CuO Catalyst Research Articles

Establishment of Integrated Analysis Method for Probing and Reconstructing Hydrogenation Mechanism of a Model Reaction

The hydrogenation of 4-nitrophenol (4-NP) has attracted much attention, since it is typically used as a model reaction for evaluating newly developed catalysts, but its mechanism is still debated. Herein, Co(OH)2-modified CuO catalyst (Co(OH)2/CuO) was used for the reduction of 4-NP to 4-aminophenol (4-AP) in an aqueous sodium borohydride (NaBH4) solution. The reaction mechanism was investigated by UV-Vis spectroscopy (UV-Vis), high-performance liquid chromatography (HPLC), HPLC-Q-orbitrap high-resolution mass spectrometry (LC-MS/MS), and 1HNMR spectroscopy (1HNMR) as an integrated technology at different concentrations of NaBH4. Samples were taken at specified time intervals and monitored using UV-Vis, HPLC, LC-MS/MS, and 1HNMR. With the help of comprehensive analysis, eight intermediates, including azo and azoxy compounds, were effectively captured, and the variation tendency of each intermediate was determined, revealing that the hydrogenation of 4-NP proceeds via a coexistence of the direct and condensation routes. The integrated analysis methods were powerful technical supports for the study of the catalysis mechanism.

Visible-light driven γ-Al2O3, CuO and γ-Al2O3/CuO nanocatalysts: Synthesis and enhanced photocatalytic activity

• A facile γ-Al 2 O 3 /CuO nanocatalyst were developed via hydrothermal process for enhance photocatalytic activity. • The degradation efficiency achieved to be 91% and 78% decomposition of MB and RhB dyes under visible light irradiation. • The higher photocatalytic performance was obtained due to efficient separation of the photo-induced electron-hole pairs and effective electron–hole generation. A novel and facile γ-Al 2 O 3 /CuO nanocomposites (NC S ) was fabricated via a hydrothermal technique for Visible light mediated photocatalytic activity. The synthesized samples of pure γ-Al 2 O 3 , CuO and γ-Al 2 O 3 /CuO NCs were analyzed using XRD, UV-DRS, PL, FT-IR, BET, and FESEM analysis techniques. The as prepared γ-Al 2 O 3 , CuO and γ-Al 2 O 3 /CuO catalysts were used to degrade Rhodamine B (RhB) and Methylene Blue (MB) textile dyes, which were studied using photocatalytic experiments. The degradation took place in the presence of visible light illumination. The degradation efficiency of γ-Al 2 O 3 , CuO, and γ-Al 2 O 3 /CuO nanocomposites for RhB and MB dyes was 52 %, 59 %, 78 %, and 65 %, 73 %, 91 %, respectively. The higher degradation efficiency was achieved by using γ-Al 2 O 3 /CuO nanocatalysts due to their efficient increase in photo-induced e - /h + charge separation and diminishes their charge carrier re-coupling factor.

CuO/ZrO2 co-promoted by ZnO, Sn, and CuP shows high efficiency for dimethyldichlorosilane production in the Rochow-Müller reaction

Multi-component promoters may efficiently improve the catalytic performance of the primary Cu-based catalysts in the Rochow-Müller reaction, but this approach is not well explored, and the roles of the promoters are not very clear. Herein, we report the ZrO2-supported CuO catalyst (CuO/ZrO2) modified with a co-promoter of ZnO, Sn, and CuP prepared by a simple dry ball-milling method. The co-promoter could significantly increase the amount of surface adsorbed oxygen and improve the reducing ability of catalysts, facilitating the formation of the active Cu3Si phase and further advancing dimethyldichlorosilane ((CH3)2SiCl2, M2) selectivity and Si conversion in the Rochow-Müller reaction. Compared to the state-of-the-art commercial catalyst, these CuO/ZrO2 catalysts with the co-promoters all showed enhanced catalytic activity. Especially, the CuO/ZrO2 catalyst with the co-existence of ZnO, Sn, and CuP promoters achieved the highest M2 selectivity and Si conversion, attributed to its most abundant surface adsorption oxygen and the strongest reducibility. This work opens up a new avenue to improve the catalytic activity of Cu-based catalysts for the Rochow-Müller reaction.

