Stability Of Cu Research Articles

The Surprising Stability of Cu3(btc)2 Metal–Organic Framework under Steam Flow at High Temperature

It is widely admitted that metal–organic frameworks (MOFs) are water sensitive and that high temperatures accelerate the hydrolysis phenomena and the collapse of the porous network. We have investigated here the resistance of the prototypical HKUST-1 MOF under steam flow at temperatures ranging from RT to 200 °C. Surprisingly, the porous framework is not degraded at 200 °C, whereas temperatures close to 100 °C lead to the total destruction of the MOF. This unexpected behavior is assigned to the extended interaction of water with the porous framework at temperature about 100 °C, whereas above 150 °C the transient interactions between gaseous water and the HKUST-1 framework limit the decomposition process.

Effect of Manganese Oxide over Cu–Mn-Based Oxygen Carriers for Chemical Looping Combustion

This study examined the effects of Mn on Cu-Mn-based mixed metal oxides used as oxygen transfer particles in the chemical looping combustion process. Chemical looping combustion of fuel is induced by the oxygen contained in the metal oxide. The oxidation reaction of the metal oxide particles reduced in the fuel reactor occurs in the air reactor. The metal oxide, which allows oxygen transfer, circulates between the fuel reactor to air reactor and supplies oxygen in the fuel reactor. Both reactors are operated at high temperatures (>850 °C) and the heat of reaction is recovered to produce electricity and heat. Oxygen carriers must have high thermal stability, high oxygen capacity, and rapid transfer rate, and should have a high attrition resistance because they are used in a circulating fluidized bed reactor. Cu exhibits high oxygen transfer rates, but it cannot be used for chemical looping combustion under high temperature conditions because of its low thermal stability. In this study, Mn was mixed to improve the thermal stability of the Cu component and the effect of these was investigated. This study examined copper metal oxide and the stability of Cu according to the temperature that the spinel structure had been synthesized. As a result, the spinel structure was well maintained in the oxidation-reduction cyclic-repeated tests and the migration of Cu was not severe. The spinel structure had high durability. Overall, Mn inhibits the migration of Cu because it forms a spinel structure with Cu.

Effect of In-Situ Dehydration on Activity and Stability of Cu–Ni–K2O/Diatomite as Catalyst for Direct Synthesis of Dimethyl Carbonate

An in-situ dehydrating system built in a continuous flow fixed-bed bubbling reactor for direct synthesis of dimethyl carbonate (DMC) was designed. 3A molecular sieve (MS) was selected as the ideal dehydrating agent and the water trapping efficiency was studied. The effect of dehydrating agent/catalyst ratio, the dehydrating temperature and pressure, as well as the space velocity on the direct DMC synthesis catalyzed by K2O-promoted Cu–Ni was further investigated. These results demonstrated that 3A MS could effectively dehydrate the reaction system at the optimal conditions of 120 °C and 1.0 MPa with gas space velocity (GHSV) of 600 h−1, thereby greatly shifting the reaction equilibrium toward high DMC yield. Higher DMC yield of 13% was achieved compared with undehydrated reaction. Moreover, the catalyst can be highly stabilized by 3A MS dehydration with stable performs over 22 h.

Bending stability of Cu0.4CrO2—A transparent p-type conducting oxide for large area flexible electronics

The current best performing p-type transparent conducting oxides are typically highly crystalline materials, deposited at high temperatures, and hence incompatible with the drive to low cost flexible electronics. We investigated a nanocrystalline, copper deficient CuxCrO2, deposited at low temperatures upon a flexible polyimide substrate. The as-deposited film without post annealing has an electrical conductivity of 6Scm−1. We demonstrate that this p-type transparent oxide retains its excellent electrical conductivity under tensile strain, withstanding more than one thousand bending cycles without visible cracks or degradation in electrical properties. In contrast, compressive strain is shown to lead to an immediate reduction in conductivity which we attribute to a de-lamination of the thin film from the substrate.

