Reaction Mechanism Of Oxidation Research Articles

Catalytic Performance and Reaction Mechanisms of Ethyl Acetate Oxidation over the Au–Pd/TiO2 Catalysts

The development of efficient and stable catalysts is of great importance for the elimination of volatile organic pollutants (VOCs). In this work, AuPdx nanoparticles (NPs) were loaded on TiO2 through the electrostatic adsorption approach to generate the yAuPdx/TiO2 (i.e., 0.35AuPd0.46/TiO2, 0.34AuPd2.09/TiO2, and 0.37AuPd2.72/TiO2; x and y are Pd/Au molar ratio and AuPdx loading, respectively; x = 0.46–2.72; and y = 0.34–0.37 wt%) catalysts, and their catalytic activities for the oxidation of ethyl acetate were determined. The results showed that the 0.37AuPd2.72/TiO2 sample exhibited the best activity (T50% = 217 °C and T90% = 239 °C at SV = 40,000 mL/(g h), Ea = 37 kJ/mol, specific reaction rate at 220 °C = 113.8 µmol/(gPd s), and turnover frequency (TOFNoble metal) at 220 °C = 109.7 × 10−3 s−1). The high catalytic performance of the 0.37AuPd2.72/TiO2 sample was attributed to the good dispersion of AuPd2.72 NPs, the strong redox ability, the large ethyl acetate adsorption capacity, and the strong interaction between AuPdx and TiO2. Acetaldehyde, ethanol, and acetic acid are the main intermediates in the oxidation of ethyl acetate, and the loading of AuPdx NPs effectively reduces the formation of the toxic by-product acetaldehyde. The oxidation of ethyl acetate over the 0.34AuPd2.09/TiO2 sample might occur via the pathway of ethyl acetate → ethanol → acetic acid → acetate → CO2 and H2O. We believe that the obtained results may provide a useful idea for the design of bimetallic catalysts under industrial conditions and for understanding the VOCs oxidation mechanisms.

Methane Oxidation over the Zeolites-Based Catalysts

Zeolites have ordered pore structures, good spatial constraints, and superior hydrothermal stability. In addition, the active metal elements inside and outside the zeolite framework provide the porous material with adjustable acid–base property and good redox performance. Thus, zeolites-based catalysts are more and more widely used in chemical industries. Combining the advantages of zeolites and active metal components, the zeolites-based materials are used to catalyze the oxidation of methane to produce various products, such as carbon dioxide, methanol, formaldehyde, formic acid, acetic acid, and etc. This multifunction, high selectivity, and good activity are the key factors that enable the zeolites-based catalysts to be used for methane activation and conversion. In this review article, we briefly introduce and discuss the effect of zeolite materials on the activation of C–H bonds in methane and the reaction mechanisms of complete methane oxidation and selective methane oxidation. Pd/zeolite is used for the complete oxidation of methane to carbon dioxide and water, and Fe- and Cu-zeolite catalysts are used for the partial oxidation of methane to methanol, formaldehyde, formic acid, and etc. The prospects and challenges of zeolite-based catalysts in the future research work and practical applications are also envisioned. We hope that the outcome of this review can stimulate more researchers to develop more effective zeolite-based catalysts for the complete or selective oxidation of methane.

A study of the oxidation mechanism of the organic pigment indigo in grottoes murals by ozone under dark conditions

In this paper, the organic pigments indigo and isatin were detected by high performance liquid chromatography (HPLC) in The Mural of Four Buddhas which is in Cave 3 from the ancient Chinese Tiantishan grottoes (Ming Dynasty, East Slope). By analysing the preservation conditions of the mural and the environmental conditions of the place where the Tiantishan grottoes are located, we speculated that the isatin detected in this mural was mainly produced by the oxidative decomposition of indigo by ozone (O3), rather than by photodegradation of indigo. We have used theoretical calculation software Gaussian09 (G09) and Amsterdam Density Functional (ADF) module in the Amsterdam Modeling Suite (AMS) software to simulate the reaction mechanism of O3 oxidation of indigo, and the end products of the oxidation of the natural plant dye indigo by O3 were identified as isatin, C16H10N2O3 and C8H6NO3 using HPLC, fluorescence spectroscopy and high performance liquid chromatography-mass spectrometry(HPLC–MS). This finding confirmed the accuracy of the mechanism of indigo fading by O3 oxidation. These findings provided a theoretical basis for subsequent research into the derivation of natural organic dyes in the face of increasing O3 pollution and for better protection of valuable historical and cultural heritage such as ancient Chinese grottoes murals.

