Bamboo-like MnO2⋅Co3O4: High-performance catalysts for the oxidative removal of toluene

The manganese-cobalt mixed oxide nanorods were fabricated using a hydrothermal method with different metal precursors (KMnO4 and MnSO4·H2O for MnOx and Co(NO3)2⋅6H2O and CoCl2⋅6H2O for Co3O4). Bamboo-like MnO2⋅Co3O4 (B-MnO2⋅Co3O4 (S)) was derived from repeated hydrothermal treatments with Co3O4@MnO2 and MnSO4⋅H2O, whereas Co3O4@MnO2 nanorods were derived from hydrothermal treatment with Co3O4 nanorods and KMnO4. The study shows that manganese oxide was tetragonal, while the cobalt oxide was found to be cubic in the crystalline arrangement. Mn surface ions were present in multiple oxidation states (e.g., Mn4+ and Mn3+) and surface oxygen deficiencies. The content of adsorbed oxygen species and reducibility at low temperature declined in the sequence of B-MnO2⋅Co3O4 (S) > Co3O4@MnO2 > MnO2 > Co3O4, matching the changing trend in activity. Among all the samples, B-MnO2⋅Co3O4 (S) showed the preeminent catalytic performance for the oxidation of toluene (T10% = 187°C, T50% = 276°C, and T90% = 339°C). In addition, the B-MnO2⋅Co3O4 (S) sample also exhibited good H2O-, CO2-, and SO2-resistant performance. The good catalytic performance of B-MnO2⋅Co3O4 (S) is due to the high concentration of adsorbed oxygen species and good reducibility at low temperature. Toluene oxidation over B-MnO2⋅Co3O4 (S) proceeds through the adsorption of O2 and toluene to form O*, OH*, and H2C(C6H5)* species, which then react to produce benzyl alcohol, benzoic acid, and benzaldehyde, ultimately converting to CO2 and H2O. The findings suggest that B-MnO2⋅Co3O4 (S) has promising potential for use as an effective catalyst in practical applications.

Calcium-Poison-Resistant Cu/YCeO2-TiO2 Catalyst for the Selective Catalytic Reduction of NO with CO and Naphthalene in the Presence of Oxygen

The pollution from industrial processes based on biomass combustion is still an ongoing problem. In the present contribution, the selective catalytic reduction of NO with CO and naphthalene is carried out in the presence of 10% oxygen. The accumulation of alkaline and alkaline earth metals during biomass combustion is here simulated by the addition of calcium to a Cu-impregnated YCeO2-TiO2 support. The results show that a high dispersion of copper is obtained, which is resistant to the accumulation of calcium. Full conversion of CO and naphthalene is achieved above 200 °C, whereas NO conversions of 80, 90, and 87% are obtained for the catalysts with Ca loadings of 2.6, 5.2, and 13%, respectively, at 350 °C. It is proposed that the high activity of the catalysts is ascribed to the formation of Cu-Ox-Ce species and that the accumulation of Ca acts as a barrier to avoid copper sintering. It was found that different forms of carbonate and nitrite/nitrate species form during reaction, coexisting as adsorbed species during the SCR reaction. The selectivity to N2 was almost 100% in all cases, due to the small presence of NO2 in the reactor outlet (no N2O was detected in any conditions).

Deciphering Indirect Nitrite Reduction to Ammonia in High-Entropy Electrocatalysts Using In Situ Raman and X-ray Absorption Spectroscopies

This research adopts a new method combining calcination and pulsed laser irradiation in liquids to induce a controlled phase transformation of Fe, Co, Ni, Cu, and Mn transition-metal-based high-entropy Prussian blue analogs into single-phase spinel high-entropy oxide and face-centered cubic high-entropy alloy (HEA). The synthesized HEA, characterized by its highly conductive nature and reactive surface, demonstrates exceptional performance in capturing low-level nitrite (NO2 -) in an electrolyte, which leads to its efficient conversion into ammonium (NH4 +) with a Faradaic efficiency of 79.77% and N selectivity of 61.49% at -0.8 V versus Ag/AgCl. In addition, the HEA exhibits remarkable durability in the continuous nitrite reduction reaction (NO2 -RR), converting 79.35% of the initial NO2 - into NH4 + with an impressive yield of 1101.48 µm h-1 cm-2. By employing advanced X-ray absorption and in situ electrochemical Raman techniques, this study provides insights into the indirect NO2 -RR, highlighting the versatility and efficacy of HEA in sustainable electrochemical applications.

