CuO Catalyst Research Articles

Selective production of furfural from the dehydration of xylose using Zn doped CuO catalyst

Furfural is a versatile biomass-derived platform compound used for the synthesis of several strategic chemicals. The sonochemically synthesized Zn doped CuO nanoparticles (NPs) were used for the production of furfural. The catalytic activity of the Zn doped CuO NPs was examined, as a model, during the dehydration reaction of xylose to furfural. In addition to that, we have also compared the catalytic activity of the Zn doped CuO NP with ZnO NPs, ZnO bulk, CuO NPs, CuO bulk, etc. This nanoscale catalyst (Zn doped CuO NP) has a large surface area, which enhances its catalytic activity and enables it to completely convert the xylose to furfural at 150 °C within 12 h without any trace of by-products, as confirmed by HPLC, 13C NMR and 1H NMR. HPLC analysis demonstrated that the yield of furfural is up to 86 mol %, compared to the 45 mol % obtained with ZnO NPs, ZnO bulk, CuO NPs, CuO bulk, etc. as catalysts.

Microenvironment of mesopores of MCM-41 supported CuO catalyst: An investigation using positronium probe

Investigation of microenvironment of mesopores in CuO loaded mesoporous materials is vital to predict its catalytic performance. Mesoporous MCM-41 supported CuO catalyst was prepared by a conventional solid state grinding method and characterized by different techniques to understand the microenvironment of mesopores. The samples were characterized using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Transmission electron microscopy (TEM) and N2 gas adsorption techniques. XRD and TEM measurements have shown the formation of CuO nanocrystallites larger than mesopores size of MCM-41. SAXS and TEM also provide evidence of fine dispersion of CuO on mesopores' inner walls of MCM-41 along with the formation of large size crystallites outside the mesopores. With the loading of CuO, N2 adsorption measurements show a negligible change in pore size along with a continuous reduction in pore volume and surface area of MCM-41. Ortho-positronium (o-Ps) probe was used to investigate the atomic level dispersion of catalyst in MCM-41 pores. A complete absence of positronium formation in the mesopores of CuO loaded samples has been observed which has been unequivocally ascribed to the inhibition of positronium formation on the pores' surfaces. The results indicate that CuO is finely dispersed at atomic level on mesopores' inner walls leading to its layer by layer growth.

Enhancement of Supercritical Water Oxidation for Municipal Sludge Degradation

Different measures to enhance the removal efficiency of municipal sludge by supercritical water oxidation were further studied in a batch reactor, including catalytic supercritical water oxidation, co-oxidation with methanol and multi-injection of oxidant experiments at 580 °C, 25 MPa within a total residence time of 10 min and a total oxidant coefficient of 1.1. The experimental results showed that splitting the same amount of oxidant and feeding into reactor at two different residence time had a significant enhancement on the removal of COD compared with NH3-N, and the optimal second injection time of oxidant was 7.5 min in this investigation. Meanwhile, CuO catalyst could increase the degradation efficiency of both COD and NH3-N, and it increased with the amount of CuO added, which was better than methanol. Moreover, combining CuO with injecting oxidant multi-stage experiment produced the maximum organics degradation efficiency of 99.9% and 83.47% for COD and NH3-N, respectively, it demonstrates lower COD degradation of 99.58% and NH3-N degradation of 35.69% utilizing methanol at fixed reaction condition.

A Novel Approach of In-Situ Electrobiosynthesis of Metal Oxide Nanoparticles Using Crude Plant Extract as Main Medium for Supporting Electrolyte

Abstract The release of dyes into the environment during textile fibre dyeing and finishing processes is a main source of water pollution. There is a need to look for effective treatment processes to overcome this problem. Photocatalytic method becomes the most effective to remove the dyes. In this study, in-situ electrobiosynthesis of various metal oxide such as silver oxide (AgO), copper oxide (CuO), zinc oxide (ZnO), and nickel oxide (NiO) using plant extract as new green electrolyte was performed with enhancement behaviour and structural of the catalyst for excellent photodegradation of malachite green (MG) dye from aqueous solution. The MG was successfully degraded at optimum condition of 10 mg/L of initial concentration with 0.5 g/L of catalyst dosage of AgO, CuO, ZnO, and NiO; at pH of 2 under visible light irradiation within 1 hour of contact time at room temperature which were 91.7 %, 94.0%, 98.5 %, and 97.3 %, respectively. Therefore, the effectiveness of eelctrobiosynthesis of AgO, CuO, ZnO, and NiO metal catalyst via electrochemical method using 100 % crude plant extract as new supporting electrolyte was established and confirmed through this study. The synthesized metal oxide catalyst has a great potential as a photocatalyst in photocatalytic reaction for degradation of organic pollutants in wastewater.