Voltammetric determination of arbutin using carbon paste electrode modified with low crystalline home-prepared rutile TiO2 nanoparticles

Carbon paste electrodes (CPE) were modified with commercial (Degussa P25, BDH, Merck, Hombikat) and home-prepared rutile TiO2 (HPRT) nanoparticles for the electrochemical determination of arbutin (AR) by differential pulse voltammetry technique. The optimization experiments were performed in Britton-Robinson buffer at pH 2–7 using modified CPEs. 15%-HPRT(25 °C)/CPE and 15%-HPRT(400 °C)/CPE showed the highest current values among all electrodes at optimum pH, accumulation potential, and duration time values (pH 2, 0.70V and 45 s); consequently, the electrodes were characterized by SEM-EDX, while TiO2 samples by BET and XRD techniques. Electrochemical surface areas of the electrodes were also determined. HPRT(25 °C) and HPRT(400 °C) samples have the lowest crystallinity which is the reason for their high performance. The linear working range of 15%-HPRT(25 °C)/CPE and 15%-HPRT(400 °C)/CPE electrodes was 0.5–120 μM. The detection limit for these electrodes was 32 and 40 nM, and the quantification limit was 107 and 135 nM, respectively. Interference studies, repeatability, reproducibility and the stability of the electrodes were examined, and a reaction mechanism for AR oxidation was proposed and promising results were obtained. The AR determination in a real sample, in the anti-blemish skin serum, was also performed successfully.

Theoretical investigation on oxygen source for selective oxidation of glycerol at Au/CeO2−x and Pt/CeO2−x interfaces

Glycerol is considered as a significant green platform chemical, and many efforts have been devoted to design and prepare the efficient catalysts to convert glycerol to glyceric acid; however, the active site as well as reaction mechanism of glycerol oxidation remains rather ambiguous in terms of different oxygen sources. Herein, we studied the oxidation reaction of glycerol to glyceric acid over the catalytic systems of Au/CeO2−x and Pt/CeO2−x on periodic density functional theory (DFT) calculation in detail. By the optimization of catalyst structure models and comparison of substrate adsorption configurations, the interfacial sites of supported catalysts (Au/CeO2−x and Pt/CeO2−x) are regarded as the intrinsic active sites. Potential energy curve confirms that the reaction mechanism of glycerol oxidation includes two main pathways: OH− and O2 as oxygen sources in base and base-free environment, respectively. Mechanism studies indicate that Au/CeO2−x interface facilitates the dehydrogenation of C−H/O−H bond, which further promotes the formation of glyceraldehyde. Moreover, Pt/CeO2−x is favorable for the transfer of intramolecular H, resulting in excellent catalytic performance for the oxidation of glyceraldehyde to glyceric acid. The O2− was involved in oxidative dehydrogenation as active oxygen in base-free condition, and Pt/CeO2−x was more favorable for base-free glycerol oxidation. This work offers detailed insights into interfacial synergy effects of supported catalytic systems and the reaction mechanism of glycerol oxidation, which will pave the way for the selection of solvent conditions toward selective oxidation reaction.

Pt–Co bimetals supported on UiO-66 as efficient and stable catalysts for the catalytic oxidation of various volatile organic compounds

Bimetallic catalysts exhibit excellent synergistic catalytic performance for volatile organic compounds (VOCs) oxidation. However, it remains challenging to design more active, selective, and stable bimetallic catalytic systems for the practical oxidation of various VOCs. Here, by integrating porous metal-organic frameworks as support, platinum as catalytic center, and cobalt as promoter, we obtained a synergistic and stable Pt–Co/UiO-66 catalytic system, with highly dispersed active sites for various VOCs oxidation. Pt–Co/UiO-66 exhibited better catalytic performances than monometallic constituents in toluene, n-hexane, and ethyl acetate oxidation. Besides, Pt–Co/UiO-66 showed high reusability, water or CO2 resistance, long-term activity over 120 h, and structural stability. Furthermore, the reaction pathway and mechanism of toluene oxidation were investigated by in-situ diffuse reflectance infrared Fourier transform spectroscopy and online gas chromatography-mass spectrometer. We believe that this work will provide a useful idea for developing effective bimetallic catalysts in environmental catalysis.

Approaching Molecular Definition on Oxide-Supported Single-Atom Catalysts.

ConspectusSingle-atom catalysts (SACs) offer unique advantages such as high (noble) metal utilization through maximum possible dispersion, large metal-support contact areas, and oxidation states usually unattainable in classic nanoparticle catalysis. In addition, SACs can serve as models for determining active sites, a simultaneously desired as well as elusive target in the field of heterogeneous catalysis. Due to the complexity of heterogeneous catalysts bearing a variety of different sites on metal particles and the respective support as well as at their interface, studies of intrinsic activities and selectivities remain largely inconclusive. While SACs could close this gap, many supported SACs remain intrinsically ill-defined due to complexities arising from the variety of different adsorption sites for atomically dispersed metals, hampering the establishment of meaningful structure-activity correlations. In addition to overcoming this limitation, well-defined SACs could even be utilized to shed light on fundamental phenomena in catalysis that remain ambiguous when studies are obscured by the complexity of heterogeneous catalysts.In this Account, we describe approaches to break down the complexity of supported single-atom catalysts through the careful choice of oxide supports with specific binding motives as well as the adsorption of well-defined ligands such as ionic liquids on single metal sites. An example of molecularly defined oxide supports is polyoxometalates (POMs), which are metal oxo clusters with precisely known composition and structure. POMs exhibit a limited number of sites to anchor atomically dispersed metals such as Pt, Pd, and Rh. Polyoxometalate-supported single-atom catalysts (POM-SACs) thus represent ideal systems for the in situ spectroscopic study of single atom sites during reactions as, in principle, all sites are identical and thus equally active in catalytic reactions. We have utilized this benefit in studies of the mechanism of CO and alcohol oxidation reactions as well as the hydro(deoxy)genation of various biomass-derived compounds. More so, the redox properties of polyoxometalates can be finely tuned by changing the composition of the support while keeping the geometry of the single-atom active site largely constant. We further developed soluble analogues of heterogeneous POM-SACs, opening the door to advanced liquid-phase nuclear magnetic resonance (NMR) and UV-vis techniques but, in particular, to electrospray ionization mass spectrometry (ESI-MS) which proves powerful in determining catalytic intermediates as well as their gas-phase reactivity. Employing this technique, we were able to resolve some of the long-standing questions about hydrogen spillover, demonstrating the broad utility of studies on defined model catalysts.

Insights into the reaction mechanism of toluene oxidation by isotope dynamic experiment and the kinetics over MCeZr/TiO2 (M = Cu, Mn, Ni, Co and Fe) catalysts

Catalytic properties of multiple metals deposited on TiO2 nanoparticles were investigated in the oxidation of toluene. Isovolume impregnation method prepared the catalysts containing Cu, Mn, Ni, Co, and Fe deposited on TiO2, including CeO2 and ZrO2. The effects of loaded metal oxides on the structure and activity of initial catalysts were investigated using various characterization techniques. Toluene's removal efficiency and CO2 selectivity in the catalyst system were classified as follows: CuCeZr/T > MnCeZr/T > NiCeZr/T > CoCeZr/T > FeCeZr/T. Presence of water vapor exhibits an inhibitory effect on the conversion of toluene, which diminishes at higher temperatures. One contribution of this paper is to obtain the oxidation pathway of toluene and the relationship between the activation energy of all-inclusive and elementary reactions based on the variation of infrared spectrum using Freeman-Carroll method. Another contribution is to clarify the share of Langmuir-Hinshelwood and Mars-van Krevelen mechanisms during the oxidation of toluene over CuCeZr/T catalyst by transient response experiments of isotopically labeled oxygen. These findings provide a feasible method for the design and synthesis of transition metal oxide catalysts for industrial applications.

High-efficiency palladium/halloysite nanotubes catalyst for toluene catalytic oxidation: Characterization, performance and reaction mechanism

In this study, the halloysite treated with nitric acid was designed as a functionalized support material for favoring surface availability and dispersion of nanometric palladium (Pd) nanoparticles. The prepared supported catalysts were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed desorption (O2-TPD). The catalytic performance and reaction mechanism of toluene oxidation were evaluated and proposed. Scanning and transmission electron microscopy images showed that 4–5 nm diameter Pd nanoparticles were uniformly dispersed on the external and edge surfaces of the A-Hal nanotubes and no obvious aggregations observed. The Pd nanoparticles were mainly present in the zero-valent state. The ratio of metallic Pd to Pd oxide species and adsorbed (Oads) to lattice (Olatt) presented a maximum value of 2.54 and 23.0, respectively, when the Pd loading was 0.5%. The prepared support catalysts exhibited a satisfactory catalytic performance and cycling stability for toluene conversion. Among the analyzed samples, the 0.5% Pd/A-Hal catalyst exhibited the highest catalytic activity for toluene oxidation, stability, and water resistance. Toluene conversions of 50% and 90% were obtained at 167 and 185 °C, respectively. In situ diffuse reflection Fourier transform spectroscopy measurements confirmed the intermediates generated during toluene oxidation and revealed that toluene oxidation occurred via the benzyl alcohol → benzaldehyde → benzoic acid → maleic anhydride reaction pathway over the obtained catalysts. These results were attributed to the high content of metal Pd species, abundant Oads species, and low-temperature reducibility. These results indicate that Hal support catalysts are promising materials for application in environmental protection.

Constructing dimensionally stable TiO2 nanotube arrays/SnO2/RuO2 anode via successive electrodeposition for efficient electrocatalytic oxidation of As(III)

Arsenic-containing water needs to be purified to reduce the global hazards of arsenic to human health and ecosystems. Herein, successive electrodeposition of SnO2 and RuO2 nanoparticles on the TiO2 nanotube arrays (TNTAs) was performed to synthesize dimensionally stable TNTAs/SnO2/RuO2 anodes for highly efficient electrocatalytic oxidation of As(III) in aqueous solution. Such a TNTAs/SnO2/RuO2 anode possessed fast charge transfer, higher oxygen evolution potential (OEP), larger electrocatalytic active area, and excellent stability, and delivered effectively electrocatalytic oxidation As(III), of which 10 mg/L of As(III) was completely oxidized into As(Ⅴ) with lower toxicity within 20 min owing to the synergistic effect of RuO2 and SnO2. Impressively, the optimized TNTAs/SnO2/RuO2-10 anode presented an excellent electrochemical stability and longer service lifetime, and its oxidation conversion efficiency of As(III) still could be maintained to be 98% as well as its kinetic reaction constant decreased by only 0.03 even after 11 recycled usage, which was ascribed to the intensified interaction between RuO2 and TNTAs/SnO2. The excellence of the innovative anode was also evidenced through its strong anti-interference ability to coexisting ions and the elucidation of the associated oxidation reaction mechanism of As(III) on the surface of the anode by electron spin resonance and radical scavenger tests. This novel electrode integrates high electrocatalytic activity, high electron transport and high stability, ensures the long-term stable use of the electrode, while realizes efficient and rapid electrocatalytic oxidation of As(III) in aquatic environments. This work provides new ideas for further improving the catalytic performance and stability of dimensionally-stable anode materials.

Numerical analysis of ammonia HCCI combustion in a free piston engine through trajectory-based combustion control

Ammonia is a promising carbon–neutral fuel, able to power heavy-duty vehicles, non-road machineries and ocean ships with zero CO2 emission. However, practical challenges still exist when applying ammonia in traditional internal combustion engines (ICEs) due to its high ignition energy, slow flame propagation and significant NOx emissions. Free piston engine (FPE) is a flexible alternative to ICE whose piston can move freely without the constraints of crankshaft. Therefore, its piston trajectory can be leveraged as a new control means to facilitate ammonia combustion. In this paper, a numerical analysis investigating ammonia HCCI combustion in FPE was presented. A physical-based model was developed at first, including a unique trajectory synthesizing mechanism and a detailed reaction mechanism of ammonia oxidation. Various asymmetric piston trajectories were then employed into the model and the simulated HCCI combustion were analyzed through six characteristics, namely indicated thermal efficiency, location of peak pressure, exhaust gas temperature, combustion duration, ignition delay, and NOx emissions. This investigation not only determines the best compression ratio (CR = 25) for ammonia ignition, but also shape the optimal piston trajectory (symmetric trajectory with Ω = 0.5) for ammonia HCCI combustion to enhance thermal efficiency and reduce NOx emission simultaneously.

Multi-scale structure characterization of ozone oxidized waxy rice starch

The elucidation of multi-scale structural variation and oxidation reaction mechanism of ozone oxidized waxy rice starch molecules remains a big challenge, limiting its development of intensive processing. In the present work, the changes in the structure of waxy rice starch after ozone treatment were systematically researched by various characterization methods. The study has shown that with the increase in ozone oxidation time, the granules of oxidized starch were polygons with multiple face depressions. It was also observed that ozone first attacked the amorphous zone of the starch granules and then penetrated the crystalline zone. Combining 1D and 2D NMR (1H NMR, 13C NMR, HSQC and HMBC) and other methods, it was proved that ozone oxidation led to ring splitting between C2 and C3 of the glucose unit. The resulting hemiacetal groups showed different types of structures. Among them, the main structures were intramolecular acetals and intermolecular hemiacetals. This research offered theoretical guidance for the utilization of ozone oxidation technology for starch modification and the development of waxy rice new foods.

Electrocatalytic oxidation of 5‐hydroxymethylfurfural for sustainable 2,5‐furandicarboxylic acid production—From mechanism to catalysts design

AbstractCatalytic conversion of biomass‐based platform chemicals is one of the significant approaches to utilize renewable biomass resources. 2,5‐Furandicarboxylic acid (FDCA), obtained by an electrocatalytic oxidation of 5‐hydroxymethylfurfural (HMF), has attracted extensive attention due to the potential of replacing terephthalic acid to synthesize high‐performance polymeric materials for commercialization. In the present work, the pH‐dependent reaction pathways and factors influencing the degree of functional group oxidation are first discussed. Then the reaction mechanism of HMF oxidation is further elucidated using the representative examples. In addition, the emerging catalyst design strategies (defects, interface engineering) used in HMF oxidation are generalized, and structure–activity relationships between the abovementioned strategies and catalysts performance are analyzed. Furthermore, cathode pairing reactions, such as hydrogen evolution reaction, CO2 reduction reaction (CO2RR), oxygen reduction reaction, and thermodynamically favorable organic reactions to lower the cell voltage of the electrolysis system, are discussed. Finally, the challenges and prospects of the electrochemical oxidation of HMF for FDCA are presented, focusing on deeply investigated reaction mechanism, coupling reaction, reactor design, and downstream product separation/purification.

Constructing a high concentration CuO/CeO2 interface for complete oxidation of toluene: The fantastic application of spatial confinement strategy

In this paper, CeO2 substrate was prepared by the sol-gel method, further CuO was introduced by adding the copper complexes with chelating agents into the sol-gel precursors of CeO2, in which different chelating agents (β-cyclodextrin, glucose and trimesic acid) were tried. This synthesis method helps the CuO species to disperse very uniformly in the CeO2 substrates. When the amount of copper oxide is up to 33 mol%, the CuO/CeO2 samples can still maintain a highly dispersed state. The CeO2 and CuO/CeO2 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programed desorption (O2-TPD), etc. It is found that the CuO/CeO2 catalyst prepared by β-cyclodextrin (βCuO/CeO2) exhibits better catalytic performance owing to the higher dispersion, higher specific surface area, more defects, more active Ce3+ and Cu+ ions, more oxygen vacancies, more surface active oxygen, relatively better low temperature reducibility, and the exposed (110) active facets. In the condition of 1000 × 10−6 toluene in air and WHSV = 60000 mL/(g·h), the T90 for toluene conversion is 227 °C. The reaction mechanism of toluene catalytic oxidation over CeO2 and βCuO/CeO2 is discussed by the study of in-situ DRIFTs. This work affords a simple and efficient method for the synthesis of highly dispersed bimetal oxide catalysts with high contents.

Lattice engineering of AuPd@Pt core–shell icosahedra for highly efficient electrocatalytic ethanol oxidation

Lattice engineering of AuPd@Pt core–shell icosahedra for the exploration of the mechanism of the ethanol oxidation reaction.

The Malaprade reaction mechanism for ethylene glycol oxidation by periodic acid based on density functional theory (DFT).

A general mechanism of the Malaprade oxidative carbon-carbon bond cleavage reaction of α-glycol in the presence of periodic acid has been proposed on the basis of density functional theory (DFT) computations. Ethylene glycol and periodic acid, both in their neutral forms, have been studied as noble substrate representatives in model reactions. The proposed reaction mechanism has been constructed based on and compared with previously published experimental kinetic, spectroscopic and temperature and pH-dependent studies. In the presented theoretical mechanistic considerations, four alternative molecular transformations have been analyzed from thermodynamic and kinetic points of view. Theoretically, the predicted activation energy barriers have been compared with experimental ones published elsewhere. The presented minimum energy pathway (MEP) unveiled the shape and conformation of the intermediate and transition state structures. The three-step reaction process involves the formation of a seven-membered quasi-ring assisted by an intramolecular hydrogen-bond intermediate structure forming one I-O bond (IC1_B), a cyclic ester intermediate forming two I-O bonds (IC2_C) and the final products formed at the two very last stages (HIO3, water and two formaldehyde molecules). The computed and energetically the most favourable reaction landscape proposed in this work uniforms and refines the mechanistic proposition given by Criegee for Malaprade type of reactions and further gives a detailed molecular understanding of the reaction rate and atomic connections en route the transformation. The molecular geometries of all stationary points (intermediate and transition state structures) lying on the potential energy hypersurface have been optimized at the four alternative DFT levels under the solvation model based on the density approximation: B3PW91, CAM-B3LYP, BMK, ωB97XD. The 6-311+G(2d,p) basis set for C, O, and H atoms and both the full (DGDZVP) and Ahlrichs-Weigend1 (def2-TZVP) basis sets for iodine atoms were used during the computations.

Electrochemistry of ethanol and dimethyl ether at a Pt electrode in a protic ionic liquid: the electrode poisoning mechanism.

A protic ionic liquid (PIL), N,N-diethyl-N-methyl ammonium trifluoromethane sulfonate, [dema][TfO] was synthesized and confirmed using 1H-NMR and ion chromatography (IC). The surface electrocatalysis of ethanol (EtOH) and dimethyl ether (DME) was investigated on a polycrystalline Pt electrode in a PIL using a cyclic voltammetry technique. The voltammetry response shows that surface Pt-oxides/hydroxides (PtOH/PtO) are formed due to the oxidation of trace water (240 ppm determined by coulometric Karl-Fischer (FT) titration) in [dema][TfO] which plays a pivotal role during the electrocatalytic oxidation of EtOH and DME in the PIL. Oxidation of EtOH and DME coincides with coverage of the Pt surface by the adsorbed oxide species that helps to activate both processes by oxidizing the adsorbed poisoning CO and CO-like intermediate species via a 'bifunctional' reaction mechanism. The influence of temperature was investigated to obtain quantitative and qualitative information on the kinetics of EtOH oxidation. Higher activation energies are measured for EtOH oxidation in [dema][TfO] than in aqueous electrolytes due to the low water content and high viscosity of the PIL. This study gave a basic insight into the mechanism of EtOH and DME oxidation reactions, and the Pt-electrode poisoning species formation mechanism in the neoteric electrolyte medium is electrochemically investigated and reported.

Insight into the Effect of Oxygen Vacancy Prepared by Different Methods on CuO/Anatase Catalyst for CO Catalytic Oxidation

In this study, CuO loaded on anatase TiO2 catalysts (CuO/anatase) with oxygen vacancies was synthesized via reduction treatments by NaHB4 and H2 (CuO/anatase-B, CuO/anatase-H), respectively. The characterizations suggest that different reduction treatments bring different concentration of oxygen vacancies in the CuO/anatase catalysts, which finally affect the CO catalytic performance. The CuO/anatase-B and CuO/anatase-H exhibit CO conversion of 90% at 182 and 198 °C, respectively, which is lower than what occurred for CuO/anatase (300 °C). The XRD, Raman, and EPR results show that the amount of the oxygen vacancies of the CuO/anatase-H is the largest, indicating a stronger reduction effect of H2 than NaHB4 on the anatase surface. The in situ DRIFTS results exhibit that the Cu sites are the adsorption sites of CO, and the oxygen vacancies on the anatase can active the O2 molecules into reactive oxygen species. According to the in situ DRIFTS results, it can be concluded that in the CO oxidation reaction, only the CuO/anatase-H catalyst can be carried out by the Mvk mechanism, which greatly improves its catalytic efficiency. This study explained the reaction mechanisms of CO oxidation on various anatase surfaces, which offers detailed insights into how to prepare suitable catalysts for low-temperature oxidation reactions.

