H2O Reaction Research Articles

Enabling Direct Photoelectrochemical H₂ Production using Alternative Oxidation Reactions on WO₃.

The efficient and inexpensive conversion of solar energy into chemical bonds, such as in H2 via thephotoelectrochemical splitting of H2O, is a promising route to produce green industrial feedstocks and renewablefuels, which is a key goal of the NCCR Catalysis. However, the oxidation product of the water splitting reaction,O2, has little economic or industrial value. Thus, upgrading key chemical species using alternative oxidationreactions is an emerging trend. WO3 has been identified as a unique photoanode material for this purpose sinceit performs poorly in the oxygen evolution reaction in H2O. Herein we highlight a collaboration in the NCCRCatalysis that has gained insights at the atomic level of the WO3 surface with ab initio computational methodsthat help to explain its unique catalytic activity. These computational efforts give new context to experimentalresults employing WO3 photoanodes for the direct photoelectrochemical oxidation of biomass-derived 5-(hydroxymethyl)furfural. While yield for the desired product, 2,5-furandicarboxylic acid is low, insights into the reactionrate constants using kinetic modelling and an electrochemical technique called derivative voltammetry, giveindications on how to improve the system.

The mechanism characterizations of methane steam reforming under coupling condition of temperature and ratio of steam to carbon

To elucidate the coupling effects of temperature and ratio of steam to carbon on the methane steam reforming process, the characterizations of methane steam reforming at different temperature and ratio of steam to carbon in term of distribution of H2 and CO, and the elementary reaction rate were investigated. Meanwhile, the formation mechanisms of H2 and CO via sensitivity analysis and reaction path analysis were obtained. The results showed that the coupling effects of temperature and ratio of steam to carbon on the methane steam reforming were higher than that of individual factor. The effects of temperature on the methane steam reforming were higher than that of the ratio of steam to carbon. The adsorption and desorption reaction of CH4 on the surface of Ni-based catalyst had the most obvious effect on the sensitivity of H2, CH4 and CO. Besides, the effects of adsorption and desorption reaction of H2O on the sensitivity of H2 were higher than that of CH4 and CO. Hydrogen was generated by the desorption reaction of H(s) in the adsorbed state and from three generating paths: a) CH4(s) dissociated directly or reacted with O(s) to form H(s); b) The dissociation reaction of H2O(s) produced H(s); c) OH(s) dissociated directly or reacted with C(s) to form H(s). Carbon monoxide was generated from single path: CH4(s)→CH3(s)→CH2(s)→CH(s)→C(s)→CO(s)→CO(g).

Behaviors of H, D, and Li in water-soaked LATP solid electrolytes at room temperature

The elastic recoil detection (ERD) technique was employed to measure the depth distributions of lithium (Li) and hydrogen isotopes (H and D) near the surface of NASICON-type LATP (Li1+xAlxTi1−x/2Ge1−x/2P3−yO12) solid electrolytes soaked in water (H2O and D2O) at room temperature for 1–80 days. The ERD spectra demonstrated H and D absorption on the LATP surface by H2O and D2O soaking and Li segregation to the top surface. Moreover, the field emission-scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) images, and atomic absorption spectrophotometry (AAS) indicated the formation of numerous black substances with approximately 0.5 × 3.0 µm2 in area and < ∼50 nm in thickness and the dissolution of Li in water. Li migration from the bulk to the surface may occur through the reactions of H2O and D2O with Ge, subsequently leading to H and D trapping at Li substitutional sites.

Hydroxylation of some emerging disinfection byproducts (DBPs) in water environment: Halogenation induced strong pH-dependency

In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halogenated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H2O2 system. For the reactions of HO• with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The kapp values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the kapp values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds. These findings provided meaningful insights into the strong pH-dependent hydroxylation of emerging DBPs on molecular level.

