Reduction Of CuO Research Articles

Probing the Atomistic Reaction Pathways in CuO/C Catalysts.

CuOx/C catalysts have been used in the selective catalytic reduction of NOx because of the exceptional low-temperature denitration (de-NOx) activity. A fundamental understanding of the reaction between CuO and C is critical for controlling the component of CuOx/C and thus optimizing the catalytic performance. In this study, a transmission electron microscope equipped with an in situ heating device was utilized to investigate the atomic-scale reaction between CuO and C. We report two reaction mechanisms relying on the volume ratio between C and CuO: (1) The reduction from CuO to Cu2O (when the ratio is < ∼31%); (2) the reduction of CuO into polycrystalline Cu (when the ratio is > ∼34%). The atomistic reduction pathway can be well interpreted by considering the diffusion of O vacancy through the first-principle calculations. The atomic-scale exploration of CuO/C offers ample prospects for the design of industrial de-NOx catalysts in the future.

Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al2 O3 for Acceptorless Alcohol Dehydrogenation.

A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.

Antioxidative copper sinter bonding under thermal aging utilizing reduction of cuprous oxide nanoparticles by polyethylene glycol

Durability of sintered Cu joints under thermal aging in the air was investigated for the reduction of Cu2O using Cu2O/polyethylene glycol (PEG) mixture. Thermal analysis of the Cu2O/PEG paste showed that the molecular weight of PEG influences the redox reaction and the subsequent bonding related to the combustion of the reducing organic solvent. Sintered Cu joints using PEG 400 exhibited high joint strength (above 30 MPa) in shear tests, even for the bonding temperature of 280 °C. The sintered Cu joints exhibited slightly increased strength during thermal aging at 250 °C in air, which was also confirmed by the microscale tensile test used for evaluating the fracture behavior of the sintered Cu structure. Microstructural analysis, including the evaluation of the crystal orientation, revealed a small change in the microstructure of sintered joints during aging. Transmission electron microscopy revealed the presence of organic membranes on slightly oxidized sintered Cu grains before thermal aging, and additional oxidation was observed after thermal aging. The progress of sintering during thermal aging in vacuum was different than that in air. It was considered that the formation of a thin Cu2O layer, controlled by the presence of organic membranes, contributed to the suppression of Cu sintering.Graphical abstract

APPLICATIOaN OF TEMPERATURE CONTROL SYSTEMS AT THE CATALYST ACTIVATION STEP IN THE METHANOL TESTPLANT

Catalyst activation is an important step in methanol synthesis process, achieved by the reduction of CuO precursor producing Cu0 active sites. Testplant’s temperature operation shall be maintainted at 220°C in order to maximize the CuO reduction process in the catalyst activation step. A temperature control system shall be applied in methanol testplant to maintain the temperature during reduction process, due to sensitivity of reduction process to temperature variation and possibility of disturbance such as change in gas flow rate which could affects the operating temperature. Temperature control systems are tested by using step response at the desired setpoint, which is 220°C at pre-heater and reactor and 60°C at sampling line. The tests are conducted by changing the setpoint value at temperature controller and previously stable flow gas in the system (disturbance rejection). The temperature control system proved to be able to response well during the test. In the end, methanol is produced from syngas, indicating catalyst activation success.

One-step synthesis of CaO/CuO composite pellets for enhanced CO2 capture performance in a combined Ca/Cu looping process via a facile gel-casting technique