Hydrogenation of methyl levulinate to γ‐valerolactone over Cu─Mg oxide using MeOH as in situ hydrogen source

AbstractBACKGROUNDγ‐Valerolactone (GVL) is a versatile biomass‐derived platform molecule that could serve as a building block to produce chemicals, materials and fuels, but the production of GVL from biomass via a cost‐competitive method is challenging. In this contribution, a robust Cu─Mg oxide was prepared as an efficient bifunctional catalyst for both H2 production by MeOH reforming and hydrogenation of methyl levulinate (ML) to GVL in MeOH medium.RESULTSCu0.87Mg0.13Ox prepared by a urea hydrolysis method offered a GVL yield up to 90.6% at 220°C in 4 h without external hydrogen. This catalyst could be reused for at least seven consecutive cycles without loss of its activity. Notably, Cu0.87Mg0.13Ox also provided nearly 70% GVL yield in methanolysis products of cellulose in the presence of humins. Characterization of the catalyst indicates that the incorporation of MgO greatly facilitates the stabilization of Cu+ species that possess a better catalytic performance in ML hydrogenation compared with metallic Cu.CONCLUSIONThis robust Cu0.87Mg0.13Ox could greatly contribute to develop a highly facile and desirable two‐step strategy for GVL production from cellulose, through the integration of ML production by methanolysis of cellulose, H2 formation by MeOH reforming and ML hydrogenation in MeOH medium. © 2018 Society of Chemical Industry

Stability of Cu(II) and Zn(II) Complexes with Pyridinecarbohydrazones of Pyridoxal-5-phosphate in Aqueous Solution

Composition of coordination compounds formed by copper(II) or zinc(II) ions and pyridine-2-, -3-, and -4-carbohydrazones of pyridoxal-5-phosphate in aqueous solution at 298.2 K, рН 7.4, I 0.25 has been studied by means of spectrophotometry. Conditional constants of the complexes stability have been determined. Cu(II) ions formed more stable ML2 coordination compounds in comparison with Zn(II), zinc(II) ions are efficiently bound to the derivative of picolinic acid hydrazide to form the ML complex.

Why Could the Nature of Surface Facets Lead to Differences in the Activity and Stability of Cu2O-Based Electrocatalytic Sensors?

By a combination of theoretical and experimental design, we unraveled the effect of {111} and {100} surface facets on the electrocatalytic sensing activities and stabilities of metal oxides by employing Cu2O crystals as a model substrate and glucose as the analyte. We started by theoretically investigating the potential energy curves for the glucose interaction with the Cu2O {111} and {100} surface facets. We found that the glucose interaction energy was significantly higher for the {100} facets than for the {111} facets. Then, we experimentally observed that their electrocatalytic sensing performance displayed shape-dependent behavior. While the catalytic activities followed the order cubes > cuboctahedrons > octahedrons, their stabilities showed the opposite trend. The higher catalytic activity enabled by the {100} facets is explained by their stronger interaction with glucose. On the other hand, the higher stability allowed by the {111} facets is justified by their lower concentration of oxygen vacanci...

Influence of post-deposition annealing on structural, morphological and optical properties of copper (II) acetylacetonate thin films

In this study, the effect of thermal annealing under vacuum conditions on structural, morphological and optical properties of thermally evaporated copper (II) acetylacetonate, cu(acac)2, thin films were investigated. The copper (II) acetylacetonate thin films were deposited using thermal evaporation technique at vacuum pressure ~1 × 10−5 mbar. The deposited films were thermally annealed at 323, 373, 423, and 473 K for 2 h in vacuum. The thermogravimetric analysis of cu(acac)2 powder indicated a thermal stability of cu(acac)2 up to 423 K. The effects of thermal annealing on the structural properties of cu(acac)2 were evaluated employing X-ray diffraction method and the analysis showed a polycrystalline nature of the as-deposited and annealed films with a preferred orientation in [1¯01] direction. Fourier transformation infrared (FTIR) technique was used to negate the decomposition of copper (II) acetylacetonate during preparation or/and annealing up to 423 K. The surface morphology of the prepared films was characterized by means of field emission scanning electron microscopy (FESEM). A significant enhancement of the morphological properties of cu(acac)2 thin films was obtained till the annealing temperature reaches 423 K. The variation of optical constants that estimated from spectrophotometric measurements of the prepared thin films was investigated as a function of annealing temperature. The annealing process presented significantly impacted the nonlinear optical properties such as third-order optical susceptibility χ(3) and nonlinear refractive index n2 of cu(acac)2 thin films.

