O2 Dissociation Research Articles

Roles of Re and Cs Promoters and Organochlorine Moderators in the Synthesis of Ethylene Oxide on Ag‐based Catalysts

AbstractC2H4−O2 reactions form ethylene oxide (EO) on Ag nanoparticles dispersed on α‐Al2O3 and promoted with alkali and other elements, with Re and Cs most frequently used in practice. Traces of alkyl chlorides (e. g., C2H5Cl) and alkanes in much larger amounts are added to reactants to balance the rate of deposition and removal (and the coverage) of Cl adatoms (Cl*) on Ag surfaces. Such Cl adlayers retain Ag surface ensembles that form O2‐derived intermediates that favor EO synthesis, but typically decrease O2 activation rates. A series of Ag/α‐Al2O3 catalysts (with and without Re or Cs) are used here to examine the role of promoters and Cl moderators through an analysis of the effects of reaction conditions and C2H5Cl levels using convection‐reaction constructs and a mechanistic formalism that considers O2 (as chemisorbed O2*) as the reactant in EO synthesis through one electrophilic O‐atom, with the second O‐atom (O*) acting as a unselective nucleophile that must be scavenged by a sacrificial reductant (C2H4 or EO); such channels are precluded by any intervening O2 dissociation events (that form two O*). O2 consumption rates in C2H4−O2 reactions decrease 10‐fold upon exposing Ag/α‐Al2O3 to C2H5Cl, evincing persistent Cl* species that block active sites and require >104 C2H4 oxidation turnovers to be removed. Activation barriers do not change but relative rates of epoxidation versus combustion increase in the presence of this refractory Cl* adlayer, which reduces the number and shrinks the size of available site ensembles without altering their intrinsic reactivity for O2 activation to form O2* but attenuating rates of its subsequent dissociation. Refractory O* adlayers also form on Ag surfaces, as shown by the accumulation of persistent O* species upon exposing reduced Ag particles to N2O. Inter‐atom repulsive forces weaken O* binding and destabilize N2O decomposition transition states to eventually allow stable N2 and O2 evolution for catalytic N2O decomposition, which occurs at landing ensembles formed at interstices of refractory adlayers. Cl* forms denser adlayers than O*, as evidenced by a 10‐fold decrease not only to C2H4−O2 rates but also to N2O stoichiometric and catalytic rates and O* uptakes. The occasional evolution of O2, which forms larger landing ensembles that more readily form 2O* from O2, occurs with higher frequency from O* than mixed O*/Cl* adlayers, and this effect of Cl* to inhibit (O−O)* dissociation is demonstrated in CO probe reaction studies, which show that highly reactive bound dioxygen species are retained to a greater extent when adlayers comprise both Cl* and O*. Re and Cs do not influence the nature of such adlayers but increase and decrease, respectively, the number of acid sites and selectivity losses via EO combustion. Their respective domains may also block a modest fraction of Ag surfaces without consequences on intrinsic O2 activation rates or EO selectivities. The effects of Re beyond those reported here may emerge upon synthetic protocols that alter Re location and Ag−Re intimacy to enable channels which utilize both O‐atoms in epoxidation.

Mechanism of phase segregation in ilmenite oxygen carriers for chemical-looping combustion

The solid particle of oxygen carrier (OC) plays a vital role in chemical looping combustion (CLC) for fossil fuel combustion and inherent carbon capture. Phase segregation or active metal surface layer formation upon redox cycle had been recently noticed to be a predominant factor causing complete failure of OCs. To explored and identified the mechanism behind rapid phase segregation and external iron-rich shell formation of ilmenite OCs during CLC process, this study investigated into OCs’ phase and element distributions, and surface layer morphologies at various redox cycles, and the cross-sectional microstructures of oxidizing OC particles with different exposure times. The detailed information on the exterior Fe-rich shell formation and the progression of phase segregation were visualized, which provided vital information for the new mechanism of rapid Fe phase migration. The new finding ruled out Kirkendall effects or the ionic diffusion mechanism. The immediate formation of surface layer was found to initiate the segregation of Fe2O3 form TiO2 phase. The rapid Fe phase migration was attributed to the driving force arising from the increased local pressure of particles and the violent exothermic oxidation on reaction front. The strong driving force could directly eject iron-containing phases from the reaction front to surface layer. In the new mechanism, different phases separated inside the reduced OC particles provided the vital intermediates for the starting points of deep phase segregation or rapid surface layer formation; O2 dissociation of on the metallic Fe outmost layer and the oxygen ion conduction in TiO2 phase seemed to provide a short-circuit diffusion pathway for particle oxidation. Finally, this study also explored the strategies that might succeed in improving the integrity of ilmenite OC particles.

