Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria

Less Is More: Selective-Atom-Removal-Derived Defective MnOx Catalyst for Efficient Propane Oxidation

Defect manipulation in metal oxide is of great importance in boosting catalytic performance for propane oxidation. Herein, a selective atom removal strategy was developed to construct a defective manganese oxide catalyst, which involved the partial etching of a Mg dopant in MnOx. The resulting MgMnOx-H catalysts exhibited superior low-temperature catalytic activity (T50 = 185 °C, T90 = 226 °C) with a propane conversion rate of 0.29 μmol·gcat.-1·h-1 for the propane oxidation reaction, which is 4.8 times that of pristine MnOx. Meanwhile, a robust hydrothermal stability was guaranteed at 250 °C for 30 h of reaction time. The comprehensive experimental characterizations revealed that the catalytic performance improvement was closely related to the defective structures including the abundant (metal and oxygen) vacancies, distorted crystals, valence imbalance, etc., which prominently weakened the Mn-O bond and stimulated the mobility of surface lattice oxygen, leading to the elevation in the intrinsic oxidation activity. This work exemplifies the significance of defect engineering for the promotion of the oxidation ability of metal oxide, which will be valuable for the further development of efficient non-noble metal catalysts for propane oxidation.

Regulating the spatial arrangement of CuO and MgO within activated carbon matrix to maximize their room temperature H2S removal

Adsorbents with dual-component active phases have attracted much attention owing to their potential application in synergistic H2S removal. The influence of spatial arrangements of two components within a support matrix on their desulfurization performance was investigated through regulating the mutual arrangements of CuO and MgO on an activated carbon surface. Their spatial locations were found to remarkably affect interfacial interactions, local pH, the conductivity of adsorbents, and electronic structure of copper oxide. A close contact of CuO with the carbon surface led to strong interactions of both components, inhibiting the reduction of CuO and decreasing its reactivity with H2S. On the other hand, a proximity of MgO to the carbon surface increased local pH, promoting the oxidation of H2S into elemental S, instead of sulfates. Cu+ in the copper oxide phase increased the desulfurization performance due to its ability to activate oxygen and to accelerate a lattice diffusion. Enhanced surface conductivity due to the interfacial interactions improved the desulfurization efficiency and favored the formation of elemental S through promoting an electron transfer in redox reactions.

Graphdiyne/metal oxide hybrid materials for efficient energy and environmental catalysis

Graphdiyne (GDY)-based materials, owing to their unique structure and tunable electronic properties, exhibit great potential in the fields of catalysis, energy, environmental science, and beyond. In particular, GDY/metal oxide hybrid materials (GDY/MOs) have attracted extensive attention in energy and environmental catalysis. The interaction between GDY and metal oxides can increase the number of intrinsic active sites, facilitate charge transfer, and regulate the adsorption and desorption of intermediate species. In this review, we summarize the structure, synthesis, advanced characterization, small molecule activation mechanism and applications of GDY/MOs in energy conversion and environmental remediation. The intrinsic structure-activity relationship and corresponding reaction mechanism are highlighted. In particular, the activation mechanisms of reactant molecules (H2O, O2, N2, etc.) on GDY/MOs are systemically discussed. Finally, we outline some new perspectives of opportunities and challenges in developing GDY/MOs for efficient energy and environmental catalysis.

Activation of Small Molecules by Modified Dodecaborate Anions

Two of the basic requirements of a good catalyst are that molecules be bound to it with energies intermediate between physisorption and chemisorption and be simultaneously activated in the process. Using density functional theory, we have studied the interaction of small molecules such as H2, O2, N2, CO2, CO, and NH3 with modified dodecaborate anion [B12H12]2-, namely, [B12X11]- and [B12X11]2- (X = H, F, CN). Calculations of the structure, stability, and electronic properties of these species interacting with the above molecules show that they meet the above requirements. In addition, [B12X11]2- (X = F, CN) species are not only more stable than [B12X11]- species but also bind to O2 more strongly than their monoanion counterparts.

Structure-Function Relationship of Highly Reactive CuOx Clusters on Co3 O4 for Selective Formaldehyde Sensing at Low Temperatures

Designing reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low-temperature oxidation of formaldehyde with CuOx clusters on Co3 O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3 O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X-ray absorption fine structure spectroscopy and temperature-programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion (ppb) at 75°C, superior to state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control.

