Catalysts For Oxidation Research Articles

In-Depth Understanding of the Oxidative Compatibility of Volatile Organic Compounds with Mn2O3 and Pt-Loaded Catalysts.

Designing suitable catalysts for efficiently degrading volatile organic compounds (VOCs) is a great challenge due to the distinct variety and nature of VOCs. Herein, the suitability of different typical VOCs (toluene and acetone) over Pt-based catalysts and Mn2O3 was investigated carefully. The activity of Mn2O3 was inferior to Pt-loaded catalysts in toluene oxidation but showed superior ability for destroying acetone, while Pt loading could boost the catalytic activity of Mn2O3 for both acetone and toluene. This suitability could be determined by the physicochemical properties of the catalysts and the structure of the VOC since toluene destruction activity is highly reliant on Pt0 in the metallic state and linearly correlated with the amount of surface reactive oxygen species (Oads), while the crucial factor that affects acetone oxidation is the mobility of lattice oxygen (Olat). The Pt/Mn2O3 catalyst shows highly active Pt-O-Mn interfacial sites, favoring the generation of Oads and promoting Mn-Olat mobility, leading to its excellent performance. Therefore, the design of abundant active sites is an effective means of developing highly adaptive catalysts for the oxidation of different VOCs.

Role of Intragap States in Sensitized Sb-Doped Tin Oxide Photoanodes for Solar Fuels Production.

In view of developing photoelectrosynthetic cells which are able to store solar energy in chemical bonds, water splitting is usually the reaction of choice when targeting hydrogen production. However, alternative approaches can be considered, aimed at substituting the anodic reaction of water oxidation with more commercially capitalizable oxidations. Among them, the production of bromine from bromide ions was investigated long back in the 1980s by Texas Instruments. Herein we present optimized perylene-diimide (PDI)-sensitized antimony-doped tin oxide (ATO) photoanodes enabling the photoinduced HBr splitting with >4 mA/cm2 photocurrent densities under 0.1 W/cm2 AM1.5G illumination and 91 ± 3% faradaic efficiencies for bromine production. These remarkable results, among the best currently reported for the photoelectrochemical Br- oxidation by dye sensitized photoanodes, are strongly related to the occupancy extent of ATO's intragap (IG) states, generated upon Sb-doping, as demonstrated by comparing their performances with PDI-sensitized analogues on both undoped SnO2- and TiO2-passivated ATO scaffolds by means of (spectro)electrochemistry and electrochemical impedance spectroscopy. The architecture of the ATO-PDI photoanodic assembly was further modified via the introduction of a molecular iridium-based water oxidation catalyst, thus proving the versatility of the proposed hybrid interfaces as photoanodic platforms for photoinduced oxidations in PEC devices.

Rational Design of Improved Ru Containing Fe-Based Metal-Organic Framework (MOF) Photoanode for Artificial Photosynthesis.

Metal-Organic Frameworks (MOFs) recently emerged as a new platform for the realization of integrated devices for artificial photosynthesis. However, there remain few demonstrations of rational tuning of such devices for improved performance. Here, a fast molecular water oxidation catalyst working via water nucleophilic attack is integrated into the MOF MIL-142, wherein Fe3O nodes absorb visible light, leading to charge separation. Materials are characterized by a range of structural and spectroscopic techniques. New, [Ru(tpy)(Qc)(H2O)]+ (tpy = 2,2':6',2″-terpyridine and Qc = 8-quinolinecarboxylate)-doped Fe MIL-142 achieved a high photocurrent (1.6 × 10-3 A·cm-2) in photo-electrocatalytic water splitting at pH = 1. Unassisted photocatalytic H2 evolution is also reported with Pt as the co-catalyst (4.8 µmol g-1 min-1). The high activity of this new system enables hydrogen gas capture from an easy-to-manufacture, scaled-up prototype utilizing MOF deposited on FTO glass as a photoanode. These findings provide insights for the development of MOF-based light-driven water-splitting assemblies utilizing a minimal amount of precious metals and Fe-based photosensitizers.

Machine-Learning-Assisted Descriptors Identification for Indoor Formaldehyde Oxidation Catalysts.

