Highly Water-Resistant La-Doped Co3O4 Catalyst for CO Oxidation

Designing water resistant high entropy oxide materials

The ubiquitous presence of moisture usually shows adverse effects on industrial catalysis. Herein, a concept of engineering entropy to design water-resistant oxide catalysts is proposed. The C3H6 oxidation by spinel ACr2O4 (A=Ni, Mg, Cu, Zn, Co) catalysts is selected as a model. Through DFT calculation, the adsorption energy of C3H6, the dissociation energy of molecular H2O on the oxide surface, and the formation energy of oxygen vacancy all suggest better performance induced by higher configurational entropy. Indeed, (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Cr2O4 experimentally show excellent water resistance (>100 h) in C3H6 oxidation, while in sharp contrast binary oxides (e.g., NiCr2O4, CoCr2O4) are deactivated in 20 h. H2O-TPD, in-situ Raman, and in-situ FTIR all confirm the low H2O adsorption energy and strong hydrothermal stability of high entropy oxide, which is attributed to their lower Gibbs free energy. This work may inspire the rational design of water-resistant catalysts.

One-Pot, Solvent Free Synthesis of 2,5-Furandicarboxylic Acid from Deep Eutectic Mixtures of Sugars as Mediated by Bifunctional Catalyst

Currently one-pot conversion of sugars to 2,5-furandicarboxylic acid (FDCA) is of significant interest due to the attainability of sugars as a feedstock and the enormous potential of FDCA as a bioplastic monomer. However, it remains challenging to construct efficient catalysts for this process. In this study, Co3O4 species were anchored to a sulfonated covalent organic framework thus affording a bifunctional catalyst (Co3O4@COF-SO3H). The sulfonic acid sites dehydrate sugars to 5-hydroxymethylfurfural (HMF), which is next oxidized to FDCA as catalyzed by the Co3O4 species. Such a process was applied in the conversion of various binary and ternary deep eutectic mixtures involving choline chloride and sugars without additional solvent. The maximum FDCA yield of 84 % was obtained using glucose-fructose eutectic mixture as the substrates. Moreover, the catalyst was recyclable and stable under the applied reaction conditions. Our process eliminates the employment of organic solvents and expensive noble metal catalysts, resulting in green and economic biomass conversions.

Modulating the Electronic Structures of Pt on Pt/TiO2 Catalyst for Boosting Toluene Oxidation

Surface hydroxyl groups commonly exist on the catalyst and present a significant role in the catalytic reaction. Considering the lack of systematical researches on the effect of the surface hydroxyl group on reactant molecule activation, the PtOx/TiO2 and PtOx-y(OH)y/TiO2 catalysts were constructed and studied for a comprehensive understanding of the roles of the surface hydroxyl group in the oxidation of volatiles organic compounds. The PtOx/TiO2 formed by a simple treatment with nitric acid presented greatly enhanced activity for toluene oxidation in which the turnover frequency of toluene oxidation on PtOx/TiO2 was around 14 times as high as that on PtOx-y(OH)y/TiO2. Experimental and theoretical results indicated that adsorption/activation of toluene and reactivity of oxygen atom on the catalyst determined the toluene oxidation on the catalyst. The removal of surface hydroxyl groups on PtOx promoted strong electronic coupling of the Pt 5d orbital in PtOx and C 2p orbital in toluene, facilitating the electron transfers from toluene to PtOx and subsequently the adsorption/activation of toluene. Additionally, the weak Pt-O bond promoted the activation of surface lattice oxygen, accelerating the deep oxidation of activated toluene. This study clarifies the inhibiting effect of surface hydroxyl groups on PtOx in toluene oxidation, providing a further understanding of hydrocarbon oxidation.

