Copper Oxide Catalysts Research Articles

Improved Catalytic Partial Oxidation of Methane via Lattice Oxygen Modification on Supported Copper Oxide Catalyst System

AbstractThirteen kinds of supported copper oxide catalysts (Cu/MOx, MOx: La2O3, Al2O3, SiO2, TiO2, CeO2, ZrO2, SnO2, SrCO3, BaCO3, Ta2O5, Nb2O5, WO3, and MoO3), which form Cu−O−M sites at the interface between CuOx and MOx or within the complex oxides (CuMOx), were tested for CH4 partial oxidation to find out catalytically active Cu−O−M combinations for production of CH3OH and HCHO. Among the thirteen Cu/MOx tested, Cu/WO3 exhibited the highest total yield of CH3OH and HCHO in a CH4‐O2‐H2O flow reaction at 400 °C. The structural and property analysis of Cu/WO3 revealed the formation of CuWO4, of which the lattice oxygen is active for the partial oxidation of CH4.

Synthesis Of Ce/Cu/Nb Catalysts, by the One-Step Polymerization Method, Applied in the Selective Oxidation Reaction of Acetonitrile

Objective: The objective of this study is to investigate the catalytic capacity of cerium, copper and niobium oxide catalysts in the oxidation reaction of acetonitrile, in order to test the catalytic behavior, conversion and selectivity of the catalysts; evaluate the different proportions of niobium used (0, 15, 30, 50 and 75% m.m) and compare the catalytic performance of the synthesized materials with other studies present in the literature. Method: The catalysts were synthesized using the one-step polymerization method and were characterized using XRD and H2-TPR techniques. Then, they were applied in the acetonitrile oxidation reaction to be evaluated for conversion and selectivity. Results and Discussion: The results obtained revealed that the catalysts played a significant role in the proposed reaction, obtaining good conversion and selectivity values, including the production of N2 as the majority. Research Implications: Considering that the oxidation of acetonitrile generates polluting gases from nitrogen compounds, the research presents a method that produces an extremely low quantity of these pollutants. This method ensures better product quality, reduces energy consumption due to the lower reaction temperature and uses cheaper and more viable catalysts. Originality/Value: This study contributes to the literature by being based on compounds not yet used together as catalysts and also for the proposed reaction. The relevance of the use of the catalyst is demonstrated through the results obtained, such as high conversions and selectivities to desirable products.

Photo-assisted oxygen-rich vacancy copper oxide catalyst to activate peroxymonosulfate (PMS) for efficient degradation of fulvic acid

In this study, novel copper oxide particles-activated peroxymonosulfate (CuO-S/PMS/UV) were employed to degrade fulvic acid(FA). Under the optimal treatment condition, the FA removal of the CuO-S/PMS/UV process was up to 97.74%. The removal rates of SUVA254, UVA365 UVA280 UVA463 and TOC within 40 min in the UV/CuO-S/PMS process were 23.4%, 95.6%, 63.2%, 100% and 40.8% respectively. The three-dimensional fluorescence spectrum analysis of FA during the degradation process revealed the disappearance of FA-associated functional structures. Furthermore, the impact of common anions in the water matrix on the degradation process was investigated, demonstrating that the system remains effective containing low concentrations of anions. Subsequently, mechanism studying showed that SO4•−, 1O2, h+, and •OH species were primarily involved in the degradation of FA, while O2•− has a limited effect in the degradation process. This study can provide valuable insights for the degradation of humic pollutants in the water environment.

Oxygen Vacancy-Controlled CuOx/N,Se Co-Doped Porous Carbon via Plasma-Treatment for Enhanced Electro-Reduction of Nitrate to Green Ammonia.

