Catalysis by Doped Oxides

CO adsorption on CeO2(111): A CCSD(T) benchmark study using an embedded-cluster model

A benchmark model that combines an embedded-cluster approach for ionic surfaces with wavefunction-based methods to predict the vibrational frequencies of molecules adsorbed on surfaces is presented. As a representative case, the adsorption of CO on the lowest index non-polar and most stable facet of CeO2, that is, (111) was studied. The CO harmonic vibrational frequencies were not scaled semiempirically but explicitly corrected for anharmonic effects, which amount to about 25 cm-1 with all tested methods. The second-order Møller-Plesset perturbation method (MP2) tends to underestimate the CO harmonic frequency by about 40-45 cm-1 in comparison with the results obtained with the coupled-cluster singles and doubles with perturbational treatment of triple excitation method [CCSD(T)] and independently from the basis set used. The best estimate for the CO vibrational frequency (low-coverage case) differs by 12 cm-1 with the experimental value obtained by infrared reflexion absorption spectroscopy of 1 monolayer CO adsorbed on the oxidized CeO2(111) surface. In addition, a conservative estimate of the adsorption energy of about -0.22 ± -0.07 eV obtained at the CCSD(T) level confirms the physisorption character of the adsorption of CO on the CeO2(111) surface.

Present and Future of Emerging Catalysts in Gas Sensors for Breath Analysis

To rationalize the noninvasive disease diagnosis by breath analysis, developing a high-performance gas sensor with exceptional sensitivity and selectivity is important to detect trace biomarkers in complex exhaled breath under harsh conditions. Among the various technological innovations, catalyst design and synthesis techniques are the foremost challenges, because gas sensing properties are predominantly determined by surface chemical reactions governed by catalytic activities. Conventional nanoparticle-based catalysts, with their simple structural features, have technical limitations in achieving the requirement for accurate breath analysis. Innovative strategies have been pursued to synthesize unconventional catalyst types with enhanced catalytic capabilities. This Perspective provides a comprehensive overview of recent advancements in catalyst technology for chemiresistive-type gas sensors used in breath analysis. It discusses various emerging catalysts, such as doping catalysts, single-atom catalysts (SACs), bimetallic alloy catalysts, high-entropy alloy (HEA) catalysts, exsolution catalysts, and catalytic filter membranes, along with their unique chemical activation mechanisms that enhance gas sensing properties for detecting target biomarkers in exhaled breath. The review also explores novel strategies for catalyst design, including computational prediction, advanced synthesis techniques, and the integration of sensor arrays with artificial intelligence (AI) to improve diagnostic reliability. By highlighting the crucial role of these emerging catalysts, this review provides valuable insights into the catalytic, synthetic, and analytical aspects that are essential for advancing breath analysis technology.

Interface Synergy of Exposed Oxygen Vacancy and Pd Lewis Acid Sites Enabling Superior Cooperative Photoredox Synthesis

Photo-driven cross-coupling of o-arylenediamines and alcohols has emerged as an alternative for the synthesis of bio-active benzimidazoles. However, tackling the key problem related to efficient adsorption and activation of both coupling partners over photocatalysts towards activity enhancement remains a challenge. Here, we demonstrate an efficient interface synergy strategy by coupling exposed oxygen vacancies (VO) and Pd Lewis acid sites for benzimidazole and hydrogen (H2) coproduction over Pd-loaded TiO2 nanospheres with the highest photoredox activity compared to previous works so far. The results show that the introduction of VO optimizes the energy band structure and supplies coordinatively unsaturated sites for adsorbing and activating ethanol molecules, affording acetaldehyde active intermediates. Pd acts as a Lewis acid site, enhancing the adsorption of alkaline amine molecules via Lewis acid-base pair interactions and driving the condensation process. Furthermore, VO and Pd synergistically promote interfacial charge transfer and separation. This work offers new insightful guidance for the rational design of semiconductor-based photocatalysts with interface synergy at the molecular level towards the high-performance coproduction of renewable fuels and value-added feedstocks.

Evolution of Heterogeneous Tunnel Structures in Cryptomelane-Type Manganese Oxides and Their Geoinspired Implications

Cryptomelane-type manganese oxides, α-MnO2 (KxMn8O16), play key roles in various fields such as geochemical processes, catalytic reactions, energy storage, and environmental sciences. The function of cryptomelane-type oxides can be affected by cation substitutions and the changes in tunnel structures. Research on natural cryptomelane minerals could provide geoinspiration for the design of new nanomaterials with cation substitutions, as well as a key to understanding the evolution of tunnel structures. In this study, natural cryptomelane minerals are characterized by the cosubstitution of iron and zinc. The localization of cosubstituted Fe and Zn in the tunnel framework has been revealed. Furthermore, the evolution of heterogeneous tunnel structures in cryptomelane has been demonstrated as a transition from large-size tunnels to small ones with high Mn(III) concentrations, indicating the significant role of Mn(III) in driving this transition. Lead (Pb2+) can be effectively trapped in the 2 × 2 tunnels. A mechanism for the attachment of cryptomelane crystals in different orientations has also been explored, showing that the migration of Mn atoms and the formation of (110) planes at specific sites contribute to lattice matching at the boundary. Our results provide geoinspired insights into controlled synthesis with Fe/Zn cosubstitution, a fundamental understanding of the evolution of tunnel structures, and functionalized applications of tunnel-based nanomaterials.

Exploring microstructures of metal-doped oxides via simulated Raman spectrum

Solid solution of metal-doped oxide has been widely used in material industry and catalysis process. Its performance is highly correlated with the distribution of doped ions. Due to the complex distribution of doped ions in solid solution and its variation with temperatures, to obtain the microstructures of metal-doped ions in solid solution remains a substantial challenge. Taken Ce1-xZrxO2 as a model, the global structure searching, structures proportion with temperature determined by Boltzmann distribution, and the weighted simulation Raman spectra were integrated to explore the microstructures of metal-doped solid solution oxides. It was further verified by application into rutile and anatase TiO2 mixture, indicating that the present method is feasible to deduce the microstructure of metal composite oxides. We anticipate that it provides a powerful solution to explore microstructures of solid solution and complex metal oxides.