Enhancing low-temperature CO removal in complex flue gases: A study on La and Cu doped Co3O4 catalysts under real-world combustion environment

Designing CO oxidation catalysts for complex flue gases conditions is particularly challenging in fire scenarios. Traditional flue gas simulations use a few representative gases but often fail to adequately evaluate catalyst performance in real-world combustion conditions. In this study, we developed doping strategies using La and Cu to enhance the water resistance of Co3O4 catalysts. Catalyst 0.1La-Co3O4-CuO/CeO2 exhibits exceptional low-temperature catalytic activity, achieving 100% conversion at 130 °C. This enhancement is largely due to the introduction of La, which increases the active Co3+/Co2+ ratio and suppresses hydroxyl group formation on the Co3O4 surface. Cu doping also changes the Co3O4 lattice structure, forming Cu+ as active sites and enhancing the activity at low temperatures. For the first time, steady-state tube furnace and fixed bed were employed to evaluate the catalytic performance of CO in actual combustion atmosphere. Catalyst 0.1La-Co3O4-CuO/CeO2 maintains excellent catalytic efficiency (T100 = 120 °C) under well-ventilated conditions. However, its activity significantly decreases in poorly ventilated environments, due to the competitive adsorption of small molecules at active sites, such as acetone, commonly found in smoke. This study provides valuable insights for designing water-resistant, low-temperature, non-noble metal catalysts and offers a methodology for evaluating CO catalytic activity in real-world environments.

Surface modification of Co3O4 nanosheets through Cd-doping for enhanced CO sensing performance

The detection of hazardous CO gas is an important research content in the domain of the Internet of Things (IoT). Herein, we introduced a facile metal-organic frameworks (MOFs)-templated strategy to synthesize Cd-doped Co3O4 nanosheets (Cd-Co3O4 NSs) aimed at boosting the CO-sensing performance. The synthesized Cd-Co3O4 NSs feature a multihole nanomeshes structure and a large specific surface area (106.579 m2·g-1), which endows the sensing materials with favorable gas diffusion and interaction ability. Furthermore, compared with unadulterated Co3O4, the 2 mol % Cd-doped Co3O4 (2% Cd-Co3O4) sensor exhibits enhanced sensitivity (244%) to 100 ppm CO at 200 °C and a comparatively low experimental limit of detection (0.5 ppm/experimental value). The 2% Cd-Co3O4 NSs show good selectivity, reproducibility, and long-term stability. The improved CO sensitivity signal is probably owing to the stable nanomeshes construction, high surface area, and rich oxygen vacancies caused by cadmium doping. This study presents a facile avenue to promote the sensing performance of p-type metal oxide semiconductors by enhancing the surface activity of Co3O4 combined with morphology control and component regulation.

High-performance photocatalytic degradation and antifungal activity of chromium-doped nickel oxide nanoparticles

The elimination of pollutants such as dyes and fungi has become a tedious process hence there is a need for multifunctional materials that can be used for the removal or degradation of various pollutants from wastewater. Here, a nickel oxide nanoparticle (NiONPs) was synthesized by the co-precipitation method. In the current study, a composite of nickel oxide nanoparticles (NiONPs) was synthesized using nitrogen and chromium as dopants to create (N/NiONPs) and (Cr/N/NiONPs), respectively and used for the removal of dyes and fungi. The synthesized nanocomposites were characterized using zeta potential (ZP), scanning electron microscopy (SEM), X-rays diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The NiONPs, N/NiONPs and Cr/N/NiONPs were tested for the degradation of two dye pollutants, Reactive blue 13 (RB13) and eosin dye. The obtained results showed that Cr/N/NiONPs were more efficient than NiONPs and N/NiONPs for dye degradation by applying the same irradiation conditions. The Cr/N/NiONPs nanocomposites showed very good degradation efficiency of dye up to 94.2% for the RB13 and 90.8% for the eosin. We also examined the antifungal action of the NiONPs, N/NiONPs and Cr/N/NiONPs against Trichoderma fungus. The results showed that the Cr/N/NiONPs have an extremely strong antifungal impact on Trichoderma. This could be explained by the strong adhesion of Cr/N/NiONPs to the Trichoderma surface due to electrostatic attraction. This work has demonstrated that it is possible to create environmentally safe materials that can be used for the degradation of different dyes and the improvement of more effective antifungal treatments with lower active agent doses for fungus control with potential big economic benefits.