Functional characterization of compound heterozygosity Hb S/Hb Deer Lodge in Brazil

IntroductionThe Hb Deer Lodge (β2 His>Arg; HBB:c.8A>G) is a structural hemoglobin variant described in some populations around the world, characterized by increased oxygen affinity, but does not confer clinical symptoms to its carriers. The coinheritance of the Hb Deer Lodge with the most common hemoglobin variant, Hb S, has been reported only once; however, functional data were not described. Here we show a case of the Hb S and Hb Deer Lodge carrier in heterozygosity. MethodsThe Hb S and Hb Deer Lodge association was identified by High-Performance Liquid Chromatography (HPLC), reverse phase HPLC and the β globin gene sequencing. The functional characterization of this interaction was obtained using the O2 dissociation curve, determination of the cooperativity between the globin chains and the Bohr effect in the presence and absence of organic phosphates. ResultsWhen the Hb S and Hb Deer Lodge were associated, there was a decrease in cooperativity, no significant changes in oxygen affinity and no significant Bohr effect changes. ConclusionDespite these genetic variations, the carrier showed no hematological alterations and no clinical symptoms, possibly due to the high oxygen affinity of the Hb Deer Lodge, which interferes with the Hb S polymerization.

Ultrasound-Driven Non-Metallic Fenton-Active Center Construction for Extensive Chemodynamic Therapy.

Chemodynamic therapy (CDT) is an emerging tumor microenvironment-responsive cancer therapeutic strategy based on Fenton/Fenton-like reactions. However, the effectiveness of CDT is subject to the slow kinetic rate and non-homogeneous distribution of H2 O2 . In this study, a conceptual non-metallic "Fenton-active" center construction strategy is proposed to enhance CDT efficiency using Bi0.44 Ba0.06 Na0.5 TiO2.97 (BNBT-6) nanocrystals. The separated charge carriers under a piezoelectric-induced electric field synchronize the oxidation of H2 O and reduction of H2 O2 , which consequently increases hydroxyl radical (·OH) yield even under low H2 O2 levels. Moreover, acceptor doping induces electron-rich oxygen vacancies to facilitate the dissociation of H2 O2 and H2 O and further promote ·OH generation. In vitro and in vivo experiments demonstrate that BNBT-6 induces extensive intracellular oxidative stress and enhances cell-killing efficiency by activating necroptosis in addition to the conventional apoptotic pathway. This study proposes a novel design approach for nanomaterials used in CDT and presents a new treatment strategy for apoptosis-resistant tumors.

Time-resolving state-specific molecular dissociation with XUV broadband absorption spectroscopy.

The electronic and nuclear dynamics inside molecules are essential for chemical reactions, where different pathways typically unfold on ultrafast timescales. Extreme ultraviolet (XUV) light pulses generated by free-electron lasers (FELs) allow atomic-site and electronic-state selectivity, triggering specific molecular dynamics while providing femtosecond resolution. Yet, time-resolved experiments are either blind to neutral fragments or limited by the spectral bandwidth of FEL pulses. Here, we combine a broadband XUV probe pulse from high-order harmonic generation with an FEL pump pulse to observe dissociation pathways leading to fragments in different quantum states. We temporally resolve the dissociation of a specific O2+ state into two competing channels by measuring the resonances of ionic and neutral fragments. This scheme can be applied to investigate convoluted dynamics in larger molecules relevant to diverse science fields.

Hierarchically porous, N-defect enriched C-nanosheets boost the H2S selective oxidation to elemental sulfur

H2S selective oxidation to elemental sulfur (S8) is a typical reaction where the mass product diffusion (e.g., S8) through the catalytic bed is crucial as well as the reagents accessibility (e.g., H2S, O2) to the active sites. The NaNO3-assisted pyrolysis of polyacrylamide was applied to synthesize defect-enriched N-doped carbon nanosheets with thickness up to c.a. 2 nm, featured by fully accessible and highly interconnected pores, for boosting the H2S selective oxidation process. The PAM-0.3-700 sample has revealed an unprecedented desulfurization activity with sulfur formation rate of 1165 gsulfur kgcat.−1 h−1, other than a remarkable stability (>80 h). Experimental and theoretical studies have unveiled the critical role of edge sites containing unpaired electrons and nitrogen species with respect to the material aptitude towards O2 dissociation and HS- activation. The material in presence of a highly interconnected porous network facilitates the reactants/product diffusion especially for catalysis operated under harsh experimental conditions.

3D Monte-Carlo simulation of Ganymede’s atmosphere

We present new model results for H2O, O2, H2, O, and H in the atmosphere of Ganymede. The results are obtained from a collision-less 3D Monte-Carlo model that includes sublimation, ion and electron sputtering, and ion and electron radiolysis. Because Ganymede has its own magnetic field, its immediate plasma environment is particularly complex. The interaction between Ganymede’s and Jupiter’s magnetospheres makes it highly variable in both space and time. The recent Juno Ganymede flyby provided us with new data on the electron local environment. Based on the electron measurements recorded by the Jovian Auroral Distributions Experiment (JADE), we implement two electron populations, one for the moon’s polar regions and one for the moon’s auroral regions. Comparing the atmospheric contribution of these newly defined electron populations to the overall source and loss processes is one of the main goals of this work.Our analysis shows that for H2O, sublimation remains the most important source process even after accounting for the new electron populations, delivering more than three orders of magnitude more H2O molecules to the atmosphere than all other source processes combined. The source fluxes for O2 and H2, on the other hand, are dominated by radiolysis induced by the auroral electrons, assuming that the electron fluxes JADE measured during Juno’s transit of Ganymede’s magnetopause current layer are representative of auroral electrons. Atomic O and H are mainly added to the atmosphere through the dissociation of O2 and H2, which is primarily induced by auroral electrons.Our understanding of Ganymede’s atmosphere today is mainly based on spectroscopic observations. The interpretation of spectroscopic data strongly depends on assumptions taken, though. Our analysis shows that for a holistic understanding of Ganymede’s atmosphere, simultaneous observations of the moon’s surface, atmosphere, and full plasma environment (thermal and energetic ions and electrons) at different times and locations (both with respect to Ganymede and with respect to Jupiter) are particularly important. Such measurements are planned by ESA’s Jupiter ICy moons Explorer (JUICE), in particular by the Particle Environment Package (PEP), which will greatly advance our understanding of Ganymede and its atmosphere and plasma environment.

Enhancing oxygen reduction reaction with Pt-decorated Cu@Pd and high-entropy alloy catalysts: Insights from first-principles analysis of Pt arrangement

The efficiency of oxygen reduction reaction (ORR) in the proton-exchange membrane fuel cells (PEMFCs) heavily relies on the surface Pt atom arrangement, which can be represented by the Pt-Pt average distance. Here, we employed density functional theory (DFT) to examine the influence of Pt arrangement on the ORR efficiency of Cu@Pd core-shell and high-entropy alloy catalysts. Our DFT calculations reveal that a shorter Pt-Pt average distance on the surface leads to a lower O2 dissociation barrier. Nevertheless, a shorter Pt-Pt average distance is not thermodynamically favored for the Cu@Pt catalyst. Moreover, we discovered a robust correlation between the level of the d-band center of the catalyst and the O2 adsorption energy. To explore the potential of controlling Pt arrangement, we investigated the use of NbMoTaW high-entropy alloy (HEA) substrates. Our findings suggest that HEA substrates provide promising surface chemistry for tuning Pt arrangement and controlling the O2 dissociation barrier.