The electrochemical nitrate reduction reaction (NO3RR) is of significance in regards of environmentally friendly issues and green ammonia production. However, relatively low performance with a competitive hydrogen evolution reaction (HER) is a challenge to overcome for the NO3RR. In this study, oxygen vacancy-controlled copper oxide (CuOx) catalysts through a plasma treatment are successfully prepared and supported on high surface area porous carbon that are co-doped with N, Se species for its enhanced electrochemical properties. The oxygen vacancy-increased CuOx catalyst supported on the N,Se co-doped porous carbon (CuOx-H/NSePC) exhibited the highest NO3RR performance with faradaic efficiency (FE) of 87.2% and yield of 7.9mg cm-2h-1 for the ammonia production, representing significant enhancements of FE and ammonia yield as compared to the un-doped or the oxygen vacancy-decreased catalysts. This high performance should be attributed to a significant increase in the catalytic active sites with facilitated energetics from strategies of doping the catalytic materials and weakening the N─O bonding strength for the adsorption of NO3 - ions on the modulated oxygen vacancies. This results show a promise that co-doping of heteroatoms and regulating of oxygen vacancies can be key factors for performance enhancement, suggesting new guidelines for effective catalyst design of NO3RR.

Efficient electrocatalytic formate oxidation on copper oxide catalyst mediated lithium recovery coupled hydrogen production

In response to the increase in retired lithium-ion batteries (LIBs), there is a rising trend in lithium recycling, which can not only address the scarcity of lithium resources but also mitigate environmental pollution caused by battery waste. In this study, we present an electrocatalytic strategy for formate oxidation reaction (FOR) aimed at facilitating lithium recovery coupled hydrogen production. The obtained results have indicated that the synthesized Cu-based oxide can efficiently catalyze FOR, achieving a current density of 500 mA cm−2 at only 1.534 V vs. RHE. According to density functional theory calculations, the adsorption strength of the intermediate specie HCOO on Cu-based oxide is reduced (−0.36 eV) compared to Ni-based oxide (−2.27 eV), resulting in a thermodynamically favorable step for the rate-determining HCOO dehydrogenation reaction. Assembling a FOR coupled hydrogen evolution reaction (HER) electrolysis system can achieve hydrogen production and Li recovery (Li recovery product is Li2CO3) by electrolyzing alkaline raffinate containing lithium. This approach eliminates the need for additional formic acid and sodium carbonate, thereby reducing material consumption and ultimately enhancing the economic efficiency of the lithium battery recovery strategy.

Dendritic copper oxide catalyst engineering weak-polarity Cu-O bond for high-efficiency nitrate electroreduction

Nitrate reduction reaction (NO3RR) is deemed a promising pathway for both ammonia synthesis and water purification. Developing a high-efficiency catalyst with excellent NH3 selectivity and catalytic stability is desirable but remains challenging. In this work, a dendritic copper oxide catalyst (Cu-B2) has been developed to efficiently catalyze NO3RR for ammonia production, the Cu-B2 exhibits excellent catalytic performance, achieving an NH3 Faradaic efficiency as high as 94 % and an NH3 yield of 16.9 mg h−1 cm−2 with a current density of 192.3 mA cm−2 at − 0.6 V (vs. RHE, reversible hydrogen electrode). During NO3RR testing, the Cu-B2 catalysts are reduced in situ to form highly active Cu0/Cu+ sites, while retaining its dendritic morphology. Compared with other catalysts, the Cu-O bond in Cu-B2 catalyst has weaker polarity, resulting in Cu0/Cu+ sites in lower oxidation states. In situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies reveal the Cu-B2 catalyst exhibits a potential-independent capability for *NO3- adsorption and high conversion efficiency of NO2- intermediate into ammonia, DFT calculations reveal that Cu-B2 exhibts higher NO3- adsorption energy and lower NO3- adsorption energy barrier than Cu-B1, thus endowing it with a remarkably improved catalytic activity and durability.