Comparison activity of pure and chromium-doped nickel oxide nanoparticles for the selective removal of dyes from water

The current study involves a synthesis of a composite of nickel oxide nanoparticles (NiONPs) with a chromium dopant to yield (Cr/NiONPs). Synthesis of nickel oxide was performed by the co-precipitation method. The synthesis of the composite was conducted by the impregnation method. FTIR, EDX, SEM, and XRD were used to characterize the synthesized materials. The synthesised materials' point zero charges (PZC) were performed using the potentiometric titration method. The obtained results show that the PZC for neat nickel oxide was around 5, and it was around 8 for Cr/NiONPs. The adsorption action of the prepared materials was examined by applying them to remove Reactive Red 2 (RR2) and Crystal Violate (CV) dyes from solutions. The outcomes demonstrated that Cr/NiONPs were stronger in the removal of dyes than NiONPs. Cr/NiONPs achieved 99.9% removal of dyes after 1 h. Adsorption isotherms involving Freundlich and Langmuir adsorption isotherms were also conducted, and the outcomes indicated that the most accurate representation of the adsorption data was offered by Langmuir adsorption isotherms. Additionally, it was discovered that the adsorption characteristics of the NiONPs and Cr/NiONPs correspond well with the pseudo-second-order kinetic model. Each of the NiONPs and Cr/NiONPs was reused five times, and the results display that the effectiveness of the removal of RR2 dye slightly declined with the increase in reuse cycles; it lost only 5% of its original efficiency after the 5 cycles. Generally, Cr/NiONPs showed better reusability than NiONPs under the same conditions.

Role of H2O in Catalytic Conversion of C1 Molecules

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.

Ultrathin MnO2 with strong lattice disorder for catalytic oxidation of volatile organic compounds

Catalytic oxidation proves the most promising technology for volatile organic compounds (VOCs) abatement. Lattice disorder plays a crucial role in the catalytic activity of catalysts due to the exposure of more active sites. Inspired by this, we successfully prepared a series of ε-MnO2 with different lattice disorder defects via several simple methods and applied them to the catalytic oxidation of two typical VOCs (toluene and acetone). Various characterizations and performance tests confirm that the ultrathin (1.4-1.8 nm) structure and strong lattice disorder can enhance the low temperature reduction and reactive oxygen species, so that MnO2-R exhibits excellent toluene and acetone oxidation activities. In-situ DRIFTS tests were carried out to detect reaction intermediates in the toluene and acetone oxidation process on the catalyst surface. Moreover, we propose a possible synergistic mechanism for toluene and acetone mixtures catalytic oxidation. This work reveals the important role of lattice disorder defects in the catalytic oxidation of VOCs on Mn-based catalysts, and deepens the insights of the reaction path in toluene and acetone catalytic oxidation.

Highly Active and Water-Resistant Cu-Doped OMS-2 Catalysts for CO Oxidation: The Importance of the OMS-2 Synthesis Method and Cu Doping

Porous cryptomelane-type Mn oxide (OMS-2) has an outstanding redox property, making it a highly desirable substitute for noble metal catalysts for CO oxidation, but its catalytic activity still needs to be improved, especially in the presence of water. Given the strong structure-performance correlation of OMS-2 for oxidation reactions, herein, OMS-2 is synthesized by solid state (OMS-2S), reflux (OMS-2R), and hydrothermal (OMS-2H) methods, aiming to improve its CO oxidation performance through manipulating synthesis parameters to tailor its particle size, morphology, and crystallinity. Characterization shows that OMS-2S has the highest CO oxidation activity in the absence of water due to its low crystallinity, high specific surface area, large oxygen vacancy content, and good redox property, but the presence of water can greatly reduce its CO oxidation activity. Doping Cu into an OMS-2 can not only improve its CO oxidation activity but also greatly improve its water tolerance. The Cu-doped OMS-2S catalyst with ∼4 wt % Cu can achieve a T90 of 49 °C (1% CO/10% O2/N2 and WHSV = 60,000 mL·g-1·h-1), ranking among the lowest reported T90 values for Mn oxide-based CO oxidation catalysts, and it can maintain nearly 100% CO conversion in the presence of 5 vol % water for over 50 h. In situ DRIFTs characterization indicates that the good water resistance of Cu-doped OMS-2S can be attributed to the significantly suppressed surface hydroxyl group generation because of Cu doping. This work demonstrates the importance of the synthesis method and Cu doping in determining the CO oxidation activity and water resistance of OMS-2 and will provide guidance for synthesizing highly active and water-resistant CO oxidation catalysts.