Fullerene Fragment Restructuring: How Spatial Proximity Shapes Defect-Rich Carbon Electrocatalysts.

Fullerene transformation emerges as a powerful route to construct defect-rich carbon electrocatalysts, but the carbon bond breakage and reformation that determine the defect states remain poorly understood. Here, we explicitly reveal that the spatial proximity of disintegrated fullerene imposes a crucial impact on the bond reformation and electrocatalytic properties. A counterintuitive hard-template strategy is adopted to enable the space-tuned fullerene restructuring by calcining impregnated C60 not only before but also after the removal of rigid silica spheres (∼300 nm). When confined in the SiO2 nanovoids, the adjacent C60 fragments form sp3 bonding with adverse electron transfer and active site exposure. In contrast, the unrestricted fragments without SiO2 confinement reconnect at the edges to form sp2-hybridized nanosheets while retaining high-density intrinsic defects. The optimized catalyst exhibits robust alkaline oxygen reduction performance with a half-wave potential of 0.82 V via the 4e- pathway. Copper poisoning affirms the intrinsic defects as the authentic active sites. Density functional theory calculations further substantiate that pentagons in the basal plane lead to localized structural distortion and thus exhibit significantly reduced energy barriers for the first O2 dissociation step. Such space-regulated fullerene restructuring is also verified by heating C60 crystals confined in gallium liquid and a quartz tube.

Exploring the effects of potassium-doping on the reactive oxygen species of CeO2 (110) for formaldehyde catalytic oxidation: A DFT study

The influence of K-doping on the reactive oxygen species and elementary reactions of HCHO catalytic oxidation has not been well understood. Herein, a density functional theory (DFT) study was conducted and found that the introduction of K-doping advantageously changed the electronic structures of both Ce and O atoms on the (110) crystal plane of CeO2. This change, in turn, facilitated the adsorption and activation of HCHO and O2 molecules, enhanced the mobility of lattice oxygen, and reduced the energy barrier associated with HCHO oxidation. The adsorbed oxygen species were generated through the direct dissociation of O2 on the CeO2 (110) surface. However, in the case of K-CeO2 (110), it was more probable for the adsorbed oxygen species to be produced by gaseous O2 filling the oxygen vacancy, followed by dissociation. Additionally, the incorporation of K-doping proved to be advantageous in facilitating the formation of hydroxyl groups by promoting the dissociation of water molecules. The inclusion of hydroxyl groups facilitated the HCHO adsorption and reduced the energy barrier for its subsequent oxidation. The findings provide new insights into the development of novel catalysts for HCHO removal with high performance through alkali metal modification.

Uncovering the role of unsaturated coordination defects in manganese oxides for concentrated solar-heating photothermal OVOCs oxidation: Experimental and DFT explorations

In this study, we innovatively develop a concentrated photothermal catalysis (CPTC) system with a cost-effective solar concentrator to efficaciously achieve light-to-heat conversion, and combine a defect engineering strategy to design Mn3O4-based catalysts with unsaturated coordination defects (O and Mn atoms) for solar-heating photothermal ethyl acetate oxidation without additional artificial-energy input. As a result, Mn3O4-3 exhibits outstanding photothermal catalytic performance for ethyl acetate and other OVOCs oxidation under weak simulated sunlight even natural sunlight irradiation. The enriched unsaturated defects in Mn3O4-3 with lower Mn-O and Mn-Mn coordination numbers not only improve the concentration of surface reactive species (Mn4+ and Oads), but also regulate the energy-band structure to further promote the light absorption capacity and charge separation. Experimental and theoretical evidences demonstrate that the generation of abundant Mn defects is conducive to the ethyl acetate dissociation/hydrolysis into key intermediates, while the existence of more O vacancies synergistically facilitates the O2 dissociation toward highly reactive O* participating in the deep oxidation of key intermediates. Moreover, in-situ DRIFTS and DFT results reveal the reaction pathway expansion (Pathway I and II) of photothermal ethyl acetate oxidation on manganese oxides under sunlight irradiation. This work provides an attractive CPTC technology for VOCs removal in energy and environmental application.