Routes to Bidirectional Cathodes for Reversible Aprotic Alkali Metal-CO2 Batteries

Aprotic alkali metal-CO2 batteries (AAMCBs) have garnered significant interest owing to fixing CO2 and providing large energy storage capacity. The practical implementation of AAMCBs is constrained by the sluggish kinetics of the CO2 reduction reaction (CO2RR) and the CO2 evolution reaction (CO2ER). Because the CO2ER and CO2RR take place on the cathode, which connects the internal catalyst with the external environment. Building a bidirectional cathode with excellent CO2ER and CO2RR kinetics by optimizing the cathode's internal catalyst and environment has attracted most of the attention to improving the electrochemical performance of AAMCBs. However, there remains a lack of comprehensive understanding. This review aims to give a route to bidirectional cathodes for reversible AAMCBs, by systematically discussing engineering strategies of both the internal catalyst (atomic, nanoscopic, and macroscopic levels) and the external environment (photo, photo-thermal, and force field). The CO2ER and CO2RR mechanisms and the "engineering strategies from internal catalyst to the external environment-cathode properties-CO2RR and CO2ER kinetics and mechanisms-batteries performance" relationship are elucidated by combining computational and experimental approaches. This review establishes a fundamental understanding for designing bidirectional cathodes and gives a route for developing reversible AAMCBs and similar metal-gas battery systems.

Mononuclear metal complex catalysts on supports: foundations in organometallic and surface chemistry and insights into structure, reactivity, and catalysis

Catalysts that consist of isolated metal atoms bonded to solid supports have drawn wide attention by researchers, with recent work emphasizing noble metals on metal oxide and zeolite supports. Progress has been facilitated by methods for atomic-scale imaging the metals and spectroscopic characterization of the supported structures and the nature of metal-support bonding, even with catalysts in the working state. Because of the intrinsic heterogeneity of support surface sites for bonding of metals and the tendency of noble metal cations on supports to be reduced and aggregated, it is challenging to determine structures of individual metal complexes among the mixtures that may be present and to determine structures of catalytically active species and reactive intermediates. A central premise of this perspective is that synthesis of supported metal complexes that have nearly uniform structures-on supports such as dealuminated HY zeolite, chosen to have relatively uniform surfaces-is a key to fundamental understanding, facilitating progress toward determining the roles of the ligands on the metals, which include the supports and reactive intermediates in catalysis. Characterization of relatively uniform and well-defined samples nonetheless requires multiple spectroscopic, microscopic, and theory-based techniques used in concert and still leaves open many questions about the nature of reactive intermediates and catalytic reaction mechanisms.

Low-temperature redox activity and alcohol ammoxidation performance on Cu- and Ru-incorporated ceria catalysts

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile.

Pd Single-Atom Loaded Ce-Zr Solid Solution Catalysts Prepared by Flame Spray Pyrolysis for Efficient CO Catalytic Oxidation

Single-atom catalysts (SACs) exhibit remarkable catalytic activity at each metal site. However, conventionally synthesized single-atom catalysts often possess low metal loading, thereby constraining their overall catalytic performance. Here, a flame spray pyrolysis (FSP) method for the synthesis of a single-atom catalyst with a high loading capacity of up to 1.4 wt.% in practice is reported. CeZrO2 acts as a carrier and provides a large number of anchoring sites, which promotes the high-density generation of Pd, and the strong interaction between the metal and the support avoids atom aggregation. Pd-CeZrO2 series catalysts have excellent CO oxidation performance. When 0.97 wt.% Pd is added, the catalytic activity is the highest, and the temperature can be reduced to 120 °C. This work presented here demonstrates that FSP, as an inherently scalable technique, allows for elevating the single-atom loading to achieve an increase in its catalytic performance. The method presented here more options for the preparation of SACs.

Weakening Mn-O Bond Strength in Mn-Based Perovskite Catalysts to Enhance Propane Catalytic Combustion

Exploring highly efficient and robust non-noble metal catalysts for VOC abatement is crucial but challenging. Mn-based perovskites are a class of redox catalysts with good thermal stability, but their activity in the catalytic combustion of light alkanes is insufficient. In this work, we modulated the Mn-O bond strength in a Mn-based perovskite via defect engineering, over which the catalytic activity of propane combustion was significantly enhanced. It demonstrates that the oxygen vacancy concentration and the Mn-O bond strength can be efficiently modulated by finely tuning the Ni content in SmNixMn1-xO3 perovskite catalysts (SNxM1-x), which in turn can enhance the redox ability and generate more active oxygen species. The SN0.10M0.90 catalyst with the lowest Mn-O bond strength exhibits the lowest apparent activation energy, over which the propane conversion rate increases by 3.6 times compared to that on the SmMnO3 perovskite catalyst (SM). In addition, a SN0.10M0.90/cordierite monolithic catalyst can also exhibit a remarkable catalytic performance and deliver excellent long-term durability (1000 h), indicating broad prospects in industrial applications. Moreover, the promotional effect of Ni substitution was further unveiled by density functional theory (DFT) calculations. This work brings a favorable guidance for the exploration of highly efficient perovskite catalysts for light alkane elimination.

CeO2-Based Frustrated Lewis Pairs via Defective Engineering: Formation Theory, Site Characterization, and Small Molecule Activation

Activation of small molecules is considered to be a central concern in the theoretical investigation of environment- and energy-related catalytic conversions. Sub-nanostructured frustrated Lewis pairs (FLPs) have been an emerging research hotspot in recent years due to their advantages in small molecule activation. Although the progress of catalytic applications of FLPs is increasingly reported, the fundamental theories related to the structural formation, site regulation, and catalytic mechanism of FLPs have not yet been fully developed. Given this, it is attempted to demonstrate the underlying theory of FLPs formation, corresponding regulation methods, and its activation mechanism on small molecules using CeO2 as the representative metal oxide. Specifically, this paper presents three fundamental principles for constructing FLPs on CeO2 surfaces, and feasible engineering methods for the regulation of FLPs sites are presented. Furthermore, cases where typical small molecules (e.g., hydrogen, carbon dioxide, methane oxygen, etc.) are activated over FLPs are analyzed. Meanwhile, corresponding future challenges for the development of FLPs-centered theory are presented. The insights presented in this paper may contribute to the theories of FLPs, which can potentially provide inspiration for the development of broader environment- and energy-related catalysis involving small molecule activation.