CH3 radical-mediated direct methane to methanol conversion over CuO supported on rutile oxides

Direct conversion of methane into methanol is an attractive strategy for the production of manifold value-added chemicals. Herein, we investigated the conversion of methane to methanol over CuO supported on the rutile metal oxides (TiO2, SnO2 and RuO2) based on results of density functional theory (DFT) calculations. The results show that the oxygen site of the supported CuO exhibits the characteristics of a radical anion. This radical anionic oxygen site enables homolytic C-H cleavage by abstracting the hydrogen atom, resulting in a CH3 radical. The CH3 radical captured by the Cu site next to the radical anionic oxygen enables the coupling of CH3 and OH to form a C-O bond, resulting in methanol. The free energy of activation for C-H activation and C-O formation were found to correlate linearly with the p band center of the radical anionic oxygen, but the slope has the opposite signs, i.e., a lower free energy of activation for C-H scission corresponds to a higher free energy formation for C-O formation. Among rutile oxides studied, SnO2 offers a balanced reactivity for C-H activation and C-O formation. These findings demonstrate the presence of the radical anionic oxygen on rutile oxide-supported CuO catalyst and their crucial role in regulating the reactivity for direct methane to methanol conversion. The mechanistic insights from this study will benefit the development of supported copper oxide catalysts for effective methane conversion.

Copper oxide nanofibers obtained by solution blow spinning as catalysts for oxygen evolution reaction

In this work, we report copper oxide nanofibers (CuO – N) synthesized by Solution Blow Spinning (SBS) for oxygen evolution reaction (OER), and their comparison with a control sample based on a commercial powder (CuO – C). Both materials were characterized by various techniques, including X-ray diffraction (XRD), magnetometry, scanning electron microscopy (SEM), and spectroscopy (Fourier transform infrared (FT-IR), Raman and X-ray photoelectron (XPS)) to determine the purity, microstructural and surface chemical properties. Subsequently, the performance of copper oxide catalysts in a 1.0 M KOH solution was investigated. Copper oxide with nanofiber morphology (CuO – N) exhibited a small overpotential of 385 mV @ 10 mA cm−2 and a Tafel coefficient of only 76 mV dec−1, i.e., fast kinetics for water splitting, a result that is modulated by oxygen vacancies (O2/O1 = 0.83). The oxygen vacancies are due to the presence of Cu1+ in the lattice. The analyses of the magnetization measurements at 5 K suggest a larger amount of Cu1+ in sample CuO – N. Therefore, this work sheds light on how to design low-cost nanofibrous catalysts based on abundant transition metals in the earth's crust by SBS, an economical and scalable technique, which is promising for energy applications.

Shielding effect in the synthesis of Gd-doped copper oxide catalysts with enhanced CO2 electroreduction to ethylene

Electrocatalytic reduction reaction of carbon dioxide (CO2RR) into ethylene can achieve efficient conversion and utilization of CO2, which also provides a new and sustainable way to mitigate climate change. Copper...

Nanocomposites based on Cu2O coated silver nanowire networks for high-performance oxygen evolution reaction.

The development of highly active, low-cost, and robust electrocatalysts for the oxygen evolution reaction (OER) is a crucial endeavor for the clean and economically viable production of hydrogen via electrochemical water splitting. Herein, cuprous oxide (Cu2O) thin films are deposited on silver nanowire (AgNW) networks by atmospheric-pressure spatial atomic layer deposition (AP-SALD). AgNW@Cu2O nanocomposites supported on conductive copper electrodes exhibited superior OER activity as compared to bare copper substrate and bare AgNWs. Moreover, a relationship between Cu2O thickness and OER activity was established. Notably, the most effective catalyst (AgNW@50nm-thick Cu2O) demonstrated very high OER activity with a low overpotential of 409 mV to deliver a current density of 10 mA cm-2 (η 10), a Tafel slope of 47 mV dec-1, a turnover frequency (TOF) of 4.2 s-1 at 350 mV, and good durability in alkaline media (1 M KOH). This highlights the potential of AgNWs as a powerful platform for the formation of highly efficient copper oxide catalysts towards OER. This work provides a foundation for the development of nanostructured Cu-based electrocatalysts for future clean energy conversion and storage systems.