Cation Concavities Induced d-Band Electronic Modulation on Co/FeOx Nanostructure to Activate Molecular and Interfacial Oxygen for CO Oxidation

Cobalt-based catalysts have been identified for effective CO oxidation, but their activity is limited by molecular O2 and interfacial oxygen passivation at low temperatures. Optimization of the d-band structure of the cobalt center is an effective method to enhance the dissociation of oxygen species. Here, we developed a novel Co/FeOx catalyst based on selective cationic deposition to anchor Co cations at the defect site of FeOx, which exhibited superior intrinsic low-temperature activity (100%, 115 °C) compared to that of Pt/Co3O4 (100%, 140 °C) and La/Co2O3 (100%, 150 °C). In contrast to catalysts with oxygen defects, the cationic Fe defect in Co/FeOx showed an exceptional ability to accept electrons from the Co 3d orbital, resulting in significant electron delocalization at the Co sites. The Co/FeOx catalyst exhibited a remarkable turnover frequency of 178.6 per Co site per second, which is 2.3 times higher than that of most previously reported Co-based catalysts. The d-band center is shifted upward by electron redistribution effects, which promotes the breaking of the antibonding orbital *π of the O═O bond. In addition, the controllable regulation of the Fe-Ov-Co oxygen defect sites enlarges the Fe-O bond from 1.97 to 2.02 Å to activate the lattice oxygen. Moreover, compared to CoxFe3-xO4, Co/FeOx has a lower energy barrier for CO oxidation, which significantly accelerates the rate-determining step, *COO formation. This study demonstrates the feasibility of modulating the d-band structure to enhance O2 molecular and interfacial lattice oxygen activation.

Coordination-Controlled Catalytic Activity of Cobalt Oxides for Ozone Decomposition

Nowadays, it is still elusive and challenging to discover the active sites of cobalt (Co) cations in different coordination structures, though Co-based oxides show their great potency in catalytic ozone elimination for air cleaning. Herein, different Co-based oxides are controllably synthesized including hexagonal wurtzite CoO-W with Co²⁺ in tetrahedral coordination (Co_Td²⁺) and CoAl spinel with dominant Co_Td²⁺, cubic rock salt CoO-R with Co²⁺ in octahedral coordination (Co_Oh²⁺), MgCo spinel with dominant Co³⁺ in octahedral coordination (Co_Oh³⁺), and Co₃O₄ with mixed Co_Td²⁺ and Co_Oh³⁺. The valences are proved by X-ray photoelectron spectroscopy, and the coordinations are verified by X-ray absorption fine structure analysis. The ozone decomposition performances are Co_Oh³⁺ ∼ Co_Oh²⁺ ≫ Co_Td²⁺, and Co_Oh³⁺ and Co_Oh²⁺ show a lower apparent activation energy of ∼42-44 kJ/mol than Co_Td²⁺ (∼55 kJ/mol). In specific, MgCo shows the highest decomposition efficiency of 95% toward 100 ppm ozone at a high space velocity of 1,200,000 mL/gh, which still retains at 80% after a long-term running of 36 h at room temperature. The high activity is explained by the d-orbital splitting in the octahedral coordination, favoring the electron transfer in ozone decomposition reactions, which is also verified by the simulation. These results show the promising prospect of the coordination tuning of Co-based oxides for highly active ozone decomposition catalysts.