Unraveling the formation of oxygen vacancies on the surface of transition metal-doped ceria utilizing artificial intelligence

Ceria has been extensively utilized in different fields, with surface oxygen vacancies playing a central role. However, versatile oxygen vacancy regulation is still in its infancy. In this work, we propose an effective strategy to manipulate the oxygen vacancy formation energy via transition metal doping by combining first-principles calculations and analytical learning. We elucidate the underlying mechanism driving the formation of oxygen vacancies using combined symbolic regression and data analytics techniques. The results show that the Fermi level of the system and the electronegativity of the dopants are the paramount parameters (features) influencing the formation of oxygen vacancies. These insights not only enhance our understanding of the oxygen vacancy formation mechanism in ceria-based materials to improve their functionality but also potentially lay the groundwork for future strategies in the rational design of other transition metal oxide-based catalysts.

Highly visible-light-active sulfur and carbon co-doped TiO2 (SC-TiO2) heterogeneous photocatalysts prepared by underwater discharge plasma

To promptly and simply create highly crystalline S/C co-doped TiO2 (SC-TiO2) photocatalysts at room temperature and atmospheric pressure, we suggest a novel plasma-assisted sol-gel synthesis method. This method is a simultaneous synthetic process, in which an underwater plasma undergoes continuous reactions to generate high-energy atomic and molecular species that enable TiO2 to achieve crystallinity, a large surface area, and a heterogeneous structure within a few minutes. In particular, it was demonstrated that the heterogeneously structured TiO2 was formed by doping that sulfur and carbon replace O or Ti atoms in the TiO2 lattice depending on the composition of the synthesis solution during underwater plasma treatment. The resultant SC-TiO2 photocatalysts had narrowed bandgap energies and extended optical absorption scope into the visible range by inducing the intermediate states within bandgap due to generation of oxygen vacancies on the surface of TiO2 through synthesis, crystallization, and doping. Correspondingly, SC-TiO2 showed a significant degradation efficiency ([k] = 6.91 h-1) of tetracycline (TC, antibiotics) under solar light irradiation, up to approximately 4 times higher compared to commercial TiO2 ([k] = 1.68 h-1), resulting in great water purification. Therefore, we anticipate that this underwater discharge plasma system will prove to be an advantageous technique for producing heterostructural TiO2 photocatalysts with superior photocatalytic efficiency for environmental applications.

Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations

Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.

Interface Defects and Carrier Regulation in MOF-Derived Co3O4/In2O3 Composite Materials for Enhanced Selective Detection of HCHO

Gas sensors for real-time monitoring of low HCHO concentrations have promising applications in the field of health protection and air treatment, and this work reports a novel resistive gas sensor with high sensitivity and selectivity to HCHO. The MOF-derived hollow In2O3 was mixed with ZIF-67(Co) and calcined twice to obtain a hollow Co3O4/In2O3 (hereafter collectively termed MZO-6) composite enriched with oxygen vacancies, and tests such as XPS and EPR proved that the strong interfacial electronic coupling increased the oxygen vacancies. The gas-sensitive test results show that the hollow composite MZO-6 with abundant oxygen vacancies has a higher response value (11,003) to 10 ppm of HCHO and achieves a fast response/recovery time (11/181 s) for HCHO at a lower operating temperature (140 °C). The MZO-6 material significantly enhances the selectivity to HCHO and reduces the interference of common pollutant gases such as ethanol, acetone, and xylene. There is no significant fluctuation of resistance and response values in the 30-day long-term stability test, and the material has good stability. The synergistic effect of the heterostructure and oxygen vacancies altered the formaldehyde adsorption intermediate pathway and reduced the reaction activation energy, enhancing the HCHO responsiveness and selectivity of the MZO-6 material.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Thermally Induced Lattice-Defective Oxygen Breathing in Perovskite-Structure Stannates with High-Contrast Reversible Thermochromism

Inorganic thermochromic materials exhibit a tunable color gamut and a wide chromatic temperature range, indicating their potential for intelligent adaptive applications in thermal warning, temperature indication, thermal regulation, and interactive light-to-thermal energy conversion. However, most metal-oxide-based thermochromic materials show weak chromaticity adaption with the change of temperature, which needs further understanding of the microscopic principle to clarify the potential route to improve the contrast and identifiability for fabricating better thermochromic materials. Using perovskite-structure (AMO3) alkaline earth metal stannate (Ba1-xSrxSnO3, 0.0 ≤ x ≤ 1.0) as a model system, this paper reports for the first time the mechanism of the properties of thermally induced defect-enhanced charge transfer-type (CTT) thermochromic materials and the strategy for regulating their thermochromic properties by A-site cations. BaSnO3 exhibits continuously reversible thermochromic properties with high contrast from weak light yellow (b* = 11) to strong bright yellow (b* = 58) between room temperature and 550 °C. In-situ high-temperature X-ray diffraction (in-situ XRD), in-situ UV-vis absorption spectroscopy (in-situ UV-vis), thermogravimetric (TG), and electron paramagnetic resonance (EPR) spectra indicate that this excellent thermochromic phenomenon is attributed to the weakening of Sn-O bond hybridization at high temperatures, as well as the formation of a large number of oxygen vacancies at the top of the valence band, and the enhanced charge transfer resulting from the generation of impurity levels in the Sn2+ 5s2 intermediate. Replacing Ba2+ by Sr2+ in Ba1-xSrxSnO3 successfully tuned the thermochromic properties, which is attributed to the Sr2+ doping level-directed oxygen defect concentration and deoxygenation rate. The demonstrated defect-enhanced charge transfer behavior promotes a feasible route for lattice oxygen-mediated thermochromic materials and provides a fundamental relationship between thermally induced defects and colorimetry.