The development of highly efficient catalysts for formaldehyde (HCHO) oxidation is of significant interest for the improvement of indoor air quality. Up to 400 works relating to the catalytic oxidation of HCHO have been published to date; however, their analysis for collective inference through conventional literature search is still a challenging task. A machine learning (ML) framework was presented to predict catalyst performance from experimental descriptors based on an HCHO oxidation catalysts database. MnOx, CeO2, Co3O4, TiO2, FeOx, ZrO2, Al2O3, SiO2, and carbon-based catalysts with different promoters were compiled from the literature. Notably, 20 descriptors including reaction catalyst composition, reaction conditions, and catalyst physical properties were collected for data mining (2263 data points). Furthermore, the eXtreme Gradient Boosting algorithm was employed, which successfully predicted the conversion efficiency of HCHO with an R-square value of 0.81. Shapley additive analysis suggested Pt/MnO2 and Ag/Ce-Co3O4 exhibited excellent catalytic performance of HCHO oxidation based on the analysis of the entire database. Validated by experimental tests and theoretical simulations, the key descriptor identified by ML, i.e., the first promoter, was further described as metal-support interactions. This study highlights ML as a useful tool for database establishment and the catalyst rational design strategy based on the importance of analysis between experimental descriptors and the performance of complex catalytic systems.

Ruthenium Nanoclusters and Single Atoms on α-MoC/N-Doped Carbon Achieves Low-input/Input-free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation.

The hydrazine oxidation-assisted H2 evolution method promises low-input and input-free hydrogen production. However, developing high-performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α-MoC/N-C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α-MoC nanoparticles-decorated N-doped carbon (α-MoC/N-C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring -80 mV and -9 mV respectively to reach 10 mA cm-2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H adsorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α-MoC/N-C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm-2 at just 64 mV. The zinc hydrazine (Zn-Hz) battery assembled with α-MoC/N-C/RuNSA cathode and Zn foil anode can exhibit 96% energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn-Hz with OHzS system enables self-powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell-integrated-electrolyzer system.

Synergistic growth of nickel and platinum nanoparticles via exsolution and surface reaction

Bimetallic catalysts combining precious and earth-abundant metals in well designed nanoparticle architectures can enable cost efficient and stable heterogeneous catalysis. Here, we present an interaction-driven in-situ approach to engineer finely dispersed Ni decorated Pt nanoparticles (1-6 nm) on perovskite nanofibres via reduction at high temperatures (600-800 oC). Deposition of Pt (0.5 wt%) enhances the reducibility of the perovskite support and promotes the nucleation of Ni cations via metal-support interaction, thereafter the Ni species react with Pt forming alloy nanoparticles, with the combined processes yielding smaller nanoparticles that either of the contributing processes. Tuneable uniform Pt-Ni nanoparticles are produced on the perovskite surface, yielding reactivity and stability surpassing 1 wt.% Pt/γ-Al2O3 catalysts for CO oxidation. This approach heralds the possibility of in-situ fabrication of supported bimetallic nanoparticles with engineered compositional distributions and performance.

Ruthenium Nanoclusters and Single Atoms on α‐MoC/N‐Doped Carbon Achieves Low‐input/Input‐free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation

The hydrazine oxidation‐assisted H2 evolution method promises low‐input and input‐free hydrogen production. However, developing high‐performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α‐MoC/N‐C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α‐MoC nanoparticles‐decorated N‐doped carbon (α‐MoC/N‐C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring ‐80 mV and ‐9 mV respectively to reach 10 mA cm‐2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H adsorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α‐MoC/N‐C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm‐2 at just 64 mV. The zinc hydrazine (Zn‐Hz) battery assembled with α‐MoC/N‐C/RuNSA cathode and Zn foil anode can exhibit 96% energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn‐Hz with OHzS system enables self‐powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell‐integrated‐electrolyzer system.

Covalent graft of Polypyridineruthenium(II) Complex-ZnTPP dyad with fullerol and immobilization onto TiO2 for enhanced photoassisted water oxidation activity

The covalent linkage of the light-harvester with the water oxidation catalyst is an effective way to construct heterogeneous catalysts with both light harvesting ability and catalytic oxygen evolution activity, and remains a challenge for simulated photosynthesis systems. Herein, two heterogeneous composite catalysts of ZnTPPtpyRubpyPHFTiO2 and ZnTPPtpyRubpyTiO2, with both the light harvesting capability and the catalytic water oxidation (CWE) performance, were successfully designed and prepared, and were fully characterized. Research indicated that the transfer mode of the photo-generated carrier for the two photo-assisted heterogeneous catalysts follows the type II mechanism, and the photo-generated holes promote the CWE activity. Compared to the dark condition (with TOF values of 42.3 and 41.8, respectively), ZnTPPtpyRubpyPHFTiO2 and ZnTPPtpyRubpyTiO2 exhibit superior CWE activity and efficiency in the illumination condition (with TOF values of 120 and 48.31, respectively). Fullerol, playing the role of an electron acceptor and an electron-pool, promotes charge separation and electron storage, which leads to a better suppression in charge recombination and enhancement in charge injection for ZnTPPtpyRubpyPHFTiO2. Therefore, ZnTPPtpyRubpyPHFTiO2 demonstrates a significantly improved catalytic activity in the illumination condition with a much higher TOF value compared to that of ZnTPPtpyRubpyTiO2.

