O2 Reaction Research Articles

Formation of β-U3O8 from UCl3 Salt Compositions under Oxygen Exposure.

Complementary X-ray absorption fine structure (XAFS) and Raman spectroscopy studies were conducted on various UCl3 concentrations in alkali chloride salt compositions. The samples were 5 mol % UCl3 in LiCl (S1), 5 mol % UCl3 in KCl (S2), 5 mol % UCl3 in LiCl-KCl eutectic (S4), 50 mol % UCl3 in KCl (S5), and 20 mol % UCl3 in KCl (S6) molar concentrations. Samples were heated to 800 °C and allowed to cool to room temperature with measurements performed at selected temperatures; the highest temperatures showed the most stability and will be primarily referenced for conclusions. The processing and interpretation of the Raman and extended X-ray absorption fine structure (EXAFS) peaks revealed several uranium-oxygen bond lengths and symmetries in the samples before, during, and after heating. Based on published thermodynamic data of similar systems, X-ray absorption fine structure spectroscopy, and identification of Raman peaks, a β variation of α-U3O8, typical at room temperature, is the suspected dominant phase of all samples at high temperatures (800 °C). In the existing literature, this β structure of U3O8 was synthesized by slow cooling of uranium oxides from 1350 °C. This paper suggests the rapid formation of the compound due to the decomposition of the uranium chlorides or oxychlorides at increasing temperatures and O2 reaction kinetics.

Kinetic analysis on low‐temperature oxidation of wood pellets by isothermal microcalorimetry

AbstractLow‐temperature chemical oxidation is the major driver of self‐heating during storage of wood pellets and its kinetics is essential to describe the heat evolution. In the present work, isothermal microcalorimetry was used to characterize heat generation behavior of three types of wood pellets (pine, fir, and redwood pellets) at 30–70°C. The obtained data were employed to derive the kinetics of low‐temperature oxidation by the peak power, iso‐conversional method, and non‐steady analysis. The consistency and applicability of the kinetics derived by the three methods were evaluated. Kinetic parameters determined by the peak power method were observed to match those from the iso‐conversional method at lower conversions of the oxidation for heat generation. The kinetics derived by the iso‐conversional method indicated the oxidation reactivity generally decreasing and activation energy increasing with the conversion because of O2 consumption and reaction mechanism changing. With the impact of O2 consumption considered separately, the kinetics from the non‐steady analysis is capable of describing the evolution of heat power with the conversion and also consistent with that from the peak power method in describing intrinsic reactivity of pellet materials. The kinetics from the peak power and iso‐conversional methods lump the impact of O2 concentration with the reaction reactivity, suggesting their applications requiring additional models for connecting with O2 consumption.

A polysaccharide from Periplaneta americana promotes macrophage M2 polarization, exhibiting anti-inflammatory and wound-healing activities

A miscellaneous polysaccharide, PAP55–3-1, with a molecular weight of 23.03 kDa, was isolated from Periplaneta americana through extraction with dilute alkali solution, ethanol precipitation, and column chromatography purification. Structural analysis shows that PAP55–3-1 is mainly composed of five monosaccharides: galactosamine hydrochloride, glucosamine hydrochloride, galactose, glucose and mannose. Its main glycosidic bonds are: Manp-(1→, Galp-(1→, →3)-Galp-(1→, →3,6)-Manp-(1→, →2,6)-Manp-(1→, →6)-Manp-(1→, →4)-Galp-(1→, →6-Glcp-(1→, →6)-Galp-(1→, →2)-Manp-(1 →, →3,4)-Glcp-(1→, →3,6)-Galp-(1→. In vitro experiments demonstrated that PAP55–3-1 can effectively inhibit reactive oxygen species (ROS) and O2− production following H2O2−induction. After H2O2−induction, HIF-1α (hypoxia-inducible factor) was translocated in mitochondria PAP55–3-1 increased localization of HIF-1α was located on mitochondria to maintain the stability of mitochondrial function stability, thereby effectively inhibiting H2O2-induced mitochondrial oxidative damage. Additionally, PAP55–3-1 inhibited the M1 polarization of macrophages stimulated by H2O2 and promoted the phenotype polarization of macrophages from M1 to M2, displaying anti-inflammatory and pro-repair properties. In vivo experimental results indicated that PAP55–3-1 promoted wound healing in mice. Immunohistochemical experiments revealed a reduction in CD68 expression and increase in CD206 expression in both positive and the high-dose polysaccharide group control group. This further demonstrated that PAP55–3-1 promotes the phenotype polarization of macrophages from M1 to M2, exerting anti-inflammatory and wound-healing activities.