First-principles study on CO oxidation on CuO(111) surface prefers the Eley−Rideal or Langmuir−Hinshelwood pathway

Using the first-principles approach, we investigated the electronic and chemical properties of cupric oxide CuO (110) and CuO (111) and substantiated their catalytic activity toward CO oxidation. It is found that CuO (111) surface is more stable than the CuO (110) surface. We firstly study that adsorption of CO and O2 on perfect, oxygen vacancies and Cu-anchored CuO (111) surface. It is found that adsorption of CO and O2 molecules are chemical. Then we selected the most stable adsorption structure of CO/O2 to investigated the CO oxidation mechanism on different surface, here we choose to study the Langmuir–Hinshelwood (LH) mechanism and Eley–Rideal (ER) mechanism. The results show that perfect and Ovacancy CuO (111) surface is more inclined to LH mechanism, while the Cu-anchored CuO (111) surface is more inclined to ER mechanism. The results show that CuO catalyst is very effective for CO oxidation. Our work provides a deep understanding for the search of economical and reasonable CO oxidation catalysts.

Investigation of the promotion effect of Mo doped CuO catalysts for the low-temperature performance of NH3-SCR reaction

A novel Mo-doped CuO catalyst is developed and used for low-temperature NH3-SCR reaction. Compared with the undoped CuO sample, the Mo doped CuO catalyst shows an increased SCR performance with above 80% NOx conversion at 175 °C. The XRD and Raman results have confirmed the incorporation of Mo metal ions into CuO lattice to form Mo-O-Cu species which may be related to the enhanced SCR activity. The XPS and UV–vis results reveal the creation of electron interaction between Cu and Mo in this Mo-O-Cu system which provides an increased amount of Lewis and Brønsted acid sites, thereby promoting the adsorption capacity of NH3 and NOx as verified by NH3-TPD and NOx-TPD characterization. Besides, it also promotes the formation of oxygen vacancies, leading to the increasing of chemisorbed oxygen species, which improves the NO oxidation to NO2 activity. Furthermore, in situ DRIFTS technology was also used to study the reaction mechanism of this Mo doped CuO catalyst. The formed NO2 could react with NHx (x = 3, 2) species to enhance the low-temperature NH3-SCR activity via the “fast-SCR” reaction pathway. The nitrate and nitrite ad-species may react with NH3 and NH4+ ad-species through the L-H pathway.

Synthesis of TixSn1-xO2 mixed metal oxide for copper catalysts as high-efficiency NH3 selective catalytic oxidation

A series of y Cu/TixSn1-xO2 catalysts for selective catalytic oxidation (NH3-SCO) were synthesized using TixSn1-xO2 as catalyst support and CuO as active species. Compared with pure TiO2 support, the strong metal-support interaction between Cu active species and TixSn1-xO2 was significantly promoted by the Sn-doping, thereby improving the catalytic activity and N2 selectivity of the catalyst, which meets the demand of diesel vehicles to completely convert NH3. The results of XRD and HRTEM showed that the particle size of 20 Cu/TiSnO2 sample is much more highly dispersed. The results of NH3-TPD and in-situ DRIFTS indicated that the copper species in 20 Cu/TixSn1-xO2 can provide more Lewis acid sites than 20 Cu/TiO2, which is conducive to the adsorption and reaction of NH3. Meanwhile, XPS results proved that adsorbed oxygen on the catalyst surface is the main active oxygen species. Finally, in-situ DRIFTs and kinetic measurements found that the NH3-SCO reaction over 20 Cu/TiSnO2 and 20 Cu/TiO2 follow the i-SCR and imide (–NH) mechanisms, respectively. This catalyst will provide solutions for the future design and application of ammonia slip from mobile and stationary sources.

