals.

Trimetallic Cu₁₀La₁Cs₁ catalysts prepared via a one-step co-electrodeposition strategy can act as a robust electrocatalyst for CO₂RR to C₂H₄.     

Carbon dioxide-expanded liquid substrate phase: an effective medium for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol

It has been shown that CO(2)-expanded cinnamaldehyde liquid phase is a unique and effective medium for cinnamaldehyde hydrogenation to cinnamyl alcohol, due to interactions between the C[double bond, length as m-dash]O group of the substrate and CO(2) molecules and increased solubility of H(2).     

Reaction kinetics of the selective liquid phase hydrogenation of styrene oxide to β-phenethyl alcohol

Liquid phase hydrogenation of styrene oxide using 1% Pd/C and NaOH as a promoter was found to give selectively β-phenethyl alcohol (PEA) under very mild conditions (313–333 K; 0.68–5.5 MPa). The kinetics of this system was investigated by collecting initial rate data in a batch slurry reactor. Rate of hydrogenation was found to decrease beyond a certain concentration of both hydrogen (>3 MPa) and styrene oxide (>0.5 kmol/m³). A Langmuir–Hinshelwood type rate equation has been proposed based on the initial rate data in the kinetic regime. The model predictions agree very well with the experimentally observed concentration–time data indicating the applicability of the proposed rate model.     

Novel evidence for the selective behaviour of tungsten carbide in liquid phase heterogeneous catalytic hydrogenation

Liquid (aqueous) phase catalytic hydrogenation of compounds containing two oxo-groups in -position (biacetyl, glyoxal, alloxan) was studied in the presence of tungsten carbide catalyst. It has been shown that only one of the oxo-groups is affected in the course of the process and is transformed into a >CH–OH group. Comparative studies carried out in the presence of platinum catalyst attest the selective behaviour of tungsten carbide.

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- - (, , ). , >C=O >CH–OH, . .

     

Novel non-hydrolytic synthesis of a V2O5-TiO2 xerogel for the selective catalytic reduction of NOx by ammonia

A vanadia-titania mesoporous xerogel (10.5 wt% V(2)O(5)) was prepared from chloride precursors using a one-step non-hydrolytic sol-gel route and subsequent drying at ambient pressure; after calcination at 773 K for 5 h no crystalline V(2)O(5) was detected and the resulting mixed oxide exhibited remarkable activity in the selective reduction of NO with NH(3).     

Recent advances in bimetallic electrocatalysts for oxygen reduction: design principles,structure-function relations and active phase elucidation

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二维材料电催化剂的构建及其CO2还原应用的研究进展

近年来,随着温室效应即全球变暖引发的环境问题越来越严峻,因此,CO2转化与再生引起了科学界的广泛关注,其中备受关注的是电催化CO2还原。而二维材料电催化剂可以将CO2还原为高附加值的多碳化合物,但催化剂的合成设计以及理论研究有待更多的研究。从发现石墨烯开始,二维材料的其他超薄层状结构的广泛研究逐渐出现。本文重点综述了石墨烯、MXenes、金属氧化物、二维MOFs和过渡金属硫族化合物等二维材料的构建以及其CO2还原电催化技术应用方面的最新进展,并简要的介绍了二维材料的分类和制备方法。讨论了电催化CO2还原的基本原理以及反应途径。指出了二维材料电催化剂面临的机遇和挑战,旨在对二维材料电催化剂的合成以及应用提供一些新的思路。