New insight into dissociation of molecular oxygen at temperatures below 5000 K

The data available in the literature on measurements of the rate coefficient of molecular oxygen dissociation were considered and structured. Modern models of hydrocarbons combustion were analyzed considering values of the O2 dissociation rate constant. Precision measurements of the rate of O2 dissociation behind shock waves at temperatures of 2500–5000 ± 50 K and pressures of 1.2–2.5 bar were carried out using atomic resonance absorption spectrometry on O atom (O-ARAS). The ARAS measurements of the absolute concentration of oxygen atoms were calibrated in the conditions of complete dissociation of N2O and O2, considering the temperature splitting of the calibration curves. Using kinetic modeling, a detailed analysis of experimental uncertainties was carried out with an assessment of the influence of impurities of various origin at the dissociation of O2. An updated expression for the rate constant of the reaction O2 + Ar = 2O + Ar was obtained in the form kdiss(±15%)=1.30·1014·exp(−108.95[kcalmol]/RT) cm3 mol−1 s−1. A significant influence of the O2 dissociation rate constant on the predictive ability of modern models of hydrocarbons (on the example of biofuels) combustion at high temperatures was shown. Recommendations were formulated on the use of the corresponding oxygen dissociation rate constant in the development and/or refinement of combustion kinetic models.

Oxidizing- and sintering- resistant PdZn@ZnO catalyst concerning methanol steam reforming for on-board hydrogen production for fuel cell vehicles

For proton exchange membrane fuel cells (PEMFCs) powered vehicles using on-board H2 production by methanol steam reforming (SRM), how to enhance the anti-oxidation and anti-sintering abilities of SRM catalysts are two challenges. Herein, to address the two challenges, a PdZn@ZnO catalyst has been synthesized by in-situ transformation of Pd@ZnO core-shell structure under thermal treatment and H2 reduction, which is a facile and green method. The PdZn@ZnO catalyst exhibited an excellent anti-oxidation ability without obvious change in catalytic activity before and after oxidation treatment. Density functional theory calculations revealed that the abundant PdZn/ZnO interface sites of PdZn@ZnO catalyst could suppress O2 dissociation and subsequent oxidation of the PdZn catalyst. In addition, ZnO shell of PdZn@ZnO prevented the encapsulated PdZn alloys from sintering, resulting in its superior stability to those of the reported catalysts. The PdZn@ZnO catalyst showed great potential for the on-board production of hydrogen for PEMFC-powered vehicles.

Enhanced formaldehyde oxidation over MnO2 and doped manganese-based catalysts: Experimental and theoretical Insights into mechanism and performance

Thermal catalytic degradation of formaldehyde (HCHO) over manganese-based catalysts is garnering significant attention. In this study, both theoretical simulations and experimental methods were employed to elucidate the primary reaction pathways of HCHO on the MnO2(110) surface. Specifically, the effects of doping MnO2 with elements such as Fe, Ce, Ni, Co, and Cu on the HCHO oxidation properties were evaluated. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS), were employed to discern the physical properties and chemical states of the active components on the catalyst surface. The comprehensive oxidation pathway of HCHO on the MnO2(110) surface includes O2 adsorption and dissociation, HCHO adsorption and dehydrogenation, CO2 desorption, H2O formation and desorption, oxygen vacancy supplementation, and other elementary reactions. The pivotal rate-determining step was identified as the hydrogen migration process, characterized by an energy barrier of 234.19 kJ mol−1. Notably, HCHOO and *CHOO emerged as crucial intermediates during the reaction. Among the doped catalysts, Fe-doped MnO2 outperformed its counterparts doped with Ce, Ni, Co, and Cu. The optimal degradation rate and selectivity were achieved at a molar ratio of Fe: Mn = 0.1. The superior performance of the Fe-doped MnO2 can be ascribed to its large specific surface area, conducive pore structure for HCHO molecular transport, rich surface-adsorbed oxygen species, and a significant presence of oxygen vacancies.