Copper Single-Atom Catalysts-A Rising Star for Energy Conversion and Environmental Purification: Synthesis, Modification, and Advanced Applications

Future renewable energy supply and green, sustainable environmental development rely on various types of catalytic reactions. Copper single-atom catalysts (Cu SACs) are attractive due to their distinctive electronic structure (3d orbitals are not filled with valence electrons), high atomic utilization, and excellent catalytic performance and selectivity. Despite numerous optimization studies are conducted on Cu SACs in terms of energy conversion and environmental purification, the coupling among Cu atoms-support interactions, active sites, and catalytic performance remains unclear, and a systematic review of Cu SACs is lacking. To this end, this work summarizes the recent advances of Cu SACs. The synthesis strategies of Cu SACs, metal-support interactions between Cu single atoms and different supports, modification methods including modification for carriers, coordination environment regulating, site distance effect utilizing, and dual metal active center catalysts constructing, as well as their applications in energy conversion and environmental purification are emphatically introduced. Finally, the opportunities and challenges for the future Cu SACs development are discussed. This review aims to provide insight into Cu SACs and a reference for their optimal design and wide application.

Cascade NH3 Oxidation and N2O Decomposition via Bifunctional Co and Cu Catalysts

The selective catalytic oxidation of NH3 (NH3-SCO) to N2 is an important reaction for the treatment of diesel engine exhaust. Co3O4 has the highest activity among non-noble metals but suffers from N2O release. Such N2O emissions have recently been regulated due to having a 300× higher greenhouse gas effect than CO2. Here, we design CuO-supported Co3O4 as a cascade catalyst for the selective oxidation of NH3 to N2. The NH3-SCO reaction on CuO-Co3O4 follows a de-N2O pathway. Co3O4 activates gaseous oxygen to form N2O. The high redox property of the CuO-Co3O4 interface promotes the breaking of the N-O bond in N2O to form N2. The addition of CuO-Co3O4 to the Pt-Al2O3 catalyst reduces the full NH3 conversion temperature by 50 K and improves the N2 selectivity by 20%. These findings provide a promising strategy for reducing N2O emissions and will contribute to the rational design and development of non-noble metal catalysts.

Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis

Singlet oxygen (1O2) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1O2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1O2 trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of 1O2 in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate 1O2-driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D 1O2 detection techniques, and provide insights into the reaction mechanisms in 1O2-dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.

Atomically dispersed copper sites on titanium zirconium oxide accelerate the simultaneous oxidative removal of organic carbon and ammonia from landfill leachate

Landfill leachate is a refractory wastewater. Low-temperature catalytic air oxidation (LTCAO) has shown considerable potential for leachate treatment owing to its green and simple operation, but the simultaneous removal of chemical oxygen demand (COD) and ammonia from leachate remains challenging. Herein, TiZrO₄ @Cu_SA hollow spheres with high-loading single-atom Cu were synthesized using isovolumic vacuum impregnation and co-calcination methods, and the catalyst was applied to the LTCAO treatment of real leachate. Consequently, the removal rate of UV₂₅₄ reached 66% at 90 °C within 5 h, while that for COD was 88%. Simultaneously, the NH₃/NH₄⁺ (33.5 mg/L, 100 wt%) in the leachate was oxidized to N₂ (88.2 wt%), NO₂^--N (11.0 wt%), and NO₃^--N (0.3 wt%) owing to the effect of free radicals. The single-atom Cu co-catalyst in TiZrO₄ @Cu_SA exhibited a localized surface plasmon resonance effect at the active center, which could quickly transfer electrons to O₂ in water to form O₂^.- with a high activation efficiency. The degradation products were determined and the deduced pathway was as follows: the bonds joining benzene rings were first broken, and then the ring structure was further opened to produce acetic acid and other simple organic macromolecules, which were finally mineralized to CO₂ and H₂O.