Surface/Interface Reconstruction In-Situ on Cu2o Catalysts with High Exponential Facets Toward Enhanced Electrocatalysis Co2 Reduction to C2+ Products

Surface/Interface Reconstruction In-Situ on Cu2o Catalysts with High Exponential Facets Toward Enhanced Electrocatalysis Co2 Reduction to C2+ Products

Oxidation of Sulfide with the Cuo Catalyst Assisted Oxygen Microbubbles in Alkaline Wastewater: Efficiency, Sulfur Conversion, and Mechanisms

Oxidation of Sulfide with the Cuo Catalyst Assisted Oxygen Microbubbles in Alkaline Wastewater: Efficiency, Sulfur Conversion, and Mechanisms

Production of γ-valerolactone over mesoporous CuO catalysts using formic acid as the hydrogen source

In the present study, the conversion of levulinic acid (LA), butyl levulinate (BL), and ethyl levulinate (EL) to valuable biomass-derived compound γ-valerolactone (GVL) is studied.

Correction: Synthesis of sub-nanometric Cu2O catalysts for Pd-free C–C coupling reactions

Correction for ‘Synthesis of sub-nanometric Cu2O catalysts for Pd-free C–C coupling reactions’ by Ankit Agrawal et al., React. Chem. Eng., 2021, 6, 929–936, https://doi.org/10.1039/D1RE00054C.

Cu2O nano-flowers/graphene enabled scaffolding structure catalyst layer for enhanced CO2 electrochemical reduction

Nanosized Cu2O catalysts with precisely controlled bud-to-blooming flower shapes are synthesised using modified polyol method. The evolution of the shape when the catalysts are applied to the gas diffusion electrodes improves the key factors influencing the catalyst layer, e.g. volume porosity and triple-phase boundary contact areas. Numerical and experimental studies revealed increased reactant molar concentration and improved CO2 mass transfer due to the structural changes, which influenced the electrochemical CO2 reduction reaction (eCO2RR). The fully bloomed Cu2O nanoflower catalyst, combined with the two-dimensional (2D) structured graphene sheet, formed a catalyst layer with scaffolding structure that exhibited the highest Faradaic efficiency (FE) of 93.20% towards CO at an applied potential of −1.0 V vs. RHE in 1 M KOH. These findings established the relationship between the catalyst layer properties and mass transfer, based on which we could describe the effect of the structural design of the catalyst layer on the eCO2RR performance.

Hybrid effect of the activated carbon and the CuO catalyst on vegetable oil steam reforming

This study aims to utilize of bio material to produce green hydrogen energy through hybrid of the activated carbon and the CuO catalyst in vegetable oil steam reformer. The experiment was done in the atmospheric pressure steam reformer. The results show that activated carbon and CuO individually performs the same trend in producing hydrogen. Their combination accelerates hydrogen production. This indicates that heat energy makes CuO alters the electron density around the reactant by combining the van der Waals force with the induction due to electron jump in its narrow ban gap. Therefore, CuO activate effectively the polar water (H2O) molecules. More energy is needed to alter the electron in stable large molecule triglyceride of vegetable oil. On the other hand, the activated carbon does it by combining the van der Waals force with the induction due to delocalized of the pi electrons travelling between carbon atoms in the graphite structure. Consequently, only the nonpolar triglyceride molecules are attracted while the polar H2O are repelled by hydrophobic force. Thus, larger energy is needed to activate electrons in H2O. When they are combined, the CuO works only on H2O while activated carbon does only on triglyceride which is highly effective. Copyright © 2018 VBRI Press.