Rare Earth Doping Engineering Tailoring Advanced Oxygen-Vacancy Co3 O4 with Tunable Structures for High-Efficiency Energy Storage

Co₃ O₄  with high theoretical capacitance is a promising electrode material for high-end energy applications, yet the unexcited bulk electrochemical activity, low conductivity, and poor kinetics of Co₃ O₄  lead to unsatisfactory charge storage capacity. For boosting its energy storage capability, rare earth (RE)-doped Co₃ O₄  nanostructures with abundant oxygen vacancies are constructed by simple, economical, and universal chemical precipitation. By changing different types of RE (RE = La, Yb, Y, Ce, Er, Ho, Nd, Eu) as dopants, the RE-doped Co₃ O₄  nanostructures can be well transformed from large nanosheets to coiled tiny nanosheets and finally to ultrafine nanoparticles, meanwhile, their specific surface area, pore distribution, the ratio of Co²⁺ /Co³⁺ , oxygen vacancy content, crystalline phase, microstrain parameter, and the capacitance performance are regularly affected. Notably, Eu-doped Co₃ O₄  nanoparticles with good cycle stability show a maximum specific capacitance of 1021.3 F g^-1 (90.78 mAh g^-1 ) at 2 A g^-1 , higher than 388 F g^-1 (34.49 mAh g^-1 ) of pristine Co₃ O₄  nanosheets. The assembling asymmetric supercapacitor delivers a high energy density of 48.23 Wh kg^-1  at high power density of 1.2 kW kg^-1 . These findings denote the significance and great potential of RE-doped Co₃ O₄  in the development of high-efficiency energy storage.

Strong Electronic Orbit Coupling between Cobalt and Single-Atom Praseodymium for Boosted Nitrous Oxide Decomposition on Co3O4 Catalyst

Nitrous oxide (N₂O) has gained increasing attention as an important noncarbon dioxide greenhouse gas, and catalytic decomposition is an effective method of reducing its emissions. Here, Co₃O₄ was synthesized by the sol-gel method and single-atom Pr was confined in its matrix to improve the N₂O decomposition performance. It was observed that the reaction rate varied in a volcano-like pattern with the amount of doped Pr. A N₂O decomposition reaction rate 5-7.5 times greater than that of pure Co₃O₄ is achieved on the catalyst with a Pr/Co molar ratio of 0.06:1, and further Pr doping reduced the activity due to PrO_x cluster formation. Combined with X-ray photoelectron spectroscopy, X-ray absorption fine structure, density functional theory and in situ near-ambient pressure X-ray photoelectron spectroscopy, it was demonstrated that the single-atom doped Pr in Co₃O₄ generates the "Pr 4f-O 2p-Co 3d" network, which redistributes the electrons in Co₃O₄ lattice and increases the t_2g electrons at the tetracoordinated Co²⁺ sites. This coupling between the Pr 4f orbit and Co²⁺ 3d orbit triggers the formation of a 4f-3d electronic ladder, which accelerates the electron transfer from Co²⁺ to the 3π* antibonding orbital of N₂O, thus contributing to the N-O bond cleavage. Moreover, the energy barrier for each elementary reaction in the decomposition process of N₂O is reduced, especially for O₂ desorption. Our work provides a theoretical grounding and reference for designing atomically modified catalysts for N₂O decomposition.

Yttrium-modified Co3O4 as efficient catalysts for toluene and propane combustion: Effect of yttrium content

A series of Y-modified cobalt oxides with various Y/(Co+Y) molar ratios (0.25 %, 0.5 %, 1 %, 3 % and 5 %) were prepared to study the effect of Y content on toluene and propane combustion. The characterization of the catalysts revealed that proper Y incorporation resulted in smaller crystallite sizes, larger specific surface areas, more oxygen vacancies and weaker Co-O bonds. As such, the Y-modified Co₃O₄ showed enhanced low-temperature reducibility, boosted oxygen mobility and better catalytic activity. However, excess Y (> 1 %) aggregates on the surface of Co₃O₄ and forms yttrium carbonate species, hindering the catalyst activity. A volcano-type relationship between the Y content and the catalytic activity was established. The optimal catalyst 1 % Y-Co (with Y/(Co+Y) molar ratio of 1 %) exhibited toluene oxidation rate of 24 nmol g^-1 s^-1 at 220 °C and propane oxidation rate of 69 nmol g^-1 s^-1 at 180 °C. Besides, 1 % Y-Co presented perfect cycling stability and long-term durability in propane oxidation. Regarding its low cost, high efficiency and good stability, 1 % Y-Co is a promising catalyst for the practical elimination of hydrocarbon emissions.