The combined Ca/Cu looping process is a promising CO2 capture technology, in which the exothermic reduction of CuO with reducing gas (e.g., CH4, H2, or CO) is used in situ to supply the heat required to calcine CaCO3 via CaO/CuO composites. Although possessing excellent redox characteristics, CaO/CuO composites suffer from severe deactivation in their CO2 capture performance during cyclic operation. Besides, developing CaO/CuO composite pellets is essential for the practical applications of the combined Ca/Cu looping process. Thus in this work, we proposed a facile gel-casting technique to achieve a one-step synthesis of CaO/CuO composite pellets with enhanced CO2 capture performance. The results show that CaO/CuO composite pellets with homogeneous elemental distribution and a molar ratio of Ca to Cu of one can be obtained by adjusting the immersion time (∼24 – 48 h) and the molar ratio of Ca to Cu (∼2) in the mixed precursor solution during the material synthesis process. The CaO/CuO composite pellets had an initial CO2 uptake capacity of 0.16 gCO2/gmaterial and a final CO2 uptake capacity of 0.10 gCO2/gmaterial after ten repeated cycles. With the addition of glucose as the pore-forming material, sintering was reduced and the modified CaO/CuO composite pellets showed a much improved CO2 capture performance. With the optimal addition amount of glucose (i.e., a mass ratio of glucose to sodium alginate of two), the best-performing modified CaO/CuO composite pellets had a final CO2 uptake capacity of 0.14 gCO2/gmaterial after ten repeated cycles, exceeding that of the unmodified counterpart by 40%. Furthermore, the mechanism of structural improvement of CaO/CuO composite pellets by adding glucose was elucidated.

(MgCoNiCuZn)O with particular microstructure and distinctive electrochemical performance prepared using ultrafast high-temperature sintering

Ultrafast high-temperature sintering (UHS) based on Joule heating of graphic felt with a 103∼104 ℃/min heating rate enabled densification of ceramics in just a few seconds. The microstructure and electrochemical performance of (MgCoNiCuZn)O was systematically investigated. The equiaxed high-entropy grains were fully encapsulated in the Cu2O/Cu shell. This microstructure was a unique characteristic of (MgCoNiCuZn)O sintered by UHS and had not been found in materials prepared by other sintered methods. The Cu2O/Cu came from the reduction of CuO with the assistance of graphic felt, applied electric field and high temperature during UHS process. Because of this special microstructure, the discharge capacitance of the as-sintered material gradually increased as the cycles proceeded during the electrochemical experiment. After 10,000 cycles, the discharge specific capacitance ranged from 27.48 F/g to 39.84 F/g, which is an increase of 44.96 %. This work provides an idea for preparing electrochemical energy storage materials by using UHS technology.

Copper Plating on SiCp by Cooling Crystallization and Its Effects on the Spreading and Infiltration of AlSi12 Alloy Melt

A new cooling crystallization method is applied to plate copper on SiCp. Cu(NO3)2·3H2O is crystallized on SiCp by decreasing the solution temperature, and is heat‐treated to obtain CuO coating which is finally reduced to copper coating. Based on the optimizing of SiCp content and CuO reduction temperature, the effects of copper plating on SiCp on the spreading and infiltration of AlSi12 alloy melt are studied. The results show that the optimum coating effect is achieved when the SiCp content is 11.63% and the reduction temperature of CuO is 475 °C. The spreading area of AlSi12 alloy melt on the 15 μm copper‐coated SiCp increases by 53.27% compared to the uncoated SiCp when holds at 950 °C for 20 min, indicating that copper plating has a significant improvement on the wettability of AlSi12 melt and SiCp. Additionally, infiltration preparation of copper‐plated SiCp/Al alloy composites is achieved at a pressure of 0.3 MPa, but not under pressureless conditions. The main reason for this is the granular Cu on SiCp cannot form a complete Cu film. Therefore, the formation of complete Cu films on SiCp is presumed to be an important development direction for solving the problem of infiltration preparing ultrathick SiCp/Al composites.