Combination of Rapid Intrinsic Activity Measurements and Machine Learning as a Screening Approach for Multicomponent Electrocatalysts

Machine learning (ML) coupled with quantum chemistry calculations predicts catalyst properties with high accuracy; however, ML approaches in the design of multicomponent catalysts primarily rely on simulation data because obtaining sufficient experimental data in a short time is difficult. Herein, we developed a rapid screening strategy involving nanodroplet-mediated electrodeposition using a carbon nanocorn electrode as the support substrate that enables complete data collection for training artificial intelligence networks in one week. The inert support substrate ensures intrinsic activity measurement and operando characterization of the irreversible reconstruction of multinary alloy particles during the oxygen evolution reaction. Our approach works as a closed loop: catalyst synthesis-in situ measurement and characterization-database construction-ML analysis-catalyst design. Using artificial neural networks, the ML analysis revealed that the entropy values of multicomponent catalysts are proportional to their catalytic activity. The catalytic activities of high-entropy systems with different components varied little, and the overall catalytic activity was greater than that of the medium-low-entropy system. These findings will serve as a guideline for the design of catalysts.

Visible active narrow/narrow band gap CuO/Cu2SnS3 nanoheterostructures as efficient nanophotocatalysts

Binary metal oxide/ternary metal sulphide based nanoheterostructures, such as CuO/Cu₂SnS₃, were prepared via a modified hydrothermal route. The prepared nanoheterostructures were characterized using scanning electron microscopy, x-ray powder diffractometer, XPS, ultraviolet-visible spectroscopy, isoelectric point, and Brunauer-Emmett-Teller techniques. The XPS results revealed the successful incorporation of Cu⁺/Cu²⁺ with different ratios. The prepared heterostructures were tested as solar active photocatalysts for Methylene Blue (MB) photodegradation. The CuO/Cu₂SnS₃ (20% Cu₂SnS₃/80% CuO) photocatalytic results exhibited a high photodegradation efficiency (90%) after 60 min. In addition, the photonic efficiency values (ζ) were calculated to be 15.9%, 44%, and 61.4% for CuO, Cu₂SnS₃, and CuO/Cu₂SnS₃ nanoheterostructures, respectively. In addition, the reactive oxidative species were detected by the trapping experiments to get a clear insight about the photocatalytic reactivity factors. Total organic carbon (TOC) was conducted to confirm the safe photodegradation of MB dye without the formation of colorless hazardous (95.5% TOC removal). Based on the electronic band structure, the mechanism of photodegradation was investigated. The currently investigated heterostructure system is narrow/narrow bandgap, which fulfills the two contradictory conditions in terms of high solar photocatalytic activity and overcomes the rapid recombination process.

Catalytic reduction of 4-nitrophenol using CuO@Na2Ti(PO4)2⋅H2O

This article presents the synthesis, property characterization and catalytic application of CuO-supported disodium titanium phosphate, (CuO@Na₂Ti(PO₄)₂⋅H₂O) for the reduction of industrial pollutant 4-nitrophenol (4-NP). A simple hydrothermal route was developed to synthesize CuO@Na₂Ti(PO₄)₂⋅H₂O catalyst (CuO@Na₂TiP) from beach sand ilmenite. The prepared CuO@Na₂TiP was characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms. The catalyst 12 wt.% CuO@Na₂TiP showed the fastest reduction kinetics for 4-NP.