Boosting the Electrocatalytic Urea Oxidation Performance by Amorphous–Crystalline Ni-TPA@NiSe Heterostructures and Mechanism Discovery

Developing cost-effective electrocatalysts and elucidating the in situ catalytic mechanism of the urea oxidation reaction (UOR) is a cornerstone for developing urea-based technology. Amorphous–crystalline (A–C) heterostructures have attracted extensive attention owing to their highly exposed active sites and superior stability. However, the complicated synthesis approach and inefficient A–C boundary severely limit their industrial application in UOR electrolysis. In this study, a simple hydrothermal method was reported to fabricate novel heterostructure nanoarrays comprising NiSe nanorods evenly integrated with nickel-terephthalic acid (Ni-TPA) nanosheets. In the A–C heterostructure electrocatalyst, highly conductive NiSe nanorods facilitate axial charge transfer in the interconnection network. TPA-induced formation of crystalline–amorphous heterostructures exposes more active sites and regulates the electronic structure of Ni. As expected, the optimal Ni-TPA@NiSe/NF electrode presents a low potential of 1.37 V to deliver 100 mA cm–2 for UOR while maintaining impressively robust stability at high current densities for at least 40 h. In situ electrochemical Raman spectroscopy and differential electrochemical mass spectrometry analyses reveal that the superior UOR activity originates from NiOOH species and the terminal product of nitrogen is generated via intramolecular N–N coupling in the urea molecule. More importantly, this study offers deep insights into designing and fabricating effective UOR electrocatalysts with abundant A–C grain boundaries.

Theoretical Study of the Atmospheric Chemistry of Methane Sulfonamide Initiated by OH Radicals and the CH3S(O)2N•H + 3O2 Reaction

In the present work, we have revisited the reaction mechanism of the atmospheric oxidation of methane sulfonamide (CH3S(═O)2NH2; MSAM) initiated by hydroxyl (OH) radicals in the gas phase. The present reaction has been studied for the first time using quantum calculations combined with chemical kinetic modeling. The abstraction of an H-atom from the -NH2 group of MSAM by OH radical to form the products CH3S(═O)2N•H + H2O was found to be a major path with a barrier height of ∼2.3 kcal mol-1 relative to the energy of the separated MSAM + •OH starting reactants. This study is the first to identify the reaction of MSAM with •OH as exclusively generating N-centered MSAM radicals. The chemical kinetic calculations for various paths associated with the MSAM + •OH reaction were performed under pre-equilibrium approximation conditions using canonical variational transition state theory, employing the small curvature tunneling method in the temperature range of 200-400 K. A recent experimental study reported that OH radical-mediated degradation of MSAM proceeds via the formation of the C-centered MSAM radical (•CH2S(═O)2NH2) product. However, the energetics and rate coefficient calculations in the present work suggest that the formation of the N-centered MSAM radical is a major path compared to that which proceeds via the C-centered MSAM radical. The overall rate coefficient for the MSAM + •OH reaction was calculated in the 200-400 K temperature range. The overall rate coefficient for the MSAM + •OH reaction was estimated to be k = 1.2 × 10-13 cm3 molecule-1 s-1 at 298 K. This rate coefficient at 298 K agrees well with the reported experimental value (1.4 × 10-13 cm3 molecule-1 s-1) at the same temperature. We also provide branching ratios for each path associated with the MSAM + •OH reaction. In addition, the atmospheric implications for the title reactions are discussed. The oxidation mechanism of the MSAM + •OH reaction suggests that the formed CH3S(═O)2N•H further reacts with atmospheric oxygen (3O2) to form the corresponding RO2 radical adduct. The downstream products of the CH3S(═O)2N•H + 3O2 reaction in the present work indicate that sulfur dioxide (SO2), carbon monoxide (CO), carbon dioxide (CO2), nitric acid (HNO3), nitrous oxide (N2O), and formic acid [HC(O)OH] are formed as final products.