Efficient CO Oxidation by 50-Facet Cu2O Nanocrystals Coated with CuO Nanoparticles

Electrochemical Synthesis of Copper Mesh-Supported Thermo-Catalysts

Metallic substrates, widely studied in the context of monolithic catalysts, offer inherent advantages in heterogeneous catalysis due to their exceptional thermal conductivity and mechanical properties. However, synthesizing stable monolithic catalysts with metallic substrates in a well-controlled manner remains a significant challenge. Here, this work introduces a simple, cost-efficient method to fabricate robust Cu mesh-supported thermo-catalysts using a modified cycling chronopotentiometry approach, where the Cu mesh serves as a donor of Cu ions. In this method, the Cu mesh surface generates two distinct layers of CuO and Cu2O. In this context, CuO acts as the active phase, accounting for the high CO oxidation activity of Cu mesh catalysts with T90 ≈ 120 °C. Additionally, these catalysts exhibit considerable potential in electrocatalysis, showcasing significant research and application value.

Functional cellulose aerogel nanocomposites with enhanced adsorption capability and excellent photocatalytic performance

A novel functional cellulose carbon aerogel@Na₂Ti₃O₇@Cu₂O (CA@Na₂Ti₃O₇@Cu₂O) nanocomposite was prepared by in situ growth technique and impregnation method, and its photocatalytic and adsorption properties were explored. The cationic intercalation structure of Na₂Ti₃O₇ nanosheets gives CA@Na₂Ti₃O₇@Cu₂O nanocomposites excellent adsorption capacity of heavy metal ions (31.0-118.7 mg/g). The Cu₂O nanoparticles in CA@Na₂Ti₃O₇@Cu₂O nanocomposite showed excellent photocatalytic activity, and the removal rate of methylene blue (MB) was up to 99 %. Furthermore, the CA@Na₂Ti₃O₇@Cu₂O nanocomposites could be easily regenerated and reused, providing a new way to effectively solve the problem of wastewater treatment containing heavy metal ions and organic dyes.

Heterojunctioned CuO/Cu2O catalyst for highly efficient ozone removal

In recent years, near surface ozone pollution, has attracted more and more attention, which necessitates the development of high efficient and low cost catalysts. In this work, CuO/Cu₂O heterojunctioned catalyst is fabricated by heating Cu₂O at high temperature, and is adopted as ozone decomposition catalyst. The results show that after Cu₂O is heated at 180°C conversion of ozone increases from 75.2% to 89.3% at mass space velocity 1,920,000 cm³/(g·hr) in dry air with 1000 ppmV ozone, which indicates that this heterojunction catalyst is one of the most efficient catalysts reported at present. Catalysts are characterized by electron paramagnetic resonance spectroscopy and ultraviolet photoelectron spectroscopy, which confirmed that the heterojunction promotes the electron transfer in the catalytic process and creates more defects and oxygen vacancies in the CuO/Cu₂O interfaces. This procedure of manufacturing heterostructures would also be applicable to other metal oxide catalysts, and it is expected to be more widely applied to the synthesis of high-efficiency heterostructured catalysts in the future.

Super-Branched PdCu Alloy for Efficiently Converting Carbon Dioxide to Carbon Monoxide

The alloying of noble metals with Cu is one of the most effective strategies for improving catalytic performance and reducing cost in electrocatalytic carbon dioxide reduction reactions (CO₂RR). Previous works usually focused on the influence of morphology and composition on the catalytic activity, but lacked the study of the valence state ratio of metals and the electron transfer behavior on alloys. In this work, PdCu-2 alloy (Pd/Cu molar ratio is 1:2) was obtained by a simple one-step solvothermal method, which can effectively convert CO₂ to CO with a maximum Faradaic efficiency (FE) of 85% at -0.9 V (vs. RHE). Then, the effect of the chemical state of Pd and Cu on the catalytic performance was investigated. The X-ray photoelectron spectroscopy (XPS) shows that the binding energy of Pd in PdCu alloy has a negative shift, which has affected the adsorption of key intermediates. When the proportion of oxidized state and zero-valent metal in the alloy is about 1:2, the PdCu alloy shows the best catalytic activity. In addition, the transient photovoltage (TPV) measurements further demonstrate that due to the introduction of Cu, the electron transfer rate of PdCu-2 becomes the slowest, which helps the accumulation of electrons on PdCu-2 and leads to the improvement of catalytic performance for electrocatalytic CO₂RR. This work can provide more insights into the alloy catalysts of electrocatalytic CO₂RR.

