Oxidation Sites Research Articles

Snowflake-like Ce-BTC@MoS2 heterojunction for high-performance uric acid detection

The analysis of uric acid (UA) in urine is adopted as a standard method for diagnosing related diseases, which provides an effective way for non-invasive detection of UA. However, no portable instruments presently can take an effective detection of UA in urine due to their detection limit, the indicator mainly impacted by sensitive materials. Hence, it is crucial to design electrochemical biosensor electrode materials with high sensitivity and the wide linear region for the detection of UA in urine. This research critically reveals a snowflake-like complex by simply combining the cerium-based metal-organic framework (Ce-BTC) and MoS2. The excellent electrochemical performance of Ce-BTC@MoS2 origins from the strong interfacial electronic interactions between Ce-BTC and MoS2 heterojunction and abundant active sites for UA oxidation. The Ce-BTC@MoS2 exhibits sensitivity (300.29 μA mM−1cm−2) for UA much higher than that of pristine Ce-BTC (129.14 μA mM−1cm−2) as well as MoS2 (209.71 μA mM−1cm−2) in the linear region from 5 to 2500 μM. The outstanding selectivity, excellent stability and attractive repeatability of the UA sensor fabricated by Ce-BTC@MoS2 have been also demonstrated, on account of the unique heterojunction of the electrode material. Additionally, the extensive linear region (0.5–4.4 mM) for the Ce-BTC@MoS2 sensor will be employed to analyze the concentration of UA in urine which can be directly measured without being processed. The prepared urine UA detector combined with the commercial blood UA detector provides an important basis for the comprehensive UA detection and clinical diagnosis.

Electronic structure, absorption spectra and oxidation dynamics in polyynes and dicyanopolyynes.

The advent of femtosecond to attosecond experimental tools has made now possible to study such ultrafast carrier dynamics, e.g., the spatial and temporal charge density evolution, after an initial oxidation or reduction in molecules, candidates for atomic wires like polyynes and dicyanopolyynes. Here, we study the electronic structure and hole transfer in symmetric molecules containing carbon, nitrogen and hydrogen, the first members in the series of polyynic carbynes and dicyanopolyynes, using methods based on density functional theory (DFT): constrained DFT (CDFT), time-dependent DFT (TDDFT) and real-time TDDFT (RT-TDDFT), with Löwdin population analysis, comparing many levels of theory and obtaining convergence of the results. For the same purposes, we develop a tight binding (TB) variant using all valence orbitals of all atoms. This TB variant is applied here in linear molecules, but it is also adequate for electronic structure, charge transfer and charge transport of non-linear molecules and clusters of molecules. We calculate the electronic structure, the time-dependent dipole moment and the probabilities of finding the hole at each site, their mean over time values, the mean transfer rates from the oxidation site to other sites and the frequency content (using charge as well as dipole moment oscillations). We take into account zero-point motion. The initial conditions for RT-TDDFT are obtained by CDFT. For TB, we explore different initial conditions: we place the hole at a particular orbital or distribute it among a number of orbitals; it is also possible to include phase differences between orbitals. Finally, we compare with available experimental data.

3d orbital electron tunning and crystal engineering enables high-capacity vanadium oxide for aqueous ammonium ion batteries

Vanadium pentoxide (V2O5) has shown great potential as the electrode for aqueous ammonium ion batteries (AAIBs) owing to its good electrochemical reversibility and high theoretical capacity. However, the electrochemical performance of V2O5 is seriously limited by the weak NH4+ adsorption capability and insufficient active sites of vanadium oxide originated from the unsuitable 3d orbital electron state. Herein, the strategy of a 3d orbital electron tunning and crystal engineering is used to increase the ammonium ion storage capacity of V2O5 electrode. The experimental results show that the modified 3d orbital state of V4+ (t2g1) can effectively increase the active sites of V2O5. Therefore, the as-prepared N-VO exhibits a high specific capacity of 249.3 mA h g−1 at 1.0 A g−1 and 69.5 mA h g−1 at 10.0 A g−1, superior to other reported anode material for AAIBs. Noticeably, the prepared resultant quasi-solid-state ammonium ion battery can display considerable cycling stability with capacity retention of 87.9% after a long cycle life of 10 000 cycles at 1 A g−1 and impressive mechanical flexibility with no capacity decay after cycling at different bending angles.