Cubic phase stability, optical and magnetic properties of Cu-stabilized zirconia nanocrystals

By means of experimental and ab initio investigations, we report on the cubic phase stability of Cu doped zirconia (ZrO2) at room temperature, and further characterize its structural, optical and magnetic properties. Various compositions of Zr1−xCuxO2 (0.01 ⩽ x ⩽ 0.25) nanocrystallites of average size ∼16 nm were synthesized using co-precipitation technique. Thermal analysis and kinetics of crystallization revealed that the cubic phase at ambient temperature can be stabilized by using a critical calcination temperature of 500 °C for 8 h in air and a critical composition of . For x < xc, some undigested monoclinic phase of ZrO2 exists together with the cubic structure. However, for x > xc, the monoclinic CuO emerges as a secondary phase with shrinkage of unit-cell volume with increasing the Cu content. At x = 0.05 and 500 °C calcination temperature, we observe a high degree of cubic crystallinity which breaks down into monoclinic phase with increasing calcination temperature beyond 550 °C. Electron magnetic resonance studies provide evidence for the substitution of Cu2+ (2D5/9,3d9) ions at Zr4+ sites with g, g and average ga = ( + 2)/3 ∼ 2.1. The temperature dependence of magnetic susceptibility measurements from 2 K to 300 K exhibits Curie–Weiss behaviour whose analysis using ga = 2.1 and spin S = 1/2 yields x = 0.028 and x = 0.068 for the nominal x = 0.05 and x = 0.20 samples, respectively. This magnetic analysis confirms the findings from x-ray diffraction that only a part of Cu is successfully doped into cubic phase of Cu-doped ZrO2. The optical bandgap decreases with increasing x, which is due to the emergence of Cu-d states at Fermi-level near the valence bands, thus making Cu-doped zirconia a hole doped (p-type) semiconductor.

(Invited) Chain Length Variation to Probe Mechanism of Accelerator Additives in Copper Electrodeposition

We evaluate the mechanism of Cu deposition in the presence of additives of different chain lengths to provide design guidelines for electroplating additives in the specific context of Cu electroplating. The effects of chloride and a series of sulfonic acid additives were assessed using a combination of electrochemical and Raman spectroscopic methods. Rotating disk linear sweep voltammetry revealed the influence of these additives on the bulk concentration of Cu+ and on the exchange current densities of the reduction of Cu2+/Cu+ and Cu+/Cu. We then used in situ shell-isolated, nanoparticle-enhanced Raman spectroscopy to correlate the additives’ effects on deposition kinetics with their chemical structures at the electrode surface. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: 1) direct tethering of mercaptoalkylsulfonate species to the electrode, 2) partial desolvation of Cu2+ by the sulfonate group to minimize its solvent reorganization energy, and 3) stabilization of Cu+ adjacent to the electrode surface by addition of halide.

Stability of Cu–Mn bimetal catalysts based on different zeolites for NOx removal from diesel engine exhaust

Cu–Mn bimetal catalysts were prepared to remove nitrogen oxides (NOx) from diesel engine exhaust at low temperatures. At a Cu/Mn ratio of 3:2, the NOx conversions at 200 °C reached 65% and 90% on Cu–Mn/ZSM-5 and Cu–Mn/SAPO-34, respectively. After a hydrothermal treatment and reaction in the presence of C3H6, the activity of Cu–Mn/SAPO-34 was more stable than that of Cu–Mn/ZSM-5. No obvious variations in the crystal structure or dealumination were observed, whereas the physical structure was best maintained in Cu–Mn/SAPO-34. The atomic concentration of Cu on the surface of Cu–Mn/SAPO-34 was quite stable, and the consumption of octahedrally coordinated Cu2+ could be recovered. Conversely, the proportion of octahedrally coordinated Cu2+ on the surface of Cu–Mn/ZSM-5 significantly decreased. Therefore, besides the structure, the redox cycle between Cu+ and octahedrally coordinated Cu2+ played an important role in the stability of the catalysts.

Atomically Dispersed Co and Cu on N-Doped Carbon for Reactions Involving C–H Activation

Atomically dispersed Co(II) cations coordinated to nitrogen in a carbon matrix (Co-N-C) catalyze oxidative dehydrogenation of benzyl alcohol in water with a specific activity approaching that of supported Pt nanoparticles. Whereas Cu(II) cations in N-doped carbon also catalyze the reaction, they are about an order of magnitude less active compared with Co(II) cations. Results from X-ray absorption spectroscopy suggest that oxygen is also bound to N-coordinated Co(II) sites but that it can be partially removed by H2 treatments at 523–750 K. The N-coordinated Co(II) sites remained cationic in H2 up to 750 K, and these stable sites were demonstrated to be active for propane dehydrogenation. In situ characterization of Cu(II) in N-doped carbon revealed that reduction of the metal in H2 started at about 473 K, indicating a much lower thermal stability of Cu(II) in H2 relative to Co(II). The demonstrated high catalytic activity and thermal stability of Co-N-C in reducing environments suggests that this material...