Rational Design and Construction of Monolithic Ordered Mesoporous Co3O4@SiO2 Catalyst by a Novel 3D Printed Technology for Catalytic Oxidation of Toluene

Here, we report a novel 3D printed layered ordered mesoporous template that can encapsulate active Co-MOFs species in a confined way to achieve the goal of monolithic catalyst. The monolithic OM-Co₃O₄@SiO₂-S catalyst can maintain a macroscopic porous layered structure and a microscopic ordered mesoporous structure. This monolithic OM-Co₃O₄@SiO₂-S catalyst has excellent catalytic performance (T₉₀ = 236 °C), water resistance, and thermal stability in the catalytic combustion of toluene. The catalytic performance of the monolithic OM-Co₃O₄@SiO₂-S catalyst is much better than that of many monolithic catalysts reported in the former. Among them, the introduction of binder aluminum phosphate (AP) can effectively enhance the rheological properties of the printing ink, achieve the purpose of ink writing monolithic layered porous material, enrich the acidic point of the monolithic catalyst, and increase the number of reactive oxygen species. This work reveals a novel monolithic catalyst forming strategy that can combine the advantages of ordered mesoporous materials with active species to form macro-layered porous materials and provide ideas and an experimental basis for the elimination of VOCs in industrial applications.

Synthesis of Needle-like Nanostructure Composite Electrode of Co3O4/rGO/NF for High-Performance Symmetric Supercapacitor

In this work, a hierarchical electrode structure of cobaltosic oxide (Co3O4) growing on a reduced graphene oxide (rGO)-covered nickel foam (NF) substrate (named Co3O4/rGO/NF) is fabricated by a facile hydrothermal and subsequent annealing process. Thousands of nanoneedle units uniformly arranged on the surface of the rGO sheet stimulate the evident increase in the specific surface area and thus produce more active sites. Because of the special hierarchical structure, the Co3O4/rGO/NF electrode shows a high specific capacitance of 1400 F g−1 at 1 A g−1 and retains 58% capacitance even when the current density increases to 30 A g−1. In addition, a symmetric supercapacitor based on the Co3O4/rGO/NF electrode is assembled, exhibiting high specific capacitance of 311 F g−1 at 1 A g−1, as well as remarkable power density and energy density (40.67 Wh kg−1 at 12 kW kg−1). The device also demonstrates a great cycling performance after 10,000 cycles under the current density of 10 A g−1, acquiring 89.69% capacitance retention of the initial state. The accessible synthetic method and superior electrochemical performance of the Co3O4/rGO/NF composite electrode implicate its extensive application prospects in terms of new energy storage.

Effect of Sn on the CO Catalytic Activity and Water Resistance of Cu-Mn Catalyst

In view of the problem that excessive CO in underground coal mine space can easily lead to a large number of casualties, Cu-Mn-Sn water-resistant eliminators with different Sn contents were prepared by a co-precipitation method. The activity of the eliminators was analyzed by using an independently developed activity testing platform, N₂ adsorption and desorption, XRD, SEM, XPS, and FTIR to characterize the activity factors and water resistance. The results showed that Cu-Mn-Sn-20 with 20% Sn content had the highest activity, which was 3.23 times that of Cu-Mn. The main reason for the increased activity is that Cu-Mn-Sn-20 doped with 20% Sn provides a larger specific surface area and more active sites and reduces the pore size, so that the crystallization degree of Cu_1.4Mn_1.5O₄ is lower. The doping of 20% Sn reduces the absorption of lattice water and coordination water and improves the water resistance of Cu-Mn-Sn-type eliminators. The Cu-Mn-Sn-20 water-resistant eliminator is used to quickly eliminate CO in underground coal mines, which is of great significance for the rescue workers in underground coal mines after disasters.