Dynamic evolution of the active center driven by hemilabile coordination in Cu/CeO2 single-atom catalyst

Hemilability is an important concept in homogeneous catalysis where both the reactant activation and the product formation can occur simultaneously through a reversible opening and closing of the metal-ligand coordination sphere. However, this effect has rarely been discussed in heterogeneous catalysis. Here, by employing a theoretical study on CO oxidation over substituted Cu₁/CeO₂ single atom catalysts, we show that dynamic evolution of metal-support coordination can significantly change the electronic structure of the active center. The evolution of the active center is shown to either strengthen or weaken the metal-adsorbate bonding as the reaction proceeds from reactants, through intermediates, to products. As a result, the activity of the catalyst can be increased. We explain our observations by extending hemilability effects to single atom heterogenous catalysts and anticipate that introducing this concept can offer a new insight into the important role active site dynamics have in catalysis toward the rational design of more sophisticated single atom catalyst materials.

Sustainable micro-activation of dissolved oxygen driving pollutant conversion on Mo-enhanced zinc sulfide surface in natural conditions

The activation of inert oxygen (O2) often consumes enormous amounts of energy and resources, which is a global challenge in the field of environmental remediation and fuel cells. Organic pollutants are abundant in electrons and are promising alternative electron donors. Herein, we implement sustainable microactivation of dissolved oxygen (DO) by using the electrons and adsorption energy of pollutants by creating a nonequilibrium microsurface on nanoparticle-integrated molybdenum (Mo) lattice-doped zinc sulfide (ZnS) composites (MZS-1). Organic pollutants were quickly removed by DO microactivation in the MZS-1 system under natural conditions without any additional energy or electron donor. The turnover frequency (TOF, per Mo atom basis) is 5 orders of magnitude higher than those of homogeneous systems. Structural and electronic characterization technologies reveal the change in the crystalline phase (Zn-S-Mo) and the activation of π-electrons on six-membered rings of ZnS after Mo doping, which results in the formation of a nonequilibrium microsurface on MZS-1. This is the key for the strong interfacial interaction and directional electron transfer from pollutants to MZS-1 through the delocalized π-π conjugation effect and from MZS-1 to DO via Zn-S-Mo, as demonstrated by electron paramagnetic resonance (EPR) techniques and density functional theory (DFT) calculations. This process achieves the efficient use of pollutants and the low-energy activation of O2 through the construction of a nonequilibrium microsurface, which shows new significance for water treatment.

Dynamic Reconstitution Between Copper Single Atoms and Clusters for Electrocatalytic Urea Synthesis

Electrocatalytic CN coupling between carbon dioxide and nitrate has emerged to meet the comprehensive demands of carbon footprint closing, valorization of waste, and sustainable manufacture of urea. However, the identification of catalytic active sites and the design of efficient electrocatalysts remain a challenge. Herein, the synthesis of urea catalyzed by copper single atoms decorated on a CeO₂ support (denoted as Cu₁ -CeO₂ ) is reported. The catalyst exhibits an average urea yield rate of 52.84 mmol h^-1 g_cat. ^-1 at -1.6 V versus reversible hydrogen electrode. Operando X-ray absorption spectra demonstrate the reconstitution of copper single atoms (Cu₁ ) to clusters (Cu₄ ) during electrolysis. These electrochemically reconstituted Cu₄ clusters are real active sites for electrocatalytic urea synthesis. Favorable CN coupling reactions and urea formation on Cu₄ are validated using operando synchrotron-radiation Fourier transform infrared spectroscopy and theoretical calculations. Dynamic and reversible transformations of clusters to single-atom configurations occur when the applied potential is switched to an open-circuit potential, endowing the catalyst with superior structural and electrochemical stabilities.

Atomically Incorporating Ni into Mesoporous CeO2 Matrix via Synchronous Spray-Pyrolysis as Efficient Noble-Metal-Free Catalyst for Low-Temperature CO Oxidation

Low-temperature catalytic CO oxidation is an important chemical process in versatile applications, such as the H₂ utilization for low-temperature H₂ air fuel cells. Pt-group metal catalysts are efficient but highly cost-consuming. This work demonstrates an excellent and sixpenny catalyst with earth-abundant Ni and Ce, in which Ni ions are atomically incorporated into the CeO₂ matrix (Ni-Ce-O_x) by synchronous spray-pyrolysis (SSP) of mixture nitrates of Ni and Ce. The Ni-Ce-O_x catalyst presents a mesoporous structure. Revealed by a model reaction of 1% CO, 1% O₂, and 98% balance He at a space velocity of 13,200 mL/g_cat/h, Ni-Ce-O_x catalysts display a typical volcano-shaped relationship between reactivity and Ni incorporation amount. The optimized Ni incorporation appears with a high Ni/Ce atomic ratio of 0.25, endowing the T₅₀ (temperature corresponding to a CO conversion of 50%), which is lower-shifted by 165 °C than that of pristine CeO₂ (266 °C). The density functional theory (DFT) calculations further indicate that the much-reduced oxygen vacancy formation energy at Ni-Ce single-atom sites boosted the adsorption activation of the CO molecule and therefore promoted the CO oxidation process. Besides, the₂ Ni-Ce-O_x from the SSP method presents better performance than the counterparts from immersion and hydrothermal methods. This work paves a way to access efficient noble-metal-free catalysts for low-temperature CO oxidation.

Designing Reactive Bridging O2- at the Atomic Cu-O-Fe Site for Selective NH3 Oxidation

Surface oxidation chemistry involves the formation and breaking of metal-oxygen (M-O) bonds. Ideally, the M-O bonding strength determines the rate of oxygen absorption and dissociation. Here, we design reactive bridging O^2- species within the atomic Cu-O-Fe site to accelerate such oxidation chemistry. Using in situ X-ray absorption spectroscopy at the O K-edge and density functional theory calculations, it is found that such bridging O^2- has a lower antibonding orbital energy and thus weaker Cu-O/Fe-O strength. In selective NH₃ oxidation, the weak Cu-O/Fe-O bond enables fast Cu redox for NH₃ conversion and direct NO adsorption via Cu-O-NO to promote N-N coupling toward N₂. As a result, 99% N₂ selectivity at 100% conversion is achieved at 573 K, exceeding most of the reported results. This result suggests the importance to design, determine, and utilize the unique features of bridging O^2- in catalysis.

Unraveling the Mechanism of Field-Induced Li+ Concentration for Improved Kinetics in Rechargeable Li-CO2 Batteries

The design of highly efficient electrocatalysts is a promising strategy to improve the electrochemical kinetics of Li-CO₂ batteries. However, electrocatalysts usually aim to reduce the energetic barrier for the corresponding electrochemical reactions; little attention has been given to modulating the kinetics that directly determine the local concentration of reaction molecules surrounding catalysts. Herein, we present a systematic study on the role of Li⁺ reunion on the improvement of reaction kinetics in Li-CO₂ batteries with a Cu cone cathode. Specifically, this local, geometry-driven tip effect can enrich the local electron concentration to facilitate Li⁺ ions diffusion from the bulk electrolyte to the surface of catalyst, leading to boosted catalytic performance. Further studies demonstrate that Cu(II/I) as a solid redox mediator dominates the reversible bulk redox reactions in a Cu cone cathode, which acts as an electron-hole transfer agent and permits the efficient reduction and oxidation of solid Li₂CO₃, contributing to an accessible theoretical discharge voltage, low charge potential below 3.2 V, impressive rate capability, and a long cycling stability (333 days) for Li-CO₂ batteries. The exploitation of the sharp-tip enhancement effect and dynamic creation of catalytic active sites is expected to become routine practice in future mechanistic studies for metal-air batteries.

Role of Surface Oxygen Vacancies and Oxygen Species on CuO Nanostructured Surfaces in Model Catalytic Oxidation and Reductions: Insight into the Structure-Activity Relationship Toward the Performance

Defect engineering, such as modification of oxygen vacancy density, has been considered as an effective approach to tailor the catalytic performance on transition-metal oxide nanostructured surfaces. The role of oxygen vacancies (O_V) on the surface of the as-prepared, zinnia-shaped morphology of CuO nanostructures and their marigold forms on calcination at 800 °C has been investigated through the study of model catalytic reactions of reduction of 4-nitrophenol and aerobic oxidation of benzyl alcohol. The O_V on the surfaces of different morphologies of CuO have been identified and quantified through Rietveld analysis and HRTEM, EPR, and XPS studies. The structure-activity relationships between surface oxygen vacancies (O_V) and catalytic performance have been systematically investigated. The enhanced catalytic performance of the cubic CuO nanostructures compared to their as-prepared forms has been attributed to the formation of surface oxygen species on the reactive and dominant (110) surface that has low oxygen vacancy formation energy. The mechanistic role of surface oxygen species in the studied reactions has been quantitatively correlated with the catalytic activity of the different morphological forms of the CuO nanostructures.

Synergy in Au-CuO Janus Structure for Catalytic Isopropanol Oxidative Dehydrogenation to Acetone

The controlled oxidation of alcohols to the corresponding ketones or aldehydes via selective cleavage of the β-C-H bond of alcohols under mild conditions still remains a significant challenge. Although the metal/oxide interface is highly active and selective, the interfacial sites fall far behind the demand, due to the large and thick support. Herein, we successfully develop a unique Au-CuO Janus structure (average particle size=3.8 nm) with an ultrathin CuO layer (0.5 nm thickness) via a bimetal in situ activation and separation strategy. The resulting Au-CuO interfacial sites prominently enhance isopropanol adsorption and decrease the energy barrier of β-C-H bond scission from 1.44 to 0.01 eV due to the strong affinity between the O atom of CuO and the H atom of isopropanol, compared with Au sites alone, thereby achieving ultrahigh acetone selectivity (99.3 %) over 1.1 wt % AuCu_0.75 /Al₂ O₃ at 100 °C and atmospheric pressure with 97.5 % isopropanol conversion. Furthermore, Au-CuO Janus structures supported on SiO₂ , TiO₂ or CeO₂ exhibit remarkable catalytic performance, and great promotion in activity and acetone selectivity is achieved as well for other reducible oxides derived from Fe, Co, Ni and Mn. This study should help to develop strategies for maximized interfacial site construction and structure optimization for efficient β-C-H bond activation.

Catalytically efficient Ni-NiOx-Y2O3 interface for medium temperature water-gas shift reaction

The metal-support interfaces between metals and oxide supports have long been studied in catalytic applications, thanks to their significance in structural stability and efficient catalytic activity. The metal-rare earth oxide interface is particularly interesting because these early transition cations have high electrophilicity, and therefore good binding strength with Lewis basic molecules, such as H₂O. Based on this feature, here we design a highly efficient composite Ni-Y₂O₃ catalyst, which forms abundant active Ni-NiO_x-Y₂O₃ interfaces under the water-gas shift (WGS) reaction condition, achieving 140.6 μmol_CO g_cat⁻¹ s⁻¹ rate at 300 °C, which is the highest activity for Ni-based catalysts. A combination of theory and ex/in situ experimental study suggests that Y₂O₃ helps H₂O dissociation at the Ni-NiO_x-Y₂O₃ interfaces, promoting this rate limiting step in the WGS reaction. Construction of such new interfacial structure for molecules activation holds great promise in many catalytic systems.

Developing effective and stable catalytic interfaces in the medium temperature region is a practical route to replace the existing water gas shift (WGS) process. Here the authors designed a composite Ni-Y₂O₃ catalyst achieving the highest WGS activity for Ni based catalysts.

Manipulating Copper Dispersion on Ceria for Enhanced Catalysis: A Nanocrystal-Based Atom-Trapping Strategy

Due to tunable redox properties and cost-effectiveness, copper-ceria (Cu-CeO2 ) materials have been investigated for a wide scope of catalytic reactions. However, accurately identifying and rationally tuning the local structures in Cu-CeO2 have remained challenging, especially for nanomaterials with inherent structural complexities involving surfaces, interfaces, and defects. Here, a nanocrystal-based atom-trapping strategy to access atomically precise Cu-CeO2 nanostructures for enhanced catalysis is reported. Driven by the interfacial interactions between the presynthesized Cu and CeO2 nanocrystals, Cu atoms migrate and redisperse onto the CeO2 surface via a solid-solid route. This interfacial restructuring behavior facilitates tuning of the copper dispersion and the associated creation of surface oxygen defects on CeO2 , which gives rise to enhanced activities and stabilities catalyzing water-gas shift reaction. Combining soft and solid-state chemistry of colloidal nanocrystals provide a well-defined platform to understand, elucidate, and harness metal-support interactions. The dynamic behavior of the supported metal species can be further exploited to realize exquisite control and rational design of multicomponent nanocatalysts.

Partially sintered copper‒ceria as excellent catalyst for the high-temperature reverse water gas shift reaction

For high-temperature catalytic reaction, it is of significant importance and challenge to construct stable active sites in catalysts. Herein, we report the construction of sufficient and stable copper clusters in the copper‒ceria catalyst with high Cu loading (15 wt.%) for the high-temperature reverse water gas shift (RWGS) reaction. Under very harsh working conditions, the ceria nanorods suffered a partial sintering, on which the 2D and 3D copper clusters were formed. This partially sintered catalyst exhibits unmatched activity and excellent durability at high temperature. The interaction between the copper and ceria ensures the copper clusters stably anchored on the surface of ceria. Abundant in situ generated and consumed surface oxygen vacancies form synergistic effect with adjacent copper clusters to promote the reaction process. This work investigates the structure-function relation of the catalyst with sintered and inhomogeneous structure and explores the potential application of the sintered catalyst in C1 chemistry.

Enhanced Catalytic Ozonation for Eliminating CH3SH via Graphene-Supported Positively Charged Atomic Pt Undergoing Pt2+/Pt4+ Redox Cycle

Constructing catalysts with electronic metal-support interaction (EMSI) is promising for catalytic reactions. Herein, graphene-supported positively charged (Pt²⁺/Pt⁴⁺) atomically dispersed Pt catalysts (AD-Pt-G) with Pt_xC₃ (x = 1, 2, and 4)-based EMSI coordination structures are achieved for boosting the catalytic ozonation for odorous CH₃SH removal. A CH₃SH removal efficiency of 91.5% can be obtained during catalytic ozonation using optimum 0.5AD-Pt-G within 12 h under a gas hourly space velocity of 60,000 mL h^-1 g^-1, whereas that of pure graphene is 40.4%. Proton transfer reaction time-of-flight mass spectrometry, in situ diffuse reflectance infrared Fourier transform spectroscopy/Raman, and electron spin resonance verify that the Pt_xC₃ coordination structure with atomic Pt²⁺ sites on AD-Pt-G can activate O₂ to generate peroxide species (*O₂) for partial oxidation of CH₃SH during the adsorption period and trigger O₃ into surface atomic oxygen (*O_ad), *O₂, and superoxide radicals (·O₂^-) to accomplish a stable, high-efficiency, and deeper oxidation of CH₃SH during the catalytic ozonation stage. Moreover, the results of XPS and DFT calculation imply the occurrence of Pt²⁺ → Pt⁴⁺ → Pt²⁺ recirculation on Pt_xC₃ for AD-Pt-G to maintain the continuous catalytic ozonation for 12 h, i.e., Pt²⁺ species devote electrons in 5d-orbitals to activate O₃, while Pt⁴⁺ species can be reduced back to Pt²⁺ via capturing electrons from CH₃SH. This study can provide novel insights into the development of atomically dispersed Pt catalysts with a strong EMSI effect to realize excellent catalytic ozonation for air purification.

Activation of Molecular O2 on CoFe2 O4 (001) Surfaces: An Embedded Cluster Study

Dioxygen activation pathways on the (001) surfaces of cobalt ferrite, CoFe₂O₄, were investigated computationally using density functional theory and the hybrid Perdew‐Burke‐Ernzerhof exchange‐correlation functional (PBE0) within the periodic electrostatic embedded cluster model. We considered two terminations: the A‐layer exposing Fe²⁺ and Co²⁺ metal sites in tetrahedral and octahedral positions, respectively, and the B‐layer exposing octahedrally coordinated Co³⁺. On the A‐layer, molecular oxygen is chemisorbed as a superoxide on the Fe monocenter or bridging a Fe−Co cation pair, whereas on the B‐layer it is adsorbed at the most stable anionic vacancy. Activation is promoted by transfer of electrons provided by the d metal centers onto the adsorbed oxygen. The subsequent dissociation of dioxygen into monoatomic species and surface reoxidation have been identified as the most critical steps that may limit the rate of the oxidation processes. Of the reactive metal‐O species, [Fe^III−O]²⁺ is thermodynamically most stable, while the oxygen of the Co−O species may easily migrate across the A‐layer with barriers smaller than the associative desorption.