Controlled synthesis of a Bi2O3–CuO catalyst for selective electrochemical reduction of CO2 to formate

The electro-reduction of CO2 to produce energy sources has been considered as a visionary pathway with the help of renewable electricity, which can achieve carbon neutrality and mitigate global warming.

Comparison of Au–Ce and Au–Cu interaction over Au/CeO2–CuO catalysts for preferential CO oxidation

Au decelerates reduction of copper species, while it improves ceria reduction.

Binary copper and manganese oxide nanoparticle supported oms-2 for enhancing activity and stability toward co oxidation reaction at low temperature

The CuO, CuMnOx and MnOx catalysts were anchored on the manganese oxide support with the structure of octahedral molecular sieves (OMS-2), which were synthesized using MnSO4 and KMnO4 as precursors by are flux method under acidic conditions, by an impregnation method and tested for CO oxidation. These catalysts and OMS-2 support were characterized by the advanced analyzations of X-ray diffraction and FTIR patterns; and SEM performances; and H2-TPR profiles. For CO oxidation reaction, CuO and CuMnOx catalysts showed extremely higher activities than that of MnOx catalyst and OMS-2 support. For the lowest temperature for 100% conversion of CO (T100), the CuO and CuMnOx catalysts were observed at 55 oC and 65 oC, respectively. Due to the present of Cu2+– O2− – Mn4+ ↔ Cu+–□–Mn3+ + O2 redox couple in the structure of these solid catalyst. Additionally, the CuMnOx catalyst showed higher activity (~ 1.74 folds) and better stability than that of CuO catalyst in CO oxidation. Due to the advance functional of binary oxide structure of CuMnOx catalyst As known, CO oxidation may follow the Mars-van-Krevelen mechanism with Cu2+– O2− – Mn4+ ↔ Cu+–□–Mn3+ + O2 redox couple. This study shows the high applicating potential of CuMnOx/OMS-2 material in exhaust treatment for environmental safety.

Catalytic oxidation and selective sensing of carbon monoxide for sense and shoot device using ZnO–CuO hybrids

In the present work, we have demonstrated that ZnO–CuO based hetero-composites exhibit selective CO sensing with T100 is in close proximity to Topt to yield simultaneous CO sensing together with its 100% catalytic oxidation for sense and shoot devices. When these heterocomposites are exposed to CO, reduction of Cu2+ ions in CuO grains leads to a strong metal semiconductor interaction (SMSI) between Cu2+/Cu+/Cu0 species (in CuO grains) and ZnO grains across the ZnO-CuO interface. The SMSI interaction promotes the generation of oxygen vacancies in neighboring ZnO lattice. Eventually activated oxygen (O*ads) and CO (CO*ads) are preferentially chemisorbed on zinc oxide (in its vacant oxygen sites) and CuO (on the surface of Cu2+/Cu+/Cu0 ions) respectively. The activated oxygen reacts immediately with adsorbed CO to yield selective CO sensing together with 100% CO oxidation. For ZnO–CuO (1:1) composites, the measured Topt (∼175 °C) and T100 (∼200 °C) temperatures are significantly lowered as compared to the respective temperatures measured for indium doped ZnO (Topt∼300 °C, T100∼550 °C) and CuO (Topt∼200 °C,T100∼300 °C) catalysts. Fine tuning of the mole fraction of ZnO and CuO are necessary for these hetero-composites to yield T100 of catalytic activity close to Topt for maximum CO sensing.

Redox Properties of Cu2O(100) and (111) Surfaces

Intense research efforts are directed toward Cu and Cu2O based catalysts as they are viewed as potential replacements for noble metal catalysts. However, applications are hampered by deactivation, e.g., through facile complete oxidation to CuO. Despite the importance of the redox processes for Cu2O catalysts, a molecular level understanding of the deactivation process is still lacking. Here we study the initial stages of oxidization of well-defined Cu2O bulk single crystals of (100) and (111) termination by means of synchrotron radiation X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Exposure of the (100) surface to 1 mbar O2 at 25 °C results in the formation of a 1.0 monolayer (ML) CuO surface oxide. The surface is covered by 0.7 ML OH groups from trace moisture in the reaction gas. In contrast, neither hydroxylation nor oxidation was observed on the (111) surface under similar mild exposure conditions. On Cu2O(111) the initial formation of CuO requires annealing to ∼400 ...