Structural Disorder of CuO, ZnO, and CuO/ZnO Nanowires and Their Effect on Thermal Conductivity

In this work, the structural defects and the thermal conductivity of CuO, ZnO, and CuO/ZnO nanowires have been studied, using molecular dynamics simulation with COMB3 potential. The initial parameters and atoms positions were taken from reports of bulk materials with tenorite and wurtzite structures, respectively. Nanowires were grown along the c-axis, as observed experimentally. The results confirm the defects apparition in the systems after simulation with a formation of grains to reduce the energy of the nanowires. In the CuO nanowires case, the lack of periodicity in the basal plane causes a contraction effect over the network parameter b of the monoclinic structure with a Cu-O distance reduction. [A constriction effect on inclined planes, as a product of surface charges, deforms the nanowire, generating undulations. In ZnO nanowires, a decrease in the Zn-Zn distance produced a contraction in the nanowire length. A constriction effect was evident on the surface charges. It presented a bond reduction effect, which was larger at the ends of the nanowire. In CuO/ZnO nanowires, the structural defects come from the distortions of the crystalline lattice of the ZnO rather than CuO. The thermal conductivity of the nanowires was calculated at temperatures between 200 K and 600 K using the Green–Kubo equation. Results showed similar values to those reported experimentally, and the characteristic maximum with similar trends to those observed in semiconductors. Our results suggest that structural defects appear in nanowires grown on the free substrate, and are not related to the lattice mismatch.

Characteristics of a pulsed hollow cathode discharge operated in an Ar+O[formula omitted] gas mixture and deposition of copper nickel oxide thin films

A hollow cathode discharge with a CuNi (Cu50Ni50) cathode is operated inside a vacuum chamber with Ar gas flowing through its nozzle. O2 gas is admitted to the vaccum chamber. Typical Ar+O2 gas pressures are in the range of 2–50 Pa. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Singly charged Ar+ and molecular O2+ ions are the most abundant ionic species. Deposition rate and heat flux to a substrate increase as function of discharge current. At high pressures, the deposition rate is further increased by the directional gas flow, which becomes more focused onto the substrate. Deposited and annealed thin films are analysed by X-ray diffraction and Raman spectroscopy. As-deposited films are composed of a mixed CuxNi1−xO cubic phase with a preferred (111) orientation. Upon annealing at 600 oC, the mixed CuxNi1−xO phase separates into two sub-phases composed of NiO and CuO. Annealed films display a photoelectrochemical (PEC) activity as a photocathode. The PEC activity deteriorates with time, however. This behaviour is related to the reduction of CuO to Cu2O.

Highly Efficient CuPd0.1/γ-Al2O3 Catalyst with Isolated Pd Species for CO2 Hydrogenation to Methanol

CO2 hydrogenation is one of the most effective solutions for mitigating excessive CO2 emissions. In this work, CuPdx/γ-Al2O3 (x = 0.05–5.7 wt %) catalysts were prepared and applied in CO2 hydrogenation to methanol. The results showed CuPd0.1/γ-Al2O3 achieved excellent CO2 hydrogenation activity. It is demonstrated that the Pd species of CuPd0.1/γ-Al2O3 is highly dispersed on the γ-Al2O3 support at the atomic level and separated from Cu nanoparticles by AC-HAADF-STEM, rather than forming CuPd alloy. Part of the hydrogen species activated by isolated Pd atoms overflows onto γ-Al2O3 and influences the reduction of CuO, thus effectively increasing the Cu+/(Cu++Cu0) ratio which is correlated with the prominent CO2 hydrogenation performance. On the other hand, we found that CH3OH retained on catalyst surface can be further reformed into CO, which significantly reduces the selectivity of CH3OH. To limit CH3OH reforming, the activity test of CuPd0.1/γ-Al2O3 in a fixed bed at different weight hourly space velocity was performed, where the remarkable methanol yields of 5.9 mmol/gcat./h were obtained.

Tuning the surface reactivity of oxides by peroxide species

The Mars-van Krevelen mechanism is the foundation for oxide-catalyzed oxidation reactions and relies on spatiotemporally separated redox steps. Herein, we demonstrate the tunability of this separation with peroxide species formed by excessively adsorbed oxygen, thereby modifying the catalytic activity and selectivity of the oxide. Using CuO as an example, we show that a surface layer of peroxide species acts as a promotor to significantly enhance CuO reducibility in favor of H2 oxidation but conversely as an inhibitor to suppress CuO reduction against CO oxidation. Together with atomistic modeling, we identify that this opposite effect of the peroxide on the two oxidation reactions stems from its modification on coordinately unsaturated sites of the oxide surface. By differentiating the chemical functionality between lattice oxygen and peroxide, these results are closely relevant to a wide range of catalytic oxidation reactions using excessively adsorbed oxygen to activate lattice oxygen and tune the activity and selectivity of redox sites.