Oxygen vacancy distributions and electron localization in a CeO2(100) nanocube

Oxygen vacancy distributions in a 5 nm CeO2 nanocube were determined using the Reverse Monte Carlo method. The oxygen vacancies tend to be located on the surface of the CeO2 nanocube, with far fewer in subsurface and internal regions.

Elucidating the structure, redox properties and active entities of high-temperature thermally aged CuOx-CeO2 catalysts for CO-PROX

CuOx-CeO2 catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N2 adsorption-desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu-Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T50% of 62 °C and the widest operation temperature window of 85-140 °C), which provided a new strategy for the design of Cu-Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuOx species and strongly bonded Cu-[Ox]-Ce species, strengthening the Cu-Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuOx-CeO2 catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuOx species and strongly bonded Cu-[Ox]-Ce species, respectively.

Shape Effects of Ceria Nanoparticles on the Water‒Gas Shift Performance of CuOx/CeO2 Catalysts

The copper–ceria (CuOx/CeO2) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx/CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R > P > C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+) through the Cu2+/Cu+ and Ce4+/Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx/CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350 °C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance.

Aqueous Na-ion capacitor with CuS graphene composite in symmetric and asymmetric configurations

The symmetric device shows a maximum specific energy density of 30 W h kg−1 at a specific power density of 380 W kg−1, which was reduced to 4 W h kg−1 at a highest specific power density of 4224 W kg−1.

Preferential Oxidation of CO over CoFe2O4 and M/CoFe2O4 (M = Ce, Co, Cu or Zr) Catalysts

CoFe2O4 prepared by sol-gel has been examined with respect to its catalytic performance for preferential CO oxidation in a H2-rich stream. In turn, the promoting effects of incorporation of Ce, Co, Cu, and Zr by impregnation on the surface of CoFe2O4 on the process are examined as well. The catalysts have been characterized by N2 adsorption, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR), and X-ray photoelectron spectra (XPS), as well as diffuse reflectance infrared DRIFTS under reaction conditions with the aim of establishing structure/activity relationships for the mentioned catalyst/process. It is shown that while the presence of the various metals on CoFe2O4 hinders a low temperature CO oxidation process, it appreciably enhances the activity above 125 °C. This is basically attributed to the surface modifications, i.e. cobalt oxidation, induced in CoFe2O4 upon introduction of the metals. In turn, no methanation activity is observed in any case except for the copper-containing catalyst, in which achievement of reduced states of cobalt appears most favored.

Elemental Core Level Shift in High Entropy Alloy Nanoparticles via X-ray Photoelectron Spectroscopy Analysis and First-Principles Calculation

High entropy alloy nanoparticles (HEA-NPs) are expanding their influence in many fields. To explore the electronic structures in such multielemental systems, HEA-NPs were synthesized on two different carbon substrates through carbothermal shock and in situ reduction methods. The relationship between the apparent core level energy shifts (negative or positive) and the electron density changes among the components of quinary-metal HEA-NPs was investigated by X-ray photoelectron spectroscopy (XPS) analysis and first-principles electronic structure calculations. It was found that Cu displays a negative core level shift while Fe, Co, Mg, Cr, and Mn display a positive core level shift. While experiments show an apparent positive core level shift for Ni, electronic structure calculations reveal that this arises from shifts in the Fermi level and that the electron density redistribution in Ni behaves more like Cu than the other elements. The findings show that the electron density redistribution in the NPs occurs from less electronegative elements to more electronegative ones. This work should guide the design of HEA-NPs to expand their potential applications in mechanical structures, medicine, catalysis, and energy storage/conversion.