Mn-Modified CuO, CuFe2O4, and γ-Fe2O3 Three-Phase Strong Synergistic Coexistence Catalyst System for NO Reduction by CO with a Wider Active Window.

A series of samples with the precursor's molar ratio of {KMn8O16}/{CuFe2O4} = 0, 0.008, 0.010, 0.016, and 0.020 were successfully synthesized for selective catalytic reduction of NO by CO. The physicochemical properties of all samples were studied in detail by combining the means of X-ray photoelectron spectroscopy, H2-temperature-programmed reduction, scanning electron microscopy mapping, X-ray diffraction (XRD), N2 physisorption (Brunauer-Emmett-Teller), NO + CO model reaction, and in situ Fourier transform infrared spectroscopy techniques. The results show that three phases of γ-Fe2O3, CuFe2O4, and CuO, which have strong synergistic interaction, coexist in this catalyst system, and different phases play a leading role in different temperature ranges. Mn species are highly dispersed in the three-phase coexisting system in the form of Mn2+, Mn3+, and Mn4+. Because of the strong interaction between Mn2+ and Fe species, a small amount of Cu2+ precipitates from CuFe2O4 and grows along the CuO(110) plane, which has better catalytic performance. Mn3+ can inhibit the conversion of γ-Fe2O3 to α-Fe2O3 at high temperature and then increases the high-temperature activity. The synergistic effect between Mn4+ and the surfaces of three phases generates active oxygen species Cu2+-O-Mn4+ and Mn4+-O-Fe3+, which can be more easily reduced to some synergistic oxygen vacancies during the reaction. Furthermore, the formed synergistic oxygen vacancies can promote the dissociation of NO and are also propitious to the transfer of oxygen species. All of these factors make the appropriate manganese-modified three-phase coexisting system have better catalytic activity than the manganese-free catalyst, making NO conversion rate reach 100% at around 250 °C and maintain to 1000 °C. Combining comprehensive analysis of various characterization results and in situ infrared as well as XRD results in the equilibrium state, a new possible NO + CO model reaction mechanism was temporarily proposed to further understand the catalytic processes.

Treatment of aqueous solutions of 1,4-dioxane by ozonation and catalytic ozonation with copper oxide (CuO)

ABSTRACT In this study, treatment for the removal of 1,4-dioxane by ozone and by catalytic ozonation using CuO as the catalyst was investigated. While the removal of 1,4-dioxane was small (20%) and mineralization negligible after 6 h of ozonation treatment, the removals of 1,4-dioxane and total organic carbon increased by factors of 10.35 and 81.25, respectively, after catalytic ozonation in the presence of CuO. The mineralization during catalytic ozonation was favoured at pH 10 (94.91 min−1), although it proceeded even at pH 3 (54.41 min−1). The CuO catalyst decreased the equilibrium concentration of soluble ozone and favoured its decomposition to reactive oxidative species. Radical scavenging experiments demonstrated that superoxide radicals were the main species responsible for the degradation of 1,4-dioxane. Further scavenging experiments with phosphate confirmed the presence of Lewis active sites on the surface of CuO, which were responsible for the adsorption and decomposition of ozone. The reaction mechanism proceeded through the formation of ethylene glycol diformate, which quickly hydrolyzed to ethylene glycol and formic acid as intermediate products. The stability of CuO indicated weak copper leaching and high catalytic activity for five recycling cycles. The toxicity of the water, assessed by Vibrio fischeri bioluminescence assays, remained the same (low toxicity) after catalytic ozonation while it increased after treatment with ozonation alone.

Rapid low-temperature synthesis of hollow CuS0.55 nanoparticles for efficient electrocatalytic water oxidation

Developing low-cost and binder-free Cu-based electrocatalysts for high-performance oxygen evolution reactions (OER) is of great importance to promote their practical applications. Herein, we demonstrate the low-temperature and rapid synthesis of hollow CuS0.55 nanoparticles on a Cu foam as highly active OER electrocatalysts through an anodic oxidation electrodeposition technique. The large electrochemically active surface area and strong adsorption ability of Cu sites to targeted OOH∗ intermediates are beneficial for enhancing catalytic properties. As a consequence, the hollow CuS0.55 nanoparticles exhibit an ultralow overpotential of 386 mV to achieve a high current density of 100 mA cm−2 in alkaline media with a very small Tafel slope of 33 mV dec−1, which is among the best reported for Cu-based electrocatalysts. The turnover frequency (TOF) is approximately 6 times higher than those of the corresponding CuS0.57 and CuO catalysts. This work provides a simple and feasible approach that can be scaled up easily to construct low-cost and efficient Cu-based OER electrocatalysts.

