Promoting Effects of In2O3 on Co3O4 for CO Oxidation: Tuning O2 Activation and CO Adsorption Strength Simultaneously

Increasing the Surface Activity of 2D Ultrathin Co3O4 by Indium Doping for TEA Sensing

Optimizing and improving the surface activity of Co3O4 sensing materials are crucial for applications in triethylamine detection. Herein, indium-doped Co3O4 hollow microflowers (InCo HMfs), assembled from ultrathin nanosheets, were prepared via a hydrolysis reaction. Three distinct crystal facets─{1 1 0}, {1 1 1}, and {0 0 1}─were observed in 2-InCo HMfs. Results from TEM, XPS, and XAS characterization show that the increase of Co2+ content induced by indium doping promotes the formation of highly active crystal planes in Co3O4. DFT calculations revealed the reasons for the improvement in the gas sensing performance of 2-InCo HMfs and the multiple effects of In ions. Our dual strategy of doping with indium and hydrolysis markedly improved the intrinsic TEA sensing performance of Co3O4, offering a novel avenue for designing high-performance TEA sensors.

Eu-doped nickel oxide for low-temperature direct decomposition of nitrous oxide

Nitrous oxide (N2O) is a potent greenhouse gas with high global warming potential. It is urgent to develop active and stabile catalysts for N2O direct catalytic decomposition (deN2O) in industrial exhaust gas. In this study, a series of Eu-doped NiO catalysts were synthesized by co-precipitation method. The catalyst with an Eu to Ni molar ratio of 0.04 showed the highest deN2O ability, reaching 100 % conversion at 400 °C without generating NOx by-products. The catalyst also displayed resilience against O2 and NO impurity gases, maintaining structural stability and achieving complete transformation of N2O at 440 °C. Eu was uniformly dispersed in NiO in the form of Eu2O3, which not only regulated the particle size and specific surface area of NiO, but also changed the surface chemistry of NiO by inducing more Ni2+ active sites and more mobile Oβ species. Eu-doping altered the decomposition mechanism of N2O from L-H to E-R mechanism, reducing the energy barrier of O2 desorption, which was the rate-determining step. During the reaction, Eu0.04Ni showed an activation behavior after cyclic use and long-term reaction and reduced T100 to 320 °C after 14-hr experiment. These findings demonstrate the potential of the catalyst for practical application and provide new routes for the direct decomposition of N2O in industrial exhaust gas.

Synergistic Surface-Interface Catalysis in Potassium-Loaded Cu/CoOx Catalysts to Boost Ethanol Production from CO2 Hydrogenation

Nowadays, ethanol production from CO2 hydrogenation has emerged as a viable pathway for CO2 capture and efficient utilization. However, catalysts based on nonprecious metals still face significant challenges in achieving high catalytic efficiency for ethanol production. In this study, we constructed K-incorporated CuCo-based catalysts, which were obtained from Cu-Co-Al layered double hydroxide precursors, for efficient CO2 hydrogenation to produce ethanol. It was shown that the incorporation of K into catalysts could finely tune the electronic structures of copper and cobalt species, thereby promoting the formation of substantial surface Co2+-Ov-Co2+ (Ov: oxygen vacancy), Co-O-K, and Cu+-O-K structures. Notably, as-constructed Cu/CoOx catalyst bearing a K loading of 3 wt % achieved an impressively high ethanol selectivity of 38.8% at 200 °C as well as a remarkably high ethanol production rate of 2.76 mmolEtOH·gcat-1·h-1 at 260 °C. Based on multiple structural characterizations, spectroscopic analysis, and density functional theory calculations, it was uncovered that defective CoOx and Cu+-O-K structures promoted the generation of formate intermediates during CO2 hydrogenation, and meanwhile, the effective coadsorption of K+ and Cu+ stabilized formate intermediates. Accordingly, active K+, Cu+ and CoOx species over CuCo-based catalysts exhibited synergistic catalysis, which significantly improved the CHx-HCOO coupling process at K-loaded Cu/CoOx interfaces to boost ethanol production. This study presents a novel surface-interface engineering approach for designing non-noble-metal-based catalysts for efficient ethanol production from CO2 hydrogenation.

Tandem indium oxide-boron nitride catalysts for oxidative dehydrogenation of propane

This study introduces a novel approach of precisely depositing In2O3 nanoislands on the edges of BN sheets using selective atomic layer deposition. The modified catalysts demonstrated a significant improvement and characterization results revealed that the presence of In2O3 nanoislands, when free of BOx overlayers, is crucial in mitigating side reactions.