Catalytic ozonation of p-xylene over Mn/Ce oxide nanorods treated by vacuum deoxidation

Xylene with high photochemical activity is commonly used as a raw material and organic solvent. The treatment of waste gases containing xylene is a necessary measure to ensure the air quality. Mn/Ce oxide nanorods were prepared using SBA-15 as a template and subjected to vacuum deoxidation for catalytic ozonation of p-xylene. Hydrothermal demolding conduced to detach the nanorods to improve the surface area and porosity, providing massive active sites for catalytic ozonation. The results indicated that numerous Mn-O-Ce solid solution structures formed in Mn/Ce composite oxides, especially Mn0.5Ce0.5Ox, to enhance weak- and medium-acid sites and oxygen vacancies (OVs) on the catalysts. Vacuum deoxidation effectively and facilely raised OVs for the catalysts. Vacuum-deoxidated Mn0.5Ce0.5Ox with the most Mn-O-Ce structures achieved the highest removal rate of p-xylene and CO2 selectivity since the most OVs and weak- and medium-acid sites appeared in it compared with the other catalysts. The mechanism of catalytic ozonation may be that p-xylene adsorbed on the acid site of vacuum-deoxidized Mn0.5Ce0.5Ox is attacked by the reactive oxygen species (ROS) generated by the dissociation of O3 on OVs. The degraded p-xylene and its intermediate are finally oxidized by ROS to CO2 and H2O.

Photocatalytic Oxidative Coupling of Methane over Au1 Ag Single-Atom Alloy Modified ZnO with Oxygen and Water Vapor: Synergy of Gold and Silver.

C-H dissociation and C-C coupling are two key steps in converting CH4 into multi-carbon compounds. Here we report a synergy of Au and Ag to greatly promote C2 H6 formation over Au1 Ag single-atom alloy nanoparticles (Au1 Ag NPs)-modified ZnO catalyst via photocatalytic oxidative coupling of methane (POCM) with O2 and H2 O. Atomically dispersed Au in Au1 Ag NPs effectively promotes the dissociation of O2 and H2 O into *OOH, promoting C-H activation of CH4 on the photogenerated O- to form *CH3 . Electron-deficient Au single atoms, as hopping ladders, also facilitate the migration of electron donor *CH3 from ZnO to Au1 Ag NPs. Finally, *CH3 coupling can readily occur on Ag atoms of Au1 Ag NPs. An excellent C2 H6 yield of 14.0 mmol g-1 h-1 with a selectivity of 79 % and an apparent quantum yield of 14.6 % at 350 nm is obtained via POCM with O2 and H2 O, which is at least two times that of the photocatalytic system. The bimetallic synergistic strategy offers guidance for future catalyst design for POCM with O2 and H2 O.

Photocatalytic Oxidative Coupling of Methane over Au1Ag Single‐Atom Alloy Modified ZnO with Oxygen and Water Vapor: Synergy of Gold and Silver

AbstractC−H dissociation and C−C coupling are two key steps in converting CH4 into multi‐carbon compounds. Here we report a synergy of Au and Ag to greatly promote C2H6 formation over Au1Ag single‐atom alloy nanoparticles (Au1Ag NPs)‐modified ZnO catalyst via photocatalytic oxidative coupling of methane (POCM) with O2 and H2O. Atomically dispersed Au in Au1Ag NPs effectively promotes the dissociation of O2 and H2O into *OOH, promoting C−H activation of CH4 on the photogenerated O− to form *CH3. Electron‐deficient Au single atoms, as hopping ladders, also facilitate the migration of electron donor *CH3 from ZnO to Au1Ag NPs. Finally, *CH3 coupling can readily occur on Ag atoms of Au1Ag NPs. An excellent C2H6 yield of 14.0 mmol g−1 h−1 with a selectivity of 79 % and an apparent quantum yield of 14.6 % at 350 nm is obtained via POCM with O2 and H2O, which is at least two times that of the photocatalytic system. The bimetallic synergistic strategy offers guidance for future catalyst design for POCM with O2 and H2O.