Effect of dimethyl ether on ignition characteristics of ammonia and chemical kinetics

The contribution of dimethyl ether(DME) to the ignition delay times(IDTs) of ammonia(NH3) was investigated behind reflected shock waves. The experiments were performed at a pressure of 0.14/1.0 MPa, temperature range of 1150–1950 K, equivalence ratio of 0.5/1.0/2.0, and NH3/DME mixing ratios of 100/0, 95/5, 90/10, and 70/30. It was observed that the addition of DME decreased the IDTs and promoted the reactivity of NH3. With the increase of DME, the effect of the equivalence ratio on the IDTs of NH3 decreased. Under higher temperature and pressure conditions, the promoting effect of DME on the ignition of NH3 was weakened. An updated mechanism is proposed to reveal the promoting effect of DME on the ignition of NH3. Mechanisms from the literature were compared against the measurements, and the updated kinetic mechanism was validated with experimental data. Good agreement between measurements and simulations were shown. Chemical kinetic analyses were performed to interpret the interactions between DME and NH3 during fuel ignition. The numerical analysis indicated that the promotion effect of DME is primarily due to an increase of the rate of production and concentration of the radical pool, especially the OH radical pool. The large number of OH radicals generated by the reaction HO2 + CH3 = OH + CH3O during the early oxidation of DME is key to the NH3 consumption and early initiation of the chain reaction.

Promoted photocatalytic hydrogen evolution via double-electron migration in Ag@g-C3N4 heterojunction

The unsaturated edge Ag introduced on the surface of photocatalysts plays an important role in boosting photo-excited electrons for the photoreduction H2O reaction. However, a moderate and tractable strategy to efficiently expose edge Ag remains an enormous challenge. For this purpose, a core skeleton with ‘Ag conductive nanosphere array’ inside and a two-dimensional sheet structure with g-C3N4 layer outside are formed. The introduction of Ag nanospheres into g-C3N4 not only enlarges the distance between g-C3N4 nanolayers, but also increases the exposure of Ag nanospheres. When Ag intimately contacts with g-C3N4, the electrons of g-C3N4 voluntarily flow to the Ag. Consequently, a built-in electric field (IEF) has been formed at interface of Ag@g-C3N4 heterojunction, which prevents the continuous flow of electrons from g-C3N4 to Ag. Under irradiation, the e− accumulated in Ag tend to recombine with the h+ in the valence band of g-C3N4 which is driven by Coulomb interaction and IEF. Ag nanospheres are fabricated as a co-catalyst to decorate the g-C3N4 nanolayer, which hinder the conglomeration of g-C3N4 nanolayers. Moreover, Ag@g-C3N4 heterojunction provides polyunsaturated edge Ag as active sites, inducing prolonged lifetime of photogenerated electrons and formed the unique charge transfer channels. In addition, abundant nitrogen vacancies are formed, which strengthens the chemisorption of H2O. As a result, supreme Ag@g-C3N4 realizes a high H2 evolution of 312.5 μmol and preserves a good sustainability. This paper emphasizes the importance of unique electron transfer pathway and chemisorption of water for photoreduction H2O.

Three-dimensionally ordered macroporous (3DOM) structure promoted the activity and H2O poisoning resistance of CeMn/3DOM-TiO2 catalyst in NH3-SCR

NH3-SCR is an effective mean of NOx removal in the non-electric industry, however, the high activation temperature and poor H2O resistance of SCR catalysts posed a barrier to its application. In this work, a series of three-dimensionally ordered macroporous (3DOM) catalysts were synthesized via a colloidal crystal template (CCT) method, and various characterizations were carried out to explore the physicochemical property of catalysts. The experiment results reveal that Ce0.2Mn0.2/3DOM-TiO2 catalyst presents the excellent low-temperature catalytic activity of nearly 100% at 100 °C. Furthermore, the enhanced H2O resistance is achieved, certified by the unaffected NO remove at 150 °C in the participation of 15 vol% H2O. The characterizations results exhibit that the improved dispersion of the active component and enhanced redox ability are conducive to the low-temperature catalytic activity. N2 adsorption and desorption experiments indicate that catalyst with 3DOM support possesses a larger pore diameter and specific surface area, which may weaken the condensation of H2O in the microporosity of catalysts and improved the H2O resistance of the catalyst. In situ DRIFTS results manifest that Ce0.2Mn0.2/3DOM-TiO2 catalyst could not only absorb more NH3 and generate more surface-active sites, but inhibit the competitive adsorption between H2O and SCR reactants.

Experimental chemical budgets of OH, HO2, and RO2 radicals in rural air in western Germany during the JULIAC campaign 2019

Abstract. Photochemical processes in ambient air were studied using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany. Ambient air was continuously drawn into the chamber through a 50 m high inlet line and passed through the chamber for 1 month in each season throughout 2019. The residence time of the air inside the chamber was about 1 h. As the research center is surrounded by a mixed deciduous forest and is located close to the city Jülich, the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements of hydroxyl (OH), hydroperoxyl (HO2), and organic peroxy (RO2) radicals were achieved by a laser-induced fluorescence instrument. The radical measurements together with measurements of OH reactivity (kOH, the inverse of the OH lifetime) and a comprehensive set of trace gas concentrations and aerosol properties allowed for the investigation of the seasonal and diurnal variation of radical production and destruction pathways. In spring and summer periods, median OH concentrations reached 6 × 106 cm−3 at noon, and median concentrations of both HO2 and RO2 radicals were 3 × 108 cm−3. The measured OH reactivity was between 4 and 18 s−1 in both seasons. The total reaction rate of peroxy radicals with NO was found to be consistent with production rates of odd oxygen (Ox= NO2 + O3) determined from NO2 and O3 concentration measurements. The chemical budgets of radicals were analyzed for the spring and summer seasons, when peroxy radical concentrations were above the detection limit. For most conditions, the concentrations of radicals were mainly sustained by the regeneration of OH via reactions of HO2 and RO2 radicals with nitric oxide (NO). The median diurnal profiles of the total radical production and destruction rates showed maxima between 3 and 6 ppbv h−1 for OH, HO2, and RO2. Total ROX (OH, HO2, and RO2) initiation and termination rates were below 3 ppbv h−1. The highest OH radical turnover rate of 13 ppbv h−1 was observed during a high-temperature (max. 40 ∘C) period in August. In this period, the highest HO2, RO2, and ROX turnover rates were around 11, 10, and 4 ppbv h−1, respectively. When NO mixing ratios were between 1 and 3 ppbv, OH and HO2 production and destruction rates were balanced, but unexplained RO2 and ROX production reactions with median rates of 2 and 0.4 ppbv h−1, respectively, were required to balance their destruction. For NO mixing ratios above 3 ppbv, the peroxy radical reaction rates with NO were highly uncertain due to the low peroxy radical concentrations close to the limit of NO interferences in the HO2 and RO2 measurements. For NO mixing ratios below 1 ppbv, a missing source for OH and a missing sink for HO2 were found with maximum rates of 3.0 and 2.0 ppbv h−1, respectively. The missing OH source likely consisted of a combination of a missing inter-radical HO2 to OH conversion reaction (up to 2 ppbv h−1) and a missing primary radical source (0.5–1.4 ppbv h−1). The dataset collected in this campaign allowed analyzing the potential impact of OH regeneration from RO2 isomerization reactions from isoprene, HO2 uptake on aerosol, and RO2 production from chlorine chemistry on radical production and destruction rates. These processes were negligible for the chemical conditions encountered in this study.

XPS analysis of graphitic carbon nitride functionalized with CoO and CoFe2O4

Materials based on graphitic carbon nitride (gCN) have drawn a great deal of attention as (photo)electrocatalysts triggering the oxygen evolution reaction (OER) in H2O splitting processes to yield hydrogen fuel. In this work, nonmonochromatized Mg Kα radiation (1253.6 eV) was used to acquire photoelectron spectroscopy data on gCN-containing composite systems supported on fluorine-doped tin oxide. The investigated materials were prepared via a straightforward decantation route to yield carbon nitride, followed by functionalization with low amounts of nanostructured co-catalysts (CoO, CoFe2O4) through radio frequency-sputtering, and final thermal treatment under an inert atmosphere. Structural and morphological analyses highlighted the formation of composite systems, in which the single constituents, featuring an intimate contact, maintained their chemical identity. This work proposes a data record including both survey scans and high-resolution spectra of C 1s, N 1s, O 1s, Co 2p, and Fe 2p core-levels for three representative specimens comprising bare and functionalized graphitic carbon nitride (gCN, gCN-CoO, and gCN-CoFe2O4). The obtained results, discussed in relation to the different chemical environments for the various elements, will be useful as a comparison for further studies in related fields.

Investigation on the reaction mechanism of methane combustion near flammability limits at elevated pressures and temperaturaes

Combustible gas explosions may occur at elevated pressure and temperature of wellbore conditions. To better understand and protect against wellbore explosion, it is necessary to study the combustion mechanism of methane at elevated pressure and temperature conditions. In this study, combustion mechanisms near the stoichiometric concentration as well as the flammability limit were investigated using a one-dimensional premixed laminar flame speed model based on the GRI 3.0 mechanism. The effects of initial pressure and initial temperature on flame temperature were analyzed. The main free radicals and reactions at different conditions were determined by sensitivity analysis. The reaction rates of the main reactions were comprehensively analyzed with previous experimental results of the flammability limit at different conditions. The mechanism of how initial pressure and initial temperature affects the flammability limit was determined. The results showed that the radical HO2 and its involved reaction HO2+CH3OH + CH3O play a crucial role in the methane combustion process at elevated pressure and temperature conditions. The initial pressure and initial temperature quantitatively affect the flammability limit mainly by affecting the reaction rates of the main reactions.

Probing the Potential Energy Profile of the I + (H2O)3 → HI + (H2O)2OH Forward and Reverse Reactions: High Level CCSD(T) Studies with Spin-Orbit Coupling Included.

Three different pathways for the atomic iodine plus water trimer reaction I + (H2O)3 → HI + (H2O)2OH were preliminarily examined by the DFT-MPW1K method. Related to previous predictions for the F/Cl/Br + (H2O)3 reactions, three pathways for the I + (H2O)3 reaction are linked in terms of geometry and energetics. To legitimize the results, the "gold standard" CCSD(T) method was employed to investigate the lowest-lying pathway with the correlation-consistent polarized valence basis set up to cc-pVQZ(-PP). According to the CCSD(T)/cc-pVQZ(-PP)//CCSD(T)/cc-pVTZ(-PP) results, the I + (H2O)3 → HI + (H2O)2OH reaction is predicted to be endothermic by 47.0 kcal mol-1. The submerged transition state is predicted to lie 43.7 kcal mol-1 above the separated reactants. The I···(H2O)3 entrance complex lies below the separated reactants by 4.1 kcal mol-1, and spin-orbit coupling has a significant impact on this dissociation energy. The HI···(H2O)2OH exit complex is bound by 4.3 kcal mol-1 in relation to the separated products. Compared with simpler I + (H2O)2 and I + H2O reactions, the I + (H2O)3 reaction is energetically between them in general. It is speculated that the reaction between the iodine atom and the larger water clusters may be energetically analogous to the I + (H2O)3 reaction. The iodine reaction I + (H2O)3 is connected with the analogous valence isoelectronic bromine/chlorine reactions Br/Cl + (H2O)3 but much different from the F + (H2O)3 reaction. Significant difference with other halogen systems, especially for barrier heights, are seen for the iodine systems.

Inhibition/Promotion Effect of C6F12O Addition on Premixed Laminar RP-3/Air Flames.

C6F12O (Novec 1230) is one of the most potential substitutes of Halon 1301. However, the study of inhibition/promotion effect of C6F12O addition on aviation kerosene is rarely reported, which greatly limits the development and application of C6F12O in oil fire accidents. In this study, numerical research was conducted to study the inhibition/promotion effect of C6F12O addition by a newly developed and optimized RP-3/C6F12O coupling skeletal mechanism. A novel methodology based on fictitious species was proposed and adopted to identify the physical dilution and thermal effects as well as the chemical radical and thermal interaction effects of C6F12O addition. It is observed that both inhibition and promotion effects can be exhibited because the chemical effect includes radical and thermal interactions at different equivalence ratios. In order to explore the kinetic reasons, the reaction path analyses were conducted. The results indicate that the HF formation reactions and the O2 consumption fluorine-containing reactions, as well as the reactions of H2O + F = OH + HF and C3F7 + O2 = C3F7O + O, were the key inhibition and promotion reaction routes, respectively. Compared with methane, the lower H/C ratio of RP-3 makes it more suitable for the use of C6F12O to suppress combustion.