Highly active Mn-VO-Co sites by cobalt doping on cryptomethane for enhanced catalytic decomposition of N2O

Direct catalytic decomposition has shown great promise in controlling the greenhouse gas N2O. Herein, we synthesize a series of cobalt-doped cryptomethane (OMS-2) catalysts for N2O catalytic decomposition by a mild one-step sol-gel method. The Co0.1-OMS-2 exhibits superior catalytic performance with 90% N2O conversion at 398 °C, which is attributed to the formation of the Mn-VO-Co structure served as active sites. The increased electron density on oxygen vacancies promotes the electron transfer between oxygen vacancies and N2O molecules, in turn facilitating the adsorption and activation of N2O. Moreover, Co doping reduces the formation energy of oxygen vacancies. However, excessive Co doping results in the decrease of highly active Mn-VO-Co sites and the formation of Co3O4, which makes Co0.3-OMS-2 exhibit poor catalytic activity. The DFT calculation illustrates that Langmuir-Hinshelwood is the primary reaction mechanism over Co0.1-OMS-2. This study broadens the materials applicable for the catalytic decomposition of N2O, offering an effective approach to modulate the electronic structure at oxygen vacancies.

Spinel cobalt-based binary metal oxides as emerging materials for energy harvesting devices: synthesis, characterization and synchrotron radiation-enabled investigation

The synthesis and characterization of spinel cobalt-based metal oxides (MCo2O4) with varying 3d-transition metal ions (Ni, Fe, Cu, and Zn) were explored using a hydrothermal process (140 °C for two hours) to be used as alternative counter electrodes for Pt-free dye-sensitized solar cells (DSSCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed distinct morphologies for each metal oxide, such as NiCo2O4 nanosheets, Cu Co2O4 nanoleaves, Fe Co2O4 diamond-like, and Zn Co2O4 hexagonal-like structures. The X-ray diffraction analysis confirmed the cubic spinel structure for the prepared MCo2O4 films. The functional groups of MCo2O4 materials were recognized in metal oxides throughout Fourier transform infrared (FTIR) analysis. The local structure analysis using X-ray absorption fine structure (XAFS) at Fe and Co K-edge identified octahedral (Oh) Co3+ and tetrahedral (Td) Co2+ coordination, with Zn2+ and Cu2+ favoring Td sites, while Ni3+ and Fe3+ preferred Oh active sites. Further investigations utilizing the Fourier transformation (FT) analysis showed comparable coordination numbers and interatomic distances ranked as Co-Cu > Co-Fe > Zn-Co > Co-Ni. Furthermore, the utilization of MCo2O4 thin films as counter electrodes in DSSC fabrication showed promising results. Notably, solar cells based on CuCo2O4 and ZnCo2O4 counter electrodes showed 1.9% and 1.13% power conversion efficiency, respectively. These findings indicate the potential of employing these binary metal oxides for efficient and cost-effective photovoltaic device production.

Unlocking Spin Gates of Transition Metal Oxides via Strain Stimuli to Augment Potassium Ion Storage

Transition metal oxides (TMOs) are key in electrochemical energy storage, offering cost-effectiveness and a broad potential window. However, their full potential is limited by poor understanding of their slow reaction kinetics and stability issues. This study diverges from conventional complex nano-structuring, concentrating instead on spin-related charge transfer and orbital interactions to enhance the reaction dynamics and stability of TMOs during energy storage processes. We successfully reconfigured the orbital degeneracy and spin-dependent electronic occupancy by disrupting the symmetry of magnetic cobalt (Co) sites through straightforward strain stimuli. The key to this approach lies in the unfilled Co 3d shell, which serves as a spin-dependent regulator for carrier transfer and orbital interactions within the reaction. We observed that the opening of these 'spin gates' occurs during a transition from a symmetric low-spin state to an asymmetric high-spin state, resulting in enhanced reaction kinetics and maintained structural stability. Specifically, the spin-rearranged Al-Co3O4 exhibited a specific capacitance of 1371 F g-1, which is 38 % higher than that of unaltered Co3O4. These results not only shed light on the spin effects in magnetic TMOs but also establish a new paradigm for designing electrochemical energy storage materials with improved efficiency.