Mesoporous CuO/TiO2 catalysts prepared by the ammonia driven deposition precipitation method for CO preferential oxidation: Effect of metal loading

Supported CuO catalysts onto a highly crystalline mesoporous TiO2 material are produced via an ammonium driven deposition precipitation method and tested for preferential oxidation of CO in H2-rich gases. The effect of Cu loading on the oxidation activity is investigated by producing samples with final Cu content varying between 2.5 and 10 wt%. According to the analysis results, the chemical nature of the CuO species differs in each sample depending on the Cu loading. All materials tested are highly selective towards CO oxidation up to 160 °C. The 5 wt% Cu loaded material demonstrates the optimum CO-PROX performance, which is ascribed to the formation of finely dispersed and easily reducible copper oxide nanoparticles. Stability and durability of the latter sample are assessed by performing multiple testing cycles corresponding to >100hrs on stream as well as by the separate and combined addition of CO2 and H2O in the feeding stream.

Novel insights into diethylamine catalytic combustion over CuO catalysts supported by SSZ-13: Undesirable product NOx as a crucial intermediate for N2 generation

Catalytic combustion of nitrogen-containing volatile organic compounds (NVOCs) could effectively control N2 generation rather than NOx, but its mechanism is still not well answered. Herein, a series of CuO supported by SSZ-13 catalysts (denoted as Cu/S) were prepared for the catalytic combustion of diethylamine (DEA), a typical NVOCs. The effects of CuO loading and calcined temperature of catalysts on the catalytic performance were investigated. Among the Cu/S catalysts, the 10CuO/S-450 catalyst exhibits the highest oxidation activity (lowest T99 of 240 °C), and widest temperature window (△T = 120 °C) for high N2 selectivity (>99%). This result is ascribed to its highest ratio of easily reduced CuO active species. Importantly, there are two important steps for DEA combustion (I: catalytic oxidation to NOx; II: selective catalytic reduction of NOx with DEA to N2). Selective catalytic reduction of NOx with DEA is the very crucial pathway for N2 generation. The easily reduced CuO species play crucial roles on both catalytic oxidation and selective catalytic reduction. In addition, water vapor (5 vol.%) slightly improved oxidation activity of DEA, and increased N2 selectivity at high temperature (>350 °C), but the catalytic oxidation activity of intermediate CO was decreased caused by the competitive adsorption of water vapor.

Efficient catalytic degradation of organic pollutants with cupric oxide nanomaterials in aqueous medium

In this work, an eco-friendly, facile, and efficient method has been applied for CuO nanostructures (NSs) synthesis using ascorbic acid as capping agent. For surface morphology, FESEM analysis was applied to reveal nanostructure with ~100 nm length, and ~90 nm width morphology which was also supported by TEM images of CuO. Thus obtained CuO NSs resulted in an optical energy having ~1.36 eV band gap obtained from Tauc plots of UV–visible plots because of strong quantum confinement effect of nanoparticles. XRD reveals a monoclinic phase of CuO NSs for which follow the reference JCPDS No. 98–004–3179 (Space group of C 12/c 1) crystal structure with high crystallinity of ~95.94% and crystallite size of ~38 nm. In addition, Williamson-Hall analysis was applied to calculate crystal lattice strain of ~3.01 × 10-3 for CuO catalyst followed by 28.36 m2/g high BET surface area (0.9999 correlation coefficient) having ~14.38 nm average BJH pore size. Furthermore, CuO NSs exhibited ultrafast and high catalytic degradation efficiency of ~90.54% for Allura Red AC dye (AR dye) in 480 s under UV light. The photodegradation kinetics followed a pseudo first-order reaction with rate constant (k) of ~0.0046 s−1 having approximately ~150.65 s of half-life (t1/2) for AR dyes in the aquatic medium as per the Langmuir–Hinshelwood model. As synthesized catalyst, CuO NSs explored good leaf-like morphology with high recycling ability after five degradation cycles of AR dye in aqueous medium.

Br-Doped CuO Multilamellar Mesoporous Nanosheets with Oxygen Vacancies and Cetyltrimethyl Ammonium Cations Adsorption for Optimizing Intermediate Species and Their Adsorption Behaviors toward CO2 Electroreduction to Ethanol with a High Faradaic Efficiency.