Effect of Coordination Environment Surrounding a Single Pt Site on the Liquid-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural

As the frontier in heterogeneous catalyst, a monomer and positively charged active sites in the single-atom catalyst (SAC), anchored by high electronegative N, O, S, P, etc., atoms, may not be active for the multispecies (O₂, substrates, intermediates, solvent etc.) involved liquid-phase aerobic oxidation. Here, with catalytic, aerobic oxidation of 5-hydroxymethylfurfural as an example, Pt SAC (Pt₁-N₄) was synthesized and tested first. With commercial Pt/C (Pt loading of 5 wt %) as a benchmark, 2,5-furandicarboxylic acid (FDCA) yield of 97.6% was obtained. Pt SAC (0.56 wt %) gave a much lower FDCA yield (28.8%). By changing the coordination atoms from highly electronegative N to low electronegative Co atoms, the prepared Pt single-atom alloy (SAA, Pt₁-Co₃) catalyst with ultralow Pt loading (0.06 wt %) gave a much high FDCA yield (99.6%). Density functional theory (DFT) calculations indicated that positively charged Pt sites (+0.712e) in Pt₁-N₄ almost lost the capability for oxygen adsorption and activation, as well as the adsorption for the key intermediate. In Pt₁-Co₃ SAA, the central negatively charged Pt atom (-0.446e) facilitated the adsorption of the key intermediate; meanwhile, the nearby Co atoms around the Pt atom constituted the O₂-preferred adsorption/activation sites. This work shows the difference between the SAC with NPs and the SAA during liquid-phase oxidation of HMF and gives a useful guide in the future single-atom catalyst design in other related reactions.

A computational investigation of the adsorption of small copper clusters on the CeO2(110) surface

We report a detailed density functional theory (DFT) study of the geometrical and electronic properties, and the growth mechanism of a Cu_n (n = 1-4) cluster on a stoichiometric, and especially on a defective CeO₂(110) surface with one surface oxygen vacancy, without using pre-assumed gas-phase Cu_n cluster shapes. This gives new and valuable theoretical insight into experimental work regarding debatable active sites of promising CuO_x/CeO₂-nanorod catalysts in many reactions. We demonstrate that CeO₂(110) is highly reducible upon Cu_n adsorption, with electron transfer from Cu_n clusters, and that a Cu_n cluster grows along the long bridge sites until Cu₃, so that each Cu atom can interact strongly with surface oxygen ions at these sites, forming stable structures on both stoichiometric and defective CeO₂(110) surface. Cu-Cu interactions are, however, limited, since Cu atoms are distant from each other, inhibiting the formation of Cu-Cu bonds. This monolayer then begins to grow into a bilayer as seen in the Cu₃ to Cu₄ transition, with long-bridge site Cu as anchoring sites. Our calculations on Cu₄ adsorption reveal a Cu bilayer rich in Cu⁺ species at the Cu-O interface.

The Electrophilicity of Surface Carbon Species in the Redox Reactions of CuO-CeO2 Catalysts

Electronic metal–support interactions (EMSI) describe the electron flow between metal sites and a metal oxide support. It is generally used to follow the mechanism of redox reactions. In this study of CuO‐CeO₂ redox, an additional flow of electrons from metallic Cu to surface carbon species is observed via a combination of operando X‐ray absorption spectroscopy, synchrotron X‐ray powder diffraction, near ambient pressure near edge X‐ray absorption fine structure spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. An electronic metal–support–carbon interaction (EMSCI) is proposed to explain the reaction pathway of CO oxidation. The EMSCI provides a complete picture of the mass and electron flow, which will help predict and improve the catalytic performance in the selective activation of CO₂, carbonate, or carbonyl species in C1 chemistry.

High-precision synthesis of α-MnO2 nanowires with controllable crystal facets for propane oxidation

α-MnO2 nanowires with different crystal facets were synthesized. The (110) crystal facet of α-MnO2 is conducive to propane catalysis, due to the lowest electron energy, effectively Mn valence adjustment and abundant oxygen vacancies.