Improved glyceraldehyde generation through FeOOH co-catalysts-modified BiVO4 featuring Bi-O-Fe active sites for photoelectrocatalytic glycerol oxidation

Heterojunction engineering is crucial for converting glycerol into valuable organic compounds via photoelectrochemistry, but controlling the structure precisely to enhance conversion efficiency remains challenging. In this study, we effectively created a compound photoanode with unique active regions by growing amorphous FeOOH co-catalysts on BiVO4. The results revealed that the Fe2+ ions located on the surface of the co-catalyst FeOOH facilitate the glycerol transformation process, whereas the electron-rich Bi-O-Fe sites contribute significantly to the preferential transformation of glycerol into glyceraldehyde. These sites not only serve as primary reactive centers, catalyzing the adsorption and conversion of glycerol hydroxyl clusters, but also act as repositories for trapping holes. This dual function accelerates the breaking of CH bonds to generate glycerol aldehyde and exhibits excellent desorption capacity, ensuring exceptional product selectivity. This led to exceptional glyceraldehyde production (709mmol m-2 h−1) compared to pristine BiVO4, showcasing a 14.98-fold increase.

Assessing the influence of welding-induced mechanics on oxidation and stress corrosion cracking in an Alloy 600-Alloy 152 M weldment under simulated PWR primary water

The impact of welding-induced mechanics on the oxidation and stress corrosion cracking (SCC) behavior of Alloy 600 in a pressurized water reactor (PWR) primary water was investigated using an Alloy 600-Alloy 152 M weldment. The microstructural analysis found a 0.05 mm-wide composition transition zone from welding. The Alloy 600 heat-affected zone (HAZ) grain size matches the Alloy 600 base (600B). Deformation hardening initially decreases and stabilizes from the fusion boundary (FB) to the 600B Comparing the microstructural characteristics of the specimen from the HAZ at about 0.5 mm from the FB with specimen 600B shows identical composition, but the former exhibits higher Vickers hardness (HV), kernel average misorientation (KAM), dislocation density, and residual stresses. Results from both short- and long-term oxidation tests indicate that the specimen from the HAZ exhibits a greater thickness of the inner oxide film, a higher number of local oxidation sites, and an increased maximum depth of intergranular (IG) oxidation compared to the 600B specimen. Multiple sets of SCC test results demonstrate that the crack growth rate (CGR) in the specimens from the HAZ is higher than that in the base, with the former showing longer IG cracks and a greater proportion of IG cracking.

Cyanide Linkage Isomerization Induced by Cobalt Oxidation-State Changes at a Co-Fe Prussian-Blue Analogue/ZnO Interface.

Understanding the interfacial composition in heterostructures is crucial for tailoring heterogenous electrochemical and photoelectrochemical processes. This work aims to elucidate the structure of a series of Co-Fe Prussian blue analogue modified ZnO (PBA/ZnO) electrodes with interface-sensitive vibrational sum frequency generation (VSFG) spectroscopy. Our measurements revealed, for the first time, a cyanide linkage isomerism at the PBA/ZnO interface, when the composite is fabricated at elevated temperatures. In situ VSFG spectro-electrochemistry measurements correlate the CoII➝CoIII oxidation with the flip of the bridging CN ligand from Co-NC-Fe coordination mode to a Co-CN-Fe one. Photoluminescence measurements and X-ray photoelectron spectroscopy reveal that this unprecedented linkage isomerism originates from surface defects, which act as oxidation sites for the PBA. The presence of such surface defects is correlated with the fabrication temperature for PBA/ZnO. Thus, this contribution identifies the interplay between the surface states of the ZnO substrates and the chemical composition of PBA at the ZnO surface, suggesting an easily accessible approach to control the chemical composition of the interface.

Induced Manipulation of Atomically Dispersed Cobalt through S Vacancy for Photocatalytic Water Splitting: Asymmetric Coordination and Dynamic Evolution.

It is still a challenge to construct single-atom level reduction and oxidation sites in single-component photocatalyst by manipulating coordination configuration for photocatalytic water splitting. Herein, the atomically dispersed asymmetric configuration of six-coordinated Co-S2O4 (two exposed S atoms, two OH groups, and two Co─O─Zn bonds) suspending on ZnIn2S4 nanosheets verified by combining experimental analysis with theoretical calculation, is applied into photocatalytic water splitting. The Co-S2O4 site immobilized by Vs acts as oxidation sites to guide electrons transferring to neighboring independent S atom, achieving efficient separation of reduction and oxidation sites. It is worth mentioning that stabilized Co-S2O4 configuration show dynamic structure evolution to highly active Co-S1O4 configuration (one exposed S atom, one OH group, and three Co─O─Zn bonds) in reaction, which lowers energy barrier of transition state for H2O activization. Ultimately, the optimized photocatalyst exhibits excellent photocatalytic activity for water splitting (H2: 80.13 µmol g-1 h-1, O2: 37.81 µmol g-1 h-1) and outstanding stability than that of multicomponent photocatalysts due to dynamic and reversible evolution between stable Co-S2O4 configuration and active Co-S1O4 configuration. This work demonstrates new cognitions on immobilized strategy through vacancy inducing, manipulating coordination configuration, and dynamic evolution mechanism of single-atom level catalytic site in photocatalytic water splitting.

Oxygen vacancy–rich K-Mn3O4@CeO2 catalyst for efficient oxidation degradation of formaldehyde at near room temperature

Synthesis of catalysts with high catalytic degradation activity for formaldehyde (HCHO) at room temperature is highly desirable for indoor air quality control. Herein, a novel K-Mn3O4@CeO2 catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-Mn3O4@CeO2 considerably enhanced the oxidation activity, and importantly, 99.3 % conversion of 10 mL of a 40 mg/L HCHO solution at 30 °C for 14 h was achieved, with simultaneous strong cycling stability. Moreover, the addition of K species considerably influenced the chemical valence state of Mn from +4 (ε-MnO2) to +8/3 (Mn3O4) on the surface of CeO2, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-Mn3O4@CeO2, and the other part exists in the tunnel structure of Mn3O4@CeO2, which is mainly used to balance the negative charge of the tunnel and prevent collapse of the structure, providing enough active sites for the catalytic oxidation of HCHO. We observed a phase transition from tunneled KMnO2 to Mn3O4 to tunneled MnO2 with the decreasing K+ content, in which K-Mn3O4@CeO2 exhibited higher HCHO oxidation activity. In addition, K-Mn3O4@CeO2 exhibited lower oxygen vacancy formation and HCHO adsorption energies in aqueous solution based on density functional theory calculations. This is because the K species provide more active oxygen species and richer oxygen vacancies on the surface of K-Mn3O4@CeO2, promote the mobility of lattice oxygen and the room-temperature reduction properties of oxygen species, and enhance the ability of the catalyst to replenish the consumed oxygen species. Finally, a possible HCHO catalytic oxidation pathway on the surface of K-Mn3O4@CeO2 catalyst is proposed.

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx.

A series of Mn and Fe metal oxide catalysts loaded onto USY, as well as single metal oxides, were prepared and characterized. The effects of interactions between the catalytic components and the introduction of gas phase NO on the catalytic ozonation of toluene were investigated. Characterization showed that there existed strong interactions between MnOx, FeOx, and USY, which enhanced the content of oxygen vacancies and acid sites of the catalysts and thus boosted the generation of reactive oxygen species and the adsorption of toluene. The MnFeOx-USY catalyst with MnOx and FeOx dimetallic oxides exhibited the most excellent performance of catalytic ozonation of toluene. On the other hand, the presence of NOx in reaction gas mixtures significantly promoted both toluene conversion and mineralization, which was attributed to the formation of nitrate species on the catalysts surface and thus the increase of both acid sites and toluene oxidation sites. Meanwhile, the reaction mechanism between O3 and C7H8 was modified in which the strong interactions between MnOx, FeOx, and USY accelerated the reaction progress based on the L-H route. In addition, the formation of the surface nitrate species not only promoted reaction progress following the L-H route but also resulted in the occurrence of the reaction via the E-R route.

Tandem Catalysis for Simultaneous Removal of NOx and C3H8 with Inhibition of N2O.

Tandem catalysis is widely adopted for multipollutant control in mobile sources but has rarely been reported in stationary source emission elimination. This work proposed a tandem arrangement way with up-streamed V2O5/TiO2 + down-streamed Cr2O3/TiO2 catalysts, which could achieve the efficient synergistic control of NOx and C3H8 in industrial flue gas. Moreover, this arrangement successfully alleviated the unwanted N2O formation during the NH3 -SCR process. Compared to the conventional impregnation method of the Cr2O3-V2O5/TiO2 catalyst, the tandem catalysts of V2O5/TiO2 + Cr2O3/TiO2 could enhance the NOx and C3H8 conversion by 4.2% and 39.5%, respectively, at 350 °C. It might be attributed to the fact that Cr species was the active site for C3H8 oxidation, and the tandem arrangement of catalysts was beneficial to even dispersion of active components on supports. Furthermore, due to the preferential NOx removal over the up-streamed V2O5/TiO2 catalyst, the tandem catalysts obviously alleviated the N2O formation caused by Cr species during the NH3-SCR process. Herein, it significantly decreased N2O formation by 240.5% at 350 °C compared to the Cr2O3-V2O5/TiO2 catalyst, achieving multipollutant emission control from industrial flue gas with the performance of "one stone three birds".

Phosphorous-doped nickel-cobalt bimetallic molybdate/three-dimensional hierarchical porous carbon for high-efficiency solid-state supercapacitors

The limited electrical conductivity and insufficient quantity of electrochemically active sites in transition-metal oxides impede their extensive utilization in high-performance supercapacitors. Herein, we present a successful synthesis of phosphorus-doped NixCo1-xMoO4 (P-NCMO) on three-dimensional hierarchical porous carbon (HPC) derived from enzymatically hydrolyzed lignin through a co-precipitation pathway and subsequent phosphorylation process. The electrochemical performance was improved by optimizing the content of P doping. Additionally, the incorporation of phosphorus into P-NCMO led to a decrease in Co-O bonding energy and facilitated the formation of molybdenum species with lower oxidation states, thereby enhancing surface redox chemistry and improving electrochemical performance. As a result, the optimized HPC/P-NCMO-2 electrode exhibits a high specific capacity of 1003 C g−1 at a current density of 1 A g−1, and it maintains 89.87 % of its initial capacity after 10,000 cycles at a current density of 1 A g−1. The optimized HPC/P-NCMO-2 assembled as the positive electrode and activated carbon as the negative electrode in an asymmetric supercapacitor delivers a high energy density of 94.7 Wh kg−1 at a power density of 800 W kg−1, while maintaining excellent cycle life.

Nitrogen doping in carbon xerogels via ammonia pyrolysis: A case study

Nitrogen-doped carbon xerogels (CXNs) were carbonized across a range of temperatures (400 °C–800 °C) using sol-gel derived resorcinol-formaldehyde xerogel to elucidate their structural evolution during carbonization in ammonia. The investigation extensively probed chemical and structural changes in CXNs at varying carbonization temperatures, employing analytical methods such as X-ray photoelectron spectroscopy, infrared spectroscopy, and energy-dispersive X-ray spectroscopy. These findings were thoroughly compared with the local structure derived from total X-ray scattering and Raman spectroscopy. The results showed a transformation in the local ordering and chemical structure of CXNs, characterized by a reduction in oxidation sites, expansion of C sp2 network structures, leading to the growth of aromatic domains, and the incorporation of nitrogen into the carbon backbone structure. Pyrolysis in ammonia notably influenced the textural structure, resulting in a partial loss of mesopores and an increased micropore volume.

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

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

Coke evolution study in a liquid atomization into gas-solid fluidized bed to convert fructose to value-added chemicals

Glucose and fructose are valuable compounds, which have the potential to displace fossil fuels as a feedstock for highly valued products. One of the promising reactions is the oxi-dehydration of fructose to produce Hydroxymethylfurfural, 2,5-diformylfuran, and furfural. Current processes to produce platform chemicals like Hydroxymethylfurfural, furfural, and 2,5-diformylfuran operate in liquid phase with homogeneous heterogeneous catalyst, but commercialization is limited by scale and environmental impact of the large volume solvent required. Here we developed a gas-phase process to convert fructose in a fluidized bed reactor over Mo − V − WO3/TiO2. However, in the catalytic oxi-dehydration of fructose, coke forms on active sites and decreases conversion but increases selectivity. Coke and reactor performance depends on fructose concentration and O2/fructose ratio. In the first 2 h, acidic amorphous coke accumulates (based on TPO, FTIR, and UV–vis). Feeding excess O2 maintains coke in an amorphous structure and liberates oxide sites. Whereas coke promotes, water block active site reducing yield. In this work, we optimized the operating parameters of fructose concentration (%) and O2/fructose ratio, while simultaneously mitigating the issues associated with coke formation and its detrimental effects.

Elucidating Pathways of Methanol Oxidation on Oxygen-Vacant NiOOH Sites Using a Synergistic in Situ Attenuated Total Reflectance Surface-Enhanced Infrared Absorption Spectroscopy and DFT Study

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for electrocatalysis design and development of Ni-based alloys. However, the mechanism of MOR on these materials remains a matter of controversy. There have been few publications on employing surface enhanced spectroscopy to adequately capture the surface chemistry of MOR on NiOOH while the existing theoretical chemistry studies on the reaction mechanism presents a multitude of inconsistent and incomplete results. Here, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) to determine the mechanism and product distribution of MOR on monometallic Ni-based catalysts in alkaline media. Critically, the DFT calculations include the role of O-vacancy of NiOOH, which is argued to be the active site for methanol oxidation. The SEIRAS results show that two bands corresponding to nas(O=C–O) of HCOO- and nas(C–O) of HCO3 -/CO3 2- appears after the commencement of MOR and varies as a function of potentials. These spectroscopic results are in good agreement with the DFT-based energetics of reaction, suggesting that the MOR mainly proceeds in the following pathway: The early consumption of methanol yields HCOO- as the major product while increasing potentials stimulate further oxidation of adsorbed HCOO* to form HCO3 -/CO3 2-. On the other hand, we show a parallel pathway for the generation of HCO3 -/CO3 2- at high potentials that bypasses the formation of HCOO*. The two main pathways presented in this study are thermodynamically more feasible than the one predominantly reported in literature for MOR on NiOOH. The two former pathways circumvent CHO and/or CO to produce HCO3 -/CO3 2-, whereas the latter involves these species as intermediates. These DFT-based hypotheses are backed up by the spectroscopic evidence that no band associated with CHO and CO can be detected by SEIRAS. This study has the potential to offer invaluable atomic-level insights into MOR on NiOOH as a stepping stone to development of high-performance multi-metallic Ni-based catalysts. Figure 1

Engineering d-p Orbital Hybridization in Mo-O Species of Medium-Entropy Metal Oxides as Highly Active and Stable Electrocatalysts toward Ampere-Level Water/Seawater Splitting.

Optimizing the electronic structure of electrocatalysts is of particular importance to enhance the intrinsic activity of active sites in water/seawater. Herein, a series of medium-entropy metal oxides of X(NiMo)O2/NF (X = Mn, Fe, Co, Cu and Zn) is designed via a rapid carbothermal shocking method. Among them, the optimized medium-entropy metal oxide (FeNiMo)O2/NF delivered remarkable HER performance, where the overpotentials as low as 110 and 141mV are realized at 1000 mAcm-2 (@60°C) in water and seawater. Meanwhile, medium-entropy metal oxide (FeNiMo)O2/NF only required overpotentials of as low as 330 and 380mV to drive 1000mAcm-2 for OER in water and seawater (@60°C). Theoretical calculations showed that the multiple-metal synergistic effect in medium-entropy metal oxides can effectively enhance the d-p orbital hybridization of Mo─O bond, reduce the energy barrier of H* adsorbed at the Mo sites. Meanwhile, Fe sites in medium-entropy metal oxide can act as the real OER active center, resulting in a good bifunctional activity. In all, this work provides a feasible strategy for the development of highly active and stable medium-entropy metal oxide electrocatalysts for ampere-level water/seawater splitting.