A review on Fe2O3‐based catalysts for toluene oxidation: catalysts design and optimization with the formation of abundant oxygen vacancies

Volatile organic compounds (VOCs) are typical pollutants with hazards for humans and the environment, and can be efficiently mitigated by catalytic combustion. Fe2O3‐based catalysts are a promising choice due to their low cost and strong redox ability. Several attempts have been made to promote the catalytic performance of Fe2O3 at low temperatures. This review summarizes the research progress on Fe2O3‐based catalysts for the oxidation of toluene, one of the most common and harmful VOC. Firstly, the properties and catalytical performance for Fe2O3‐based catalysts were summarized, and the reaction mechanisms for toluene oxidation on the surface of Fe2O3 were detailed to comprehend the role of oxygen vacancy. Then, the modification for single Fe2O3 catalysts, including synthesis parameters, structure and morphology control, has been introduced to reveal the correlation between physicochemical properties of catalysts and their activity. In addition, composite Fe2O3 catalysts, which can promote catalytic performance significantly due to the synergetic effect between different components, were comprehended. Finally, waste‐derived Fe2O3 catalysts with sustainable merit as converting waste into worth have been discussed. Moreover, the advanced machine learning tools, which are helpful in accelerating catalyst design, configuration optimization and reactivity prediction, have been introduced as an emerging research opportunity for the future.

A Low-Noble-Metal Ru@CoMn2O4 Spinel Catalyst for the Efficient Oxidation of Propane

Noble metals have become a research hotspot for the oxidation of light alkanes due to their low ignition temperature and easy activation of C-H; however, sintering and a high price limit their industrial applications. The preparation of effective and low-noble-metal catalysts still presents profound challenges. Herein, we describe how a Ru@CoMn2O4 spinel catalyst was synthesized via Ru in situ doping to promote the activity of propane oxidation. Ru@CoMn2O4 exhibited much higher catalytic activity than CoMn2O4, achieving 90% propane conversion at 217 °C. H2-TPR, O2-TPD, and XPS were used to evaluate the catalyst adsorption/lattice oxygen activity and the adsorption and catalytic oxidation capacity of propane. It could be concluded that Ru promoted synergistic interactions between cobalt and manganese, leading to electron transfer from the highly electronegative Ru to Co2+ and Mn3+. Compared with CoMn2O4, 0.1% Ru@CoMn2O4, with a higher quantity of lattice oxygen and oxygen mobility, possessed a stronger capability of reducibility, which was the main reason for the significant increase in the activity of Ru@CoMn2O4. In addition, intermediates of the reaction between adsorbed propane and lattice oxygen on the catalyst were monitored by in situ DRIFTS. This work highlights a new strategy for the design of a low-noble-metal catalyst for the efficient oxidation of propane.

Characterization of the Bottlenecks and Pathways for Inhibitor Dissociation from [NiFe] Hydrogenase.

[NiFe] hydrogenases can act as efficient catalysts for hydrogen oxidation and biofuel production. However, some [NiFe] hydrogenases are inhibited by gas molecules present in the environment, such as O2 and CO. One strategy to engineer [NiFe] hydrogenases and achieve O2- and CO-tolerant enzymes is by introducing point mutations to block the access of inhibitors to the catalytic site. In this work, we characterized the unbinding pathways of CO in the complex with the wild-type and 10 different mutants of [NiFe] hydrogenase from Desulfovibrio fructosovorans using τ-random accelerated molecular dynamics (τRAMD) to enhance the sampling of unbinding events. The ranking provided by the relative residence times computed with τRAMD is in agreement with experiments. Extensive data analysis of the simulations revealed that from the two bottlenecks proposed in previous studies for the transit of gas molecules (residues 74 and 122 and residues 74 and 476), only one of them (residues 74 and 122) effectively modulates diffusion and residence times for CO. We also computed pathway probabilities for the unbinding of CO, O2, and H2 from the wild-type [NiFe] hydrogenase, and we observed that while the most probable pathways are the same, the secondary pathways are different. We propose that introducing mutations to block the most probable paths, in combination with mutations to open the main secondary path used by H2, can be a feasible strategy to achieve CO and O2 resistance in the [NiFe] hydrogenase from Desulfovibrio fructosovorans.