Electrochemical Reduction of Nitrate to Ammonia Using Copper Oxide Catalysts

The electrochemical conversion of nitrates to ammonia offers a promising alternative to the energy- and resource-intensive Haber-Bosch process while simultaneously removing nitrates, a common water pollutant. However, this process is hindered by the eight-electron reduction required to convert nitrate to ammonia, as well as competing hydrogen evolution reactions and other nitrate reduction pathways. Efficient catalysts are essential to address these challenges, and recent studies suggest that oxide catalysts with oxygen vacancies can optimize adsorption energies of intermediates and improve catalytic performance. Copper oxides with oxygen vacancy display high ammonia selectivity in nitrate reduction, but the complexity in vacancy enrichment and the inferior hydrogen adsorption on oxides make nitrate reduction an inefficient process.In this study, a CuOx composite electrode was synthesized using the hydrothermal method, and its performance was evaluated for efficient conversion of nitrate to ammonia. The synthesized CuOx nanostructure was characterized using X-ray diffraction to determine phase purity and crystal structure, while surface morphology of prepared samples was examined with high resolution transmission electron microscope. The results of X-ray photoelectron spectroscopy suggested that there were abundant oxygen vacancies on the surface of the CuOx, which can act as nitrate adsorption sites. The obtained CuOx composite electrode performs at a high ammonia Faradaic efficiency of over 80% and long-term stability due to interfacial coupling effects. These findings highlight the potential of CuOx catalysts for electrochemical nitrate reduction, offering new opportunities for sustainable nitrogen management and water treatment.

Kinetic and thermodynamic analysis of ammonia electro-oxidation over alumina supported copper oxide (CuO/Al2O3) catalysts for direct ammonia fuel cells

In this work, ammonia electrooxidation (AEO) is studied to probe the electrochemical behavior of aqueous NH3 as direct fuel by implication of gamma alumina supported copper oxide catalysts (CuO/Al2O3). Precipitation and impregnation techniques are adapted to synthesize the substrate Al2O3, and loading of different ratios (1%, 2%, 3%, 4%) of active precursor i.e., CuO, respectively. Small average crystallite sizes (DAvg) in range of 1.46–6.76 nm and smaller particle sizes from micrographs proposed a superb activity of the catalysts. Modified GCE exhibited the excellent conductive properties towards standard redox probe K4[Fe(CN)6] and KCl, displaying a high active electrochemical surface area of up to 0.0021 cm2. Current profiles in response to increase in scan rates, concentrations of ammonia and temperature have been observed in 0.1 M KOH, thereby estimating the thermodynamic and kinetic constraints of the AEO process. Attributed to the electroactive properties towards AEO, CuO/Al2O3 is found to exhibit the desirable physiochemical properties owing to large oxidation current, large diffusion coefficient “D°” (3.6 × 10-9 cm2 s-1), large rate constant “ko” (1.2 × 10-5 cm s-1), large system entropy “ΔS” (-108 J K-1 mol-1), high change in enthalpy “ΔH” (72.3 J mol-1) and low activation energy “ΔG” (32.8 kJ mol-1). Resultingly, the oxidation of ammonia is found to be facile and robust by incorporation of CuO/Al2O3 catalysts owing to large ko, ΔH and ΔH. This study opened a gateway towards eco-benign and economical efficient energy generation and viable market entry of direct ammonia fuel cells.

Flexible regulation of persulfate activation mechanisms through tuning Cu valence in CuBTC-derived copper oxide catalysts for improved pollutant degradation

Radical and nonradical dominated persulfate activation processes have pros and cons in the degradation of pollutants. It is challenging to flexibly tune the contribution ratios of radicals and nonradicals in a persulfate activation process for improved pollutant degradation. Herein, we successfully synthesize copper oxide catalysts derived from metal-organic frameworks. By varying the annealing temperature, valence states of copper can be regulated in the catalyst, thereby enabling the switching between radical and nonradical mechanisms for persulfate activation. Copper oxides annealed at 300 °C (CuBTC-300) demonstrate high performance in peroxydisulfate (PDS) activation for the degradation of bisphenol A (BPA), with the synergy of radical and nonradical mechanisms. The surface activated PDS-catalyst complex and OH are identified as the reactive oxidative species involved in this process. On one hand, PDS undergoes a one-electron transfer reaction with Cu(I) sites in Cu2O, generating SO4−, which subsequently converts into OH for BPA degradation. On the other hand, the combination of PDS molecules with CuO forms surface-activated complexes, depriving electrons from BPA. The increased content of Cu(II) in the catalyst gradually directs PDS activation towards the nonradical pathway. As the annealing temperature increases from 300 °C to 500 °C, the contribution of nonradical oxidation to BPA degradation increases from 58.65 % to 100 %. This work provides new insights into flexibly regulating persulfate activation mechanisms via rational catalysts design.