Reduced Graphene Oxide as a Catalyst Binder: Greatly Enhanced Photoelectrochemical Stability of Cu(In,Ga)Se2 Photocathode for Solar Water Splitting

AbstractThe photoelectrochemical (PEC) properties of a Cu(In,Ga)Se2 (CIGS) photocathode covered with reduced graphene oxide (rGO) as a catalyst binder for solar‐driven hydrogen evolution are reported. Chemically reduced rGO with various concentrations is deposited as an adhesive interlayer between CIGS/CdS and Pt. PEC characteristics of the CIGS/CdS/rGO/Pt are improved compared to the photocathode without rGO due to enhancement of charge transfer via efficient lateral distribution of photogenerated electrons by conductive rGO to the Pt. More importantly, the introduction of rGO to the CIGS photocathode significantly enhances the PEC stability; in the absence of rGO, a rapid loss of PEC stability is observed in 2.5 h, while the optimal rGO increases the PEC stability of the CIGS photocathode for more than 7 h. Chemical and structural characterizations show that the loss of the Pt catalyst is one of the main reasons for the lack of long‐term PEC stability; the introduction of rGO, which acts as a binder to the Pt catalysts by providing anchoring sites in the rGO, results in complete conservation of the Pt and hence much enhanced stability. Multiple functionality of rGO as an adhesive interlayer, an efficient charge transport layer, a diffusion barrier, and protection layer is demonstrated.

Ceria nanoparticles shape effects on the structural defects and surface chemistry: Implications in CO oxidation by Cu/CeO2 catalysts

Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.

Distribution and mobility of exogenous copper as influenced by aging and components interactions in three Chinese soils.

Copper contamination of soils is a global environmental problem. Soil components (organic matter, clay minerals, and microorganisms) and retention time can govern the adsorption, fixation, and distribution of copper. This study evaluated the interaction effects of soil components and aging on the distribution of exogenous copper. Three typical Chinese soils (Ultisol, Alfisol, and Histosol) were collected from Hunan, Henan, and Heilongjiang Provinces. Soils were incubated with rice straw (RS) and engineered bacteria (Pseudomonas putida X4/pIME) in the presence of exogenous copper for 12months. Sequential extraction was employed to obtain the distribution of Cu species in soils, and the mobility factors of Cu were calculated. The relationships between soil properties and Cu fractions were analyzed with stepwise multiple linear regression. The results show that organic carbon plays a more important role in shaping the distribution of relatively mobile Cu, and iron oxides can be more critical in stabilizing Cu species in soils. Our results suggest that organic matter is the most important factor influencing copper partitioning in Ultisols, while iron oxides are more significant in Alfisols. The mobility of exogenous Cu in soils depends largely on organic carbon, amorphous Fe, and aging. The introduction of both rice straw and rice straw + engineered bacteria enhanced the stabilization of Cu in all the three soils during aging process. The introduction of bacteria could reduce copper mobility, which was indicated by the lowest mobility factors of Cu for the treatment with bacteria in Black, Red, and Cinnamon soils at the first 4, 8, and 8months, respectively. Different measures should be taken into account regarding the content of organic matter and iron oxides depending on soil types for the risk assessment and remediation of Cu-contaminated soils.

Catalyst electro-redeposition controls morphology and oxidation state for selective carbon dioxide reduction

The reduction of carbon dioxide to renewable fuels and feedstocks offers opportunities for large-scale, long-term energy storage. The synthesis of efficient CO2 reduction electrocatalysts with high C2:C1 selectivity remains a field of intense interest. Here we present electro-redeposition, the dissolution and redeposition of copper from a sol–gel, to enhance copper catalysts in terms of their morphology, oxidation state and consequent performance. We utilized in situ soft X-ray absorption spectroscopy to track the oxidation state of copper under CO2 reduction conditions with time resolution. The sol–gel material slows the electrochemical reduction of copper, enabling control over nanoscale morphology and the stabilization of Cu+ at negative potentials. CO2 reduction experiments, in situ X-ray spectroscopy and density functional theory simulations revealed the beneficial interplay between sharp morphologies and Cu+ oxidation state. The catalyst exhibits a partial ethylene current density of 160 mA cm–2 (−1.0 V versus reversible hydrogen electrode) and an ethylene/methane ratio of 200.