Creating Atomically Iridium-Doped PdOx Nanoparticles for Efficient and Durable Methane Abatement.

The urgent environmental concern of methane abatement, attributed to its high global warming potential, necessitates the development of methane oxidation catalysts (MOC) with enhanced low-temperature activity and durability. Herein, an iridium-doped PdOx nanoparticle supported on silicalite-1 zeolite (PdIr/S-1) catalyst was synthesized and applied for methane catalytic combustion. Comprehensive characterizations confirmed the atomically dispersed nature of iridium on the surface of PdOx nanoparticles, creating an Ir4f-O-Pdcus microstructure. The atomically doped Ir transferred more electrons to adjacent oxygen atoms, modifying the electronic structure of PdOx and thus enhancing the redox ability of the PdIr/S-1 catalysts. This electronic modulation facilitated methane adsorption on the Pd site of Ir4f-O-Pdcus, reducing the energy barrier for C-H bond cleavage and thereby increasing the reaction rate for methane oxidation. Consequently, the optimized PdIr0.1/S-1 showed outstanding low-temperature activity for methane combustion (T50 = 276 °C) after aging and maintained long-term stability over 100 h under simulated exhaust conditions. Remarkably, the novel PdIr0.1/S-1 catalyst demonstrated significantly enhanced activity even after undergoing harsh hydrothermal aging at 750 °C for 16 h, significantly outperforming the conventional Pd/Al2O3 catalyst. This work provides valuable insights for designing efficient and durable MOC catalysts, addressing the critical issue of methane abatement.

3D-interconnected N-doped porous carbon with hierarchical pore structure as a high-efficiency catalyst for H2S oxidation at room temperature

Nitrogen-doped porous carbons (NPCs) have been regarded as an efficient metal-free catalyst for H2S oxidation. However, critical factors affecting their desulfurization ability are still unclear, making it difficult to accurately adjust their desulfurization performance to meet industrial requirements. Herein, a novel 3D-interconnected NPC with hierarchical pore structure was synthesized by one-step “leavening” strategy using rice husk and (NH4)2C2O4 as a carbon source and foaming agent, respectively, for H2S oxidation at room temperature. Pyrolysis temperature is the major factor for physicochemical properties of NPCs, and breakthrough sulfur capacity of the optimal NPC reaches up to 1036.68 mg/g, which can remain stable during three desulfurization-regeneration cycles. Comparative experiment shows that H2S capacity of NPC is 1.8 and 4.0 times those of PC and NC, respectively, revealing the excellent desulfurization performance of NPC. The structure-effect relationships between H2S and NPC reveal that both textural and chemical properties of NPC, especially specific surface area, structural defect, and pyrrolic N, play dominant roles in H2S removal. It is very necessary to balance the relationship between textural performances and pyrrolic N to synthesize optimal NPC catalyst. This work provides a valuable reference for rational design of high-efficiency carbon-based catalysts for persistent desulfurization at room temperature.

Microcosmic insights into Hg0-SO2 interaction on CuFe2O4 catalyst

CuFe2O4 is considered as a very promising kind of catalysts for Hg0 oxidation in the industrial flue gas. The flue gas produced by solid-fuel combustion usually contains acid gas component SO2, which can exhibit the versatile effects on Hg0 oxidation. However, the effects of SO2 on Hg0 oxidation catalyzed by CuFe2O4 catalyst and its reaction mechanism remain elusive. Herein, the reaction mechanism governing the effects of SO2 on Hg0 oxidation was investigated via the Hg0 oxidation experiments and density functional theory (DFT) calculations. The experimental results show that the temperature change and SO2 presence can affect the Hg0 removal efficiency of CuFe2O4 catalyst. SO2 has a certain degree of inhibition effect on the Hg0 oxidation of CuFe2O4 catalyst. The inhibition effect of SO2 is relatively weak in the low temperature range of 50–150 °C, which is closely associated with the competitive adsorption between SO2 and Hg0. SO2 exhibits a relatively strong inhibition effect on Hg0 oxidation in the high temperature range of 200–350 °C, which is related to the high-temperature sulfation of CuFe2O4 catalyst surface. Mercury species on the CuFe2O4 catalyst surface mainly exists in the forms of HgSO4 and HgO in the presence of SO2. The DFT-calculation results indicate that the conversion process of SO2 to SO3 includes two steps: SO2 adsorption and SO2 oxidation. The activation energy barrier of SO2 oxidation reaction is 216.42 kJ/mol. The oxidation of Hg0 on the surface of CuFe2O4 catalyst includes four steps: Hg0 adsorption, Hg* oxidation into HgO*, HgO*-to-HgSO4* conversion and HgSO4 desorption. HgSO4 is formed by the bimolecular reaction of HgO* and SO3* on CuFe2O4 catalyst. Hg* oxidation into HgO* is found to be the rate-determining step of HgSO4 formation.