Glycine–Nitrate Combustion Synthesis of Cu-Based Nanoparticles for NP9EO Degradation Applications

Copper-based nanoparticles were synthesized using the glycine–nitrate process (GNP) by using copper nitrate trihydrate [Cu(NO3)2·3H2O] as the main starting material, and glycine [C2H5NO2] as the complexing and incendiary agent. The as-prepared powders were characterized through X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy analysis. Using Cu(NO3)2·3H2O as the oxidizer (N) and glycine as fuel (G), we obtained CuO, mixed-valence copper oxides (CuO + Cu2O, G/N = 0.3–0.5), and metallic Cu (G/N = 0.7). The XRD and BET results indicated that increasing the glycine concentration (G/N = 0.7) and reducing the particle surface area increased the yield of metallic Cu. The effects of varying reaction parameters, such as catalyst activity, catalyst dosage, and H2O2 concentration on nonylphenol-9-polyethoxylate (NP9EO) degradation, were assessed. With a copper-based catalyst in a heterogeneous system, the NP9EO and total organic carbon removal efficiencies were 83.1% and 70.6%, respectively, under optimum operating conditions (pH, 6.0; catalyst dosage, 0.3 g/L; H2O2 concentration, 0.05 mM). The results suggest that the removal efficiency increased with an increase in H2O2 concentration but decreased when the H2O2 concentration exceeded 0.05 mM. Furthermore, the trend of photocatalytic activity was as follows: G/N = 0.5 > G/N = 0.7 > G/N = 0.3. The G/N = 0.5 catalysts showed the highest photocatalytic activity and resulted in 94.6% NP9EO degradation in 600 min.

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1-xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm-2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec-1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1-xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

Dispersion of copper oxide species on nanostructured ceria

Copper oxides species deposited on ceria rods, particles, and cubes were examined for low-temperature oxidation of CO. It was found that the shape of ceria altered the dispersion and chemical state of copper species considerably. CuO_x monolayers and bilayers were formed on ceria rods and particles, while multilayers and faceted particles co-existed on ceria cubes. The formation of Cu⁺ species at the copper-ceria interface involved a significant charge transfer from copper oxides to the ceria surface via a strong electronic interaction, which was more pronounced on ceria rods. The concentrations of surface Cu⁺ and oxygen vacancies followed the order rods > particles > cubes, in line with their catalytic activity for CO oxidation at 343 K.

Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.

A Facile Route to Fabricate Superhydrophobic Cu2O Surface for Efficient Oil–Water Separation

The mixture of insoluble organics and water seriously affects human health and environmental safety. Therefore, it is important to develop an efficient material to remove oil from water. In this work, we report a superhydrophobic Cu2O mesh that can effectively separate oil and water. The superhydrophobic Cu2O surface was fabricated by a facile chemical reaction between copper mesh and hydrogen peroxide solution without any low surface reagents treatment. With the advantages of simple operation, short reaction time, and low cost, the as-synthesized superhydrophobic Cu2O mesh has excellent oil–water selectivity for many insoluble organic solvents. In addition, it could be reused for oil–water separation with a high separation ability of above 95%, which demonstrated excellent durability and reusability. We expect that this fabrication technique will have great application prospects in the application of oil–water separation.

Effect of Y Modified Ceria Support in Mono and Bimetallic Pd–Au Catalysts for Complete Benzene Oxidation

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction.

Improved thermal stability of a copper-containing ceria-based catalyst for low temperature CO oxidation under simulated diesel exhaust conditions

CuO supported on a commercial mixed cerium–zirconium oxide shows remarkable improvement in CO oxidation after high temperature hydrothermal aging.

Effect of SiO2 support properties on the performance of Cu–SiO2 catalysts for the hydrogenation of levulinic acid to gamma valerolactone using formic acid as a hydrogen source

Vapor phase catalytic transfer hydrogenation of levulinic acid with formic acid was carried out over Cu–SiO₂ catalysts having different physicochemical properties.

An atomic-level insight into the basic mechanism responsible for the enhancement of the catalytic oxidation of carbon monoxide on a Cu/CeO2 surface

Reaction mechanism of CO molecules onto a Cu/CeO₂ surface and morphological changes.

Facile fabrication of CuO/Cu2O composites with high catalytic performances

CuO/Cu₂O composites having good catalytic properties for the reduction of 4-nitrophenol have been prepared facilely for wastewater treatment.

Designing CuOx Nanoparticle-Decorated CeO2 Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials

This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts.