Oxygen Vacancy Promoted O2 Activation over Perovskite Oxide for Low-Temperature CO Oxidation

Cation-Induced Self-Assembly of α-MnO2 Nanowires into High-Purity Self-Standing Three-Dimensional Network Aerogels for Catalytic Decomposition of Carcinogenic Formaldehyde at Ambient Temperature

Formaldehyde (HCHO), a ubiquitous gaseous pollutant in indoor environments, threatens human health under long-term exposure, necessitating its effective elimination. Due to its advantages in enhancing mass transfer and effectively exposing active sites, aerogels with a three-dimensional (3D) interconnected network structure are expected to achieve efficient and stable decomposition of HCHO at ambient temperature. However, how to realize the self-assembly of transition metal oxides to construct high-purity 3D network aerogels is still a huge challenge. Herein, the cation-induced self-assembly strategy was developed to construct high-purity self-standing 3D network manganese dioxide aerogels. The interaction between cations and the surface groups of nanowires is crucial for successful self-assembly, which leads to the cross-winding of nanowires with each other, forming a 3D-structured network. The K+-induced 3D-MnO2 exhibited excellent catalytic performance for HCHO, which could continuously and steadily decompose HCHO into CO2 and H2O at ambient temperature. Thanks to the 3D interconnected network structure, on the one hand, it provides a large specific surface area and porosity, reducing mass transfer resistance and promoting the adsorption of HCHO and O2 molecules. On the other hand, it is more important to fully expose the active sites, which can generate more surface active oxygen species and achieve effective recycling and regeneration. Importantly, 3D-MnO2 has a strong ability to capture and activate water molecules in the atmosphere, which could be further involved in the replenishment of the consumed hydroxyl groups. This study proposes a strategy for self-assembly of transition metal oxides through cation-induction, which provides a new catalyst design approach for the room temperature decomposition of VOCs.

Selective recovery of manganese from spent ternary lithium-ion batteries for efficient catalytic oxidation of VOCs: Unveiling the mechanism of activity Enhancement in recycled catalysts

With the widespread application of ternary lithium-ion batteries (TLBs) in various fields, the disposal of spent TLBs has become a globally recognized issue. This study proposes a novel method for reutilizing metal resources from TLBs. Through selective oxidation, manganese in a leaching solution of TLBs was converted into MnO2 with α, γ, and δ crystal phases (referred to as T-MnO2) for catalytic oxidation of volatile organic compounds (VOCs), while efficiently separating manganese from high-value metals such as nickel, cobalt, and lithium, achieving a manganese recovery rate of 99.99%. Compared to similar MnO2 prepared from pure materials, T-MnO2 exhibited superior degradation performance for toluene and chlorobenzene, with T90 decreasing by around 30 °C. The acidic synthesis environment provided by the leaching solution and the doping of trace metals altered the physicochemical properties of T-MnO2, such as increased specific surface area, elevated surface manganese valence, and improved redox performance and oxygen vacancy properties, enhancing its catalytic oxidation capacity. Furthermore, the degradation pathway of toluene on T-γ-MnO2 was inferred using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and in-situ DRIFTs. This study provides a novel approach for recycling spent TLBs and treating VOCs catalytically.

Enhancing the Performance of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) Perovskites as Catalysts for CO Oxidation by Decreasing the Ba Content

Mixed oxides featuring perovskite-type structures (ABO3) offer promising catalytic properties for applications focused on the control of atmospheric pollution. In this work, a series of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) samples have been synthesized, characterized and tested as catalysts for CO oxidation reaction in conditions close to that found in the exhausts of last-generation automotive internal combustion engines. All samples were observed to be active as catalysts for CO oxidation during CO-TPRe tests, with Ba0.7MnO3 (B0.7M) being the most active one, as it presents the highest amount of oxygen vacancies (which act as active sites for CO oxidation) and Mn (IV), which features the highest levels of reducibility and the best redox properties. B0.7M has also showcased a high stability during reactions at 300 °C, even though a slightly lower CO conversion is achieved during the second consecutive reaction cycle. This performance appears to be related to the decrease in the Mn (IV)/Mn (III) ratio.

Synthesis of La1-xSrxCoO3-δ and its catalytic oxidation of NO and its reaction path

The oxidation rate of NO to NO2 is a critical parameter in the removal of NOx within selective catalytic reduction (SCR) systems. LaCoO3-δ is a kind of potential catalyst to enhance the oxidation of NO to NO2, it may offers an economic and stable alternative to noble metal catalysts, particularly at elevated temperatures. This study aimed to enhance the catalytic efficiency of LaCoO3-δ through strontium (Sr) doping. La1-xSrxCoO3-δ (with varying x values of 0.1, 0.2, 0.3, 0.4) was synthesized using a sol-gel method. La1-xSrxCoO3-δ exhibited superior NO oxidation catalytic activity compared to LaCoO3-δ, with the most notable enhancement observed at x = 0.3 (84 % conversion). This improvement can be attributed to the substitution of La3+ with Sr2+, which induces lattice distortion and charge imbalance, thereby creating more oxygen vacancies that enhance the catalytic oxidation capability of La1-xSrxCoO3-δ. However, it's important to note that an excessive amount of Sr can result in the formation of SrCO3 deposits on the surface of La1-xSrxCoO3-δ, thereby diminishing its catalytic oxidation performance. The catalytic oxidation reaction behavior adhered most closely to the O2-adsorbed E-R model, the surface defects in La1-xSrxCoO3-δ playing a pivotal role in the catalytic reaction.

The Surface/Interface Modulation of Platinum Group Metal (PGM)-Free Catalysts for VOCs and CO Catalytic Oxidation

Effective management of volatile organic compounds (VOCs) and carbon monoxide (CO) is critical to human health and the ecological environment. Catalytic oxidation is one of the most promising technologies for achieving efficient VOCs and CO emission control. Platinum group metal (PGM)-free catalysts are recently receiving sustainable attention in catalyzing VOCs and CO removal due to their low cost, superior catalytic activity, and excellent stability, but PGM-free catalysts face challenges in low-temperature catalytic efficiency. In this mini-review, starting with discussing the catalytic mechanism of VOCs and CO oxidation, we summarize the surface/interface modulation strategies of PGM-free catalysts to promote oxygen and VOCs/CO molecule activation for enhanced low-temperature oxidation activity, including oxygen vacancy engineering, heteroatom doping, surface acidity modification, and active interface construction. We highlight the currently remaining challenges and prospects of advanced PGM-free catalyst development for highly efficient VOCs and CO emission control in practical applications.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Strengthening the Synergy between Oxygen Vacancies in Electrocatalysts for Efficient Glycerol Electrooxidation

Defect-engineered bimetallic oxides exhibit high potential for the electrolysis of small organic molecules. However, the ambiguity in the relationship between the defect density and electrocatalytic performance makes it challenging to control the final products of multi-step multi-electron reactions in such electrocatalytic systems. In this study, controllable kinetics reduction is used to maximize the oxygen vacancy density of a Cu─Co oxide nanosheet (CuCo2O4 NS), which is used to catalyze the glycerol electrooxidation reaction (GOR). The CuCo2O4-x NS with the highest oxygen-vacancy density (CuCo2O4-x-2) oxidizes C3 molecules to C1 molecules with selectivity of almost 100% and a Faradaic efficiency of ≈99%, showing the best oxidation performance among all the modified catalysts. Systems with multiple oxygen vacancies in close proximity to each other synergistically facilitate the cleavage of C─C bonds. Density functional theory calculations confirm the ability of closely spaced oxygen vacancies to facilitate charge transfer between the catalyst and several key glycolic-acid (GCA) intermediates of the GOR process, thereby facilitating the decomposition of C2 intermediates to C1 molecules. This study reveals qualitatively in tuning the density of oxygen vacancies for altering the reaction pathway of GOR by the synergistic effects of spatial proximity of high-density oxygen vacancies.

Dual-Photosensitizer Synergy Empowers Ambient Light Photoactivation of Indium Oxide for High-Performance NO2 Sensing

Light-activated chemiresistors offer a powerful approach to achieving lower-temperature gas sensing with unprecedented sensitivities. However, an incomplete understanding of how photoexcited charge carriers enhance sensitivity obstructs the rational design of high-performance sensors, impeding the practical utilization under commonly accessible light sources instead of ultraviolet or higher-energy sources. Here, a rational approach is presented to modulate the electronic properties of the parent metal oxide phase, exemplified by this model system of Bi-doped In2O3 nanofibers decorated with Au nanoparticles (NPs) that exhibit superior NO2 sensing performance. Bi doping introduces mid-gap energy levels into In2O3, promoting photoactivation even under visible blue light. Additionally, green-absorbing plasmonic Au NPs facilitate electron transfer across the heterojunction, extending the photoactive region toward the green light. It is revealed that the direct involvement of photogenerated charge carriers in gas adsorption and desorption processes is pivotal for enhancing gas sensing performance. Owing to the synergistic interplay between the Bi dopants and the Au NPs, the Au-BixIn2-xO3 (x = 0.04) sensing layers attain impressive response values (Rg/Ra = 104 at 0.6 ppm NO2) under green light illumination and demonstrate practical viability through evaluation under simulated mixed-light conditions, all of which significantly outperforms previously reported visible light-activated NO2 sensors.

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter

Particulate matter, represented by soot particles, poses a significant global environmental threat, necessitating efficient control technology. Here, we innovatively designed and elaborately fabricated ordered hierarchical macroporous catalysts of Ce0.8Zr0.2O2 (OM CZO) integrated on a catalyzed diesel particulate filter (CDPF) using the self-assembly method. An oxygen-vacancy-enriched ordered macroporous Ce0.8Zr0.2O2 catalyst (VO-OM CZO) integrated CDPF was synthesized by subsequent NaBH4 reduction. The VO-OM CZO integrated CDPF exhibited a markedly enhanced soot oxidation activity compared to OM CZO and powder CZO coated CDPFs (T50: 430 vs 490 and 545 °C, respectively). The well-defined OM structure of the VO-OM CZO catalysts effectively improves the contact efficiency between soot and the catalysts. Meanwhile, oxygen vacancies trigger the formation of a large amount of highly reactive peroxide species (O22-) from molecular oxygen (O2) through electron abstraction from the three adjacent Ce3+ (3Ce3+ + Vö + O2 → 3Ce4+ + O22-), contributing to the efficient soot oxidation. This work demonstrates the fabrication of the ordered macroporous CZO integrated CDPF and reveals the importance of structure and surface engineering in soot oxidation, which sheds light on the design of highly efficient PM capture and removal devices.

Essential role of lattice oxygen in hydrogen sensing reaction

Understanding the sensing mechanism of metal oxide semiconductors is imperative to the development of high-performance sensors. The traditional sensing mechanism only recognizes the effect of surface chemisorbed oxygen from the air but ignores surface lattice oxygen. Herein, using in-situ characterizations, we provide direct experimental evidence that the surface chemisorbed oxygen participated in the sensing process can come from lattice oxygen of the oxides. Further density functional theory (DFT) calculations prove that the p-band center of O serves as a state of art for regulating the participation of lattice oxygen in gas-sensing reactions. Based on our experimental data and theoretical calculations, we discuss mechanisms that are fundamentally different from the conventional mechanism and show that the easily participation of lattice oxygen is helpful for the high response value of the materials.

Oxygen vacancy-rich Ag/CuO nanoarray mesh fabricated by laser ablation for efficient bacterial inactivation

The contamination of drinking water by microbes is a critical health concern, underscoring the need for safe, reliable, and efficient methods to treat pathogenic microorganisms. While most sterilization materials are available in powder form, this presents safety risks and challenges in recycling. Herein, this study reports the preparation of an innovative copper oxide supported silver monolithic nanoarray mesh with abundant oxygen vacancies (Ag/CuO-VO) by laser ablation. The instantaneous high temperature caused by laser ablation preserves the material's original structure while generating oxygen vacancies on the CuO surface. The Ag/CuO-VO mesh demonstrated a remarkable ability to inactivate over 99% of Escherichia coli (E. Coli) within 20 min. The oxygen vacancies in the Ag/CuO-VO enhance interactions between oxygen species and the Ag/CuO-VO, leading to the accumulation of large amounts of reactive oxygen species (ROS). The generated ROS effectively disrupt both layers of the bacterial cell wall - the peptidoglycan and the phospholipid - as confirmed by Fourier Transform Infrared (FTIR) spectroscopy, culminating in cell death. This research presents a monolithic material capable of inactivating pathogenic microorganisms efficiently, offering a significant advancement in water sterilization technology.