Bioinspired Water Preorganization in Confined Space for Efficient Water Oxidation Catalysis in Metallosupramolecular Ruthenium Architectures.

ConspectusNature has established a sustainable way to maintain aerobic life on earth by inventing one of the most sophisticated biological processes, namely, natural photosynthesis, which delivers us with organic matter and molecular oxygen derived from the two abundant resources sunlight and water. The thermodynamically demanding photosynthetic water splitting is catalyzed by the oxygen-evolving complex in photosystem II (OEC-PSII), which comprises a distorted tetramanganese-calcium cluster (CaMn4O5) as catalytic core. As an ubiquitous concept for fine-tuning and regulating the reactivity of the active site of metalloenzymes, the surrounding protein domain creates a sophisticated environment that promotes substrate preorganization through secondary, noncovalent interactions such as hydrogen bonding or electrostatic interactions. Based on the high-resolution X-ray structure of PSII, several water channels were identified near the active site, which are filled with extensive hydrogen-bonding networks of preorganized water molecules, connecting the OEC with the protein surface. As an integral part of the outer coordination sphere of natural metalloenzymes, these channels control the substrate and product delivery, carefully regulate the proton flow by promoting pivotal proton-coupled electron transfer processes, and simultaneously stabilize short-lived oxidized intermediates, thus highlighting the importance of an ordered water network for the remarkable efficiency of the natural OEC.Transferring this concept from nature to the engineering of artificial metal catalysts for fuel production has fostered the fascinating field of metallosupramolecular chemistry by generating defined cavities that conceptually mimic enzymatic pockets. However, the application of supramolecular approaches to generate artificial water oxidation catalysts remained scarce prior to our initial reports, since such molecular design strategies for efficient activation of substrate water molecules in confined nanoenvironments were lacking. In this Account, we describe our research efforts on combining the state-of-the art Ru(bda) catalytic framework with structurally programmed ditopic ligands to guide the water oxidation process in defined metallosupramolecular assemblies in spatial proximity. We will elucidate the governing factors that control the quality of hydrogen-bonding water networks in multinuclear cavities of varying sizes and geometries to obtain high-performance, state-of-the-art water oxidation catalysts. Pushing the boundaries of artificial catalyst design, embedding a single catalytic Ru center into a well-defined molecular pocket enabled sophisticated water preorganization in front of the active site through an encoded basic recognition site, resulting in high catalytic rates comparable to those of the natural counterpart OEC-PSII.To fully explore their potential for solar fuel devices, the suitability of our metallosupramolecular assemblies was demonstrated under (electro)chemical and photocatalytic water oxidation conditions. In addition, testing the limits of structural diversity allowed the fabrication of self-assembled linear coordination oligomers as novel photocatalytic materials and long-range ordered covalent organic framework (COF) materials as recyclable and long-term stable solid-state materials for future applications.

Removing the Barrier in O-O Bond Formation Via the Combination of Intramolecular Radical Coupling and the Oxide Relay Mechanism.

The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the noncoordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, thereby acting as an oxide relay (OR) mechanism for O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, resulting in the Ru(tPaO) catalyst, which has shown even more efficient performance in experimental characterization. In this study, we explore the feasibility of the OR mechanism in the newly reported Ru(tPaO) molecular catalyst. We investigated the catalytic cycle using density functional theory and identified a variation of the OR mechanism that involves radical oxygen atoms in O-O bond formation. We have also determined that the subsequent hydroxide nucleophilic attack is the sole rate-limiting step in the catalytic cycle. All activation free energies are very low, with a free-energy barrier of 2.1 kcal/mol for O-O bond formation and 4.2 kcal/mol for OH- nucleophilic attack.

A Density Functional Theory Analysis of Electrochemical Oxidation of Methane to Alcohol over High-Entropy Oxide (CoCrFeMnNi)3O4 Catalysts.