Reactions of NO and H2O on the PuO2 {111} surface: A DFT study

The effect of the Hubbard U parameter is explored in periodic boundary condition PBE+U calculations of a variety of properties of bulk PuO2 and its {111} surface. Comparison is made with experimentally-determined bulk and surface properties, including band gap and lattice parameter, hybridization of the Pu 5f and O 2p states at the top of the valence band, peak separation in the valence band, and the {111} surface work function. Comparative PBE0 calculations, and the Bader charges of the atoms in the {111} surface, are also assessed. A U value of 3 eV is recommended, and is used in PBE+U study of H2O and NO reacting both individually and sequentially on PuO2 {111}. For NO interacting individually, approach to the surface is orientation-dependent, and surface-bound NO forms defect surface states between the valence and conduction bands. For water reactions with and without NO present on the surface, the Pu 5f band centre plays a major role in the reactions. When NO is present, a linear relation emerges between water adsorption energy and 5f band centre relative to the Fermi level. Both Pu 5f band centre relative to the Fermi level and the energetic gap between the 5f band centre and 2p band centre of the water O govern the barrier to water splitting.

Highly active and stable CuxFey/AC-H catalysts with CuFe2O4 for NO reduction by CO in the presence of H2O and SO2 under regeneration gas

For industrial flue gas, the synergistic removal of NOx and CO pollutants is in high demand but still has not been realized due to the presence of O2. We propose firstly that activated carbon regeneration gas provides suitable O2-free conditions for NO reduction by CO, but high contents of 5% SO2 and 5% H2O affect the catalyst activity. Here, we report a bimetallic modified catalyst CuxFey/AC-H that exhibits high catalytic activity under the abovementioned conditions due to the high amount of CuFe2O4. By regulating the Cu/Fe ratio, the formation of CuFe2O4 active sites is promoted, which improves the redox properties, adsorption and activation capacity of NO, the ratio of high valence metal, and content of synergistic oxygen vacancies. Based on in situ DRIFTS and fixed-bed FTIR/MS combined platform, it was found that the side reaction of H2O with the intermediate of −NCO forms NH3 above 250 °C and with CO forms H2 above 400 °C·NH3 and H2 provide additional reaction pathways of Fast-SCR and H2-SCR to significantly improve the reaction activity with 92.0% of NO conversion at 450 °C and 108,000 mL g−1h−1 on Cu2Fe2/AC-H. According to DFT calculations, CuFe2O4 active sites provide the high binding energy of sulfation, and then Cu2Fe2/AC-H demonstrates excellent activity and long-term stability with 72.2% of NO conversion at high contents of SO2 and H2O for 48 h. And CuxFey/AC-H provides great potential prospects for the application of NO reduction by CO under activated carbon regeneration gas.

New insight into formation mechanism, source and control strategy of severe O3 pollution: The case from photochemical simulation in the Wuhan Metropolitan Area, Central China

The Wuhan Metropolitan Area, located in Central China, has experienced severe O3 pollution in recent years; thus urging to diagnose formation regime and propose reasonable control strategies. Multi-source data of air pollutants and meteorological factors in 4 cities during August 2019 when severe regional O3 pollution occurred were obtained; then, in-situ O3 formation mechanism, the O3-precursors sensitivity, the sources and control strategies of O3 were evaluated based on the combination of the 0-D photochemical observation-based model and the positive matrix factorization model through the analysis of local ozone budget, the relative incremental reactivity, an empirical kinetic model approach and source apportionment. The results indicated the P(O3) (net O3 production rate) was 25 ppbv h−1 in Ezhou and 11–13 ppbv h−1 in other 3 cities. The dominated photochemical production of O3 was NO + HO2 reaction (62–71%), whereas the main pathway to destroy O3 during daytime was NO2 + OH (>70%) and nocturnal loss of O3 with alkenes even reached up to 39–46%. Generally, O3 formation was sensitive to AVOC (Anthropogenic Volatile Organic Compounds), in which reactive aromatics, OVOCs (Oxygenated VOCs), and alkenes (xylenes, ethylene, isoprene, methyl vinyl ketone, hexanal, toluene and methacrolein, specifically) as well as abundant i-pentane should be targeted to alleviate O3 pollution. The highly reactive VOCs sources for O3 formation in this region were vehicular exhaust (28–41%), industrial emissions (20–29% except Ezhou), and solvent use (17–29% except Huangshi). Co-reduction of O3 precursors in aforementioned reactive emissions according to optimal ratios of AVOC to NO2, i.e., 5:1 (Wuhan and Huanggang), 4:1 (Ezhou), and 6:1 (Huangshi), could achieve local O3 effective mitigation. Surprisingly, P(O3) could reduce by 38% and 48% under 40% AVOC cut accompanied by NO2 in more contaminated cities (Wuhan and Ezhou). Overall, our study provides new insight to future collaborative O3 alleviation strategies formulation in Central China, which quantified O3 formation at different precursors levels in different cities suffering from regional O3 pollution, concluded best precursors control ratios and confirmed validity of O3 mitigation through precursors-oriented emission reduction in vital sources.