Insight into the Effect of Oxygen Vacancy Prepared by Different Methods on CuO/Anatase Catalyst for CO Catalytic Oxidation

In this study, CuO loaded on anatase TiO2 catalysts (CuO/anatase) with oxygen vacancies was synthesized via reduction treatments by NaHB4 and H2 (CuO/anatase-B, CuO/anatase-H), respectively. The characterizations suggest that different reduction treatments bring different concentration of oxygen vacancies in the CuO/anatase catalysts, which finally affect the CO catalytic performance. The CuO/anatase-B and CuO/anatase-H exhibit CO conversion of 90% at 182 and 198 °C, respectively, which is lower than what occurred for CuO/anatase (300 °C). The XRD, Raman, and EPR results show that the amount of the oxygen vacancies of the CuO/anatase-H is the largest, indicating a stronger reduction effect of H2 than NaHB4 on the anatase surface. The in situ DRIFTS results exhibit that the Cu sites are the adsorption sites of CO, and the oxygen vacancies on the anatase can active the O2 molecules into reactive oxygen species. According to the in situ DRIFTS results, it can be concluded that in the CO oxidation reaction, only the CuO/anatase-H catalyst can be carried out by the Mvk mechanism, which greatly improves its catalytic efficiency. This study explained the reaction mechanisms of CO oxidation on various anatase surfaces, which offers detailed insights into how to prepare suitable catalysts for low-temperature oxidation reactions.

Batoko plum (Flacourtia inermis) peel extract attenuates deteriorative oxidation of selected edible oils

The oxidation of oils has an adverse effect on the organoleptic properties and shelf-life of stored oils. Flacourtia inermis is one of the underutilized fruits grown in Sri Lanka with promising antioxidant properties. F. inermis peel extract (FIPE) was used to retard rancidity in edible oils. The efficacy of added FIPE (500, 1000, 2000 ppm) on sunflower oil (SO) and virgin coconut oil (VCO) was monitored at 3-day intervals at 65 ± 5 °C against a positive control (α-tocopherol at 500 ppm level) using Free Fatty Acid (FFA) and Peroxide Value (PV). Oils without FIPE were used as the control. Antioxidant efficacy (IC50) and Total Phenol Content (TPC) of FIPE were determined by DPPH assay and the Folin-Ciocalteu method. Fourier transform infrared spectroscopy was used to monitor the oxidative stability. The IC50 value and TPC of FIPE were 227.14 ± 4.12 µg·mL-1 and 4.87 ± 0.01 mg GAE/g extract, respectively. After 21 days, VCO (control) sample exhibited significantly (p < 0.05) higher FFA and PV than the treatments. FIPE exhibited comparable results with α-tocopherol. Conclusively, FIPE had strong antioxidant properties and thus, could be used as an alternative to α-tocopherol to improve the oxidative stability of virgin coconut oil and sunflower oil. However, only minor differences in the FTIR spectra were detected in treated and untreated virgin coconut and sunflower oil samples after 21 days storage at 65 ± 5 °C.

Strategies for Improved Electrochemical CO2 Reduction to Value-added Products by Highly Anticipated Copper-based Nanoarchitectures

Uncontrolled CO₂ emission from various industrial and domestic sources is a considerable threat to environmental sustainability. Scientists are trying to develop multiple approaches to not only reduce CO₂ emissions but also utilize this potent pollutant to get economically feasible products. The electrochemical reduction of CO₂ (ERC) is one way to effectively convert CO₂ to more useful products (ranging from C1 to C5). Nevertheless, this process is kinetically hindered and less selective towards a specific product and, consequently, requires an efficient electrocatalyst with characteristics like selectivity, stability, reusability, low cost, and environmentally benign. Owing to specified commercial features, copper (Cu)-based materials are highly anticipated and widely investigated for the last two decades. However, their non-modified polycrystalline Cu forms usually lack selectivity and lower overpotential of CO₂ reduction. Therefore, extensive research is in progress to induce various alterations ranging from morphological and surface chemistry tuning to structural and optoelectrical characteristics modifications. This review provides an overview of those strategies to improve the CO₂ conversion efficiency through Cu-based ERC into valuable C1, C2_, and higher molecular weight hydrocarbons. The thermodynamics and kinetics of CO₂ reduction via Cu-based electrocatalysts are discussed in detail with the support of the first principle DFT-based models. In the last portion of the review, the reported mechanisms for various products are summarized, with a short overview of the outlook. This review is expected to provide important basics as well as advanced information for experienced as well as new researchers to develop various strategies for Cu and related materials to achieve improved ERC.

Potential Link between Cu Surface and Selective CO2 Electroreduction: Perspective on Future Electrocatalyst Designs

Electrochemical reduction of carbon dioxide (CO₂ RR) product distribution has been identified to be dependent on various surface factors, including the Cu facet, morphology, chemical states, doping, etc., which can alter the binding strength of key intermediates such as *CO and *OCCO during reduction. Therefore, in-depth knowledge of the Cu catalyst surface and identification of the active species under reaction conditions aid in designing efficient Cu-based electrocatalysts. This progress report categorizes various Cu-based electrocatalysts into four main groups, namely metallic Cu, Cu alloys, Cu compounds (Cu + non-metal), and supported Cu-based catalysts (Cu supported by carbon, metal oxides, or polymers). The detailed mechanisms for the selective CO₂ RR are presented, followed by recent relevant developments on the synthetic procedures for preparing Cu and Cu-based nanoparticles. Herein, the potential link between the Cu surface and CO₂ RR performance is highlighted, especially in terms of the chemical states, but other significant factors such as defective sites and roughened morphology of catalysts are equally considered during the discussion of current studies of CO₂ RR with Cu-based electrocatalysts to fully understand the origin of the significant enhancement toward C₂ formation. This report concludes by providing suggestions for future designs of highly selective and stable Cu-based electrocatalysts for CO₂ RR.