Solar H2O2 production with carbon dots and nickel co-modified titania nanotube photocatalyst stabilized at water/benzyl alcohol interface

An interfacial reaction system with the advantage of in situ H2O2 production and separation has been developed, in which titania nanotube (TNT) photocatalyst modified by nickel species and carbon dots (CDs) can self-stabilize at interface of water/benzyl alcohol. Under visible light irradiation, the CDs/Ni-TNT yields H2O2 with an initial rate of 385.6 μmol/g/h. The improved activity could be attributed to multiple effects such as sufficient oxygen adsorption and mass transfer, separated reduction and oxidation sites at different phases, and rapid diffusion of H2O2 from the interfacial region into bulk aqueous solution.

Effect of combinations of 3,4‐dihydroxyphenylacetic acid and its esters on the oxidative stability of fish oil–containing trace water

AbstractThe current study aims to comprehend the effect of the various combinations of 3,4‐dihydroxyphenylacetic acid (3,4‐DHPA) and its esters in varying molar ratios on retarding oxidation in bulk refined fish oil in the presence of 0.3% w/w water. All the esters and 3,4‐DHPA exhibited better performance than the synthetic antioxidant butylated hydroxytoluene. In the presence of trace water, the parent compound was found to have a synergistic effect with hexyl ester when used at a molar ratio of 2:1, respectively, exhibiting a higher percent reduction among all the esters and their combinations. The study also showed that the presence of extraneous water can significantly accelerate the oxidation (twofold) in a bulk fish oil system. This suggests that the microenvironment of the oil is altered when water is present and that association colloids play a key role in enhancing the rate of oxidation. Thus, while designing a competent mixture of antioxidants, the specific site of oxidation involved and the surface‐active components should be taken into consideration to efficiently retard oxidation.Practical Applications: Analyzing the impact of trace amounts of water on the efficiency of natural antioxidants, including 3,4‐DHPA and its lipophilic esters, helps to comprehend the required optimal antioxidant concentrations for such a dynamic bulk oil system. The study finds application in controlling oxidation in PUFA‐rich oils containing surface‐active minor components that can accelerate oxidation. The results of the study show that 3,4‐DHPA and its esters could be a potential replacement for the synthetic antioxidant BHT in all aspects.

A rational construction of FexOy-N-ZSM-5 catalyst with graphene structures and FeNx sites for the selective catalytic oxidation of triethylamine

Stabilizing metal species at the atomic level and tuning their catalytic properties is a significant challenge. Herein, an N-doped FexOy-N-ZSM-5 catalyst with layered and chain-like graphene structures is reported. The catalyst can selectively catalyze the oxidation of triethylamine (TEA) with an efficiency of 99.7 % at 240 °C, and maintain an N2 yield of 97.6 % over the reaction temperature range of 240–360 °C. The results indicate that the layered graphene in the catalyst provide anchor sites for active Fe, while the abundant chain-like graphene act as connectors between ZSM-5 and the layered graphene, offering ample opportunities for TEA and its intermediates to contact the catalyst surface. This increases the number of active sites on the catalyst, thereby enhancing the catalytic performance of FexOy-N-ZSM-5. Notably, due to the interaction between FeOx and FeNx species, FexOy-N-ZSM-5 exhibits excellent thermal stability and water resistance, demonstrating promising potential for practical.

Plasma-catalytic direct oxidation of methane to methanol over Cu-MOR: Revealing the zeolite-confined Cu2+ active sites

Efficient methane conversion to methanol remains a significant challenge in chemical industry. This study investigates the direct oxidation of methane to methanol under mild conditions, employing a synergy of non-thermal plasma and Cu-MOR (Copper-Mordenite) catalysts. Catalytic tests demonstrate that the Cu-MOR IE-3 catalyst (i.e., prepared by three cycles of ion exchange) exhibits superior catalytic performance (with 51 % methanol selectivity and 7.9 % methane conversion). Conversely, the Cu-MOR catalysts prepared via wetness impregnation tend to over-oxidize CH4 to CO and CO2. Through systematic catalyst characterizations (XRD, TPR, UV–Vis, HRTEM, XPS), we elucidate that ion exchange mainly leads to the formation of zeolite-confined Cu2+ species, while wetness impregnation predominantly results in CuO particles. Based on the catalytic performance, catalyst characterizations and in-situ FTIR spectra, we conclude that zeolite-confined Cu2+ species serve as the active sites for plasma-catalytic direct oxidation of methane to methanol.