Fabrication of MnCoOx composite oxides for catalytic CO oxidation via a solid-phase synthesis: The significant effect of manganese precursor

A series of Mn3Co16Ox composite oxides catalysts were fabricated via a solid-phase synthesis using different manganese precursors (namely as manganese acetate (A), nitrate (N), and sulfate (S)). It has been...

Hierarchical N-Doped CuO/Cu Composites Derived from Dual-Ligand Metal-Organic Frameworks as Cost-Effective Catalysts for Low-Temperature CO Oxidation

Development of multi-ligand metal-organic frameworks (MOFs) and derived heteroatom-doped composites as efficient non-noble metal-based catalysts is highly desirable. However, rational design of these materials with controllable composition and structure remains a challenge. In this study, novel hierarchical N-doped CuO/Cu composites were synthesized by assembling dual-ligand MOFs via a solvent-induced coordination modulation/low-temperature pyrolysis method. Different from a homogeneous system, our heterogeneous nucleation strategy provided more flexible and cost-effective MOF production and offered efficient direction/shape-controlled synthesis, resulting in a faster reaction and more complete conversion. After pyrolysis, they further transformed to a unique metal/carbon matrix with regular morphology and, as a hot template, guided the orderly generation of metal oxides, eliminating sintering and agglomeration of metal oxides and initiating a synergistic effect between the N-doped metal oxide/metal and carbon matrix. The prepared N-doped CuO/Cu catalysts held unique water resistance and superior catalytic activity (100% CO conversion at 140 °C).

A Hydrothermally Stable Single-Atom Catalyst of Pt Supported on High-Entropy Oxide/Al2O3: Structural Optimization and Enhanced Catalytic Activity

A catalyst with high-entropy oxide (HEO)-stabilized single-atom Pt can afford low-temperature activity for catalytic oxidation and remarkable durability even under harsh conditions. However, HEO is easy to harden during sintering, which results in a few defective sites for anchoring single-atom metals. Herein, we present a sol-gel-assisted mechanical milling strategy to achieve a single-atom catalyst of Pt-HEO/Al₂O₃. The strong interaction between HEO and Al₂O₃ effectively inhibits the growth of HEO microparticles, which leads to generation of more surface defects because of the nanoscale effect. Meanwhile, another strong interaction between Pt and HEO stabilizes single-atom Pt on HEO. Temperature-programmed techniques further verify that the reactivity of surface lattice oxygen species is enhanced because of the Pt-O-M bonds on the surface of HEO. Unlike conventional single-atom Pt catalysts, Pt-HEO/Al₂O₃ as a heterogeneous catalyst not only exhibits superior stability against hydrothermal aging but also presents long-term reaction stability for CO catalytic oxidation, which exceeds 540 h. The present work opens a new door for rational design of hydrothermally stable single-atom Pt catalysts, which are highly promising in practical applications.

Strong Structural Modification of Gd to Co3O4 for Catalyzing N2O Decomposition under Simulated Real Tail Gases

In this paper, Gd-promoted Co₃O₄ catalysts were prepared via a facile coprecipitation method for low-temperature catalytic N₂O decomposition. Due to the addition of Gd, the crystallite size of Co₃O₄ in the Gd_0.06Co catalyst surprisingly decreased to 4.9 nm, which is much smaller than most additive-modified Co₃O₄ catalysts. This huge change in the catalyst's textural structure endows the Gd_0.06Co catalyst with a large specific surface area, plentiful active sites, and a weak Co-O bond. Hence, Gd_0.06Co exhibited superior activity for catalyzing 2000 ppmv N₂O decomposition, and the temperature for the complete catalytic elimination of N₂O was as low as 350 °C. Meanwhile, compared with pure Co₃O₄, E_a decreased from 77.4 to 46.8 kJ·mol^-1 and TOF of the reaction increased from 1.16 × 10^-3 s^-1 to 5.13 × 10^-3 s^-1 at 300 °C. Moreover, Gd_0.06Co displayed a quite stable catalytic performance in the presence of 100 ppmv NO, 5 vol % O₂, and 2 vol % H₂O.