Low-temperature CO preferential oxidation in H2-rich stream over Indium modified Pd-Cu/Al2O3 catalyst

The impact of Indium (In) doping upon the catalytic performance of Pd-Cu/Al2O3 for carbon monoxide preferential oxidation (CO-PROX) in hydrogen (H2) rich atmosphere at low temperature has been studied. A series of catalysts with extremely low palladium (Pd) loading (0.06 wt%) are synthesized by the facile co-impregnation method. When the In/copper (Cu) atomic ratio equals 0.25, Pd-Cu-In0.25/Al2O3 can keep 40% CO conversion and 100% carbon dioxide (CO2) selectivity at least 120 min at 30 °C, which is significantly superior to the catalytic performance of Pd-Cu/Al2O3. The elaborate characterization findings reveal that the added In species to Pd-Cu/Al2O3 causes Indium oxide (In2O3) to generate, which produces the interaction of In2O3 with Pd-Cu/Al2O3, further promoting the dispersion of copper chloride hydroxide (Cu2Cl(OH)3). Moreover, the modification of In facilitates the re-oxidation of Pd0 to Pd+ through reducing the formation of palladium hydride (PdHx) during the CO-PROX reaction. Meanwhile, the addition of In leads to the decrease of Cu+ electron cloud density, making it easier to be oxidized to Cu2+. Collectively, the easy re-oxidation of Pd0 and Cu+ is favorable to fulfill the Wacker cycle between Pd and Cu species, thus improving the catalytic performance for CO-PROX.

Constructing surface oxygen defects at CuO-Co3O4 interface to boost toluene oxidation over CuO/Co3O4 catalysts

As a typical heterogeneous catalytic process, the catalytic combustion of toluene over Co3O4-based catalysts is strongly depends on the surface properties of catalysts, especially the concentration of surface oxygen defects. Here, a novel way was proposed to construct chemically bonded CuO-Co3O4 interface by chemical deposition of CuO onto Co3O4 nanoflowers. The interfacial refinement effect between CuO and Co3O4 support disrupted the ordered atomic arrangement and created countless unsaturated coordination sites at CuO-Co3O4 interface, inducing a significant generation of surface oxygen defects. Surface-rich oxygen vacancies enhanced the capacity of 20%CuO/Co3O4-R to adsorb and activate oxygen species. Benefiting from this, 90 % toluene conversion was reached at 228 °C over 20%CuO/Co3O4-R, which was much lower than that over 20%CuO/Co3O4-S prepared by impregnation method and CuO/Co3O4-mix obtained by mechanically mixing way. In-situ DRIFTS analysis revealed that toluene could be directly decomposed into benzaldehyde at the highly defective CuO-Co3O4 interface, leading to toluene oxidation following the path of toluene → benzaldehyde → benzoate → maleic anhydride → water and carbon dioxide over 20%CuO/Co3O4-R, which was significantly different from decomposition mechanism over 20%CuO/Co3O4-S. Additionally, 20%CuO/Co3O4-R displayed terrific recyclability and outstanding stability, showing good application potential.

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity

Exfoliated M-Al layered double hydroxide (M-Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co-Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co-Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co-Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co-Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation.

Boosting N2O Catalytic Decomposition by the Synergistic Effect of Multiple Elements in Cobalt-Based High-Entropy Oxides

Nitrous oxide (N2O) has a detrimental impact on the greenhouse effect, and its efficient catalytic decomposition at low temperatures remains challenging. Herein, the cobalt-based high-entropy oxide with a spinel-type structure (Co-HEO) is successfully fabricated via a facile coprecipitation method for N2O catalytic decomposition. The obtained Co-HEO catalyst displays more remarkable catalytic performance and higher thermal stability compared with single and binary Co-based oxides, as the temperature of 90% N2O decomposition (T90) is 356 °C. A series of characterization results reveal that the synergistic effect of multiple elements enhances the reducibility and augments oxygen vacancy in the high-entropy system, thus boosting the activity of the Co-HEO catalyst. Moreover, density functional theory (DFT) calculations and the temperature-programmed surface reaction (TPSR) with isotope labeling demonstrate that N2O decomposition on the Co-HEO catalyst follows the Langmuir-Hinshelwood (L-H) mechanism with the promotion of abundant oxygen vacancies. This work provides a fundamental understanding of the synergistic catalytic effect in N2O decomposition and paves the way for the novel environmental catalytic applications of HEO.

Enhanced CO oxidation performance over hierarchical flower-like Co3O4 based nanosheets via optimizing oxygen activation and CO chemisorption

Enhancing low-temperature activity is a focus for carbon monoxide (CO) elimination by catalytic oxidation. In this work, the hierarchical flower-like silver (Ag) modified cobalt oxides (Co3O4) nanosheets were prepared by solvothermal method and applied into catalytic CO oxidation. The doped Ag species in the form of AgCoO2 induced the prolongated surface Co-O bond and weaker bond intensity. Consequently, the oxygen activation/migration ability and redox capacity of Ag0.02Co were enhanced with more oxygen vacancies. The chemisorbed CO was preferentially converted to CO2 but not carbonates. The inhibited carbonates accumulation could avoid the coverage of active sites. According to Density functional theory (DFT) calculations, the electron transfer from AgCoO2 to Co3O4 promote electron donation ability of Co3O4 layer, benefiting for oxygen activation. Moreover, the longer Co-C and C-O bond length suggest the weakened chemisorption strength and higher active of CO molecule. The Ag modified Co3O4 exhibited more satisfactory activity at lower temperature. Typically, it realized 100% CO conversion at 90 °C, and displayed 6.3-fold higher reaction rate than pristine Co3O4 at 40 °C. Moreover, the Ag0.02Co exhibited outstanding long-term stability and water resistance. In summary, the optimized oxygen activation, CO chemisorption and interfacial electron transfer synergistically boosted the CO oxidation activity on Ag modified Co3O4.

A and B sites doped CaAl12O19: Phase component, energy band, color and photoluminescence tuning, color performance prediction and application for pigments

The polyacrylamide gel method was used to fabricate the Ca1-xCoxAl12O19, Ca1-xNixAl12O19, CaAl12-xInxO19 and CaAl12-xWxO19 (x = 0-0.5) pigments. The phase compositions, energy bands, color and photoluminescence properties of the pigments can be controlled by adjusting the type and content of doping ions. The color of CaAl12O19 changed from white to blue with the Co2+ ion doping, from white to gray green with the Ni2+ ion doping, and from white to bright white with the In3+ and W6+ ions doping. The genetic algorithm optimized back propagation neural network can predict the color properties of CaAl12O19 based pigments. The application of the pigments shows that they can be used in painting, coating and other fields. The Co2+ and Ni2+ doped CaAl12O19 exhibits high blue emission, while In3+ and W6+ doped CaAl12O19 shows strong green emission and the luminescence is highly dependent on the type and content of dopant ion, phase composition and energy transfer.

Low-Temperature Propane Activation and Mineralization over a Co3O4 Sub-nanometer Porous Sheet: Atomic-Level Insights

Light alkanes make up a class of widespread volatile organic compounds (VOCs), bringing great environmental hazards and health concerns. However, the low-temperature catalytic destruction of light alkanes is still a great challenge to settle due to their high reaction inertness and weak polarity. Herein, a Co3O4 sub-nanometer porous sheet (Co3O4-SPS) was fabricated and comprehensively compared with its bulk counterparts in the catalytic oxidation of C3H8. Results demonstrated that abundant low-coordinated Co atoms on the Co3O4-SPS surface boost the activation of adsorbed oxygen and enhance the catalytic activity. Moreover, Co3O4-SPS has better surface metal properties, which is beneficial to electron transfer between the catalyst surface and the reactant molecules, promoting the interaction between C3H8 molecules and dissociated O atoms and facilitating the activation of C-H bonds. Due to these, Co3O4-SPS harvests a prominent performance for C3H8 destruction, 100% of which decomposed at 165 °C (apparent activation energy of 49.4 kJ mol-1), much better than the bulk Co3O4 (450 °C and 126.9 kJ mol-1) and typical noble metal catalysts. Moreover, Co3O4-SPS also has excellent thermal stability and water resistance. This study deepens the atomic-level insights into the catalytic capacity of Co3O4-SPS in light alkane purification and provides references for designing efficacious catalysts for thermocatalytic oxidation reactions.

Disentangling Local Interfacial Confinement and Remote Spillover Effects in Oxide-Oxide Interactions

Supported oxides are widely used in many important catalytic reactions, in which the interaction between the oxide catalyst and oxide support is critical but still remains elusive. Here, we construct a chemically bonded oxide-oxide interface by chemical deposition of Co3O4 onto ZnO powder (Co3O4/ZnO), in which complete reduction of Co3O4 to Co0 has been strongly impeded. It was revealed that the local interfacial confinement effect between Co oxide and the ZnO support helps to maintain a metastable CoOx state in CO2 hydrogenation reaction, producing 93% CO. In contrast, a physically contacted oxide-oxide interface was formed by mechanically mixing Co3O4 and ZnO powders (Co3O4-ZnO), in which reduction of Co3O4 to Co0 was significantly promoted, demonstrating a quick increase of CO2 conversion to 45% and a high selectivity toward CH4 (92%) in the CO2 hydrogenation reaction. This interface effect is ascribed to unusual remote spillover of dissociated hydrogen species from ZnO nanoparticles to the neighboring Co oxide nanoparticles. This work clearly illustrates the equally important but opposite local and remote effects at the oxide-oxide interfaces. The distinct oxide-oxide interactions contribute to many diverse interface phenomena in oxide-oxide catalytic systems.

Synergistic contribution of metal-acid sites in selective hydrodeoxygenation of biomass derivatives over Cu/CoOx catalysts

The efficient hydrodeoxygenation (HDO) of biomass derivatives to yield specific products is a significant yet challenging task. In the present study, a Cu/CoO_x catalyst was synthesized using a facile co-precipitation method, and subsequently used for the HDO of biomass derivatives. Under optimal reaction conditions, the conversion of 5-hydroxymethylfurfural reached 100% with a selectivity of ∼99% to 2,5-diformylfuran. In combination with the experimental results, systematic characterizations revealed that CoO_x, as the acid site, tended to adsorb CO bonds, and the metal sites of Cu⁺ were inclined to adsorb CO bonds and enhance CO bond hydrogenation. Meanwhile, Cu⁰ was the main active site for 2-propanol dehydrogenation. The excellent catalytic performance could be attributed to the synergistic effects of Cu and CoO_x. Further, by optimizing the ratio of Cu to CoO_x, the Cu/CoO_x catalysts exhibited notable performance in HDO of acetophenone, levulinic acid, and furfural, which verified the universality of the catalysts in the HDO of biomass derivatives.

Interfacial Coordinational Bond Triggered Photoreduction Membrane for Continuous Light-Driven Precious Metals Recovery

Chemical/electric energy-driven processes dominate the traditional precious metal (PM) recovery market. The renewable energy-driven selective PM recycling approach crucial for carbon neutrality is under exploration. Herein, via an interfacial structure engineering approach, coordinational-active pyridine groups are covalently integrated onto the photoactive semiconductor SnS₂ surface to construct Py-SnS₂. Triggered by the preferred coordinational binding force between PMs and pyridine groups, together with the photoreduction capability of SnS₂, Py-SnS₂ shows significantly enhanced selective PM-capturing performance toward Au³⁺, Pd⁴⁺, and Pt⁴⁺ with recycling capacity up to 1769.84, 1103.72, and 617.61 mg/g for Au³⁺, Pd⁴⁺, and Pt⁴⁺, respectively. Further integrating the Py-SnS₂ membrane into a homemade light-driven flow cell, 96.3% recovery efficiency was achieved for continuous Au recycling from a computer processing unit (CPU) leachate. This study reported a novel strategy to fabricate coordinational bonds triggered photoreductive membranes for continuous PM recovery, which could be expanded to other photocatalysts for broad environmental applications.

Effect of Cu-Doped Co-Mn Spinel for Boosting Low-Temperature NO Reduction by CO: Exploring the Structural Properties, Performance, and Mechanisms

Cobalt-manganese spinel catalysts performed unsatisfactory activity at low-temperature and narrow reaction temperature window, which greatly limited the application in NO reduction by CO. Herein, we synthesize a series of Cu-doped CoMn₂O₄ catalysts and apply to NO reduction by CO. The Cu_0.3Co_0.7Mn₂O₄ exhibited superior catalytic performance, reaching 100% NO conversion and 80% N₂ selectivity at 250 °C. Detailed structural analysis showed that the introduced Cu replaces some Co in tetrahedral coordination to induce a strong synergistic effect between different metals. This endows the catalyst with the promotion of both electron transfer and oxygen vacancy generation on the catalyst surface. Importantly, the reaction mechanism and pathway were further revealed by in situ diffusion Fourier transform infrared spectroscopy (DRIFTS) and density functional theory (DFT) calculations. The results indicated that the cycle of oxygen vacancy mainly determines the catalytic activity of NO reduction by CO. Notably, Cu doping significantly lowered the energy barrier of the rate-determining step (*CO + O → *O_v + CO₂), facilitating the desorption of the CO₂ and exposing the active sites for efficient NO reduction with CO. This work offers an effective way for designing the catalyst in NO reduction by CO and provides a reference for exploring the catalytic mechanism of the reaction.

Oxygen Vacancy Promoted O2 Activation over Mesoporous Ni-Co Mixed Oxides for Aromatic Hydrocarbon Oxidation

Whether the oxygen vacancies of heterogeneous catalysts improve their catalytic activity or not has recently been the topic of intense debate in the oxidation of hydrocarbons. We designed an effective strategy to construct mesoporous Ni-Co mixed oxides via a ligand-assisted self-assembly approach. The surface oxygen vacancy concentrations of the mesoporous Ni-Co mixed oxide catalysts were regulated by changing the doping amount of Ni or the reduction method, and the relationship between oxygen vacancies and catalytic activity was studied. Controlled experiments and DFT calculations revealed that oxygen molecules were more favorably adsorbed and activated on oxygen vacancies to form active oxygen species. Increasing the oxygen vacancy concentration within a certain range can effectively enrich the active oxygen species, therefore improving the oxidation rate of ethylbenzene. The optimized mCo₃O₄-0.1NiO catalyst exhibited a remarkable catalytic activity for the solvent-free oxidation of ethylbenzene to acetophenone, typically including 68.0% conversion and 95.4% selectivity (20 mg mCo₃O₄-0.1NiO, 10 mL ethylbenzene, and 0.6 MPa O₂).

Lattice Compressive Strain of Co3O4 Induced by Synthetic Solvents Promotes Efficient Oxidation of Benzene at Low Temperature

A series of Co₃O₄ with different surface defective structures were prepared by the solvothermal method and tested for the activity of benzene oxidation. The characterizations revealed that the synthetic solvent had a dramatic effect on the composition of Co₃O₄ precursors as well as the physicochemical properties of Co₃O₄. Although all Co₃O₄ exhibited a cubic spinel structure, Co₃O₄ prepared with triethylene glycol (Co-TEG) had the highest compressive strain due to the nature of high viscosity of triethylene glycol. These in turn affected the surface chemical structure and the low-temperature redox properties. Co-TEG exhibited the best benzene oxidation activity and showed excellent stability and good water resistance. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to study the oxidation process of benzene. It was found that Co-TEG with more defective structures had abundant surface adsorbed oxygen and active lattice oxygen, which promoted the conversion of benzene and the corresponding intermediates at low temperature.

New insight into electrochemical denitrification using a self-organized nanoporous VO-Co3O4/Co cathode: Plasma-assistant oxygen vacancies catalyzed efficient nitrate reduction

A novel self-organized nanoporous V_O-Co₃O₄/Co cathode was prepared via anodization and plasma treatment and obtained a significant nitrate reduction efficiency. In the anodization, an oxide layer with the nano-sized pore structure initially grew in-situ on the Co substrate and showed a better surface area. Subsequently, He-plasma increased surface oxygen vacancies (V_O) from 24 % to 57 %. Electrons in vacancies were charged into empty e_g orbital of low-spin Co³⁺(O_h, octahedral) and firstly generated high-spin Co²⁺(O_h) with the configuration of t_2g⁶e_g¹, accounting for 71.7 % of cobalt species. Accordingly, two original mechanisms (Vo-catalyzed and Co²⁺(O_h)-catalyzed) were concluded in this study. Oxygen vacancies increased the charge intensity and served as absorption sites in nitrate reduction. Meanwhile, massive Co²⁺(O_h) provided electrons in the e_g orbital with a higher energy state and mediated the faster electron transfer through a Co²⁺-Co³⁺-Co²⁺ redox cycle, compared with Co²⁺ (T_d, tetrahedral). Ultimately, a faster reaction kinetic of 0.0220 min^-1 was achieved by V_O-Co₃O₄ than other cathodes e.g., Co₃O₄ (0.0150 min^-1). Such V_O-Co₃O₄/Co cathode-based denitrification strategy displayed great advantages in engineering application and completely removed 90 % of TN from actual wastewater.

Ni-O4 as Active Sites for Efficient Oxygen Evolution Reaction with Electronic Metal-Support Interactions

Precise adjustment of the metal site structure in single-atom catalysts (SACs) plays a key role in addressing the oxygen evolution reaction (OER). Herein, we report the synthesis of O-doped Ni SACs anchored on porous graphene-like carbon (Ni-O-G) using molten salts (ZnCl₂ and NaCl) as templates, in which the unique Ni-O₄ structure serves as the active sites. Ni-O-G, with an overpotential of only 238 mV (@ 10 mA cm^-2), is one of the more advanced catalysts. An array of characterizations and density functional theory calculations show that the Ni-O₄ coordination enables Ni to be closer to the Fermi level compared to traditional Ni-N₄, enhancing the electronic metal-support interaction to facilitate OER kinetics. Thus, this work offers an alternative strategy for the structural modulation of Ni SACs and the effect of different coordination elements with the same atomic coordination structure on the intrinsic OER activity.

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.

Ga-Promoted CuCo-Based Catalysts for Efficient CO2 Hydrogenation to Ethanol: The Key Synergistic Role of Cu-CoGaOx Interfacial Sites

Currently, direct catalytic CO₂ hydrogenation to produce ethanol is an effective and feasible way for the resource utilization of CO₂. However, constructing non-precious metal catalysts with satisfactory activity and desirable ethanol selectivity remains a huge challenge. Herein, we reported gallium-promoted CuCo-based catalysts derived from single-source Cu-Co-Ga-Al layered double hydroxide precursors. It was manifested that the introduction of Ga species could strengthen strong interactions between Cu and Co oxide species, thereby modifying their electronic structures and thus facilitating the formation of abundant metal-oxide interfaces (i.e., Cu⁰/Cu⁺-CoGaO_x interfaces). Notably, the as-constructed Cu-CoGa catalyst with a Ga:Co molar ratio of 0.4 exhibited a high ethanol selectivity of 23.8% at a 17.8% conversion, along with a high space-time yield of 1.35 mmol_EtOH·g_cat^-1·h^-1 for ethanol under mild reaction conditions (i.e., 220 °C, 3 MPa pressure), which outperformed most non-noble metal-based catalysts previously reported. According to the comprehensive structural characterizations and in situ diffuse reflectance infrared Fourier transform spectra of CO₂/CO adsorption and CO₂ hydrogenation, it was unambiguously revealed that CH_x could be formed at oxygen vacancies of defective CoGaO_x species, while CO could be stabilized by Cu⁺ species, and thus the catalytic synergistic role of Cu⁰/Cu⁺-CoGaO_x interfacial sites promoted the generation of CH_x and CO intermediates to participate in the CH_x-CO coupling process and simultaneously inhibited alkylation reactions. The present work points out a promising new strategy for constructing CuCo-based catalysts with favorable interfacial sites for highly efficient CO₂ hydrogenation to produce ethanol.

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.

Vital Role of Synthesis Temperature in Co–Cu Layered Hydroxides and Their Fenton-like Activity for RhB Degradation

Cu and Co have shown superior catalytic performance to other transitional elements, and layered double hydroxides (LDHs) have presented advantages over other heterogeneous Fenton catalysts. However, there have been few studies about Co–Cu LDHs as catalysts for organic degradation via the Fenton reaction. Here, we prepared a series of Co–Cu LDH catalysts by a co-precipitation method under different synthesis temperatures and set Rhodamine B (RhB) as the target compound. The structure-performance relationship and the influence of reaction parameters were explored. A study of the Fenton-like reaction was conducted over Co–Cu layered hydroxide catalysts, and the variation of synthesis temperature greatly influenced their Fenton-like catalytic performance. The Co–Cut=65°C catalyst with the strongest LDH structure showed the highest RhB removal efficiency (99.3% within 30 min). The change of synthesis temperature induced bulk-phase transformation, structural distortion, and metal–oxygen (M–O) modification. An appropriate temperature improved LDH formation with defect sites and lengthened M–O bonds. Co–Cu LDH catalysts with a higher concentration of defect sites promoted surface hydroxide formation for H2O2 adsorption. These oxygen vacancies (Ovs) promoted electron transfer and H2O2 dissociation. Thus, the Co–Cu LDH catalyst is an attractive alternative organic pollutants treatment.

Promoting effects of indium doped Cu/CeO2 catalysts on CO2 hydrogenation to methanol

Combining catalyst modification by indium doping and chemometric optimization, the Cu/CeO2 system showed high selectivity to methanol (99.3%) with no CO formation during CO2 hydrogenation.

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...

Unraveling the Surface Hydroxyl Network on In2O3 Nanoparticles with High-Field Ultrafast Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

Hydroxyl groups are among the major active surface sites over metal oxides. However, their spectroscopic characterizations have been challenging due to limited resolutions, especially on hydroxyl-rich surfaces where strong hydroxyl networks are present. Here, using nanostructured In₂O₃ as an example, we show significantly enhanced discrimination of the surface hydroxyl groups, owing to the high-resolution ¹H NMR spectra performed at a high magnetic field (18.8 T) and a fast magic angle spinning (MAS) of up to 60 kHz. A total of nine kinds of hydroxyl groups were distinguished and their assignments (μ₁, μ₂, and μ₃) were further identified with the assistance of ¹⁷O NMR. The spatial distribution of these hydroxyl groups was further explored via two-dimensional (2D) ¹H-¹H homonuclear correlation experiments with which the complex surface hydroxyl network was unraveled at the atomic level. Moreover, the quantitative analysis of these hydroxyl groups with such high resolution enables further investigations into the physicochemical property and catalytic performance characterizations (in CO₂ reduction) of these hydroxyl groups. This work provides insightful understanding on the surface structure/property of the In₂O₃ nanoparticles and, importantly, may prompt general applications of high-field ultrafast MAS NMR techniques in the study of hydroxyl-rich surfaces on other metal oxide materials.

Highly Ordered Mesoporous Co3 O4 Electrocatalyst for Efficient, Selective, and Stable Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Electrochemical oxidation of biomass substrates to valuable bio-chemicals is highly attractive. However, the design of efficient, selective, stable, and inexpensive electrocatalysts remains challenging. Here it is reported how a 3D highly ordered mesoporous Co3 O4 /nickel foam (om-Co3 O4 /NF) electrode fulfils those criteria in the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to value-added 2,5-furandicarboxylic acid (FDCA). Full conversion of HMF and an FDCA yield of >99.8 % are achieved with a faradaic efficiency close to 100 % at a potential of 1.457 V vs. reversible hydrogen electrode. Such activity and selectivity to FDCA are attributed to the fast electron transfer, high electrochemical surface area, and reduced charge transfer resistance. More impressively, remarkable catalyst stability under long-term testing is obtained with 17 catalytic cycles. This work highlights the rational design of metal oxides with ordered meso-structures for electrochemical biomass conversion.