A silver–copper oxide catalyst for acetate electrosynthesis from carbon monoxide

A silver–copper oxide catalyst for acetate electrosynthesis from carbon monoxide

Electron-transfer pathways insights into contaminants oxidized by [tbnd]Cu-OOSO3- intermediate: Effects of oxidation states of Cu and solution pH values

The copper-peroxy complex (Cu-OOSO3-) metastable intermediate has been confirmed to oxidize contaminants via a single-electron-transfer pathway or an oxygen-atom-transfer pathway. And the effects of Cu oxidation states and reaction pH conditions on the intermediate properties have not been explored in depth. Here, copper oxide (CuOx) catalysts with different Cu oxidation states were synthesized by a simple precipitation method by controlling the reaction temperature from 0 to 45 °C. CuOx displayed a strong catalytic dependence on the Cu oxidation state, and CuOx-30 with Cu average valence on the catalyst surface of 1.61 was more reactive for catalytic degradation of bisphenol A with peroxymonosulfate (PMS). Notably, CuOx-30, with the best electron-accepting ability, was easier to bonding with PMS to form the Cu-OOSO3- reactive complex, and the generated intermediate exhibited the strongest capacity to obtain electrons from contaminants. Moreover, the electron-transfer pathways were closely related to the average valence of Cu, and the contribution of the oxygen-atom-transfer pathway changed volcanic with increasing Cu valence. Meanwhile, the reaction predominantly involved the oxygen-atom-transfer pathway under acidic conditions (pH=3), while the contribution of the single-electron-transfer pathway raised with increasing pH values. Hence, this work was devoted to providing new insights into the CuOx-inducing PMS activation and vital supplementary to the properties of the Cu-OOSO3- intermediate.

Beneficial Effect of β‐Cyclodextrin Assisted Synthesis of CuO/Hydroxyapatite Catalyst in Toluene Oxidation

AbstractTwo hydroxyapatite supported CuO (10 wt% Cu) catalysts were prepared using the wet impregnation method via the conventional process and with the addition of native β‐cyclodextrin using Cu(NO3)2.3H2O as copper precursor and adopting a ratio of β‐cyclodextrin to copper of 0.1. After the impregnation step, the materials were dried at 80 °C and calcined in flowing dry air at 400 °C. The copper supported materials were characterized in the dried state and after calcination by means of conventional methods including X‐ray diffraction, TG‐MS, H2‐TPR‐MS, Raman spectroscopy, UV‐vis‐DR, ToF‐SIMS and XPS. It was found that β‐cyclodextrin hasd a profound impact on the final properties of the catalysts, both in terms of reducibility and dispersion of active species. It is suggested that at the early stages of the calcination, some hydroxyl groups of the β‐CD units in close contact with Ca2+ of hydroxyapatite could play the role of spacers between the copper‐based entities thus minimizing the aggregation process of the CuO nanoparticles. Finally, these copper oxide catalysts prepared from β‐cyclodextrin were able to oxidize toluene more efficiently than the conventional catalyst. The copper oxide particles generated by the thermal decomposition of Cu2(OH)3(NO3) were smaller than those formed with copper nitrate alone and exhibited a higher reducibility, two key determinants for VOC total oxidation on transition metal oxides.

Highly Selective Electrochemical CO2 Reduction to C2 Products on a g-C3N4-Supported Copper-Based Catalyst.