Selective breaking and re-joining of CuO nanowires by nanosecond laser irradiation

Nanostructures incorporating copper oxide (CuO), a narrow bandgap p-type semiconductor, are well suited for applications such as gas/biosensors, field emission devices, and photodetectors. However, the use of CuO nanocomponents in these applications is currently limited by the availability of fabrication and in situ processing techniques. In this paper, we show that the electrical and mechanical properties of CuO nanowire (NW) networks can be adjusted through sequential processing with nanosecond laser radiation. This new two-stage process involves selective breakage/cleaving of CuO NWs with an initial set of laser pulses, followed by irradiation with a second set of laser pulses applied in an optimized orientation to tailor bonding and junction formation between pairs and bundles of previously separated CuO NWs. We find that stage one processing introduces a high concentration of oxygen vacancies in NWs leading to the nucleation of dislocations and high strain. This localized strain is responsible for the breaking of individual NWs, while the high oxygen vacancy concentration modifies the electrical conductivity within each NW. The second stage involves re-orientation of the laser beam, followed by additional laser irradiation of the NW network. This has been found to result in the bonding of NWs and the creation of junctions in regions where CuO NWs are in contact. Laser-induced heating under these conditions produces melting in the contact areas between NWs and is accompanied by the reduction of CuO to form Cu2O as verified via XPS and Raman analysis. XRD and TEM observations demonstrate that plastic deformation within CuO NWs dominates in stage one laser processing. The enhancement of electrical conductivity observed, following stage two processing, is attributed due to an increase in the concentration of laser-induced oxygen vacancies as well as the formation of localized bridging and junction sites in the overall NW network.

Coupled oxygen desorption and structural reconstruction accompanying reduction of copper oxide.

Understanding structural transformation and phase transition accompanying reactions in a solid as a catalyst or oxygen carrier is important to the design and optimization of many catalytic or chemical looping reaction processes. Herein, we combined density functional theory calculation with the stochastic surface walking global optimization approach to track the structural transformation accompanying the reduction of CuO upon releasing oxygen. We then used machine learning (ML) methods to correlate the structural properties of CuOx with varying x. By decomposing a reduction step into oxygen detachment and structural reconstruction, we identified two types of pathways: (1) uniform reduction with minimal structural changes; (2) segregated reduction with significant reconstruction. The results of ML analysis showed that the most important feature is the radial distribution functions of Cu-O at a percentage of oxygen vacancy [C(OV)] < 50% and Cu-Cu at C(OV) > 50% for CuOx formation. These features reflect the underlying physicochemical origin, i.e., Cu-O breaking and Cu-Cu formation in the respective stage of reduction. Phase diagram analysis indicates that CuO will be reduced to Cu2O under a typical oxygen uncoupling condition. This work demonstrates the complexity of solid structural transformation and the potential of ML methods in studying solid state materials involved in many chemical processes.

Blast furnace gas decarbonisation through Calcium Assisted Steel‐mill Off‐gas Hydrogen production. Experimental and modelling approach