The direct conversion of methane into alcohol is a promising approach for achieving a low-carbon future, yet it remains a major challenge. In this study, we utilize density functional theory to explore the potential of the (CoCrFeMnNi)3O4 (CCFMNO) high entropy oxide (HEO) for electrochemical oxidation of methane to methanol and ethanol, alongside their competition with CO2 production. Our primary focus in this study is on thermodynamics, enabling a prompt analysis of the catalyst's potential, with the calculation of electrochemical barriers falling beyond our scope. Among all potential active sites within CCFMNO HEO, we identify Co as the most active site for methane activation when using carbonate ions as oxidants. This results in methanol production with a limiting potential of 1.4 VCHE, and ethanol and CO2 productions with a limiting potential of 1.2 VCHE. Additionally, our findings suggest that the occupied p-band center of O* on CCFMNO HEO is a potential descriptor for identifying the most active site within CCFMNO HEO. Overall, our results indicate that CCFMNO HEO holds promise as catalysts for methane oxidation to alcohols, employing carbonate ions as oxidants.

Ammonia and toluene oxidation: Mutual activating effect of copper and cerium on catalytic efficiency

Copper and cerium containing hydrotalcite-like precursors Cux-Cey-Mg-Al were synthesized by mutual co-precipitation followed by calcination at 800 °C. The obtained mixed metal oxides were studied as catalysts for selective ammonia oxidation (NH3-SCO) and toluene combustion. Various techniques, such as temperature-programmed reduction with hydrogen, temperature-programmed desorption of toluene, scanning electron microscopy and reactive frontal chromatography were used to characterize the catalysts. Series 800-Cux-Ce2.5 showed the highest catalytic efficiency in both reactions, allowing complete NH3 and C7H8 conversion below 350 °C and 500 °C, respectively. CeO2 crystallites (12–18 nm), as well as dispersed CuO oxide forms were found in the most active samples. Both phases affect pollutants conversion, however, for ammonia oxidation the occurrence of Cu2+ is essential, while for toluene oxidation, the formation of Ce4+ is sufficient. Over the most active sample (800-Cu5-Ce2.5) the complete conversion in mutual oxidation of NH3 and toluene was achieved below 450 °C.

Oxygen vacancy-induced nonradical degradation of nitroso-containing organics in Fe3O4@N[sbnd]C electro-Fenton reaction at a wide pH range

In this work, Fe3O4-anchored nitrogen-doped carbon catalyst (Fe3O4@N–C) with abundant oxygen vacancies (Vo) and mesoporous structure was successfully synthesized for electro-Fenton (EF) catalytic process. The catalyst demonstrated impressive degradation efficiency towards nitroso-containing organics due to the superior electronic transfer of N–C skeleton and Vo, making it easier for the electron-deficient –NO2 groups to adsorb on the catalyst surface and oxidize rapidly. Typically, the degradation efficiency of p-nitrophenol (PNP) reached 95.6 % in natural pH. Notably, the catalyst exhibited excellent performance over a wide pH range (3 ∼ 11), and has strong anti-interference performance against anions and natural organic matter in water matrix. Mechanism analysis indicated that Vo could promote the formation of highly active electron-rich Fe(II) species, and promote the activation of H2O2 and O2 as additional active sites, thus, a large amount of ·OH and O2·- would be produced and then quickly converted into 1O2. As a result, 1O2 is the main reactive species for PNP degradation in Fe3O4@N–C electro-Fenton reaction. The results will provide insights into the design of high-performance catalysts for the selective oxidation of organic pollutants in wastewater.

Rb‐Promoted Au/CeO2 Nanocatalyst for Remarkably‐Enhanced Aniline Conversion to Azoxybenzene with Ultrahigh Selectivity

Aromatic azo compounds have proven to be a relevant class of building blocks in chemical synthesis. However, uncontrollable selectivity towards azo compounds and low reactant conversion in traditional synthetic methods seriously impede their applications. Herein, Rb‐doped Au/CeO2 nanocatalyst (Rb‐Au/CeO2) was prepared and utilized as a highly efficient supported metal catalyst for the selective oxidation of anilines to azocompounds using hydrogen peroxide as an oxidant, which reached ultrahigh selectivity (92%) towards azoxybenzene and complete aniline conversion (100%). The addition of Rb+ accelerates the electron transformation of Au to produce Au+, which is ready for catalysis. This research presents a promising Rb‐doped strategy for achieving complete aniline conversion and high selectivity towards azoxybenzene, opening up new possibilities for the application of aromatic azo compounds in chemical synthesis.