Herein, a novel approach used to enhance the conversion of electrochemical CO2 reduction (CO2R), as well as the capacity to produce C2 products, is reported. A copper oxide catalyst supported by graphite phase carbon nitride (CuO/g-C3N4) was prepared using a one-step hydrothermal method and exhibited a better performance than pure copper oxide nanosheets (CuO NSs) and spherical copper oxide particles (CuO SPs). The Faradaic efficiency reached 64.7% for all the C2 products, specifically 37.0% for C2H4, with a good durability at -1.0 V vs. RHE. The results suggest that the interaction between CuO and the two-dimensional g-C3N4 planes promoted CO2 adsorption, its activation and C-C coupling. This work offers a practical method that can be used to enhance the activity of electrochemical CO2R and the selectivity of C2 products through synergistic effects.

Boosting electrocatalytic nitrate reduction reaction for ammonia synthesis by plasma-induced oxygen vacancies over MnCuOx

Ammonia production from electrocatalytic nitrate reduction reaction (NO3RR) is a significant research field to potentially substitute the Haber-Bosch process. However, low ammonia selectivity due to competitive hydrogen evolution reaction is an issue for the NO3RR. In this study, a series of manganese copper oxide (MnCuOx) catalysts with different concentrations of oxygen vacancies have been prepared via Ar or O2 plasma treatments. MnCuOx-H with high concentration of oxygen vacancies showed a high NH3 yield rate of 9.4 mg cm-2h−1 and Faradaic efficiency of 86.4 %. The high performance of MnCuOx-H for the NO3RR can be resulted from the feature that the more oxygen vacancies formed from the plasma treatment could facilitate adsorption and weakening NO bonds of NO3. This strategy suggests a novel guidance to the catalyst design for NO3RR, which requires great improvements in terms of NH3 selectivity and production rate.

Mixed Metal Oxides for Oxygen Reduction Reaction: Strategies for Suppressing H2O2 Formation

Widespread implementation of fuel cell technology has been hampered by challenges originating from the oxygen reduction reaction (ORR). Even the most advanced ORR catalysts present high overpotentials and poor selectivity for the reduction of O2 to H2O. A substantial amount of H2O2 is generated as a product of incomplete reduction.We developed a series of cost-effective cobalt-doped copper oxide (Cu[Co]Ox) catalysts supported on Au. These catalysts not only show lower overpotentials but also very high selectivity for the complete reduction of O2 to H2O.Specifically, Cu-rich compositions, such as Cu0.8Co0.2Ox/Au, demonstrated remarkable activity and > 97% selectivity for H2O over a sizeable potential range (1.0 – 0.6 V) relevant to ORR. These catalysts were found to even outperform Pt in both activity, selectivity, and performance stability.These catalysts have been investigated using in situ Raman Spectroscopy and X-Ray Photoelectron Spectroscopy. Our studies indicate that the doped materials have a Co-active site embedded within the CuOx framework. The resulting sites lower the free energy of the potential determining step and enhance yield for the complete reduction to H2O. Specifically, these catalysts preferentially cleave the O-O bonds result in high selectivity for the 4e pathway. Figure 1

Boosting electrocatalytic CO2–to–ethanol production via asymmetric C–C coupling

Electroreduction of carbon dioxide (CO2) into multicarbon products provides possibility of large-scale chemicals production and is therefore of significant research and commercial interest. However, the production efficiency for ethanol (EtOH), a significant chemical feedstock, is impractically low because of limited selectivity, especially under high current operation. Here we report a new silver–modified copper–oxide catalyst (dCu2O/Ag2.3%) that exhibits a significant Faradaic efficiency of 40.8% and energy efficiency of 22.3% for boosted EtOH production. Importantly, it achieves CO2–to–ethanol conversion under high current operation with partial current density of 326.4 mA cm−2 at −0.87 V vs reversible hydrogen electrode to rank highly significantly amongst reported Cu–based catalysts. Based on in situ spectra studies we show that significantly boosted production results from tailored introduction of Ag to optimize the coordinated number and oxide state of surface Cu sites, in which the *CO adsorption is steered as both atop and bridge configuration to trigger asymmetric C–C coupling for stablization of EtOH intermediates.