Boosting Electrocatalytic Oxygen Evolution: Superhydrophilic/Superaerophobic Hierarchical Nanoneedle/Microflower Arrays of CexCo3-xO4 with Oxygen Vacancies

The oxygen evolution reaction has become the bottleneck of electrochemical water splitting for its sluggish kinetics. Developing high-efficiency and low-cost non-noble-metal oxide electrocatalysts is crucial but challenging for industrial application. Herein, superhydrophilic/superaerophobic hierarchical nanoneedle/microflower arrays of Ce-substituted Co₃O₄ (Ce_xCo_3-xO₄) in situ grown on the nickel foam are successfully constructed. The hierarchical architecture and superhydrophilic/superaerophobic interface can be facilely regulated by controlling the introduction of Ce into Co₃O₄. The unique feature of hierarchical architecture and superhydrophilic/superaerophobic interface is in favor of electrolyte penetration and bubbles release. In addition, the presence of oxygen vacancy and Ce endows the catalyst with enhanced intrinsic activity. Benefiting from these advantages, the optimized Ce_0.12Co_2.88O₄ catalyst shows a superior electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 282 mV at 20 mA cm^-2, and a Tafel slope of 81.4 mV dec^-1. The turnover frequency of 0.0279 s^-1 for Ce_0.12Co_2.88O₄ is 9.3 times larger than that for Co₃O₄ at an overpotential of 350 mV. Moreover, the optimized Ce_0.12Co_2.88O₄ catalyst shows a robust long-term stability in alkaline media.

Defective transition metal hydroxide-based nanoagents with hypoxia relief for photothermal-enhanced photodynamic therapy

Recently, phototherapy has attracted much attention due to its negligible invasiveness, insignificant toxicity and excellent applicability. The construction of a newly proposed nanosystem with synergistic photothermal and photodynamic tumor-eliminating properties requires a delicate structure design. In this work, a novel therapeutic nanoplatform (denoted as BCS-Ce6) based on defective cobalt hydroxide nanosheets was developed, which realized hypoxia-relieved photothermal-enhanced photodynamic therapy against cancer. Defective cobalt hydroxide exhibited high photothermal conversion efficacy at the near-infrared region (49.49% at 808 nm) as well as enhanced catalase-like activity to produce oxygen and greatly boost the singlet oxygen generation by a photosensitizer, Ce6, realizing efficacious dual-modal phototherapy. In vivo and in vitro experiments revealed that BCS-Ce6 can almost completely extinguish implanted tumors in a mouse model and present satisfactory biocompatibility during the treatment. This work sets a new angle of preparing photothermal agents and constructing comprehensive therapeutic nanosystems with the ability to modulate the hypoxic tumor microenvironment for efficient cancer therapy.

Promotional effect of Mn-doping on the catalytic performance of NiO sheets for the selective oxidation of styrene

The direct oxidation of styrene into high-value chemicals under mild reaction conditions remains a great challenge in both academia and industry. Herein, we report a successful electronic structure modulation of intrinsic NiO sheets via Mn-doping towards the oxidation of styrene. By doping NiO with only a small content of Mn (Mn/Ni atomic ratio of 0.030), a 75.0% yield of STO can be achieved under the optimized reaction conditions, which is 2.13 times higher than that of the pure NiO. In addition, the catalyst exhibits robust stability and good recycling performance. The performance enhancement originates from the synergistic effect regarding the abundant Ni(II) species, the rich oxygen vacancy sites and the large amount of surface redox centers. This work provides new findings of the elemental-doping-induced multifunctionality in designing powerful catalysts for the efficient and selective oxidation of styrene and beyond.