Gelation embolism agents suppress clinical TACE-incited pro-metastatic microenvironment against hepatocellular carcinoma progression

Current embolic agents in transcatheter arterial chemoembolization (TACE) of hepatocellular carcinoma (HCC) encounter instability and easy leakage, discounting TACE efficacy with residual HCC. Moreover, clinical TACE aggravates hypoxia and pro-metastatic microenvironments, rendering patients with HCC poor prognosis. Herein, we developed Zein-based embolic agents that harness water-insoluble but ethanol-soluble Zein to encompass doxorubicin (DOX)-loaded mesoporous hollow MnO2 (HMnO2). The conditions and capacity of HMnO2 to generate reactive oxygen species (ROS) were assayed. Mechanical examinations of Zein-HMnO2@DOX were performed to evaluate its potential as the embolic agent. Invitro experiments were carried out to evaluate the effect of Zein-HMnO2@DOX on HCC. The subcutaneous HCC mouse model and rabbit VX2 HCC model were established to investigate its anti-tumor and anti-metastasis efficacy and explore its potential anti-tumor mechanism. The high adhesion and crosslinking of Zein with HMnO2@DOX impart Zein-HMnO2@DOX with strong mechanical strength to resist deformation and wash-off. Zein gelation and HMnO2 decomposition in response to water and acidic tumor microenvironment, respectively, enable continuous DOX release and Fenton-like reaction for reactive oxygen species (ROS) production and O2 release to execute ROS-enhanced TACE. Consequently, Zein-based embolic agents outperform clinically-used lipiodol to significantly inhibit orthotopic HCC growth. More significantly, O2 release down-regulates hypoxia inducible factor (HIF-1α), vascular endothelial growth factor (VEGF) and glucose transporter protein 1 (GLUT1), which thereby re-programmes TACE-aggravated hypoxic and pro-metastatic microenvironments to repress HCC metastasis towards lung. Mechanistic explorations uncover that such Zein-based TACE agents disrupt oxidative stress, angiogenesis and glycometabolism pathways to inhibit HCC progression. This innovative work not only provides a new TACE agent for HCC, but also establishes a new strategy to ameliorate TACE-aggravated hypoxia and metastasis motivation against clinically-common HCC metastasis after TACE operation. Excellent Young Science Fund for National Natural Science Foundation of China (82022033); National Natural Science Foundation of China (Grant No. 82373086, 82102761); Major scientific and technological innovation project of Wenzhou Science and Technology Bureau (Grant No. ZY2021009); Shanghai Young Top-Notch Talent.

Microblog‐Assisted Synthesis of Schiff Base Network Polymers for SO2/Epoxide Copolymerization and Thermal Degradation Kinetics of the Products

AbstractThis study successfully prepared three environmentally friendly Schiff base network (SNW) polymers, SNW‐1, SNW‐2, and SNW‐3, using melamine and aldehyde compounds as raw materials through a microwave‐assisted synthesis method. The SNW materials were applied to catalyze the copolymerization reaction of SO2 and epoxides. Through detailed analysis of the chemical structure and properties of SNW‐1, SNW‐2, and SNW‐3, their catalytic efficiency was thoroughly investigated. Three thermal degradation kinetic models, Flynn–Wall–Ozawa (FWO), Kissinger, and Coats–Redfern, were employed to calculate the kinetic parameters of the thermal degradation of poly(cyclohexene sulfite) (PCS). Potential thermal degradation mechanisms were speculated. Additionally, the Kissinger model accurately described the thermal degradation kinetics features of PCS. Based on experimental results and kinetic analysis, this paper elucidates the potential mechanism of the copolymerization reaction of SO2 and epoxides. The study indicates that microwave‐assisted synthesis exhibits convenience and high efficiency in preparing efficient catalysts, demonstrating significant potential across various application domains.

Experimental and theoretical investigation of benzothiazole oxidation by OH in air and the role of O2.

Benzothiazole (BTH) and its derivatives are amongst a group of emerging contaminants that are widely distributed in the environment due to their extensive use in many different consumer products. In air, reaction with the hydroxyl radical (OH) is expected to be a major loss process for BTH in the gas phase, but the kinetics and mechanisms are unknown. Here, we report a combination of experiments and theory to determine both the rate constant and products of the reaction of OH with the smallest member of the series, benzothiazole, in the gas phase. The mechanism first involves an attack by OH on BTH to produce several OHBTH intermediates. This is followed by O2 reactions with OHBTH, leading to several stable products successfully predicted by theory. Relative rate studies at 1 atm in air and 298 K using benzene as a reference gave a rate constant for the BTH + OH reaction of 2.1 ± 0.1 × 10-12 (1σ) cm3 per molecule per s, which translates to a lifetime in air of 5.5 days at 1 × 106 OH cm-3. Four hydroxybenzothiazole products reflecting attack on different carbon atoms of the benzene ring were measured (n-OHBTH, where n = 4, 5, 6, 7), with the relative product yields well predicted by the calculated formation energies of the pre-reaction OH⋯BTH complex. Attack of OH on the -CH of the thiazole ring leads to the formation of 2-OHBTH, representing a smaller fraction of the overall reaction, and is shown to proceed through a more complex mechanism than attack on the benzene ring. A theoretical approach to predicting chromatographic retention times of the products based on solvation free energies (ΔGsolv) was successful for most of the products. These studies illustrate how the powerful combination of experiment and theory can be used to predict products of atmospheric oxidation of emerging contaminants and ultimately used to assess their impacts on the environment.

Direct observation of the complex S(IV) equilibria at the liquid-vapor interface

The multi-phase oxidation of S(IV) plays a crucial role in the atmosphere, leading to the formation of haze and severe pollution episodes. We here contribute to its understanding on a molecular level by reporting experimentally determined pKa values of the various S(IV) tautomers and reaction barriers for SO2 formation pathways. Complementary state-of-the-art molecular-dynamics simulations reveal a depletion of bisulfite at low pH at the liquid-vapor interface, resulting in a different tautomer ratio at the interface compared to the bulk. On a molecular-scale level, we explain this with the formation of a stable contact ion pair between sulfonate and hydronium ions, and with the higher energetic barrier for the dehydration of sulfonic acid at the liquid-vapor interface. Our findings highlight the contrasting physicochemical behavior of interfacial versus bulk environments, where the pH dependence of the tautomer ratio reported here has a significant impact on both SO2 uptake kinetics and reactions involving NOx and H2O2 at aqueous aerosol interfaces.

Distinguishing Surface and Bulk Reactivity: Concentration-Dependent Kinetics of Iodide Oxidation by Ozone in Microdroplets.

Iodine oxidation reactions play an important role in environmental, biological, and industrial contexts. The multiphase reaction between aqueous iodide and ozone is of particular interest due to its prevalence in the marine atmosphere and unique reactivity at the air-water interface. Here, we explore the concentration dependence of the I- + O3 reaction in levitated microdroplets under both acidic and basic conditions. To interpret the experimental kinetics, molecular simulations are used to benchmark a kinetic model, which enables insight into the reactivity of the interface, the nanometer-scale subsurface region, and the bulk interior of the droplet. For all experiments, a kinetic description of gas- and liquid-phase diffusion is critical to interpreting the results. We find that the surface dominates the iodide oxidation kinetics under concentrated and acidic conditions, with the reactive uptake coefficient approaching an upper limit of 10-2 at pH 3. In contrast, reactions in the subsurface dominate under more dilute and alkaline conditions, with inhibition of the surface reaction at pH 12 and an uptake coefficient that is 10× smaller. The origin of a changing surface mechanism with pH is explored and compared to previous ozone-dependent measurements.

Unsymmetric Ir2 and RhIr Dinuclear Complexes Supported by a Linear Tetraphosphine meso-dpmppp, Showing High Reactivity for O2, H2, and HCl.

Unsymmetric dinuclear Ir(I) complexes, [Ir2Cl2(L)(meso-dpmppp)] (L = XylNC (1aIr2), tBuNC (1bIr2), CO (1cIr2)), were synthesized using meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), which supports cis-P,P (M1) and trans-P,P (M2) metal sites, and exhibited high reactivity for O2, H2, and HCl. The IrRh heterodinuclear complexes, [M1M2Cl2(L)(meso-dpmppp)] (1xM1M2) (M1M2 = IrRh, RhIr; L = XylNC, CO (x = a, c)), were also synthesized and used together with the Rh2 complexes (1a,cRh2) to elucidate the role of each metal site. For the reactions of O2, 1aIr2 and 1aRhIr showed higher reactivity than those of 1aIrRh and 1aRh2, giving η2-peroxide complexes [{M1Cl2}{M2(η2-O2)(XylNC)}(meso-dpmppp)] (2aIr2, 2aRhIr), from which O2 would not dissociate. All the CO complexes 1cM1M2 (M1, M2 = Ir or Rh) showed no reactivity for O2. In the reactions with H2, 1aIr2 reacted with H2 to give the dihydride complex, [{IrCl2}{Ir(H)2L}(meso-dpmppp)] (11aIr2) and the tetrahydride complex, [{Ir(H)Cl2}(μ-H){Ir(H)2L}(meso-dpmppp)] (12aIr2), while 1aRhIr gave the dihydride complex, and 1aIrRh and 1aRh2 gave no hydride complexes. Reactions of 1a,cM1M2 with HCl afforded the dihydride complexes, [{IrCl3}(μ-H){Ir(H)Cl(XylNC)}(meso-dpmppp)] (14aIr2), [{Ir(H)Cl2}(μ-H){M2Cl2(L)}(meso-dpmppp)] (M2 = Ir, L = CO (15cIr2); M2 = Rh, L = XylNC (15aIrRh), CO (15cIrRh)), and [{Rh(H)Cl2}(μ-Cl){Ir(H)Cl(XylNC)}(meso-dpmppp)] (18aRhIr), the structures varying depending on M1 and M2 as well as L.

Effects of microbe-derived antioxidants on growth performance, hepatic oxidative stress, mitochondrial function and cell apoptosis in weaning piglets

BackgroundWeaning causes redox dyshomeostasis in piglets, which leads to hepatic oxidative damage. Microbe-derived antioxidants (MA) have great potential for anti-oxidation. This study aimed to investigate changes in hepatic redox system, mitochondrial function and apoptosis after weaning, and effects of MA on growth performance and liver health in weaning piglets.MethodsThis study consisted of 2 experiments. In the both experiments, piglets were weaned at 21 days of age. In Exp. 1, at 21 (W0), 22 (W1), 25 (W4), 28 (W7), and 35 (W14) days of age, 6 piglets were slaughtered at each timepoint. In Exp. 2, piglets were divided into 2 groups: one received MA gavage (MA) and the other received saline gavage (CON). At 25 days of age, 6 piglets from each group were sacrificed.ResultsIn Exp. 1, weaning caused growth inhibition and liver developmental retardation from W0 to W4. The mRNA sequencing between W0 and W4 revealed that pathways related to “regulation of apoptotic process” and “reactive oxygen species metabolic process” were enriched. Further study showed that weaning led to higher hepatic content of reactive oxygen species (ROS), H2O2 and O2−. Weaning enhanced mitochondrial fission and suppressed their fusion, activated mitophagy, thus triggering cell apoptosis. In Exp. 2, MA improved growth performance of piglets with higher average daily gain (ADG) and average daily feed intake (ADFI). The hepatic ROS, as well as products of oxidative damage malonaldehyde (MDA) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) in the MA group decreased significantly than that of the CON group. The MA elevated mitochondrial membrane potential, increased activity of mitochondrial respiratory chain complexes (MRC) I and IV, enhanced mitochondrial fusion and reduced mitophagy, thus decreasing cell apoptosis.ConclusionsThe present study showed that MA improved the growth performance of weaning piglets and reversed weaning-induced oxidative damage, mitochondrial dysfunction, and apoptosis. Our results suggested that MA had promising prospects for maintaining liver health in weaning piglets and provided a reference for studies of liver diseases in humans.Graphical

Effect of calcite on the thermal decomposition of pyrite: Thermodynamics, phase transformation, microstructure evolution and kinetics

Pyrite, a common iron mineral in refractory iron ores, emits SO2 during oxidative roasting, contributing to environmental pollution. This study investigated the effect of calcite on the thermal decomposition of pyrite, focusing on thermodynamics, phase transformation, microstructural evolution, and non-isothermal kinetics, with emphasis on SO2 formation inhibition. Results showed that pyrite decomposed first to pyrrhotite, then to magnetite and hematite, with SO2 as the primary gaseous product. Higher temperatures and lower oxygen concentrations favored S2 gas formation. Non-isothermal decomposition of pyrite occurred between 400–725°C, initiated at the particle surface, and significantly increased product porosity, resulting in butterfly-shaped hematite. The addition of calcite resulted in the reaction of SO2 with calcite to form anhydrite on the particle surface, inhibiting the release of SO2. Initially, the thermal decomposition of pyrite proceeded with a low apparent activation energy, making the reaction relatively easy. However, the presence of calcite significantly increased the apparent activation energy and inhibited the thermal decomposition reaction.

H2S gas sensing enhancement of Au-decorated SnO2 nanospheres synthesized using hydrothermal and microwave methods

In this study, non-oriented Au-decorated SnO2 nanospheres (NSs) were synthesized using hydrothermal and microwave methods. The SnO2 spheres ranged from hundreds of nanometers to a microscale. The oxygen vacancy on the surface increased after Au adsorption on the surface of the SnO2 NSs, ultimately showing a synergistic effect with the spillover effect of the existing Au catalyst. Specifically, at 100 °C and 200 °C, the response to 10 ppm H2S gas improved to 16.14 and 46.81, respectively. These gas sensing effects were approached individually by being divided into two disadvantages (oxygen adsorption and homojunction) and five advantages (oxygen vacancies, spill-over, surface area, H2S + SnO2 reaction, and H2S + O2 reaction). Based on this reference, we investigated SnO2 NSs of various sizes and functions by adjusting the process variables.

An Experimental and Kinetic Modeling Study of the Laminar Burning Velocities of Ammonia/n-Heptane Blends

Ammonia is carbon-free and is a very promising renewable fuel. The ammonia/diesel dual-fuel combustion strategy is an important combustion strategy for ammonia internal combustion engines. To achieve clean and efficient combustion with a high ammonia blending ratio in ammonia engines, it is important to thoroughly investigate the combustion characteristics and chemical reaction mechanisms of ammonia/diesel fuel blends. Based on the constant volume combustion vessel experiments, the laminar burning velocities (LBVs) of ammonia/n-heptane blends were measured at the conditions of an ammonia–energy ratio of 60–100%, at initial pressures of 0.1–0.5 MPa and initial temperatures of 338–408 K, and under an equivalence ratio regime of 0.8–1.3. The experimental results indicate that the laminar burning velocities of ammonia/n-heptane fuel blends increase with a decreasing ammonia–energy ratio. Specifically, with an ammonia–energy ratio of 60%, an initial temperature of 373 K, an initial pressure of 0.1 MPa, and an equivalence ratio of 1.1, the measured LBV is approximately 20 cm/s, which is about 61% faster than that of pure ammonia flames under the same conditions. A previously developed chemical kinetic mechanism is employed to simulate the new experimental data, and the model exhibits overall good performance. The sensitivity analyses have been conducted to highlight the important reaction pathways. The elementary reaction O2 + Ḣ<=>Ö + ȮH demonstrates the most significant promotional effect on the laminar burning velocities, while the interaction reaction pathways of via H-abstraction from n-heptane by ṄH2 radicals are not showing obvious effects on the simulation results under the studied conditions.

O2-Dependence of reactions of 1,2-dimethoxyethanyl and 1,2-dimethoxyethanylperoxy isomers

Reaction mechanisms of R˙ and ROO˙ radicals derived from low-temperature oxidation of 1,2-dimethoxyethane (CH3O(CH2)2OCH3) were investigated using speciation from multiplexed photoionization mass spectrometry (MPIMS) measurements via Cl-initiated oxidation, in conjunction with electronic structure calculations. The experiments were conducted at 5 bar, from 450 K – 650 K, and O2 concentrations from 1 · 1014 cm–3 – 6 · 1018 cm–3 to probe the effects on competing reaction channels of 1,2-dimethoxyethanyl (R˙) and 1,2-dimethoxyethanylperoxy (ROO˙) isomers. Several species were detected with photoionization spectral fitting – ethene, formaldehyde, methyl vinyl ether, and 2-methoxyacetaldehyde – and, as determined by electronic structure calculations, may form via unimolecular decomposition of 1,2-dimethoxyethanyl or 1,2-dimethoxyethanylperoxy. O2-dependent yield ratios show that the formation pathways for all species undergo a competition between O2-addition and unimolecular decomposition. Adiabatic ionization energies were also calculated and utilized along with exact mass determinations to infer contributions for other species derived exclusively from first- and second-O2-addition, including 1,2-dimethoxyethene, cyclic ethers, and dicarbonyls.In addition to species formed from conventional low-temperature oxidation pathways, an important conclusion is derived from the detection of species produced from an O2-addition step involving ĊH2CH2OCH3 (R˙′), which forms via prompt dissociation of the primary 1,2-dimethoxyethanyl radical (ĊH2O(CH2)2OCH3). Species derived from R˙′ + O2 – 1,3-dioxolane and methyl acetate – were detected at [O2] = 1.2 · 1017 cm–3 and formed on timescales parallel to the main R˙ + O2 reactions. In addition, ion signal at m/z 106 was detected and increased with O2 concentration from which connections are drawn to ketohydroperoxides produced by Q˙′OOH + O2. Detection of such species indicate that β-scission of 1,2-dimethoxyethanyl is sufficiently facile such that timescales of R˙′ + O2 compete with conventional R˙ + O2 pathways.

The Interaction-Asymptotic Region Decomposition Method in Jacobi Coordinates: Triatomic Reactive Scatterings.

The interaction-asymptotic region decomposition (IARD) technique has been proven to be a good solution to the long-standing coordinate problem in reactive scattering calculations. In this work, the IARD technique was further developed using Jacobi coordinates for the interaction region, instead of the previously used hyperspherical coordinates. Although the Jacobi coordinate may not be as optimal as the hyperspherical coordinates for describing the interaction region in reactive scattering processes, it has simpler kinetic operators and provides a more physically intuitive picture. By developing an intermediate interpolation method, which could efficiently transform the overlapped wave functions from the asymptotic regions to the interaction region, the new implementation of the IARD technique for triatomic reactive scatterings is similarly efficient and accurate. The differential cross sections of the H+H2, and product state-resolved reaction probabilities of the F+HD and16O+36O2 reactions, which involve products of extremely low translational energy and are challenging for a single coordinate-based method, were calculated as numerical examples to show the ability of the new method.

PM2.5 episodes in northern Taiwan under southerly winds in late winter

When northern Taiwan is influenced locally, PM2.5 events occur in specific conditions. If it is also affected by long-range transport from mainland China in the northwest, the probability of these PM2.5 events increases. The current study applies WRF/CMAQ to study such case but focus on the local. From April 7 to 9, 2019, the Pacific high pressure extended westward, causing the prevailing weak southerly wind near Taiwan. The intensity of the Pacific high pressure weakened, and the wind speed near Taiwan also weakened. Therefore, the PM2.5 concentration in Taiwan increased. In northern Taiwan, the hourly PM2.5 concentration will inevitably increase to approximately 70 μg m−3. The ISAM of the CMAQ model demonstrates that local contributions to daily PM2.5 concentrations at the four representative monitoring stations in northern Taiwan are 3.5 to 16.2 μg m−3, greater than those from central, southern, and eastern Taiwan, from 1.8 to 6.7 μg m−3. We use the integrated process rate (IPR) and integrated reaction rate (IRR) of CMAQ to explore the formation mechanisms of PM2.5. The main causes of the increase in PM2.5 concentration are horizontal advection (HADV), aerosol processes (AERO), emissions (EMIS), and a small amount of cloud processes and aqueous chemistry (CLDS). The main source of NO3− is the reaction between OH and NO2 during the day and the reaction between N2O5 and water vapor at night. The gaseous HNO3 concentration reaches a peak near noon or soon after. The aerosol ANO3 concentration is high in the early morning. We also use the Sulfur Tracking Method (STM) of CMAQ to explore the sources of SO42−. Mainly it is from the local reaction of SO2 and H2O2. Finally, we apply AERO7 in CMAQ to explore the main sources of carbon components. The organic carbon (OC) concentration is much greater than the element carbon (EC) concentration, which indicates a strong local photochemical effect in northern Taiwan. OC mainly comes from low-volatility/semivolatile oxidized combustion OC, followed by low-volatility/semivolatile POA. Similar weather conditions occur in autumn, winter, and spring. When the weak southerly wind was around Taiwan, PM2.5 in northern Taiwan was noticed.

N2O Decomposition on Singly and Doubly (K and Li)-Doped Co3O4 Nanocubes─Establishing Key Factors Governing Redox Behavior of Catalysts.

The intimate mechanism of N2O decomposition on bare and redox-tuned Co3O4 nanocubes (achieved by single (Li or K) and double (Li and K) doping) was elucidated. The catalysts synthesized by the hydrothermal method were characterized by X-ray electron absorption fine structure measurements, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and Kelvin Probe techniques. TPSR and steady-state isothermal catalytic tests reveal that the N2O turnover frequencies are critically sensitive to the work function of the catalysts, adjusted purposely by doping. For the catalysts obtained by one-pot hydrothermal synthesis, lithiation of the Co3O4 nanocubes leads to the formation of {Li'8a, Co·16d} species, decreasing steadily the work function and the activity, while for the catalysts prepared by postsynthesis impregnation, formation of {Li'8a, Co'16d, Co··16c} species leads to a volcano-type dependence of the catalytic activity and the work function in parallel. The beneficial effect of potassium was discussed in terms of mitigation of surface potential buildup due to the accumulation of ionosorbed oxygen intermediates (surface electrostatics), which hinders the interfacial electron transfer. Analysis of the catalytic activity response to the redox tuning of Co3O4, substantiated by DFT calculations, allowed for a straightforward conceptualization of the redox nature of the N2O decomposition in terms of the lineup of frontier orbitals of the N2O/N2O- and O2-/O2 reactants with the surface DOS structure and the resultant molecular orbital interactions. The positions of the virtual bonding 3πg0(N2O)-α-3dz2 and the occupied 2πg1(O2-)-α-3dz2 states relative to the Fermi energy level play a crucial role in the regulation of the forward and backward interfacial electron transfer events, which drive the redox process.

Enthalpy of the Cerium (Ce) Chemi-Ionization Reaction and CeO+, CeC+, and CeCO+ Bond Energies Determined by Energy-Resolved Guided Ion Beam Mass Spectrometry Experiments.

Cerium (Ce) oxide, carbide, and carbonyl cation bond energies and the exothermicity of the Ce chemi-ionization (CI) reaction with atomic oxygen were investigated using guided-ion beam tandem mass spectrometry (GIBMS). The kinetic energy dependent product cross sections for reactions of Ce+ with O2, CO, and CO2 and CeO+ with O2, CO, Xe, and Ar were measured using GIBMS. For the reactions of Ce+ with O2 and CO2, CeO+ is formed through an exothermic reaction, whereas CeO+ formation is endothermic in the reaction with CO. This reaction also forms CeC+ and CeCO+ is formed in the reaction of Ce+ with CO2, both in endothermic processes. Reactions of CeO+ with all four gases led to endothermic collision-induced dissociation as well as exchange reactions to form CeO2+ for the O2 and CO reactants. Bond dissociation energies (BDEs) at 0 K were determined through analyses of the kinetic energy dependent cross sections for all endothermic reactions. We determined that the BDEs of CeO+, CeC+, and CeCO+ are 8.46 ± 0.15, 3.93 ± 0.16, and ≥0.25 ± 0.07 eV, respectively, where the CeO+ BDE is a weighted average of 6 independent 0 K threshold measurements. The CeO+ BDE is combined with the ionization energy (IE) of Ce to determine an exothermicity of 2.91 ± 0.15 eV for the Ce + O → CeO+ + e- chemi-ionization reaction. Combined with neutral BDEs from the literature, the thermochemistry determined here also provides IE(CeO) = 5.03 ± 0.12 eV and IE(CeC) = 6.50 ± 0.16 eV. Theoretical calculations for ground and some excited states were performed for CeO+, CeC+, and CeCO+ to provide insight into the bonding and a comparison with the experimentally determined BDEs for each molecule.

Full-dimensional coupled-channel statistical approach to atom-triatom systems and applications to H/D + O3 reaction.

The statistical quantum model (SQM), which assumes that the reactivity is controlled by entrance/exit channel quantum capture probabilities, is well suited for chemical reactions with a long-lived intermediate complex. In this work, a time-independent coupled-channel implementation of the SQM approach is developed for atom-triatom systems in full dimensionality. As SQM treats the capture dynamics quantum mechanically, it is capable of handling quantum effects such as tunneling. A detailed study of the H/D + O3 capture dynamics was performed by applying the newly developed SQM method on an accurate global potential energy surface. Agreement with previous ring polymer molecular dynamics (RPMD) results on the same potential energy surface is excellent except for very low temperatures. The SQM results are also in reasonably good agreement with available experimental rate coefficients. The strong H/D kinetic isotope effect underscores the dominant role of quantum tunneling under an entrance channel barrier at low temperatures.

Highly Selective Synthesis of Acetic Acid from Hydroxyl‐Mediated Oxidation of Methane at Low Temperatures

Direct methane conversion and, in particular, the aerobic oxidation to acetic acid, remain an eminent challenge. Here, we reported a zeolite‐supported Au‐Fe catalyst (Au‐Fe/ZSM‐5) that converted methane to acetic acid with molecular oxygen as an oxidant in the presence of CO. Specifically, Au nanoparticles catalyzed the formation of hydroxyl species from the reaction of CO, O2, and H2O, meanwhile ZSM‐5‐supported atomically dispersed Fe species were responsible for the hydroxyl‐mediated coupling of CH4 and CO to generate acetic acid. The reaction over 50 mg of Au‐Fe/ZSM‐5 under 62 bar (CH4: CO: O2 = 14: 14: 3) at 120 °C for 3.0 h yielded 5.7 millimoles of acetic acid per gram of the catalyst (mmol gcat‐1) with the selectivity of 92%, outperformed most of reported catalysts. Significantly, the catalyst remained active even at 60 °C. We anticipate that this hydroxyl‐mediated route may guide the design of optimized catalysts for the direct methane functionalization at low temperatures.