The Calcium Assisted Steel-mill Off-gas Hydrogen production process (CASOH) is able to upgrade and decarbonise blast furnace gases (BFG), which is the main source of CO2 emissions in integrated steel making plants. The three main reaction stages of the process (i.e. H2 production via calcium-assisted water-gas-shift of BFG, Cu oxidation and CO2 sorbent regeneration) have been investigated in a lab-scale fixed bed reactor, using readily available functional materials (i.e. a commercial Cu-based catalyst and calcined limestone for the CO2 capture). The reactivity and stability of the materials have been studied after multiple cycles resembling the operating conditions expected in a TRL7 CASOH pilot plant under construction. A one-dimensional reactor model has been developed to simulate in detail the CASOH process and successfully validated with the experimental results obtained in the packed-bed reactor. Synthetic BFG mixed with steam has been converted into a product gas containing up to 40 vol% of H2 in N2 during the CASOH stage at atmospheric pressure and average temperatures in the bed around 650 ºC. During the Cu oxidation stage, the O2 contained in inlet air has been completely converted leading to moderate temperatures in the oxidation front (i.e. around 800 ºC). The oxidation at 4 bar has minimized the CO2 leakage during this stage. Finally, the reduction of CuO with simulated BFG and CH4 has produced in-situ sufficient heat to partially calcine at temperatures around 880ºC the CaCO3 present in the reactor leaving the solids ready for subsequent reaction cycles, while a CO2-rich gas is produced. The experimental and modelling results obtained in this work will be used to firstly design the experimental campaigns at the TRL7 CASOH pilot, and subsequently to interpret and scale up the pilot results using the validated model.

Copper-coated graphite electrodes for the facile preparation of copper oxide particles anchored on functionalized holey graphene sheets

Functionalizing graphene with sulfur can enhance its electrical and electrochemical properties. Furthermore, generation of pores in graphene nanosheets could create suitable channels for the transfer of electrons/ions, and consequently, could provide easier access to the interior of graphene sheets with long aspect ratio. Moreover, metal oxide particles, especially copper oxides, anchored on graphene sheets have a wide range of applications. However, most of the reported procedures for the preparation of copper oxide/graphene composites are two-step and time-consuming. This study reports a fast, facile and cost-effective two-step approach for the preparation of copper oxide particles anchored on sulfur-functionalized holey graphene sheets. Copper-coated graphite electrodes were used for the first time as the electrodes for the electrochemical preparation of graphene, followed by a hydrothermal treatment to create holes in graphene sheets. The structural and morphological evaluations indicated that the electrochemical exfoliation of copper-coated graphite electrodes had led to the decoration of cubic CuO nanoparticles on the surface of sulphur-functionalized graphene sheets. Finally, the hydrothermal process resulted in the formation of holey graphene and the reduction of CuO to Cu2O with its shape evolution from cubic to rod-like.

Grain refining enables mixed Cu+/Cu0 states for CO2 electroreduction to C2+ products at high current density

The oxidation status of Cu-based materials have been proved to be essential to the catalytical performances of electrochemical CO2 reduction. The coexistence of Cu+ and Cu0 species is generally considered as the origin of superior catalytic performance, yet the Cu+ moieties are subject to reduction under negative potentials especially at high current density. In this work, we report a grain refining approach to tune the oxidation states of Cu-based catalysts by modulating the electron transfer during electrochemical CO2 reduction reaction (CO2RR) process when the in-situ electroreduction of Cu+ species occurs. Cu2O nanospheres with abundant grain boundaries exhibited lower electron conductivity compared with Cu2O nanospheres with less grain boundaries, which can hinder the complete reduction of Cu2O and maintain Cu+ species under high current densities. As a result, the multi-grain Cu2O showed a maximum FE of ∼79% for C2+ products at a high current density of 800 mA cm−2, notably surpassing the later. Experimental and theoretical analyses indicated that mixed Cu+/Cu0 states of multi-grain Cu2O during reaction, favoring the C-C coupling process towards C2+ products. This work demonstrates the feasibility to tune the real valence state of catalytic sites under operational conditions by nanostructure engineering.