Metal oxide catalyst-aided solvent regeneration: A promising method to economize post-combustion CO2 capture process

Abstract Despite the in-depth understanding of the amine-based post-combustion CO2 capture technique gained by research efforts made over the decades, its large-scale practicality is hindered by extensive energy input in desorption and solvent degradation issues. The most thoroughly studied alkanolamine solvent, monoethanolamine (MEA), is still unable to capture a significant portion of CO2 emissions at a bearable economic penalty, owing to these serious drawbacks. Herein, we demonstrate catalytic regeneration of MEA solvent with five commercially available metal oxide catalysts Ag2O, Nb2O5, NiO, CuO, and MnO2 which would render this process suitable for achieving a bearable penalty. CO2-rich MEA solvent with an initial loading of 0.50 mol CO2/mol MEA was used in this study. A temperature range of interest was selected to perform the experiments in order to identify the optimal operating temperature for each of the catalysts used in this study. The results show that all of the catalysts used in this study improve the MEA regeneration where Ag2O presents the best regeneration performance followed by Nb2O5 by desorbing up to 3.6 and 2.5 times greater CO2 amounts with faster desorption rates, respectively. Overall, the results show that the MEA solvent can be regenerated at temperature as low as 80 °C, and hence a significant reduction in heat requirement for solvent regeneration is possible. Besides, at this temperature, thermal degradation of the solvent can be avoided completely. Furthermore, as a considerable improvement in the CO2 desorption rate and cyclic capacity is achieved by the catalytic regeneration process, the size of the stripper and the solvent circulation rate can be reduced, which will decrease the capital and operating cost as well.

Silicon nanoparticles prepared from industrial wastes as high-performing anode materials for lithium ion batteries

Silicon (Si) nanostructures are considered to be the most promising anode materials for next-generation lithium batteries (LIBs) because of the very high theoretical capacity of Si. However, how to achieve a large-scale and cost-effective manufacture of them is still a big challenge. In this work, we report a facile and scalable method for preparation of two crystalline Si nanoparticle samples of 3P-2h (derived from a mixture of Cu, CuO and Cu2O catalyst) and S21-2h (derived from Cu2O catalyst). These Si samples are extracted from the wastes after reacting a metallurgical-grade Si with hydrogen chloride (HCl) gas catalyzed by the Cu catalysts. The latter is the typical industrial process used for production of organosilane monomers. The synthesized Si nanoparticles had a size of 100–300 nm. When used as anode materials for lithium ion batteries, 3P-2h delivered a reversible capacity of 636 mAh g−1 while S21-2h showed a reversible capacity of 529 mAh g−1 at 50 mA g−1 after 50 cycles, better than that of the bulk Si sample. These improved electrochemical properties are attributed to the formed nanostructure and the void spaces among the Si nanoparticles which can buffer the volume expansion and shorten the diffusion path of Li-ion. This work demonstrates the feasibility for a facile, green and scalable preparation of Si nanoparticles as high-performing anode material from industrial waste.

Catalytic effect of metal oxides on CO2 absorption in an aqueous potassium salt of lysine

We report the catalytic effects of metal oxides on the CO2 absorption rate in an aqueous potassium salt of l-lysine-HCl using the vapor liquid equilibrium method. The best CO2 absorption rate obtained through testing metal oxides in a highly concentrated potassium salt of amino acids (2.0M) was identified using CuO. The recyclability of the metal oxides was tested over three cycles. The catalyst CuO was found to enhance the absorption rate of CO2 by 61%. A possible mechanism was proposed based on NMR spectroscopy studies. Further, the effect of change in liquid absorbent viscosity on CO2 absorption is discussed.

CuO Nanoparticles as An Efficient Heterogeneous Catalyst for the 1,3‐Dipolar Cycloaddition of Dicarbonyl Compounds to Azides

AbstractSubstituted 1,2,3‐triazoles are important heterocyclic molecules with applications in diverse research areas. The organocatalytic (3+2) cycloaddition reaction of azides with active methylene compounds has proven to be a powerful strategy for the synthesis of a variety of 1,2,3‐triazoles with different substituents. However the reported methods in the literature, commonly used a homogenous organocatalyst. Considering this point, here we have reported a novel heterogeneous protocol for the synthesis of 1,4,5‐trisubstituted 1,2,3‐triazoles by reaction of different dicarbonyl compounds with aryl azides catalyzed by copper oxide nanoparticles under microwave irradiation. The important features of this methodology are high yield products, short reaction times and recyclability of the CuO catalyst.