Insight into the Improvement Effect of Nitrogen Dopant in Ag/Co3O4 Nanocubes for Soot Oxidation: Experimental and Theoretical Studies

Different doping amounts of N-doped Ag/Co₃O₄ nanocubes were synthesized for the first time for catalytic soot oxidation. The N-doped sample exhibited remarkably improved catalytic activity, of which the maximum decrease in temperature for 90% soot conversion was almost 40 ℃. Characterization results analyzed by TEM, XPS, EPR, H₂-TPR, O₂-TPD, etc. revealed that the incorporation of N atoms can alter the electronic structure, leading to the generation of more oxygen vacancies and enhancement of lattice oxygen mobility. Meanwhile, larger surface area, rugged morphology and promoted reducibility also contribute to the performance improvement. DFT calculations on the differential charge density, Gibbs free energy, etc. were performed to investigate the intrinsic reasons on an atomic level. Due to the relatively higher electronegativity, N dopant could be an electron-appealing center to promote efficient electron transfer, resulting in the redistribution of charge density and formation of conductive Co-N bonds. This variation in electronic structure favors lowering the formation energy of oxygen vacancies and facilitating the activation of the lattice oxygen originated from the highly hybridized Co-O bonds, which ultimately reduces the activation barriers for reactants/intermediates and accelerates the reaction kinetics. This study evidenced that N doping could be an effective strategy to promote catalytic soot oxidation.

Recent advances in catalytic systems in the prism of physicochemical properties to remediate toxic CO pollutants: A state-of-the-art review

Carbon monoxide (CO) is the most harmful pollutant in the air, causing environmental issues and adversely affecting humans and the vegetation and then raises global warming indirectly. CO oxidation is one of the most effective methods of reducing CO by converting it into carbon dioxide (CO₂) using a suitable catalytic system, due to its simplicity and great value for pollution control. The CO oxidation reaction has been widely studied in various applications, including proton-exchange membrane fuel cell technology and catalytic converters. CO oxidation has also been of great academic interest over the last few decades as a model reaction. Many review studies have been produced on catalysts development for CO oxidation, emphasizing noble metal catalysts, the configuration of catalysts, process parameter influence, and the deactivation of catalysts. Nevertheless, there is still some gap in a state of the art knowledge devoted exclusively to synergistic interactions between catalytic activity and physicochemical properties. In an effort to fill this gap, this analysis updates and clarifies innovations for various latest developed catalytic CO oxidation systems with contemporary evaluation and the synergistic relationship between oxygen vacancies, strong metal-support interaction, particle size, metal dispersion, chemical composition acidity/basicity, reducibility, porosity, and surface area. This review study is useful for environmentalists, scientists, and experts working on mitigating the harmful effects of CO on both academic and commercial levels in the research and development sectors.

Chemisorbed Superoxide Species Enhanced the High Catalytic Performance of Ag/Co3O4 Nanocubes for Soot Oxidation

The respective action mode between surface-adsorbed oxygen and bulk lattice oxygen during catalytic soot oxidation is still not fully recognized. Herein, a series of Ag-loaded Co₃O₄ catalysts with different Ag loading amounts were prepared by the impregnation method, and 5% Ag/Co₃O₄ presented competitive catalytic activity toward soot combustion with a T₅₀ below 290 °C in 10% O₂/N₂. This remarkable improvement in catalytic performance could be primarily attributed to the enhanced Ag-Co₃O₄ metal-support interaction induced by the formation of uniform, dispersive, and suitable size metallic Ag nanoparticles. The activation, activity, consumption-regeneration, identification, and reaction of surface-adsorbed oxygen along with the activity of bulk lattice oxygen were characterized by various designed and in situ techniques. The results demonstrated that the chemisorbed superoxide species (O₂^-) play the potentially responsible role for boosting soot combustion, while the bulk lattice oxygen is much less active within the tested temperatures, inducing a negligible activity contribution. Moreover, soot-temperature programmed reduction, isothermal kinetic study, and density functional theory calculation provided supplementary support for the enhancement effect of Ag-Co₃O₄ combination in the activation and utilization of surface-adsorbed oxygen. The overall objective of this work is to identify the role of surface-adsorbed oxygen and bulk lattice oxygen for soot oxidation over Ag/Co₃O₄ catalysts.

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.