NiOx-coated/Zn-doped CuO photoelectrodes with efficient charge transfer, protection from photocorrosion, and improved photocurrent density and photostability

In this study, Zn-doped CuO photoelectrodes were fabricated to investigate whether Zn doping would improve the photocurrent density by enhancing crystallinity, reducing charge transfer resistance and producing more efficient charge transfer in CuO photoelectrodes. In particular, the photocurrent density of a 5 at% Zn-doped CuO photoelectrode was − 2.32 mA/cm2, which was significantly higher than that of a bare CuO photoelectrode (−1.54 mA/cm2). However, the photostability of the doped CuO photoelectrodes was still low at 55.2 %, so protective layers with various NiOx concentrations were deposited on the photoelectrodes, and their photostability was analyzed. By comparing the XPS Cu 2p spectra of bare CuO, 5 at% Zn-doped CuO and 0.045 at% NiOx-coated/5 at% Zn-doped CuO photoelectrodes measured before and after photostability measurements, we investigated the reduction of CuO, which causes photocorrosion. The results of this study showed that Zn doping and NiOx deposition greatly improved the structural, electrical and photoelectrical properties of the CuO photoelectrodes. The photostability of the 0.045 at% NiOx-coated/5 at% Zn-doped CuO photoelectrode was very high, at 92.9 %, and the photocurrent density also improved to − 2.47 mA/cm2.

Enhanced Oxide Reduction by Hydrogen at Cuprous Oxide–Copper Interfaces near Ascending Step Edges

Understanding the dynamic processes involved in the interaction of hydrogen with oxides is of fundamental importance in catalysis. This paper probes the reduction of Cu2O-“29” surfaces by hydrogen at room temperature combining in situ ambient pressure scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Reduction of the atomic layer thin Cu2O film is observed to be preferentially initiated at step edges and terrace defects, where perfect Cu2O(111) terraces are found to be stable toward hydrogenation under the same conditions. After a long induction period, regions of partially reduced Cu2O-“29” and metallic Cu coexist before the surface is fully reduced to Cu(111). The reduction rate strongly depends on the nature of nearby Cu step edges. We propose a mechanism for the reduction of Cu2O-“29” by hydrogen where free copper atoms from ascending metallic step edges facilitate the formation of active ensembles for H2 dissociation and transfer H to the edges of Cu2O regions.

Lab-scale experimental demonstration of Ca[sbnd]Cu chemical looping for hydrogen production and in-situ CO2 capture from a steel-mill

In the present work, a lab-scale packed bed reactor has been used to decarbonize mixtures of inlet gases simulating the typical composition of blast furnace gases (BFG) and convert them to H2-rich streams by means of the CaCu chemical looping concept. The reactor was packed with 355 g of Cu-based oxygen carrier (OC) supported on Al2O3 and natural Ca-based sorbent. The three main reaction stages; namely (i) Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH), (ii) Cu oxidation and (iii) Regeneration of carbonated Ca-based sorbent were examined. In CASOH stage, BFG is converted into H2-rich stream (17% by vol.) under the experimental conditions of 600 °C, 5.0 bar and S/CO molar ratio of 2.0. A controlled oxidation causes a mere 3.5% of CaCO3 to decompose during the Cu-oxidation stage. This resulted in a nearly pure N2 stream at 600 °C and 5.0 bar operating conditions. During the regeneration stage, BFG and mixture of BFG and CH4 is used as a reducing fuel. To ensure the amount of heat needed for the decomposition of CaCO3 during the reduction of CuO, a 1.4 CuO/CaCO3 molar ratio has been used. It resulted in 46% CO2 in N2 at the end of the reduction/calcination stage.

Imaging Cu2O nanocube hollowing in solution by quantitative in situ X-ray ptychography

Understanding morphological changes of nanoparticles in solution is essential to tailor the functionality of devices used in energy generation and storage. However, we lack experimental methods that can visualize these processes in solution, or in electrolyte, and provide three-dimensional information. Here, we show how X-ray ptychography enables in situ nano-imaging of the formation and hollowing of nanoparticles in solution at 155 °C. We simultaneously image the growth of about 100 nanocubes with a spatial resolution of 66 nm. The quantitative phase images give access to the third dimension, allowing to additionally study particle thickness. We reveal that the substrate hinders their out-of-plane growth, thus the nanocubes are in fact nanocuboids. Moreover, we observe that the reduction of Cu2O to Cu triggers the hollowing of the nanocuboids. We critically assess the interaction of X-rays with the liquid sample. Our method enables detailed in-solution imaging for a wide range of reaction conditions.