Effect of various metal oxides phases present in CuMnOx catalyst for selective CO oxidation

Hopcalite (CuMnOx) is a highly efficient catalyst for low temperature oxidation of Carbon monoxide (CO). As synthesized by Co-precipitation method, it shows the high activity for CO oxidation. The coordination between CuO and MnOx in CuMnOx catalyst improves the catalytic activity for CO oxidation. In this research work, we investigate the individual catalytic activity of CuO and MnOx and compare with the multiphase CuMnOx catalyst. The performance of multiphase catalysts CuO and MnO2 were numerous times higher as compared to single phase CuMnOx. The activity order of catalysts for CO oxidation was as follows: CuMnOx> MnOx > CuOx. The success of CuMnOx catalyst has prompted a great deal of research work into each component and nature of active sites. In CuMnOx catalyst, the MnOx acts as an oxygen donor and CuO acts as an oxygen acceptor. The presence of MnOx is possible to assist in the reduction of CuO, due to the coordination between CuO and MnOx. The calcination strategies of precursors highly affect the physicochemical and catalytic properties of the catalysts for CO oxidation. The reactive calcination (RC) conditions (4.5% CO in air) for prepared catalysts showed the best activity result for CO oxidation, as compared to the traditional method of calcination.

A comparative study of CO oxidation over Cu-O-Ce solid solutions and CuO/CeO2 nanorods catalysts

The distribution of copper species (on the surface or in the bulk of CeO2 support) and the interfacial interactions between CuO and CeO2 are critical in understanding the synergistic effect on the catalytic activity of CeO2 supported CuO catalysts. In this report, Cu-O-Ce solid solutions and CuO impregnated on CeO2 nanorods catalysts (CuO/CeO2) with various compositions were prepared using thermal decomposition and hydrothermal methods, to understand the distribution effect of copper species on low temperature CO oxidation. The incorporation of copper ions into CeO2 lattice in both types of catalysts was confirmed by X-ray diffraction (XRD), Raman spectroscopy, and hydrogen temperature programmed reduction (H2-TPR) analysis, indicating a strong CuO-CeO2 interfacial interaction and formation of oxygen vacancies which compensates the charge difference between copper (I/II) and cerium (III/IV) ions. A series of temperature programmed reduction-temperature programmed oxidation (TPR-TPO) thermal cycling studies were conducted to understand the interactions between three assigned copper species (α, β, and γ) with CeO2 support and the corresponding catalytic performance of the catalysts. In addition, an improved low temperature catalytic performance for the CuO/CeO2 nanorods catalysts was observed, which was attributed to stronger interactions between copper species and CeO2 nanorods enriched with surface defects (steps and voids etc.).

The influence on the structural and redox property of CuO by using different precursors and precipitants for catalytic soot combustion

To gain fundamental understanding on the catalytic property of individual CuO for soot combustion, a series of CuO samples have been prepared with a simple precipitation method by using different Cu precursors and precipitants. Pure monoclinic CuO crystalline phase has been detected by XRD and Raman for all the samples. However, by changing the precursors and precipitants, the morphology and texture property of the CuO samples can be influenced. Furthermore, the redox property of the CuO catalysts can also be altered. Soot-TPR results have testified that four types of active sites with varied activity are present on the surface of all the samples, but only the two types of active sites that can be reduced by soot particles below 500 °C are believed to contribute effectively to soot combustion. It has been discovered that the surface oxygen mobility and abundance are the crucial factors to determine the soot combustion activity of CuO catalysts. Because of the optimal balance of these two factors, CuO-Cu(NO3)2-Na2CO3, a CuO catalyst prepared by the combination of Cu(NO3)2 precursor and aqueous Na2CO3 precipitant, displays the highest soot combustion activity among all the catalysts.

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

AbstractCarbon dioxide (CO2) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2O remains under debate because of the complex surface structure of Cu2O under reducing conditions, leading to limited guidance in designing improved Cu2O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu2O(111) for the CO2 reduction reaction (CO2RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (CuCUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO2RR. Moreover, the CO2RR was evaluated over Cu2O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2RR and suppress the HER.