It is a prospective tactic to actualize the carbon cycle via CO2 electroreduction reaction (CO2ER) into ethanol, where the crucial point is to design highly active and selective electrocatalysts. In this work, Br-doped CuO multilamellar mesoporous nanosheets with oxygen vacancies and cetyltrimethyl ammonium (CTA+) cations adsorption were synthesized on Cu foam by one-step liquid-phase method at room temperature. The nanosheets with numerous mesopores and rough edges provided abundant active sites for the adsorption of CO2 molecules and brought about a long retention time for intermediates. The dopant of Br- ions induced copious oxygen vacancies on CuO lattices, thereby reducing the activation energy of CO2 molecules and optimizing intermediate species and their adsorption behaviors, while adsorbed CTA+ cations modulated the O affinity of the Cu sites, favoring *OCH2CH3 intermediate converting to ethanol. The optimized Br1.95%-CuO can effectively catalyze CO2ER to C2H5OH in 0.1 M KHCO3. The faradaic efficiency of C2H5OH reached 53.3% with the partial current density of 7.1 mA cm-2 at a low potential of -0.6 V. In addition, after 14 h CO2ER test at -0.6 V, the current density and faradaic efficiency of C2H5OH on Br1.95%-CuO retained 99.6 and 93.9% of their original values, respectively, indicating its prominent catalytic stability. This work provided a novel strategy for designing a CuO catalyst by nonmetal doping and long-chain organic molecules adsorption with multiple active sites for optimizing intermediate species and their adsorption behaviors toward CO2ER to ethanol.

Highly Efficient CO2 Electroreduction to Methanol through Atomically Dispersed Sn Coupled with Defective CuO Catalysts

AbstractUsing renewable electricity to drive CO2 electroreduction is an attractive way to achieve carbon‐neutral energy cycle and produce value‐added chemicals and fuels. As an important platform molecule and clean fuel, methanol requires 6‐electron transfer in the process of CO2 reduction. Currently, CO2 electroreduction to methanol suffers from poor efficiency and low selectivity. Herein, we report the first work to design atomically dispersed Sn site anchored on defective CuO catalysts for CO2 electroreduction to methanol. It exhibits high methanol Faradaic efficiency (FE) of 88.6 % with a current density of 67.0 mA cm−2 and remarkable stability in a H‐cell, which is the highest FE(methanol) with such high current density compared with the results reported to date. The atomic Sn site, adjacent oxygen vacancy and CuO support cooperate very well, leading to higher double‐layer capacitance, larger CO2 adsorption capacity and lower interfacial charge transfer resistance. Operando experiments and density functional theory calculations demonstrate that the catalyst is beneficial for CO2 activation via decreasing the energy barrier of *COOH dissociation to form *CO. The obtained key intermediate *CO is then bound to the Cu species for further reduction, leading to high selectivity toward methanol.

Highly Efficient CO2 Electroreduction to Methanol through Atomically Dispersed Sn Coupled with Defective CuO Catalysts.

Using renewable electricity to drive CO2 electroreduction is an attractive way to achieve carbon-neutral energy cycle and produce value-added chemicals and fuels. As an important platform molecule and clean fuel, methanol requires 6-electron transfer in the process of CO2 reduction. Currently, CO2 electroreduction to methanol suffers from poor efficiency and low selectivity. Herein, we report the first work to design atomically dispersed Sn site anchored on defective CuO catalysts for CO2 electroreduction to methanol. It exhibits high methanol Faradaic efficiency (FE) of 88.6 % with a current density of 67.0 mA cm-2 and remarkable stability in a H-cell, which is the highest FE(methanol) with such high current density compared with the results reported to date. The atomic Sn site, adjacent oxygen vacancy and CuO support cooperate very well, leading to higher double-layer capacitance, larger CO2 adsorption capacity and lower interfacial charge transfer resistance. Operando experiments and density functional theory calculations demonstrate that the catalyst is beneficial for CO2 activation via decreasing the energy barrier of *COOH dissociation to form *CO. The obtained key intermediate *CO is then bound to the Cu species for further reduction, leading to high selectivity toward methanol.