Improving the Catalytic Performance of BaMn0.7Cu0.3O3 Perovskite for CO Oxidation in Simulated Cars Exhaust Conditions by Partial Substitution of Ba

The sol-gel method, adapted to aqueous media, was used for the synthesis of BaMn0.7Cu0.3O3 (BMC) and Ba0.9A0.1Mn0.7Cu0.3O3 (BMC-A, A = Ce, La or Mg) perovskite-type mixed oxides. These samples were fully characterized by ICP-OES, XRD, XPS, H2-TPR, BET, and O2-TPD and, subsequently, they were evaluated as catalysts for CO oxidation under different conditions simulating that found in cars exhaust. The characterization results show that after the partial replacement of Ba by A metal in BMC perovskite: (i) a fraction of the polytype structure was converted to the hexagonal BaMnO3 perovskite structure, (ii) A metal used as dopant was incorporated into the lattice of the perovskite, (iii) oxygen vacancies existed on the surface of samples, and iv) Mn(IV) and Mn(III) coexisted on the surface and in the bulk, with Mn(IV) being the main oxidation state on the surface. In the three reactant atmospheres used, all samples catalysed the CO to CO2 oxidation reaction, showing better performances after the addition of A metal and for reactant mixtures with low CO/O2 ratios. BMC-Ce was the most active catalyst because it combined the highest reducibility and oxygen mobility, the presence of copper and of oxygen vacancies on the surface, the contribution of the Ce(IV)/Ce(III) redox pair, and a high proportion of surface and bulk Mn(IV). At 200 °C and in the 0.1% CO + 10% O2 reactant gas mixture, the CO conversion using BMC-Ce was very similar to the achieved with a 1% Pt/Al2O3 (Pt-Al) reference catalyst.

Understanding the effects of A-site Ag-doping on LaCoO3 perovskite for NO oxidation: Structural and magnetic properties

The partial substitution of A-site in perovskites is a major strategy to enhance the catalytic oxidation activity. This study explores the use of silver (Ag) to partially replace the lanthanum (La) ion at the A-site in LaCoO3 perovskite, investigating the role of Ag in the ABO3 perovskite structure, elucidating the nitric oxide (NO) oxidation mechanism over La1-xAgxCoO3 (x = 0.1-0.5) perovskites. La0.7Ag0.3CoO3 with an Ag-doping amount of 0.3, exhibited the highest NO oxidation activity of 88.5% at 275 °C. Characterization results indicated that Ag substitution enhanced the perovskite, maintaining its original phase structure, existing in the form of a mixture of Ag0 and Ag+ in the La1-xAgxCoO3 (x = 0.1-0.5) perovskites. Notably, Ag substitution improved the specific surface area, reduction performance, Co3+, and surface adsorption oxygen content. Additionally, the study investigated the relationship between magnetism and NO oxidation from a magnetism perspective. Ag-doping strengthened the magnetism of La-Ag perovskite, resulting in stronger adsorption of paramagnetic NO. This study elucidated the NO oxidation mechanism over La-Ag perovskite, considering structural and magnetic properties, providing valuable insights for the subsequent development and industrial application of high oxidation ability perovskite catalysts.

Role of the In-Situ-Formed Surface (Pt-S-O)-Ti Active Structure in SO2-Promoted C3H8 Combustion over a Pt/TiO2 Catalyst

Typically, SO2 unavoidably deactivates catalysts in most heterogeneous catalytic oxidations. However, for Pt-based catalysts, SO2 exhibits an extraordinary boosting effect in propane catalytic oxidation, but the promotive mechanism remains contentious. In this study, an in situ-formed tactful (Pt-S-O)-Ti structure was concluded to be a key factor for Pt/TiO2 catalysts with a substantial SO2 tolerance ability. The experiments and theoretical calculations confirm that the high degree of hybridization and orbital coupling between Pt 5d and S 3p orbitals enable more charge transfer from Pt to S species, thus forming the (Pt-S-O)-Ti structure with the oxygen atom dissociated from the chemisorbed O2 adsorbed on oxygen vacancies. The active oxygen atom in the (Pt-S-O)-Ti active structure is a robust site for C3H8 adsorption, leading to a better C3H8 combustion performance. This work can provide insights into the rational design of chemical bonds for high SO2 tolerance catalysts, thereby improving economic and environmental benefits.

The controlled engineering of surface oxygen defects on Bi2Zr2O7 compounds for catalytic soot combustion by adjusting the preparation methods

The quantity of surface oxygen vacancies/defects is critical to promote the reactivity of metal oxide catalysts. Therefore, for the controlled engineering of Bi2Zr2O7 with rich surface defects for soot combustion, four different methods have been adopted. Bi2Zr2O7 compounds with a defective fluorite phase but with varied surface vacancy concentrations have been successfully synthesized by various methods. The best catalyst (Bi2Zr2O7-CP) was fabricated by a facile co-precipitation method. Both O2- and O22- were the active surface sites whose number positively correlated to the number of surface oxygen vacancies and determined the activity. Moreover, a sample with more surface vacancies usually had weaker Zr-O bonds, which could be the intrinsic factor to enhance the activity. In addition, a novel and simple method has been developed to accurately titrate the absolute amount of soot reactive oxygen sites and calculate the TOF values. In conclusion, by optimizing the preparation methods, Bi2Zr2O7 catalysts with rich surface defects can be tuned, which may help in designing more applicable soot oxidation catalysts.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

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.

Enhanced degradation of micropollutants by visible light photocatalysts with strong oxygen activation ability

Visible light photocatalysis is widely considered a sustainable approach to break down micropollutants without chemical addition. To promote the output of photogenerated carriers under visible light, a Z-scheme plasmonic photocatalyst Bi-CeO2/Ag0/BiO2 was designed and fabricated to activate dissolved oxygen in water for micropollutant degradation. The doped Bi not only improved the separation of electron-hole, but also narrowed the band gap of CeO2 to enhance its absorption of visible light. Notably, metallic silver (Ag0) works as an electronic transmission vehicle from Bi-CeO2 to BiO2 in a Z-scheme mechanism. Likewise, the surface plasmon resonance effect of Ag0 also enhanced the absorption of visible light. Furthermore, the Bi doping induced abundant surface oxygen vacancies on CeO2 for enhanced capability and selectivity towards O2 adsorption and activation, which favored the generation of O2•- by photogenerated electrons to degrade sulfamethoxazole, enrofloxacin, and bisphenol A. Theoretical calculation results also confirmed the O2•--driven degradation pathway for sulfamethoxazole. Therefore, the Z-scheme Bi-CeO2/Ag0/BiO2 not only extends the photocatalytic reactivity of CeO2-based catalysts to the visible light range, but also provides a chemical-free method to effectively degrade micropollutants.

One-Dimensional Oxide Nanostructures Possessing Reactive Surface Defects Enabled a Lithium-Rich Region and High-Voltage Stability for All-Solid-State Composite Electrolytes

The development of highly safe and low-cost solid polymer electrolytes for all-solid-state lithium batteries (ASSLBs) has been hindered by low ionic conductivity, poor stability under high-voltage conditions, and severe lithium-dendrite-induced short circuits. In this study, Li-doped MgO nanofibers bearing reactive surface defects of scaled-up production are introduced to the poly(ethylene oxide) (PEO)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) system. The characterizations and density functional theory calculations reveal that TFSI- is strongly adsorbed on the nanofibers based on the electrostatic interactions of surface oxygen vacancies and the formation of Li-N and Li-O bonds derived from the exposed Li. Additionally, the introduced Li exposed near oxygen vacancies may be liberated from the lattice and engage in the formation of Li-rich domains. Therefore, a high ionic conductivity of 1.48 × 10-4 S cm-1 for the solid electrolyte at 30 °C and excellent cycling stability for the assembled battery, with a discharge capacity retention of 85.2% after 1500 cycles at 2C, can be achieved. Furthermore, the increased coordination of EO chains in the Li-rich region and chemical interactions with nanofibers substantially improve the antioxidant stability of the solid electrolyte, endowing the LiNi0.8Co0.1Mn0.1O2/Li battery with a long lifespan of more than 700 cycles. The results of this study suggest that the surface defects of 1D oxide nanostructures can substantially improve the Li+ diffusion kinetics. This study provides insight into the construction of Li-rich regions for high-voltage ASSLBs.

Surface oxygen vacancy-dependent molecular oxygen activation for propane combustion over α-MnO2

Oxygen vacancies (OV), as the sites of molecular oxygen adsorption and activation, play an important role in the catalytic combustion process of volatile organic compounds (VOCs). Revealing the relationship between OV concentration and molecular oxygen activation behavior is of significance to construct the efficient catalysts. Herein, α-MnO2 with different OV concentrations was prepared to investigate the molecular oxygen activation for C3H8 combustion. It is disclosed that the enhanced OV concentration in α-MnO2 induced the reconfiguration of surface metal atoms, resulting in the transformation of oxygen activation configuration from end-on mode to side-on mode. Oxygen molecules in side-on mode possessed more localized electron density and weaker coordination bond strength with surrounding Mn atoms, which were more favorable to adsorb C3H8 molecules and activate C-H bond for the improved combustion performance. This work provides a new understanding to reveal that the increased OV concentration contributes to more efficient VOCs combustion.

Ca substitution improves the catalytic activity of perovskite LaCoO3 toward toluene: comprehension of electronic structure alteration

For perovskite La1-xCaxCoO3 (Ca-x, x = 0-0.3), Ca-0.2 with the closest O p band center to the Fermi level, displays the best catalytic activity for toluene oxidation. The O p band center determines the reducibility and active oxygen content. This finding is beneficial for the design of highly active perovskite catalysts.

Kinetic and Computational Studies of CO Oxidation and PROX on Cu/CeO2 Nanospheres

As supported CuO is well-known for low temperature activity, CuO/CeO2 nanosphere catalysts were synthesized and tested for CO oxidation and preferential oxidation of CO (PROX) in excess H2. For the first reaction, ignition was observed at 95 °C, whereas selective PROX occurred in a temperature window from 50 to 100 °C. The catalytic performance was independent of the initial oxidation state of the catalyst (CuO vs. Cu0), suggesting that the same active phase is formed under reaction conditions. Density functional modeling was applied to elucidate the intermediate steps of CO oxidation, as well as those of the comparably less feasible H2 transformation. In the simulations, various Cu and vacancy sites were probed as reactive centers enabling specific pathways.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11244-023-01848-x.

Light-driven uranyl-organic frameworks used as signal-enhanced photoelectrochemical sensors for monitoring anthrax

The semiconductor-like characteristics and light absorption ability of metal-organic frameworks (MOFs) make it have the potential for photoelectrochemical sensing. Compared with composite and modified materials, the specific recognition of harmful substances directly using MOFs with suitable structures can undoubtedly simplify the fabrication of sensors. Herein, two photosensitive uranyl-organic frameworks (UOFs) named HNU-70 and HNU-71 were synthesized and explored as the novel "turn-on" photoelectrochemical sensors, which can be directly applied to monitor the biomarker of anthrax (dipicolinic acid). Both sensors have good selectivity and stability towards dipicolinic acid with the low detection limits of 1.062 and 1.035 nM, respectively, which are far lower than the human infection concentration. Moreover, they exhibit good applicability in the real physiological environment of human serum, demonstrating a good application prospect. Spectroscopic and electrochemical studies show that the mechanism of photocurrent enhancement results from the interaction between dipicolinic acid and UOFs, which facilitates the photogenerated electron transport.

Catalytic Ozonation of Polluter Benzene from -20 to >50 °C with High Conversion Efficiency and Selectivity on Mullite YMn2O5

Catalytic decomposition of aromatic polluters at room temperature represents a green route for air purification but is currently challenged by the difficulty of generating reactive oxygen species (ROS) on catalysts. Herein, we develop a mullite catalyst YMn₂O₅ (YMO) with dual active sites of Mn³⁺ and Mn⁴⁺ and use ozone to produce a highly reactive O* upon YMO. Such a strong oxidant species on YMO shows complete removal of benzene from -20 to >50 °C with a high CO_x selectivity (>90%) through the generated reactive species O* on the catalyst surface (60 000 mL g^-1 h^-1). Although the accumulation of water and intermediates gradually lowers the reaction rate after 8 h at 25 °C, a simple treatment by ozone purging or drying in the ambient environment regenerates the catalyst. Importantly, when the temperature increases to 50 °C, the catalytic performance remains 100% conversion without any degradation for 30 h. Experiments and theoretical calculations show that such a superior performance stems from the unique coordination environment, which ensures high generation of ROS and adsorption of aromatics. Mullite's catalytic ozonation degradation of total volatile organic compounds (TVOC) is applied in a home-developed air cleaner, resulting in high efficiency of benzene removal. This work provides insights into the design of catalysts to decompose highly stable organic polluters.

Fe-Doped Metal Complex (LaCo0.9Fe0.1O3) and g-C3N4 Formed a Nanoheterojunction for the Photocatalytic Decomposition of Water

Photocatalytic water decomposition provides an environmentally friendly method of hydrogen production similar to "photosynthesis", while current research aims to develop affordable yet efficient photocatalysts. Oxygen vacancy is one of the most significant defects in metal oxide semiconductors, including perovskite, which substantially influences the semiconductor material's efficiency. To enhance the oxygen vacancy in the perovskite, we worked on doping Fe. A perovskite oxide nanostructure of LaCo_xFe_1-xO₃ (x = 0.2, 0.4, 0.6, 0.8, and 0.9) was prepared by the sol-gel method, and a series of LaCo_xFe_1-xO₃ (x = 0.2, 0.4, 0.6, 0.8, and 0.9)/g-C₃N₄ nanoheterojunction photocatalysts were synthesized using mechanical mixing and solvothermal methods for LaCo_xFe_1-xO₃ (x = 0.2, 0.4, 0.6, 0.8, and 0.9). Fe was successfully doped into the perovskite (LaCoO₃), and the formation of an oxygen vacancy was verified by various detection methods. In our photocatalytic water decomposition experiments, we observed that LaCo_0.9Fe_0.1O₃ demonstrated a significant increase in its maximum hydrogen release rate, reaching 5249.21 μmol h^-1 g^-1, which was remarkably 17.60 times higher than that of LaCoO₃-undoped Fe. Similarly, we also explored the photocatalytic activity of the nanoheterojunction complex LaCo_0.9Fe_0.1O₃/g-C₃N₄, and it exhibited pronounced performance with an average hydrogen production of 7472.67 μmol h^-1 g^-1, which was 25.05 times that of LaCoO₃. We confirmed that the oxygen vacancy plays a crucial role in photocatalysis.

The Enhancement of CO Oxidation Performance and Stability in SO2 and H2S Environment on Pd-Au/FeOX/Al2O3 Catalysts

Carbon monoxide (CO) is a colourless, odourless, and toxic gas. Long-term exposure to high concentrations of CO causes poisoning and even death; therefore, CO removal is particularly important. Current research has focused on the efficient and rapid removal of CO via low-temperature (ambient) catalytic oxidation. Gold nanoparticles are widely used catalysts for the high-efficiency removal of high concentrations of CO at ambient temperature. However, easy poisoning and inactivation due to the presence of SO₂ and H₂S affect its activity and practical application. In this study, a bimetallic catalyst, Pd-Au/FeO_x/Al₂O₃, with a Au:Pd ratio of 2:1 (wt%) was formed by adding Pd nanoparticles to a highly active Au/FeO_x/Al₂O₃ catalyst. Its analysis and characterisation proved that it has improved catalytic activity for CO oxidation and excellent stability. A total conversion of 2500 ppm of CO at -30 °C was achieved. Furthermore, at ambient temperature and a volume space velocity of 13,000 h^-1, 20,000 ppm CO was fully converted and maintained for 132 min. Density functional theory (DFT) calculations and in situ FTIR analysis revealed that Pd-Au/FeO_x/Al₂O₃ exhibited stronger resistance to SO₂ and H₂S adsorption than the Au/FeO_x/Al₂O₃ catalyst. This study provides a reference for the practical application of a CO catalyst with high performance and high environmental stability.

Oxygen Vacancy Promoted Generation of Monatomic Oxygen Anion over Ni2+ -Doped MgO for Efficient Glycolysis of Waste PET

Developing efficient and eco-friendly catalysts for selective degradation of waste polyethylene terephthalate (PET) is critical to the circular economy of plastics. Herein, we report the first monatomic oxygen anion (O^- )-rich MgO-Ni catalyst based on a combined theoretical and experimental approach, which achieves a bis(hydroxyethyl) terephthalate yield of 93.7 % with no heavy metal residues detected. DFT calculations and electron paramagnetic resonance characterization indicate that Ni²⁺ doping not only reduces the formation energy of oxygen vacancies, but also enhances local electron density to facilitate the conversion of adsorbed oxygen into O^- . O^- plays a crucial role in the deprotonation of ethylene glycol (EG) to EG^- (exothermic by -0.6 eV with an activation barrier of 0.4 eV), which is proved effective to break the PET chain via nucleophilic attack on carbonyl carbon. This work reveals the potential of alkaline earth metal-based catalysts in efficient PET glycolysis.

Metal ion endogenous cycles of CoFe2O4-x induced boosted photocatalytic/PMS degradation toward polycyclic aromatic hydrocarbons

The rational design of photocatalytic nanomaterials with unique structures is critical for remediating environmental problems and thus reducing ecological risks. In this work, we employed H₂ temperature-programmed reduction to modify MFe₂O₄ (M = Co, Cu, and Zn) photocatalysts for obtaining additional oxygen vacancies. After activation of PMS, naphthalene and phenanthrene degradation rates in the soil phase were increased by 3.24-fold and 1.39-fold, respectively, and 1.38-fold for naphthalene in the aqueous phase by H-CoFe₂O_4-x. The extraordinary photocatalytic activity is attributed to the oxygen vacancies on the H-CoFe₂O_4-x surface, which promote electron transfer and thus enhance the redox cycle from Co(III)/Fe(III) to Co(II)/Fe(II). In addition, oxygen vacancies are used as electron traps to hinder the recombination of photogenerated carriers and accelerate the generation of hydroxyl and superoxide radicals. Quenching tests showed that the addition of p-benzoquinone resulted in the greatest decrease in the degradation rate of naphthalene (inhibition of about 85.5%), demonstrating that O₂˙^- radicals are the main active species in the photocatalytic degradation of naphthalene. H-CoFe₂O_4-x showed improved degradation performance in synergy with PMS (82.0%, k_app = 0.00714 min^-1) while maintaining excellent stability and reusability. Hence, this work provides a promising approach for the design of efficient photocatalysts to degrade persistent organic pollutants in soil and aqueous environments.

Large-Area and Visible-Light-Driven Heterojunctions of In2O3/Graphene Built for ppb-Level Formaldehyde Detection at Room Temperature

Achieving convenient and accurate detection of indoor ppb-level formaldehyde is an urgent requirement to ensure a healthy working and living environment for people. Herein, ultrasmall In₂O₃ nanorods and supramolecularly functionalized reduced graphene oxide are selected as hybrid components of visible-light-driven (VLD) heterojunctions to fabricate ppb-level formaldehyde (HCHO) gas sensors (named InAG sensors). Under 405 nm visible light illumination, the sensor exhibits an outstanding response toward ppb-level HCHO at room temperature, including the ultralow practical limit of detection (pLOD) of 5 ppb, high response (R_a/R_g = 2.4, 500 ppb), relatively short response/recovery time (119 s/179 s, 500 ppb), high selectivity, and long-term stability. The ultrasensitive room temperature HCHO-sensing property is derived from visible-light-driven and large-area heterojunctions between ultrasmall In₂O₃ nanorods and supramolecularly functionalized graphene nanosheets. The performance of the actual detection toward HCHO is evaluated in a 3 m³ test chamber, confirming the practicability and reliability of the InAG sensor. This work provides an effective strategy for the development of low-power-consumption ppb-level gas sensors.

Nanosized Ti-Based Perovskite Oxides as Acid-Base Bifunctional Catalysts for Cyanosilylation of Carbonyl Compounds

The development of effective solid acid-base bifunctional catalysts remains a challenge because of the difficulty associated with designing and controlling their active sites. In the present study, highly pure perovskite oxide nanoparticles with d⁰-transition-metal cations such as Ti⁴⁺, Zr⁴⁺, and Nb⁵⁺ as B-site elements were successfully synthesized by a sol-gel method using dicarboxylic acids. Moreover, the specific surface area of SrTiO₃ was increased to 46 m² g^-1 by a simple procedure of changing the atmosphere from N₂ to air during calcination of an amorphous precursor. The resultant SrTiO₃ nanoparticles showed the highest catalytic activity for the cyanosilylation of acetophenone with trimethylsilyl cyanide (TMSCN) among the tested catalysts not subjected to a thermal pretreatment. Various aromatic and aliphatic carbonyl compounds were efficiently converted to the corresponding cyanohydrin silyl ethers in good-to-excellent yields. The present system was applicable to a larger-scale reaction of acetophenone with TMSCN (10 mmol scale), in which 2.06 g of the analytically pure corresponding product was isolated. In this case, the reaction rate was 8.4 mmol g^-1 min^-1, which is the highest rate among those reported for heterogeneous catalyst systems that do not involve a pretreatment. Mechanistic studies, including studies of the catalyst effect, Fourier transform infrared spectroscopy, and temperature-programmed desorption measurements using probe molecules such as pyridine, acetophenone, CO₂, and CHCl₃, and the poisoning effect of pyridine and acetic acid toward the cyanosilylation, revealed that moderate-strength acid and base sites present in moderate amounts on SrTiO₃ most likely enable SrTiO₃ to act as a bifunctional acid-base solid catalyst through cooperative activation of carbonyl compounds and TMSCN. This bifunctional catalysis through SrTiO₃ resulted in high catalytic performance even without a heat pretreatment, in sharp contrast to the performance of basic MgO and acidic TiO₂ catalysts.

Tailoring the Composition of BaxBO3 (B = Fe, Mn) Mixed Oxides as CO or Soot Oxidation Catalysts in Simulated GDI Engine Exhaust Conditions

Mixed oxides with perovskite-type structure (ABO₃) are promising catalysts for atmospheric pollution control due to their interesting and tunable physicochemical properties. In this work, two series of Ba_xMnO₃ and Ba_xFeO₃ (x = 1 and 0.7) catalysts were synthesized using the sol-gel method adapted to aqueous medium. The samples were characterized by μ-XRF, XRD, FT-IR, XPS, H₂-TPR, and O₂-TPD. The catalytic activity for CO and GDI soot oxidation was determined by temperature-programmed reaction experiments (CO-TPR and soot-TPR, respectively). The results reveal that a decrease in the Ba content improved the catalytic performance of both catalysts, as B0.7M-E is more active than BM-E for CO oxidation, and B0.7F-E presents higher activity than BF for soot conversion in simulated GDI engine exhaust conditions. Manganese-based perovskites (BM-E and B0.7M-E) achieve better catalytic performance than iron-based perovskite (BF) for CO oxidation reaction due to the higher generation of actives sites.

Role of La-based perovskite catalysts in environmental pollution remediation

Since the advent of the industrial revolution, there has been a constant need of efficient catalysts for abatement of industrial toxic pollutants. This phenomenon necessitated the development of eco-friendly, stable, and economically feasible catalytic materials like lanthanum-based perovskite-type oxides (PTOs) having well-defined crystal structure, excellent thermal, and structural stability, exceptional ionic conductivity, redox behavior, and high tunability. In this review, applicability of La-based PTOs in remediation of pollutants, including CO, NO x and VOCs was addressed. A framework for rationalizing reaction mechanism, substitution effect, preparation methods, support, and catalyst shape has been discussed. Furthermore, reactant conversion efficiencies of best PTOs have been compared with noble-metal catalysts for each application. The catalytic properties of the perovskites including electronic and structural properties have been extensively presented. We highlight that a robust understanding of electronic structure of PTOs will help develop perovskite catalysts for other environmental applications involving oxidation or redox reactions.

Radical-/non-radical-mediated catalyst activation of peroxymonosulfate for efficient atrazine degradation

Efficient degradation technologies are urgent to be developed to avoid the ecological and healthy hazards brought from atrazine (ATZ). LaCoO_3-δ/peroxymonosulfate (PMS) system was proved to have strong degradation capabilities to contaminants. In this work, we intended to investigate the effect of the synthesis method on LaCoO_3-δ. However, the hydrothermal method yielded a new material (H-Co) with better catalytic performance than LaCoO_3-δ, which showed stable catalytic ability at pH 3.0-9.0 and 5 consecutive cycles. The coexistence of inorganic Cl^-, SO₄^2-, NO₃^-, H₂PO₄^-, HCO₃^- and organic humic acids exerted little influences on the H-Co/PMS system. In addition, the actual livestock and poultry breeding wastewater could be well degraded and mineralized by the H-Co/PMS system. Free radical burst experiments and EPR characterization were performed to verify the synergistic effects of free radicals and non-free radicals during ATZ degradation. Based on SEM, XRD, O₂-TPD, FTIR, XPS, and electrochemistry characterizations, the efficient catalytic ability of H-Co could be attributed to the abundant oxygen vacancies, surface hydroxyl groups, zero-valent cobalt sites and high electronic conductivity. The degradation pathways were proposed based on the detection of degradation intermediates of ATZ by UPLC-MS. Moreover, the toxic of ATZ during the oxidation was evaluated by TEXT and E. coli inhibition assay. This work comprehensively analyzed the catalytic reaction mechanism of the H-Co/PMS system and provided a feasible pathway for the treatment of the actual livestock and poultry breeding wastewater.

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.

Electrochemical activation of persulfate by Al-doped blue TiO2 nanotubes for the multipath degradation of atrazine

The combination of electrolysis and persulfate activation (E/PDS) is a cost-effective method for the treatment of refractory organics. However, persulfate is difficult to be activated into radicals at the anode, resulting in insufficient electro-activation efficiency. Herein, Al doped blue TiO₂ nanotube electrodes (Al-bTNT) were first employed as cost-effective anode materials to fully activate PDS to radicals. In E/PDS, the kinetic constant of atrazine removal by Al-bTNT (0.048 min^-1) substantially outperformed the other anodes, including the blue TiO₂ nanotube electrodes (bTNT) (0.024 min^-1), Ti₄O₇ (0.02 min^-1), and B doped diamond (BDD) anodes (0.023 min^-1). The Al-bTNT-E/PDS exhibited a low energy consumption (E_EO = 0.72 kWh m^-3) and a high mineralization rate. Based on the results of electron paramagnetic resonance, quenching experiments, and probe experiments, we propose that atrazine degrades in the Al-bTNT-E/PDS system mainly via a novel radical pathway that involves both·OH and SO₄·^- and the generated SO₄·^- is responsible for the enhanced removal rate. The oxygen vacancies (V_O) generated from interstitial Al may serve as the active sites to adsorb and dissociate the persulfate molecules based on extensive characterizations. The attempt at soil-washing wastewater disposal indicated the synergistic system possessed good potential for future practical application.

Tailoring Spin State of Perovskite Oxides by Fluorine Atom Doping for Efficient Oxygen Electrocatalysis

Promoting the initially deficient but economical catalysts to high-performing competitors is important for developing superior catalysts. Unlike traditional nano-morphology construction methods, this work focuses on intrinsic catalytic activity enhancement via heteroatom doping strategies to induce lattice distortion and optimize spin-dependent orbital interaction to alter charge transfer between catalysts and reactants. Experimentally, a series of different concentrations of fluorine-doped lanthanum cobaltate (F_x -LaCoO₃ ) exhibiting excellent electrocatalytic activity is synthesized, including a low overpotential of 390 mV at j = 10 mA cm^-2 for OER and a large half-wave potential of 0.68 V for ORR. Meanwhile, the assembled rechargeable Zn-air batteries deliver an excellent performance with a large specific capacity of 811 mAh/g_Zn under 10 mA cm^-2 and stability of charge/recharge (120 h). Theoretically, taking advantage of density functional theory calculations, it is found that the prominent OER/ORR performance arises from the spin state transition of Co³⁺ (Low spin state (LS, t_2g ⁶ e_g ⁰ ) → Intermediate spin state (IS, t_2g ⁵ e_g ¹ ) and the mediated d-band center upshift by F atom incorporation. This work establishes a novel avenue for designing superior electrocatalysts in perovskite-based oxides by regulating spin states.

In Situ Monitoring of the Spatial Distribution of Oxygen Vacancies and Enhanced Photocatalytic Performance at the Single-Particle Level

Oxygen vacancies (OVs) on specific sites/facets can strengthen the interaction between reactants and oxide surfaces, facilitating interfacial charge transfer. However, precise monitoring of the spatial distribution of OVs remains a grand challenge. We report here that a single-particle spectroscopy technique addresses this challenge by establishing a positive correlation relationship between defects and bound exciton luminescence across different facets. Taking monoclinic BiVO₄ as an example, on the basis of theoretical guidance, by in situ tracking the PL lifetimes and PL spectra of different facets on single particles before and after hydrogen treatment, we provide evidence that the PL emission originates from the OV state and determine that OVs is more inclined to be generated at the {010} facets. This anisotropic defect engineering significantly prolongs the lifetime of carriers and accelerates the activation of molecular oxygen. These findings not only verify preference rules of OVs in metal oxides but also provide a time-space-resolved monitoring method.

Enhanced H2O2 utilization efficiency in Fenton-like system for degradation of emerging contaminants: Oxygen vacancy-mediated activation of O2

Hydrogen peroxide (H₂O₂) is the most commonly used oxidant in advanced oxidation processes for emerging organic contaminant degradation. However, the activation of H₂O₂ to generate reactive oxygen species is always accompanied by O₂ generation resulting in H₂O₂ waste. Here, we prepare a Ti doped Mn₃O₄/Fe₃O₄ ternary catalyst (Ti-Mn₃O₄/Fe₃O₄) to create abundant oxygen vacancies (OVs), which yields electron delocalization impacts on enhancing the electrical conductivity, accelerating the activation of O₂ to produce H₂O₂. In Ti-Mn₃O₄/Fe₃O₄/H₂O₂ system, OVs-mediated O₂/O₂^•-/H₂O₂ redox cycles trigger the activation of locally generated O₂, boost the regeneration of O₂^•- and on site produce H₂O₂ for replenishment. This leads to a 100% removal of tiamulin in 30 min at an unprecedented H₂O₂ utilization efficiency of 96.0%, which is 24 folds higher than that with Fe₃O₄/H₂O₂. Importantly, further integration of Ti-Mn₃O₄/Fe₃O₄ catalysts into membrane filtration achieved high rejections of tiamulin (> 83.9%) from real surface water during a continuous 12-h operation, demonstrating broad pH adaptability, excellent catalytic stability and leaching resistance. This work demonstrates a feasible strategy for developing OVs-rich catalysts for improving H₂O₂ utilization efficiency via activation of locally generated oxygen during the Haber-Weiss reaction.

Activity and Thermal Aging Stability of La1-xSrxMnO3 (x = 0.0, 0.3, 0.5, 0.7) and Ir/La1-xSrxMnO3 Catalysts for CO Oxidation with Excess O2

The catalytic oxidation of CO is probably the most investigated reaction in the literature, for decades, because of its extended environmental and fundamental importance. In this paper, the oxidation of CO on La_1-xSr_xMnO₃ perovskites (LSMx), either unloaded or loaded with dispersed Ir nanoparticles (Ir/LSMx), was studied in the temperature range 100-450 °C under excess O₂ conditions (1% CO + 5% O₂). The perovskites, of the type La_1-xSr_xMnO₃ (x = 0.0, 0.3, 0.5 and 0.7), were prepared by the coprecipitation method. The physicochemical and structural properties of both the LSMx and the homologous Ir/LSMx catalysts were evaluated by various techniques (XRD, N₂ sorption-desorption by BET-BJH, H₂-TPR and H₂-Chem), in order to better understand the structure-activity-stability correlations. The effect of preoxidation/prereduction/aging of the catalysts on their activity and stability was also investigated. Results revealed that both LSMx and Ir/LSMx are effective for CO oxidation, with the latter being superior to the former. In both series of materials, increasing the substitution of La by Sr in the composition of the perovskite resulted to a gradual suppression of their CO oxidation activity when these were prereduced; the opposite was true for preoxidized samples. Inverse hysteresis phenomena in activity were observed during heating/cooling cycles on the prereduced Ir/LSMx catalysts with the loop amplitude narrowing with increasing Sr-content in LSMx. Oxidative thermal sintering experiments at high temperatures revealed excellent antisintering behavior of Ir nanoparticles supported on LSMx, resulting from perovskite's favorable antisintering properties of high oxygen storage capacity and surface oxygen vacancies.

Recent Status and Developments of Vacancies Modulation in the ABO3 Perovskites for Catalytic Applications

Perovskite oxides (ABO₃ ) have attracted comprehensive interest for wide range of functional applications (especially for chemical catalysis) due to their high design flexibility, controllable vacancies sites creation, abundant chemical properties, and stable crystal structure. Herein, the previous research and potential development of ABO₃ through adjusting the vacancy at different sites (A-site, B-site, and O-site) to enhance catalytic performance are systematically analyzed and generalized. Briefly, the ABO₃ with different vacancies sites prepared by multifarious direct and indirect methods, accompanied with the improved physical-chemical properties, endow them with distinct and intensified development of catalysis application. In addition, the impressive optimization proved by the vacancies sites adjustment over the ABO₃ is studied to continuously facilitate the advance in some common catalysis reactions, further expanding to other optimized functional applications. At last, the constructive suggestions for fine regulation and analysis of vacancies sites over ABO₃ are also put forward.

Rational Regulation of Reducibility and Acid Site on Mn-Fe-BTC to Achieve High Low-Temperature Catalytic Denitration Performance

Selective catalytic reduction with ammonia is the mainstream technology of flue gas denitration (de-NO_x). The reducibility and acid site are two important factors affecting the de-NO_x performance, and effective regulation between them is the key to obtain a highly efficient de-NO_x catalyst. Herein, a series of Mn-Fe-BTC with different ratios of Mn and Fe are synthesized, among which 2Mn-1Fe-BTC with 2:1 molar ratio of Mn and Fe has excellent low-temperature (LT) de-NO_x performance (above 90% NO conversion between 60 and 270 °C) and good tolerance to H₂O and SO₂ poisoning (88% NO conversion at 150 °C with 100 ppm of SO₂ and/or 6% H₂O). It is revealed that the reducibility properties and acid sites of Mn-Fe-BTC can be flexibly tuned by the ratio of Mn and Fe. The difference in electronegativity between Fe and Mn leads to the redistribution of valence electrons, which enables the controllable reducibility of Mn-Fe-BTC. Furthermore, different amounts of Mn and Fe lead to different electron transport, which determines the type and number of acid sites. The synergistic effect of Mn and Fe endows Mn-Fe-BTC with enhanced surface molecular adsorption capacity and enables the catalyst to selectively chemisorb NH₃ and NO at different active sites. This research provides guidance for the flexible regulation of reducibility and acid site of LT de-NO_x catalyst.

Lattice Oxygen Lability of La-Hexaaluminates Substituted by Different Metals and Their Effects on the Thermal Stability of Supported Nano-Ir Particles

Oxide supports with high lattice oxygen lability can stabilize the supported nanoparticles at high temperatures. The lattice oxygen lability of lanthanum hexaaluminates (LHAs) substituted with other metals (such as Mg and Fe) as well as their effects on the thermal stability of supported Ir particles were investigated via CO chemisorption, hydrogen temperature-programmed reduction (H₂-TPR), oxygen temperature-programmed desorption (O₂-TPD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP), and scanning electron microscopy/transmission electron microscopy (SEM/TEM) techniques. The H₂-TPR results showed that the lattice oxygen lability of lanthanum iron hexaaluminate (LFA) was much higher than that of lanthanum magnesium hexaaluminate (LMA). This variation could be attributed to the difference in the reducibility of Fe/Mg atoms and their substitution sites in the crystallographic lattice. Under the reductive condition, the H₂-TPR presented that the amount of reducible lattice oxygen of LFA supported by metallic Ir decreased significantly, implying the existence of the migration of lattice oxygen and formation of oxygen vacancies, as revealed by O₂-TPD and XPS results. After thermal aging at 1200 °C, the amount of residual Ir in LFA was about 4 times that of LMA, as shown in the ICP results. The mean size and dispersion of Ir particles in LFA were better than those in LMA, as revealed by the SEM/TEM results, showing the superior thermal stability of the Ir particles in LFA support. Hence, this study concludes that the lattice oxygen lability plays an important role in improving the thermal stability of the Ir@LHAs at high temperatures. Based on characterization results, a model was proposed to explain the interaction between Ir and LHAs and its effect on the thermal stability of the Ir particles.

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.

One-pot room-temperature synthesis of a BiOCl hierarchical microsphere assembled from nanosheets with exposed {001} facets for enhanced photosensitized degradation

BiOCl hierarchical microspheres assembled from nanosheets with exposed {001} facets were successfully synthesized using PEG-2000 as template by a one-pot room-temperature hydrolysis method. The PEG-modified BiOCl photocatalyst exhibits a significantly enhanced RhB photosensitized degradation activity under visible light. After 10 min white LED irradiation, the degradation efficiency of RhB by the PEG-modified BiOCl sample S _0.07 reaches 99.5%. The degradation rate constant of the PEG-modified sample S _0.07 over RhB is 0.4568 min^-1, which is 6.76 times that of the unmodified sample S ₀ (0.0676 min^-1). After 4 min of xenon lamp (λ ≥ 420 nm) irradiation, the degradation rate of RhB by S _0.07 is almost 100%. The exposed {001} facets with surface defects contribute to the superior adsorption capacity of BiOCl towards RhB, which immensely accelerates the electron transfer efficiency from the excited RhB into the conduction band of BiOCl, forming superoxide radical (˙O₂ ^-) active species to degrade the pollutants. Moreover, the superior RhB-sensitized BiOCl system provides high photocatalytic degradation activity over MO. This work provides a facile and efficient BiOCl synthesis method that is conducive to large-scale production and simultaneously opens up new ideas for the synthesis of other photocatalysts.