Growth and shape stability of Cu-Ni core-shell nanoparticles: an atomistic perspective.

The growth and shape stability of bi-metallic cubic Cu-Ni nanoparticles are studied using atomic-level simulations. Cubic nano-crystals coated with an ultra-thin Cu layer can be readily obtained when Ni cubic nanoparticles are used as the seeds. At elevated temperatures, the Cu seed with extending Ni branches preserves its shape compared to the Ni seed with extending Cu branches.

Mechanism of NH3 Selective Catalytic Reduction Reaction for NOx Removal from Diesel Engine Exhaust and Hydrothermal Stability of Cu–Mn/Zeolite Catalysts

Zeolite-supported catalysts are effective in selective catalytic reduction (SCR) of NOx from the diesel engine exhaust, whereas the reaction mechanism remains unclear. In this work, in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectroscopy was used to investigate the SCR reaction mechanism on Cu–Mn/ZSM-5 and Cu–Mn/SAPO-34. Langmuir–Hinshelwood (L-H) and Eley–Rideal (E-R) reaction mechanisms were both involved in the SCR reaction. In the L-H reaction mechanism, NO2 and NH4+ were two important intermediates. The transformation of bidentate nitrates to monodentate nitrates, and further to NO2, played an important role. The amount of bidentate nitrates and monodentate nitrates on Cu–Mn/ZSM-5 was much less than that on Cu–Mn/SAPO-34. It led to less NO removal through the L-H reaction mechanism on Cu–Mn/ZSM-5. The formation and consumption of coordinated NH3, as the intermediate in the E-R reaction mechanism, was similar on both catalysts. Therefore, the different catalytic activities ...

Microstructure and Mechanical Properties of Equiatomic CrMnCoNiCu High Entropy Alloy

Microstructure and mechanical properties of equiatomic CrMnCoNiCu alloy in which Fe was substituted by Cu from Cantor alloy was studied. The separation of solid solution phase into two solid solutions (Cr-Co rich and Cu-rich phases) were observed in CrMnCoNiCu. The coarsening and widening of interdendritic Cu-rich phase after homogenization was observed and supported by the increase of XRD peak height from Cu-rich phase compared to that from Cr-Co rich phase after homogenization. The increase of the peak from Cu-rich phase can be attributed to the thermodynamic stability of Cu due to positive mixing enthalpy of adding Cu. The stress-strain curves of CrMnCoNiCu alloy exhibited the reasonably high strength and excellent deformability for the cast alloy. The yield stress of CrMnCoNiCu was observed to be 390MPa and it could be deformed without crack formation up to the true strain 0.85 to reach the flow stress as high as 662Mpa.

Designed formation of NiO@C@Cu2O hybrid arrays as battery-like electrode with enhanced electrochemical performances

Abstract Here, the core-core-shell architectural hybrid electrodes were successfully fabricated by coating of NiO nanosheets on Cu 2 O nanorod arrays with the help of carbon layers (NiO@C@Cu 2 O NAs), which was directly grown on Cu foam as battery-like electrode for supercapacitor. Starting from commercial Cu foam, the whole synthesis process mainly involved sequential solution immersion, a carbonization treatment and hydrothermal reaction, all of which were simple and potentially scalable. This core-core-shell hierarchical architecture can not only shorten ion diffusion path and optimize charge transport, but also enhance contact surface area. In addition, the carbon layer as an intermediate layer can shorten the charge transfer distance and protect the structural stability of Cu 2 O. Moreover, ultrathin nanosheet-like NiO coated on the C@Cu 2 O backbones can provide more contact area with the electrolyte, which is beneficial for the improvement of areal specific capacitance. Serving as the supercapacitor electrodes, the resulting NiO@C@Cu 2 O NAs hybrid electrodes exhibited excellent performance, e.g. high specific capacitances of 2.18 F cm −2 , and a superior long-cycle lifetime and high cycling stability (91.5% after 10,000 cycles). Such enhanced NiO@C@Cu 2 O NAs with core-core-shell hybrid structure are promising battery-like electrode for supercapacitors in future applications.