Photocatalytic performance of binary and ternary Pt–Cu2O–BiVO4 catalysts under visible-light irradiation

Various Pt–Cu2O–BiVO4 ternary and binary hybrid composite catalysts were synthesized using in-situ methods. Cuprous oxide and platinum were obtained by chemical reduction of copper sulfate and hexachloroplatinic acid, respectively, while BiVO4 was synthetized by ultrasonic spray pyrolysis. All the synthesis routes allowed the formation of ternary and binary catalysts without the presence of impurities. The materials were structurally characterized using X-ray diffraction, morphologically by scanning electron microscopy and transmission electron microscopy, optically with UV–vis diffuse reflectance spectroscopy, and photocatalytically during the degradation of methyl orange (MO) under visible-light irradiation. TEM images confirmed the formation of heterojunctions and the deposition of metallic particles on the semiconductor surfaces. A similar performance was displayed by Cu2O/Pt–BiVO4, Pt-(Cu2O/BiVO4), Pt–BiVO4 and Cu2O/BiVO4 photocatalysts showing ca. 90% of MO degradation, which could indicate a competitive mechanism between Pt and Cu2O as co-catalysts of ternary composites. A significant content of Cu2O in the photocatalysts generated an important dye absorption, like in Cu2O and Pt–Cu2O catalysts. Cu2O/Pt–BiVO4 exhibited the highest production of hydroxyl radicals, indicating the important role of Pt deposition to increase the photocatalytic performance of the semiconductors via the electron sink effect.

Synthesis of Cu2O Nanostructures with Tunable Crystal Facets for Electrochemical CO2 Reduction to Alcohols.

Electrochemical CO2 reduction enables the conversion of intermittent renewable energy to value-added chemicals and fuel, presenting a promising strategy to relieve CO2 emission and achieve clean energy storage. In this work, we developed nanosized Cu2O catalysts using the hydrothermal method for electrochemical CO2 reduction to alcohols. Cu2O nanoparticles (NPs) of various morphologies that were enclosed with different crystal facets, named as Cu2O-c (cubic structure with (100) facets), Cu2O-o (octahedron structure with (111) facets), Cu2O-t (truncated octahedron structure with both (100) and (111) facets), and Cu2O-u (urchin-like structure with (100), (220), and (222) facets), were prepared by regulating the content of a polyvinyl pyrrolidone (PVP) template. The electrochemical CO2 reduction performance of the different Cu2O NPs was evaluated in the CO2-saturated 0.5 M KHCO3 electrolyte. The as-synthesized Cu2O nanostructures were capable of reducing CO2 to produce alcohols including methanol, ethanol, and isopropanol. The alcohol selectivity of the different Cu2O NPs followed the order of Cu2O-t < Cu2O-u < Cu2O-c < Cu2O-o (with the total Faradaic efficiencies of alcohol products of 10.7, 25.0, 26.2, and 35.4%). The facet-dependent effects were associated with the varied concentrations of oxygen-vacancy defects, different energy barriers of CO2 reduction, and distinct Cu-O bond lengths over the different crystal facets. The desired Cu2O-o catalyst exhibited good reduction activity with the highest partial current density of 0.51 mA/cm2 for alcohols. The Faradaic efficiencies of alcohol products were 4.9% for methanol, 17.9% for ethanol, and 12.6% for isopropanol. The good electrochemical CO2 reduction performance was also associated with the surface reconstruction of Cu2O, which endowed the catalyst with abundant Cu0 and Cu+ sites for promoted CO2 activation and stabilized CO* adsorption for enhanced C-C coupling. This work will provide a new route for enhancing the alcohol selectivity of nanostructured Cu2O catalysts by crystal facet engineering.