Recent Advances in Mechanistic Understanding of Metal-Free Carbon Thermocatalysis and Electrocatalysis with Model Molecules

Metal-free carbon, as the most representative heterogeneous metal-free catalysts, have received considerable interests in electro- and thermo-catalytic reactions due to their impressive performance and sustainability. Over the past decade, well-designed carbon catalysts with tunable structures and heteroatom groups coupled with various characterization techniques have proposed numerous reaction mechanisms. However, active sites, key intermediate species, precise structure-activity relationships and dynamic evolution processes of carbon catalysts are still rife with controversies due to the monotony and limitation of used experimental methods. In this Review, we summarize the extensive efforts on model catalysts since the 2000s, particularly in the past decade, to overcome the influences of material and structure limitations in metal-free carbon catalysis. Using both nanomolecule model and bulk model, the real contribution of each alien species, defect and edge configuration to a series of fundamentally important reactions, such as thermocatalytic reactions, electrocatalytic reactions, were systematically studied. Combined with in situ techniques, isotope labeling and size control, the detailed reaction mechanisms, the precise 2D structure-activity relationships and the rate-determining steps were revealed at a molecular level. Furthermore, the outlook of model carbon catalysis has also been proposed in this work.

On the application of Marcus-Hush theory to small polaron chemical dynamics in oxides: its relationship to the Holstein model and the importance of lattice-orbital symmetries

The chemical dynamics of small polaron hopping within oxides is often interpreted through two-site variations on Marcus-Hush theory, while from a physics perspective small polaron hopping is more often approached from Holstein's solid-state formalism. Here we seek to provide a chemically oriented viewpoint, focusing on small polaron hopping in oxides, concerning these two phenomenological frameworks by employing both tight-binding modelling and first-principles calculations. First, within a semiclassical approach the Marcus-Hush relations are overviewed as a two-site reduction of Holstein's model. Within the single-band regime, similarities and differences between Holstein derived small polaron hopping and the Marcus-Hush model are also discussed. In this context the emergence of adiabaticity (or, conversely, diabaticity) is also explored within each framework both analytically and by directly evolving the system wavefunction. Then, through first-principles calculations of select oxides we explore how coupled lattice and orbital symmetries can impact on hopping properties - in a manner that is quite distinct typical chemical applications of Marcus-Hush theory. These results are then related back to the Holstein model to explore the relative applicability of the two frameworks towards interpreting small polaron hopping properties, where it is emphasized that the Holstein model offers an increasingly more appealing physicochemical interpretation of hopping processes as band and/or coupling interactions increase. Overall, this work aims to strengthen the physically oriented exploration of small polarons and their physicochemical properties in the growing oxide chemistry community.

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.

Heterometal Dopant Changes the Mechanism of Proton-Coupled Electron Transfer at the Polyoxovanadate-Alkoxide Surface

The transfer of two H-atom equivalents to the titanium-doped polyoxovanadate-alkoxide, [TiV5O6(OCH3)13], results in the formation of a V(III)-OH2 site at the surface of the assembly. Incorporation of the group (IV) metal ion results in a weakening of the O-H bonds of [TiV5O5(OH2)(OCH3)13] in comparison to its homometallic congener, [V6O6(OH2)(OCH3)12], resembling more closely the thermodynamics reported for the one-electron reduced derivative, [V6O6(OH2)(OCH3)12]1-. An analysis of early time points of the reaction of [TiV5O6(OCH3)13] and 5,10-dihydrophenazine reveals the formation of an oxidized substrate, suggesting that proton-coupled electron transfer proceeds via initial electron transfer from substrate to cluster prior to proton transfer. These results demonstrate the profound influence of heterometal dopants on the mechanism of PCET with respect to the surface of the assembly.

Nano cerium oxide and cerium/zinc nanocomposites characterization and therapeutic role in combating obesity via controlling oxidative stress and insulin resistance in rat model

BACKGROUND

CeO2NPs and ZnONPs can curb the increase of cholesterol and triglycerides observed in rats with non-alcoholic fatty liver disease. It was suggested that CeO2 NPs could potentially have an insulin-sensitizing effect, specifically on adipose tissue and skeletal muscle. It was reported that ZnONPs combat the increase of insulin resistance observed in obese rats and could be beneficial value in NAFLD. In our previous work, ZnO-NPs manifested valuable anti-obesity effects via lowering body weight gain, oxidative stress, BMI, lipids, and insulin resistance.

METHODS

In the present study, cerium oxide nanoparticles (A-1) and cerium/zinc nanocomposites (A-2 and A-3) were synthesized by solgel to investigate their role on oxidative stress, adipocyte hormones, and insulin resistance in an obese rat model. X-ray diffraction, HRTEM, SEM, and XPS were carried out to confirm the crystal structure, the particle size, the morphology of the nanoparticles and the oxidation states.

RESULTS

The Rietveld refinement has also been executed on A-1 (chi2 = 1.00; average Bragg = 2.92%; R-factor = 2.45%) and on A-2 (Rw = 9.87%, Rex= 9.68%, χ2 = 1.04, GoF = 1.02). The XPS spectra indicated the presence of Ce in + 4 and + 3 oxidation states and Zn as ZnO and ZnO.OH. Cerium oxide and ZnO crystal sizes lie in the range 40.53-45.01 and 40.53-45.01 nm, respectively. The results indicated that treating obese rats with any of the tested nano compounds (5 mg or 10 mg/Kg) lowered plasma cholesterol, triglycerides, LDL, insulin resistance, glucose, and BMI significantly relative to obese group values. On the other hand, HDL increased significantly in obese rats after treatment with either A-2 or A-3 compared to obese rats. The current investigation showed antioxidant activities for A-1, A-2, and A3 as evidenced by the significant increase in GSH level and a significant decrease in MDA.

CONCLUSION

It was found that A-1, A-2, and A-3 have an efficient therapeutic role in treating of obesity-related hyperlipidemia, oxidative stress and insulin resistance. The results of A-2 and A-3 were more pronounced than those of A-1. The use of Zn/Ce nanocomposite (that have positive characteristics) in combating obesity and its complications could be become a new trend in therapeutic application for a management of obesity.

Revealing the intrinsic nature of Ni-, Mn-, and Y-doped CeO2 catalysts with positive, additive, and negative effects on CO oxidation using operando DRIFTS-MS

The catalytic activity of a transition metal (host) oxide can be influenced by doping with a second cation (dopant), but the key factors dominating the activity of the doped catalyst are still controversial. Herein, CeO2 doped with Ni, Mn, and Y catalysts prepared using aerosol pyrolysis were used to demonstrate the positive, negative, and additive effects on CO oxidation as a model reaction. Various characterization results indicated that Ni, Mn, and Y had been successfully doped into the CeO2 lattice. The catalytic activities of each catalyst for CO conversion were in the order of Ni-CeO2 > Mn-CeO2 > CeO2 > Y-CeO2. Operando DRIFTS-MS and various characterization methods were applied to reveal the intrinsic nature of the doping effects. The accumulation rate of the surface bidentate carbonates determined the CO oxidation. A definition to evaluate the doping effect was proposed, which is anticipated to be useful for developing a rational catalyst with a high CO oxidation activity. The CO oxidation reactivities displayed strong correlations with the surface factors obtained from operando DRIFTS-MS analysis and the structure factors from XPS and Raman analyses.

Unveiling the Surface Chemical Reactions during Multi-Phase Catalytic Oxidation of Soot on Nanoengineering/Interfacing/Doping-Prepared Mn-CeO2 Catalysts Using TG-MS and Operando DRIFTS-MS

The aerosol pyrolysis method from nitrate precursors was used to prepare the Mn-CeO2 catalyst containing Mn2O3, CeO2, and Mn-doped CeO2 nanoparticles for catalyzing carbonous soot oxidation. The prepared Mn-CeO2 catalysts have high specific surface areas, Ce3+ ratio, and oxygen vacancy defects; these are a benefit for soot oxidation. The T50 for soot oxidation on the 0.57Mn-CeO2 catalyst is as low as 355 °C, which is 329 °C lower than that for soot oxidation without a catalyst. The catalysts were characterized using XRD, SEM-EDS, HRTEM, XPS, Raman spectroscopy, H2-TPR-MS, O2-TPD-MS, soot-TPR-MS, and operando DRIFTS-MS. The functions of Mn2O3, CeO2, and Mn-doped CeO2 in the 0.57Mn-CeO2 catalyst are unveiled. Mn-doped CeO2 plays a key role and CeO2 participates in soot oxidation, while Mn2O3 is used to enhance higher ratios of Ce3+, via the reaction of Mn3+ + Ce4+ = Mn4+ + Ce3+. The mechanism of soot oxidation on Mn-CeO2 was proposed.

Modeling Single-Atom Catalysis

Electronic structure calculations represent an essential complement of experiments to characterize single-atom catalysts (SACs), consisting of isolated metal atoms stabilized on a support, but also to predict new catalysts. However, simulating SACs with quantum chemistry approaches is not as simple as often assumed. In this work, the essential factors that characterize a reliable simulation of SACs activity are examined. The Perspective focuses on the importance of precise atomistic characterization of the active site, since even small changes in the metal atom's surroundings can result in large changes in reactivity. The dynamical behavior and stability of SACs under working conditions, as well as the importance of adopting appropriate methods to solve the Schrödinger equation for a quantitative evaluation of reaction energies are addressed. The Perspective also focuses on the relevance of the model adopted. For electrocatalysis this must include the effects of the solvent, the presence of electrolytes, the pH, and the external potential. Finally, it is discussed how the similarities between SACs and coordination compounds may result in reaction intermediates that usually are not observed on metal electrodes. When these aspects are not adequately considered, the predictive power of electronic structure calculations is quite limited.

Enhanced Oxygen Storage Capacity of Porous CeO2 by Rare Earth Doping

CeO2 is an important rare earth (RE) oxide and has served as a typical oxygen storage material in practical applications. In the present study, the oxygen storage capacity (OSC) of CeO2 was enhanced by doping with other rare earth ions (RE, RE = Yb, Y, Sm and La). A series of Undoped and RE-doped CeO2 with different doping levels were synthesized using a solvothermal method following a subsequent calcination process, in which just Ce(NO3)3∙6H2O, RE(NO3)3∙nH2O, ethylene glycol and water were used as raw materials. Surprisingly, the Undoped CeO2 was proved to be a porous material with a multilayered special morphology without any additional templates in this work. The lattice parameters of CeO2 were refined by the least-squares method with highly pure NaCl as the internal standard for peak position calibrations, and the solubility limits of RE ions into CeO2 were determined; the amounts of reducible-reoxidizable Cen+ ions were estimated by fitting the Ce 3d core-levels XPS spectra; the non-stoichiometric oxygen vacancy (VO) defects of CeO2 were analyzed qualitatively and quantitatively by O 1s XPS fitting and Raman scattering; and the OSC was quantified by the amount of H2 consumption per gram of CeO2 based on hydrogen temperature programmed reduction (H2-TPR) measurements. The maximum [OSC] of CeO2 appeared at 5 mol.% Yb-, 4 mol.% Y-, 4 mol.% Sm- and 7 mol.% La-doping with the values of 0.444, 0.387, 0.352 and 0.380 mmol H2/g by an increase of 93.04, 68.26, 53.04 and 65.22%. Moreover, the dominant factor for promoting the OSC of RE-doped CeO2 was analyzed.

Magnetic Field-Enhanced Oxygen Evolution Reaction via the Tuneability of Spin Polarization in a Half-Metal Catalyst

The magnetic field response of an electrochemistry process, such as the oxygen evolution reaction (OER), provides not only a strategy for enhanced catalytic activity by applying an external field but also a platform for revealing the functionality of the multiple degrees of freedom of the catalyst. However, the mechanism of the magnetic field tuneable OER is controversial. The strong correlation between the d and p orbitals of transition metal and oxygen still puzzles the dominant role of spin in an OER process. Here in this study, we have employed the manganite La_0.7Sr_0.2Ca_0.1MnO₃ as the ferromagnetic OER catalyst, which has a ferromagnetic/paramagnetic transition (T_C) around the room temperature. It is found that the overpotential can be reduced by ∼18% after applying a 5 kOe magnetic field. Furthermore, this magnetic field can trigger a further improvement of the OER performance, and it demonstrates a strong temperature dependence which is incongruent with its magnetoresistive behavior. So our experiments suggest that the observed magnetic response originates dominantly from the triplet state of the O₂, where the spin-polarized d and oxygen p orbitals lower the Gibbs free energy for every reaction step in OER. This study offers experimental evidence on comprehending the spin degree in the OER process, meanwhile benefiting the further design and engineering of the promising magnetic electrochemistry catalysts.

Thermocatalytic Degradation of Gaseous Formaldehyde Using Transition Metal-Based Catalysts

Formaldehyde (HCHO: FA) is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)-based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost-effectiveness. Herein, a comprehensive review is offered to highlight the current progress in TMO-based thermocatalysts (e.g., manganese, cerium, cobalt, and their composites) in association with the strategies established for catalytic removal of FA. Efforts are hence made to describe the interactive role of key factors (e.g., exposed crystal facets, alkali metal/nitrogen modification, type of precursors, and alkali/acid treatment) governing the catalytic activity of TMO-based thermocatalysts against FA. Their performance has been evaluated further between two distinctive operation conditions (i.e., low versus high temperature) based on computational metrics such as reaction rate. Accordingly, the superiority of TMO-based composite catalysts over mono- and bi-metallic TMO catalysts is evident to reflect the abundant surface oxygen vacancies and enhanced FA adsorptivity of the former group. Finally, the present challenges and future prospects for TMO-based catalysts are discussed with respect to the catalytic oxidation of FA. This review is expected to offer valuable information to design and build high performance catalysts for the efficient degradation of volatile organic compounds.

Nested Metal Catalysts: Metal Atoms and Clusters Stabilized by Confinement with Accessibility on Supports

Supported catalysts that are important in technology prominently include atomically dispersed metals and metal clusters. When the metals are noble, they are typically unstable-susceptible to sintering-especially under reducing conditions. Embedding the metals in supports such as organic polymers, metal oxides, and zeolites confers stability on the metals but at the cost of catalytic activity associated with the lack of accessibility of metal bonding sites to reactants. An approach to stabilizing noble metal catalysts while maintaining their accessibility involves anchoring them in molecular-scale nests that are in or on supports. The nests include zeolite pore mouths, zeolite surface cups (half-cages), raft-like islands of oxophilic metals bonded to metal oxide supports, clusters of non-noble metals (e.g., hosting noble metals as single-atom alloys), and nanoscale metal oxide islands that selectively bond to the catalytic metals, isolating them from the support. These examples illustrate a trend toward precision in the synthesis of solid catalysts, and the latter two classes of nested catalysts offer realistic prospects for economical large-scale application.

Hydrothermal synthesis of ZnZrO2/chitosan (ZnZrO2/CS) nanocomposite for highly sensitive detection of glucose and hydrogen peroxide

In this work, pure ZnZrO₂ and chitosan supported (ZnZrO₂/CS) nanocomposite have been synthesized at low coast by hydrothermal method. FT-IR, Micro Raman, PXRD, HR-SEM-EDAX, HR-TEM, AFM, BET and XPS were used to analyze the structural and morphological properties of the fabricated nanocomposites. The fabricated ZnZrO₂ and ZnZrO₂/CS nanocomposites were measured for their electrocatalytic activity towards glucose and hydrogen peroxide determinations. The ZnZrO₂/CS sensor exhibited wide detection range (5 μM to 5.85 mM), high sensitivity (6.78 μA mM^-1 cm^-2), LOD (2.31 μM), and long-term stability for glucose detection in alkaline solution. Also, as a multifunctional electrochemical sensor, ZnZrO₂/CS sensor exhibits excellent sensing ability towards hydrogen peroxide, with a wide dynamic range (20 μM to 6.85 mM), a high sensitivity (2.22 μA mM^-1 cm^-2), and a LOD (2.08 μM) (S/N = 3). The electrochemical measurement shows that the ZnZrO₂/CS sensor has excellent catalytic activity and a much LOD than ZnZrO₂. The modified electrode showed excellent anti interference nature. Furthermore, this ZnZrO₂/CS electrode was used to detection of glucose and H₂O₂ in human blood serum and HeLa cells respectively.

Molecular Dynamics Approach to the Physical Mixture of In2O3 and ZrO2: Defect Formation and Ionic Diffusion

Recent research on the use of physical mixtures In₂O₃-ZrO₂ has raised interesting questions as to how their combination enhances catalytic activity and selectivity. Specifically, the relationship between oxygen diffusion and defect formation and the epitaxial tension in the mixture should be further investigated. In this study, we aim to clarify some of these relationships through a molecular dynamics approach. Various potentials for the two oxides are compared and selected to describe the physical mixture of In₂O₃ and ZrO₂. Different configurations of each single crystal and their physical mixture are simulated, and oxygen defect formation and diffusion are measured and compared. Significant oxygen defect formation is found in both crystals. In₂O₃ seems to be stabilized by the mixture, while ZrO₂ is destabilized. Similar results were found for the ZrO₂ doping with In and ln₂O₃ doping with Zr. The results explain the high activity and selectivity catalyst activity of the mixture for the production of isobutylene from ethanol.

Catalytic Activity of Ni Based Materials Prepared by Different Methods for Hydrogen Production via the Water Gas Shift Reaction

Water gas shift reactions (WGS) were evaluated over Ni/CeO2 and Ni/CeSmO catalysts for hydrogen production. The effects of catalyst preparation method and Sm loading were investigated. The Ni/ceria and Ni/CeSmO catalysts were synthesized by combustion, sol gel and sol gel-combustion method. After WGS tests, the catalysts were determined the carbon deposition by thermogravimetric analysis. The thermogravimetric analysis and temperature programmed NH3 desorption showed that addition of Sm promoter made higher the weak acid sites and lower the amount of carbon deposition than the unpromoted catalyst due to it being easily removed. CO chemisorption result indicated that Ni/Ce5%SmO catalyst prepared by combustion method has the highest Ni metal dispersion and metallic surface area compared to the other catalysts. The enhancement of WGS activity of this catalyst is due to more surface active sites being exposed to reactants. Furthermore, H2-temperature programmed reduction analysis confirmed an easiest reduction of this catalyst. This behavior accelerates the redox process at the ceria surface and enhances the oxygen vacancy concentration. The catalytic activity measurements exhibited that the optimum Sm loading was 5% wt. and the best catalyst preparation was the combustion method. The high surface area and small crystallite size of the 5%Ni/Ce5%SmO (combustion) catalyst resulted in sufficient dispersion, which closely related to the WGS activity of the catalyst.

Photocatalytic Degradation of Crystal Violet Dye under Visible Light by Fe-Doped TiO2 Prepared by Reverse-Micelle Sol-Gel Method

A reverse-micelle sol-gel method was chosen for the preparation of Fe-doped TiO₂ samples that were employed in the photodegradation of the crystal violet dye under visible light irradiation in a batch reactor. The dopant amount was varied to assess the optimal photocatalyst composition towards the target dye degradation. The photocatalysts were characterized through a multi-technique approach, envisaging XRPD and QPA as obtained by Rietveld refinement, FE-SEM analysis, DR UV-vis spectroscopy, N₂ adsorption/desorption isotherms measurement at -196 °C, ζ-potential measurement, and XPS analysis. The physical-chemical characterization showed that the adopted synthesis method allows obtaining NPs with uniform shape and size and promotes the introduction of Fe into the titania matrix, finally affecting the relative amounts of the three occurring polymorphs of TiO₂ (anatase, rutile and brookite). By increasing the Fe content, the band gap energy decreases from 3.13 eV (with undoped TiO₂) to 2.65 eV (with both 2.5 and 3.5 wt.% nominal Fe contents). At higher Fe content, surface Fe oxo-hydroxide species occur, as shown by DR UV-vis and XP spectroscopies. All the Fe-doped TiO₂ photocatalysts were active in the degradation and mineralization of the target dye, showing a TOC removal higher than the undoped sample. The photoactivity under visible light was ascribed both to the band-gap reduction (as confirmed by phenol photodegradation) and to dye sensitization of the photocatalyst surface (as confirmed by photocatalytic tests carried out using different visible-emission spectra LEDs). The main reactive species involved in the dye degradation were determined to be positive holes.

Construction and Enhanced Efficiency of Bi2MoO6/ZnO Compo-Sites for Visible-Light-Driven Photocatalytic Performance

Bi₂MoO₆ was one of the important bismuth-based semiconductors with a narrow bandgap, and has been widely used in selective oxidation catalysts, supercapacitors, and energy-storage devices. A series of Bi₂MoO₆/ZnO composite photocatalysts with different mass ratios were synthesized by the hydrothermal method. The synthesized samples were characterized by XRD, PL, UV-Vis, SEM, TEM, XPS, and BET analysis techniques. Under visible light conditions, Methylene blue (MB) was used as the target degradation product to evaluate its photocatalytic performance. The results showed that the degradation rate constant of Bi₂MoO₆/ZnO (0.4-BZO) was about twice that of the traditional photocatalysis of ZnO. The Bi₂MoO₆/ZnO composite catalyst maintained stable performance after four consecutive runs. The high photocatalytic activity of Bi₂MoO₆/ZnO was attributed to the efficient electron transport of the heterojunction, which accelerates the separation of electron-hole pairs and reduces the probability of carrier recombination near the Bi₂MoO₆/ZnO heterojunction. Bi₂MoO₆/ZnO nanocomposites have potential applications in the field of photodegradation.

Oxygen Healing and CO2 /H2 /Anisole Dissociation on Reduced Molybdenum Oxide Surfaces Studied by Density Functional Theory

Reduced molybdenum oxides are versatile catalysts for deoxygenation and hydrodeoxygenation reactions. In this work, we have performed spin-polarized DFT calculations to investigate oxygen healing energies on reduced molybdenum oxides (reduced α-MoO₃ , γ-Mo₄ O₁₁ and MoO₂ ). We find that Mo⁺⁴ on MoO₂ (100) is the most active for abstracting an oxygen from the oxygenated compounds. We further explored CO₂ adsorption and dissociation on reduced α-MoO₃ (010) and MoO₂ (100). In comparison to reduced α-MoO₃ (010), CO₂ adsorbs more strongly on MoO₂ (100). We find that CO₂ dissociates on MoO₂ (100) via a two-step process, the overall barrier for which is 0.6 eV. This barrier is 1.7 eV lower than that on reduced α-MoO₃ (010), suggesting a much higher activity for deoxygenation of CO₂ to CO. As H₂ dissociation is shown to be the rate-limiting step for hydrodeoxygenation reactions, we also studied activation barriers for H₂ chemisorption on MoO₂ (100). We find that the chemisorption barriers are 0.7 eV lower than that reported on reduced α-MoO₃ (010). Finally, we have studied the dissociation (C-O cleavage) of anisole (a lignin-based biofuel model compound) on MoO₂ (100). We find that anisole binds very strongly on MoO₂ (100) with an adsorption energy of -1.47 eV. According to Sabatier's principle, strongly adsorbing reactants poison the catalyst surface, which may explain the low activity of MoO₂ observed during experiments for hydrodeoxygenation of anisole.

Leveraging Pt/Ce1-xLaxO2-δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

The interfacial oxygen-defective sites of oxide-supported metal catalysts are generally regarded as active centers in diverse redox reactions. Identification of their structure-property relationship at the atomic scale is of great importance but challenging. Herein, a series of La³⁺-doped three-dimensionally ordered macroporous CeO₂ (3D-Ce_1-xLa_xO_2-δ) were synthesized and applied as supports for Pt nanoparticles. The pieces of evidence from a suite of in-situ/ex-situ characterizations and theoretical calculations revealed that the La³⁺-mono-substituted La-□(-Ce)₂ sites (where □ represents an oxygen vacancy) exhibited superior charge transfer ability, behaving as trapping centers for Pt nanoparticles. The resulting interfacial Pt^δ+/La-□(-Ce)₂ sites served as the reversible active species in the aerobic oxidation of 5-hydroxymethylfurfural to boost catalytic performance by simultaneously promoting oxygen activated capacity and the cleavage of O-H/C-H bonds of adsorbed hydroxymethyl groups. Consequently, the Pt/3D-Ce_0.9La_0.1O_2-δ catalyst possessing the highest number of Pt^δ+/La-□(-Ce)₂ sites showed the best catalytic performance with 99.6% yield to 2,5-furandicarboxylic acid in 10 h. These results offer more insights into the promoting mechanism of interfacial oxygen-defective sites for the liquid-phase aerobic oxidation of aldehydes and alcohols.

Pyrochlores for Advanced Oxygen Electrocatalysis

Fuel cells (FCs), water electrolyzers (WEs), unitized regenerative fuel cells (URFCs), and metal-air batteries (MABs) are among the emerging electrochemical technologies for energy storage, fuel (H₂), oxidant (O₂), and clean energy production. Their commercial applications are hindered by the low oxygen reduction reaction/oxygen evolution reaction (ORR/OER) bifunctional activity (for URFCs and MABs), OER selectivity (brine electrolysis in seawater and Martian environments), and high cost of the benchmark electrocatalysts (OER: RuO₂, IrO₂ and ORR: Pt/C) which affects the performance and affordability of the devices. Low-cost electrocatalysts with highly symmetric ORR/OER bifunctional activity and high OER selectivity are crucial for large-scale FC, WE, URFC, and MAB application. Recent studies have revealed that tuning the structure of pyrochlore oxides provides a pathway to enhancing OER and ORR activity over a wide range of pH. Pyrochlore oxides commonly contain a cubic A₂B₂O_7-x structure with two types of tetrahedrally coordinated O atoms containing (1) A-O-A and (2) A-O-B types with a cationic radii mismatch of r_A/r_B > 1.5 and propensity toward oxygen vacancy formation. The variety of pyrochlore oxides and their tunable properties make them attractive for a wide spectrum of applications. Among all the metal oxides, Ru-based pyrochlores (e.g., Pb₂Ru₂O_7-x) exhibit the best bifunctional oxygen electrocatalytic activity, i.e., low bifunctionality index (BI), in alkaline medium. Furthermore, pyrochlores exhibit high OER selectivity in brine electrolytes due to the presence of surface oxygen vacancies, making them suitable for space applications (brine electrolysis on Mars) and coastal hydrogen generation. Their bifunctional activity and selectivity can be further amplified by (1) substituting "A" and "B" sites of pyrochlores (AA'BB'O_7-x), (2) tuning metal oxidation states of A and B by varying synthesis conditions, and (3) modulating oxygen vacancy concentration, each of which yield favorable structural and electronic variations. In recent years, research on the synthesis and understanding of pyrochlores has significantly enhanced their viability, offering a new horizon in the quest for economical and active electrocatalysts. However, an account that focuses on critical developments in this field is still lacking.In this Account, we focus on the recent development of a variety of pyrochlore electrocatalysts to understand intrinsic structure-activity-selectivity-stability relationships in these materials. Recent developments and applications of pyrochlore-based electrocatalysts are discussed under the following headings: (1) modulation of crystal and electronic structure of pyrochlores, (2) structure-activity-stability relationships of different pyrochlores for OER and ORR, (3) development of OER-selective pyrochlores for brine electrolysis, and (4) the application of pyrochlores in electrochemical devices. Finally, we highlight some unaddressed issues such as the precise identification of active sites, which can be addressed in the future through advanced in situ and ex situ characterization techniques coupled with the density functional theory-based analyses. This Account provides foundational understanding to guide the comprehensive development of highly active, selective, stable and low-cost structurally engineered pyrochlores for high performance electrochemical devices.

Adatom Bonding Sites in a Nickel-Fe3 O4 (001) Single-Atom Model Catalyst and O2 Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light

Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe3 O4 (001). We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O2 to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts.

Ultrasonic treatment enhances the formation of oxygen vacancies and trivalent manganese on α-MnO2 surfaces: Mechanism and application

Catalytic activity is the main obstacle limiting the application of peroxymonosulfate (PMS) activation on transition metal oxide catalysts in organic pollutant removal. Herein, ultrasonic treatment was applied to α-MnO₂ to fabricate a new u-α-MnO₂ catalyst for PMS activation. Dimethyl phthalate (DMP, 10 mg/L) was almost completely degraded within 90 min, and the pseudofirst-order rate constant for DMP degradation in the u-α-MnO₂/PMS system was ∼7 times that in the initial α-MnO₂/PMS system. The ultrasonic treatment altered the crystalline and pore structures of α-MnO₂ and produced defects on the u-α-MnO₂ catalyst. According to the XPS, TG, and EPR results, higher contents of trivalent Mn and oxygen vacancies (OVs) were produced on the catalyst surfaces. The OVs induced the decomposition of PMS to produce ¹O₂, which was identified as the main reactive oxygen species (ROS) responsible for DMP degradation. The u-α-MnO₂ catalyst presented great reusability, especially by ultrasonic regeneration of OVs toward the used catalyst. This study provides new insights into regulating OVs generation and strengthening catalyst activity in the PMS activation process for its application in water purification.

Molybdenum Modified Sol–Gel Synthesized TiO2 for the Photocatalytic Degradation of Carbamazepine under UV Irradiation

Pharmaceutical CEC compounds are a potential threat to man, animals, and the environment. In this study, a sol–gel-derived TiO2 (SynTiO2) was produced and subsequently sonochemically doped with a 1.5 wt% Mo to obtain the final product (Mo (1.5 wt%)/SynTiO2). The as-prepared materials were characterized for phase structure, surface, and optical properties by XRD, TEM, N2 adsorption–desorption BET isotherm at 77 K, and PSD by BJH applications, FTIR, XPS, and UV-Vis measurements in DRS mode. Estimated average crystallite size, particle size, surface area, pore-volume, pore size, and energy bandgap were 16.10 nm, 24.55 nm, 43.30 m2/g, 0.07 cm3/g, 6.23 nm, and 3.05 eV, respectively, for Mo/SynTiO2. The same structural parameters were also estimated for the unmodified SynTiO2 with respective values of 14.24 nm, 16.02 nm, 133.87 m2/g, 0.08 cm3/g, 2.32 nm, and 3.3 eV. Structurally improved (Mo (1.5 wt%)/SynTiO2) achieved ≈100% carbamazepine (CBZ) degradation after 240 min UV irradiation under natural (unmodified) pH conditions. Effects of initial pH, catalyst dosage, initial pollutant concentration, chemical scavengers, contaminant ions, hydrogen peroxide (H2O2), and humic acid (HA) were also investigated and discussed. The chemical scavenger test was used to propose involved photocatalytic degradation process mechanism of CBZ.