Elucidating the Nature of the Cu(I) Active Site in CuO/TiO2 for Excellent Low-Temperature CO Oxidation

Stabilized Cu⁺ species have been widely considered as catalytic active sites in composite copper catalysts for catalytic reactions with industrial importance. However, few examples comprehensively explicated the origin of stabilized Cu⁺ in a low-cost and widely investigated CuO/TiO₂ system. In this study, mass producible CuO/TiO₂ catalysts with interface-stabilized Cu⁺ were prepared, which showed excellent low-temperature CO oxidation activity. A thorough characterization and theoretical calculations proved that the strong charge-transfer effect and Ti-O-Cu hybridization in Ti-doped CuO(111) at the CuO/TiO₂ interface contributed to the formation and stabilization of Cu⁺ species. The CO molecule adsorbed on Cu⁺ and reacted directly with Ti doping-promoted active lattice oxygen via a Mars-van Krevelen mechanism, leading to the enhanced low-temperature activity.

Nanoengineering ABO3 active sites from low-energy routes (TX100-stabilised water-in-oil microemulsions, surface segregation and surface complexation on colloidal AlOOH/sol-gel Al2O3 surfaces) for pollution control catalysis

It is shown that water-in-oil microemulsions (m/e or μE) can produce BaCeO3 (BCO) and LaCoO3 (LCO) precursors. The nanoparticles (NPs) adsorb on AlOOH sols, in much the same way as Turkevich previously immobilised platinum group metal sols. BCO is active in CO and propane oxidation and NO removal under stoichiometric exhaust conditions, but LCO is a better oxidation catalyst. Activity was also seen when Ba,Ce and La,Co are inserted into/segregate at the surface of AlOOH/Al2O3. However, there is only formation of low levels of BCO, CAIO3 (CAO), LCO and LaAIO3 (LAO) perovskites, along with aluminates and separate oxides. The complexing of cations by AlOOH surface-held oxalate ions, albeit with different efficiencies, has also been explored. All three routes yield active catalysts with micro-domains of crystallinity; microemulsions produce the best defined perovskite NPs, but even those from surface segregation have higher turnover numbers than traditional Pt catalysts. Perovskite NPs may open up green chemistry for air pollution control that is consistent with a circular economy.

Vertically-aligned Co3O4 arrays on Ni foam as monolithic structured catalysts for CO oxidation: effects of morphological transformation

A generic hydrothermal synthesis route has been successfully designed and utilized to in situ grow highly ordered Co3O4 nanoarray (NA) precursors on Ni substrates, forming a series of Co3O4 nanoarray-based monolithic catalysts with subsequent calcination. The morphology evolution of Co3O4 nanostructures which depends upon the reaction time, with and without CTAB or NH4F is investigated in detail, which is used to further demonstrate the growth mechanism of Co3O4 nanoarrays with different morphologies. CO is chosen as a probe molecule to evaluate the catalytic performance over the synthesized Co-based oxide catalysts, and the effect of morphological transformation on the catalytic activity is further confirmed via using TEM, H2-TPR, XPS, Raman spectroscopy and in situ Raman spectroscopy. As a proof of concept application, core-shell Co3O4 NAs-8 presenting hierarchical nanosheets@nanoneedle arrays with a low density of nanoneedles exhibits the highest catalytic activity and long-term stability due to its low-temperature reducibility, the lattice distortion of the spinel structure and the abundance of surface-adsorbed oxygen (Oads). It is confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir-Hinshelwood mechanism via using in situ Raman spectroscopy. It is expected that the in situ synthesis of well-defined Co3O4 monolithic catalysts can be extended to the development of environmentally-friendly and highly active integral materials for practical industrial catalysis.

A Au monolayer on WC(0001) with unexpected high activity towards CO oxidation

Catalysts with weak adsorption yet high reactivity towards CO are urgently required to solve the serious problem of CO poisoning that occurs in many important reactions, e.g., in fuel cells. Using the combination of density functional calculations and ab initio molecular dynamic simulations, we found a promising electrocatalyst for this purpose: a Au monolayer on WC(0001) (Au_ML/WC), which has both high oxygen reduction activity and high tolerance to CO poisoning. The advantages of using Au_ML/WC as an electrocatalyst in fuel cells are demonstrated through analyses of energetics of different reaction steps as well as interaction properties of reactants and products. We anticipate that the present results are useful to advance the development of efficient catalysts with high tolerance to CO poisoning.