scholarly journals Selective reduction of CO to acetaldehyde with CuAg electrocatalysts

2020 ◽  
Vol 117 (23) ◽  
pp. 12572-12575 ◽  
Author(s):  
Lei Wang ◽  
Drew C. Higgins ◽  
Yongfei Ji ◽  
Carlos G. Morales-Guio ◽  
Karen Chan ◽  
...  
Keyword(s):  
Density Functional ◽  
Selective Reduction ◽  
Density Functional Theory Calculations ◽  
Hydrogen Electrode ◽  
Reaction Conditions ◽  
Faradaic Efficiency ◽  
Catalyst Composition ◽  
Alkaline Reaction ◽  
Fuels And Chemicals ◽  
Co Reduction

Electrochemical CO reduction can serve as a sequential step in the transformation of CO2into multicarbon fuels and chemicals. In this study, we provide insights on how to steer selectivity for CO reduction almost exclusively toward a single multicarbon oxygenate by carefully controlling the catalyst composition and its surrounding reaction conditions. Under alkaline reaction conditions, we demonstrate that planar CuAg electrodes can reduce CO to acetaldehyde with over 50% Faradaic efficiency and over 90% selectivity on a carbon basis at a modest electrode potential of −0.536 V vs. the reversible hydrogen electrode. The Faradaic efficiency to acetaldehyde was further enhanced to 70% by increasing the roughness factor of the CuAg electrode. Density functional theory calculations indicate that Ag ad-atoms on Cu weaken the binding energy of the reduced acetaldehyde intermediate and inhibit its further reduction to ethanol, demonstrating that the improved selectivity to acetaldehyde is due to the electronic effect from Ag incorporation. These findings will aid in the design of catalysts that are able to guide complex reaction networks and achieve high selectivity for the desired product.

scholarly journals Fast operando spectroscopy tracking in situ generation of rich defects in silver nanocrystals for highly selective electrochemical CO2 reduction

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xinhao Wu ◽  
Yanan Guo ◽  
Zengsen Sun ◽  
Fenghua Xie ◽  
Daqin Guan ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Co2 Reduction ◽  
Density Functional Theory Calculations ◽  
Defect Concentration ◽  
Hydrogen Electrode ◽  
Efficient Catalyst ◽  
Faradaic Efficiency ◽  
Electrochemical Co2 Reduction ◽  
Cell Reactor

AbstractElectrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. Here, we report an efficient catalyst (Ag-D) with suitable defect concentration operando formed during ECR within several minutes. Utilizing the powerful fast operando X-ray absorption spectroscopy, the evolving electronic and crystal structures are unraveled under ECR condition. The catalyst exhibits a ~100% faradaic efficiency and negligible performance degradation over a 120-hour test at a moderate overpotential of 0.7 V in an H-cell reactor and a current density of ~180 mA cm−2 at −1.0 V vs. reversible hydrogen electrode in a flow-cell reactor. Density functional theory calculations indicate that the adsorption of intermediate COOH could be enhanced and the free energy of the reaction pathways could be optimized by an appropriate defect concentration, rationalizing the experimental observation.

scholarly journals Colloidal silver diphosphide (AgP2) nanocrystals as low overpotential catalysts for CO2 reduction to tunable syngas

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Hui Li ◽  
Peng Wen ◽  
Dominique S. Itanze ◽  
Zachary D. Hood ◽  
Xiao Ma ◽  
...  
Keyword(s):  
Density Functional ◽  
Co2 Reduction ◽  
Intermediate Formation ◽  
Density Functional Theory Calculations ◽  
Photocurrent Density ◽  
Faradaic Efficiency ◽  
Onset Potential ◽  
Fold Reduction ◽  
Co Conversion ◽  
Co Reduction

AbstractProduction of syngas with tunable CO/H2 ratio from renewable resources is an ideal way to provide a carbon-neutral feedstock for liquid fuel production. Ag is a benchmark electrocatalysts for CO2-to-CO conversion but high overpotential limits the efficiency. We synthesize AgP2 nanocrystals (NCs) with a greater than 3-fold reduction in overpotential for electrochemical CO2-to-CO reduction compared to Ag and greatly enhanced stability. Density functional theory calculations reveal a significant energy barrier decrease in the formate intermediate formation step. In situ X-ray absorption spectroscopy (XAS) shows that a maximum Faradaic efficiency is achieved at an average silver valence state of +1.08 in AgP2 NCs. A photocathode consisting of a n+p-Si wafer coated with ultrathin Al2O3 and AgP2 NCs achieves an onset potential of 0.2 V vs. RHE for CO production and a partial photocurrent density for CO at −0.11 V vs. RHE (j−0.11, CO) of −3.2 mA cm−2.

scholarly journals Tracking structural evolution: operando regenerative CeOx/Bi interface structure for high-performance CO2 electroreduction

2020 ◽  
Author(s):  
Ruichao Pang ◽  
Pengfei Tian ◽  
Hongliang Jiang ◽  
Minghui Zhu ◽  
Xiaozhi Su ◽  
...  
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Structural Evolution ◽  
Density Functional Theory Calculations ◽  
Active Phase ◽  
Interface Structure ◽  
Operating Conditions ◽  
Faradaic Efficiency ◽  
Co2 Electroreduction ◽  
Water Activation

Abstract Unveiling the structural evolution and working mechanism of catalysts under realistic operating conditions is crucial for the design of efficient electrocatalysts for CO2 electroreduction, yet remains highly challenging. Here, by virtue of operando structural measurements at multiscale levels, it is identified under CO2 electroreduction conditions that an as-prepared CeO2/BiOCl precatalyst gradually evolves into CeOx/Bi interface structure with enriched Ce3+ species, which serves as the real catalytically active phase. The derived CeOx/Bi interface structure compared to pure Bi counterpart delivers substantially enhanced performance with a formate Faradaic efficiency approaching 90% for 24 hours in a wide potential window. The formate Faradaic efficiency can be further increased by using isotope D2O instead of H2O. Density functional theory calculations suggest that the regenerative CeOx/Bi interfacial sites can not only promote water activation to increase local *H species for CO2 protonation appropriately, but also stabilize the key intermediate *OCHO in formate pathway.

scholarly journals Silver-catalysed azide–alkyne cycloaddition (AgAAC): assessing the mechanism by density functional theory calculations

2016 ◽  
Vol 3 (9) ◽  
pp. 160090 ◽  
Author(s):  
Biswadip Banerji ◽  
K. Chandrasekhar ◽  
Sunil Kumar Killi ◽  
Sumit Kumar Pramanik ◽  
Pal Uttam ◽  
...  
Keyword(s):  
Density Functional ◽  
Click Reaction ◽  
Cycloaddition Reaction ◽  
Triazole Ring ◽  
Density Functional Theory Calculations ◽  
Dipolar Cycloaddition ◽  
Reaction Conditions ◽  
Functional Theory ◽  
Click Reactions ◽  
Counter Ions

‘Click reactions’ are the copper catalysed dipolar cycloaddition reaction of azides and alkynes to incorporate nitrogens into a cyclic hydrocarbon scaffold forming a triazole ring. Owing to its efficiency and versatility, this reaction and the products, triazole-containing heterocycles, have immense importance in medicinal chemistry. Copper is the only known catalyst to carry out this reaction, the mechanism of which remains unclear. We report here that the ‘click reactions’ can also be catalysed by silver halides in non-aqueous medium. It constitutes an alternative to the well-known CuAAC click reaction. The yield of the reaction varies on the type of counter ion present in the silver salt. This reaction exhibits significant features, such as high regioselectivity, mild reaction conditions, easy availability of substrates and reasonably good yields. In this communication, the findings of a new catalyst along with the effect of solvent and counter ions will help to decipher the still obscure mechanism of this important reaction.

scholarly journals Exposed facet-controlled N2 electroreduction on distinct Pt3Fe nanostructures of nanocubes, nanorods and nanowires

2020 ◽  
Author(s):  
Wu Tong ◽  
Bolong Huang ◽  
Pengtang Wang ◽  
Qi Shao ◽  
Xiaoqing Huang
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Active Surface ◽  
Reduction Reaction ◽  
Active Surface Area ◽  
Hydrogen Electrode ◽  
Functional Theory ◽  
Effective Strategies ◽  
Exposed Facet ◽  
Coupling Correlation

Abstract Understanding the correlation between exposed surfaces and performances of controlled nanocatalysts can aid effective strategies to enhance electrocatalysis, but this is as yet unexplored for the nitrogen reduction reaction (NRR). Here, we first report controlled synthesis of well-defined Pt3Fe nanocrystals with tunable morphologies (nanocube, nanorod and nanowire) as ideal model electrocatalysts for investigating the NRR on different exposed facets. The detailed electrocatalytic studies reveal that the Pt3Fe nanocrystals exhibit shape-dependent NRR electrocatalysis. The optimized Pt3Fe nanowires bounded with high-index facets exhibit excellent selectivity (no N2H4 is detected), high activity with NH3 yield of 18.3 μg h−1 mg−1cat (0.52 μg h−1 cm−2ECSA; ECSA: electrochemical active surface area) and Faraday efficiency of 7.3% at −0.05 V versus reversible hydrogen electrode, outperforming the {200} facet-enclosed Pt3Fe nanocubes and {111} facet-enclosed Pt3Fe nanorods. They also show good stability with negligible activity change after five cycles. Density functional theory calculations reveal that, with high-indexed facet engineering, the Fe-3d band is an efficient d-d coupling correlation center for boosting the Pt 5d-electronic exchange and transfer activities towards the NRR.

scholarly journals Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction

2020 ◽  
Vol 118 (2) ◽  
pp. e2010868118
Author(s):  
Peng Zhu ◽  
Chuan Xia ◽  
Chun-Yen Liu ◽  
Kun Jiang ◽  
Guanhui Gao ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Density Functional ◽  
Liquid Electrolyte ◽  
Liquid Fuels ◽  
Acid Solutions ◽  
Faradaic Efficiency ◽  
Continuous Generation ◽  
Liquid Products ◽  
Cu Catalyst ◽  
Co Reduction

Electrochemical CO2 or CO reduction to high-value C2+ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm−2, ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor.

scholarly journals Graphdiyne based metal atomic catalysts for synthesizing ammonia

2020 ◽  
Author(s):  
Huidi Yu ◽  
Yurui Xue ◽  
Lan Hui ◽  
Chao Zhang ◽  
Yan Fang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electron Transfer ◽  
Density Functional ◽  
Reaction Pathway ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Faradaic Efficiency ◽  
Nitrogen Reduction ◽  
Strongly Coupled ◽  
Neutral Media

Abstract Exploring new catalysts for nitrogen reduction at ambient pressures and temperatures with ultrahigh ammonia (NH3) yield and selectivity is still a giant challenge. In this work, atomic catalysts with separated Pd atoms on graphdiyne (Pd-GDY) have been synthesized and show fascinating electrocatalytic properties for nitrogen reduction. Outstandingly, the catalyst shows the highest average NH3 yield of 4.45 ± 0.30 mgNH3 mgPd−1 h−1, almost tens of orders larger than previously reported ones, and 100% reaction selectivity in neutral media. And Pd-GDY exhibits almost no decreases in the NH3 yield and Faradaic efficiency. Density functional theory calculations show that the reaction pathway prefers to perform at the (Pd, C1, C2) active area due to the strongly coupled (Pd, C1, C2) which elevates the selectivity via enhanced electron-transfer. By adjusting the p-d coupling accurately, the reduction of self-activated nitrogen is promoted by anchoring atom selection, and the side effects are minimized.

scholarly journals The role of oxygen and water on molybdenum nanoclusters for electro catalytic ammonia production

2014 ◽  
Vol 5 ◽  
pp. 111-120 ◽  
Author(s):  
Jakob G Howalt ◽  
Tejs Vegge
Keyword(s):  
Density Functional ◽  
Proton Conductor ◽  
Density Functional Theory Calculations ◽  
Nitrogen Adsorption ◽  
Oxygen Adsorption ◽  
Ammonia Production ◽  
Hydrogen Electrode ◽  
Theoretical Investigations ◽  
Lower Oxygen

The presence of water often gives rise to oxygen adsorption on catalyst surfaces through decomposition of water and the adsorbed oxygen or hydroxide species often occupy important surfaces sites, resulting in a decrease or a total hindrance of other chemical reactions taking place at that site. In this study, we present theoretical investigations of the influence of oxygen adsorption and reduction on pure and nitrogen covered molybdenum nanocluster electro catalysts for electrochemical reduction of N2 to NH3 with the purpose of understanding oxygen and water poisoning of the catalyst. Density functional theory calculations are used in combination with the computational hydrogen electrode approach to calculate the free energy profile for electrochemical protonation of O and N2 species on cuboctahedral Mo13 nanoclusters. The calculations show that the molybdenum nanocluster will preferentially bind oxygen over nitrogen and hydrogen at neutral bias, but under electrochemical reaction conditions needed for nitrogen reduction, oxygen adsorption is severely weakened and the adsorption energy is comparable to hydrogen and nitrogen adsorption. The potentials required to reduce oxygen off the surface are −0.72 V or lower for all oxygen coverages studied, and it is thus possible to (re)activate (partially) oxidized nanoclusters for electrochemical ammonia production, e.g., using a dry proton conductor or an aqueous electrolyte. At lower oxygen coverages, nitrogen molecules can adsorb to the surface and electrochemical ammonia production via the associative mechanism is possible at potentials as low as −0.45 V to −0.7 V.

scholarly journals Chemoselective catalytic hydrodefluorination of trifluoromethylalkenes towards mono-/gem-di-fluoroalkenes under metal-free conditions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jingjing Zhang ◽  
Jin-Dong Yang ◽  
Jin-Pei Cheng
Keyword(s):  
Density Functional Theory ◽  
Fluorine Atom ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Reaction Conditions ◽  
Functional Theory ◽  
Stepwise Mechanism ◽  
Metal Free ◽  
Great Demand ◽  
Good Group

AbstractFluorine-containing moieties show significant effects in improving the properties of functional molecules. Consequently, efficient methods for installing them into target compounds are in great demand, especially those enabled by metal-free catalysis. Here we show a diazaphospholene-catalyzed hydrodefluorination of trifluoromethylalkenes to chemoselectively construct gem-difluoroalkenes and terminal monofluoroalkenes by simple adjustment of the reactant stoichiometry. This metal-free hydrodefluorination features mild reaction conditions, good group compatibility, and almost quantitative yields for both product types. Stoichiometric experiments indicated a stepwise mechanism: hydridic addition to fluoroalkenes and subsequent β-F elimination from hydrophosphination intermediates. Density functional theory calculations disclosed the origin of chemoselectivity, regioselectivity and stereoselectivity, suggesting an electron-donating effect of the alkene-terminal fluorine atom.

scholarly journals Solvent-controlled photocatalytic divergent cyclization of alkynyl aldehydes: access to cyclopentenones and dihydropyranols

2021 ◽  
Author(s):  
Haiqian Zhu ◽  
Hanliang Zheng ◽  
Junhua Zhang ◽  
Jian Feng ◽  
Lichun Kong ◽  
...  
Keyword(s):  
Density Functional ◽  
Hydrogen Transfer ◽  
Density Functional Theory Calculations ◽  
Bioactive Molecules ◽  
Molecular Scaffolds ◽  
Reaction Conditions ◽  
Direct Construction ◽  
Functional Theory ◽  
Alkoxy Radicals ◽  
Powerful Strategy

Abstract Divergent synthesis is a powerful strategy for the fast assembly of different molecular scaffolds from the identical starting materials. We describe here a novel solvent-controlled photocatalytic divergent cyclization of alkynyl aldehydes with sulfonyl chlorides for the direct construction of highly functionalized cyclopentenones and dihydropyranols that widely exist in bioactive molecules and natural products. Density functional theory calculations suggest that an unprecedented N,N-dimethylacetamide-assisted 1,2-hydrogen transfer of alkoxy radicals is responsible for the cyclopentenone formation, whereas a C-C cleavage accounts for the selective production of dihydropyranols in acetonitrile. Given the simple and mild reaction conditions, excellent functional group compatibility, forming up to four chemical bonds, and tunable selectivity, it may find wide applications in synthetic chemistry.

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