Graphene-supported MB36 clusters (M=Fe, Co, Ni) as a single-atom electrocatalyst for the oxygen reduction reaction: A DFT study

This study delves into the potential of MB36 clusters (where M = Fe, Co, Ni) supported on graphene as effective single-atom catalysts (SACs). Our research is methodically segmented into several stages, each designed to validate the feasibility of the proposed material. We begin by investigating the potential energy surface of MB36 clusters. Our findings reveal a preference for metallic atoms to position themselves above the central hexagonal vacancy of the B36 cluster. This factor significantly contributes to the stabilization of the resultant MB36 system. Subsequently, we employ ab-initio molecular dynamic simulations to affirm the stability of the graphene-supported MB36 clusters. In the final stage, we evaluate the system's catalytic capability for the oxygen reduction reaction (ORR) by calculating the dissociation energy of O2 and OOH post their adsorption on the M atom of the graphene-supported MB36 cluster. These simulations suggest that FeB36 could maintain stability at room temperature, exhibiting activation energies for O2 and OOH dissociation lower than those previously reported on Fe/N/C-type SACs, approaching those found on the Pt(111) surface, the most efficient ORR electrocatalyst. This computational study suggests that graphene-supported FeB36 clusters could emerge as a promising candidate for SACs.

Isoprene peroxy chemistry operates competitively in areas of East China

We validated the recently updated Caltech Isoprene Mechanism (CIM), which represents the complex dynamics of isoprene peroxy isomers through repetitive O2 addition and dissociation reactions, using a dataset synthesized from two field measurements taken place in both urban and rural areas of East China. The dataset covers a large span of nitric oxide (NO) levels ranging from tens of ppt characteristic of clean rural air to tens of ppb typically found in the polluted urban environment. An observationally constrained zero-dimensional box model that incorporates the CIM mechanism was constructed to simulate the daytime profiles of methacrolein (MACR) and methyl vinyl ketone (MVK), two major first-generation products that account for over half of the total carbon oxidation flow of isoprene. A closer agreement with the measurements was found compared with the traditional mechanism that prescribes a fixed yield of MACR and MVK across all NO levels. This result demonstrates that the isoprene peroxy dynamics operate competitively in the area and play a governing role in the final distribution of isoprene oxidation products. The atmospheric implication is that, with effective measures taken to reduce pollutant emissions in East China, the prevailing chemical regime at play has evolved and implementing the updated isoprene mechanism into regional models will have a profound impact on the predicted radical cycling and ozone production of the local atmosphere.

Modeling Equilibration Dynamics of Hyperthermal Products of Surface Reactions Using Scalable Neural Network Potential with First-Principles Accuracy.

Equilibration dynamics of hot oxygen atoms following the dissociation of O2 on Pd(100) and Pd(111) surfaces are investigated by molecular dynamics simulations based on a scalable neural network potential enabling first-principles description of the interaction of O2 and O interacting with variable Pd supercells. By analyzing hundreds of trajectories with appropriate initial sampling, the measured distance distribution of equilibrated atom pairs on Pd(111) is well reproduced. However, our results on Pd(100) suggest that the ballistic motion of hot atoms predicted previously is a rare event under ideal conditions, while initial molecular orientation and surface thermal fluctuation could significantly affect the overall postdissociation dynamics. On both surfaces, dissociated hyperthermal oxygen atoms primarily locate their nascent positions and experience a similar random walk motion nearby.