Theoretical studies on the kinetics and dynamics of the BeH+ + H2O reaction: comparison with the experiment.

The reaction of BeH+ with background gaseous H2O may play a role in qubit loss for quantum information processing with Be+ as trapped ions, and yet its reaction mechanism has not been well understood until now. In this work, a globally accurate, full-dimensional ground-state potential energy surface (PES) for the BeH+ + H2O reaction was constructed by fitting a total of 170 438 ab initio energy points at the level of RCCSD(T)-F12/aug-cc-pVTZ using the fundamental invariant-neural network method. The total root-mean-square error of the final PES was 0.178 kcal mol-1. For comparison, quasi-classical trajectory calculations were carried out on the PES at an experimental temperature of 150 K. The obtained thermal rate constant and product branching ratio of the BeD+ + H2O reaction agreed quite well with experimental results. In addition, the vibrational state distributions and energy disposals of the products were calculated and rationalized using the sudden vector projection model.

Barrier heights, reaction energies and bond dissociation energies for RH + HO2 reactions with coupled-cluster theory, density functional theory and diffusion quantum Monte Carlo methods.

Hydrogen abstraction reactions by the HO2 radical from hydrocarbon molecules are an important class of reactions in the autoignition of hydrocarbon fuels. Performance of DLPNO-CC and DFT methods using three hybrids and four double hybrids as well as FN-DMC with the single-Slater-Jastrow trial wavefunction on barrier heights and reaction energies of RH + HO2 reactions as well as bond dissociation energies of the involved X-H molecules is evaluated by comparison with the highly accurate CCSD(T)-F12b/CBS results in this study. Our results show that the DLPNO-CCSD(T)-F12 method can achieve highly accurate barrier heights, reaction energies and X-H bond energies for RH + HO2 reactions at a relatively low computational cost, and it is applicable to the H-abstraction reactions of larger molecules. Among all DFAs, MN15 and the employed double hybrids can achieve accurate barrier heights and reaction energies with MADs of less than or around 2 kJ mol-1, but their error on X-H bond energies is more pronounced. Only DSD-BLYP and DSD-PBEB95 can provide X-H bond energies with MADs less than 4 kJ mol-1. Considering dispersion correction in DFT calculations does not improve these barrier heights and reaction energies. The error of FN-DMC on barrier heights and reaction energies is slightly larger than that of MN15 and those of double hybrids, but it can achieve results within chemical accuracy for these reactions and the X-H bond energies.

Effect of formic acid on O2 + OH˙CHOH → HCOOH + HO2 reaction under tropospheric condition: kinetics of cis and trans isomers.

Formic acid (HCOOH) is one of the highly abundant acids in the troposphere. It is important in the formation of atmospheric aerosols and impacts the acidity of rainwater. In the present scenario, the model chemistry of HCOOH(FA) sources and sinks is poorly understood. In this work, we apply quantum chemical methods coupled with advanced statistical rate theories to understand the production of FA and its catalytic behavior under tropospheric conditions. The potential energy surfaces (PES) for O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) reactions were constructed using the CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd) level and rate constants for the production of FA were predicted using Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation with Eckart tunnelling and canonical variational transition state theory (CVT) with small curvature tunnelling (SCT) between the temperature range of 200-320 K and pressure range of 0.001 to 10 bar. The reaction follows the formation of cis and trans intermediates followed by spontaneous decomposition via concerted HO2 elimination to form stable post intermediates, which then leads to the straight formation of cis and trans formic acid. The current study also helps understand the role of cis and trans contribution to the total rate constants. The results show that O2 + OH˙CHOH is dominated by both cis and trans isomers; however, the trans isomer plays a more important role in the catalytic reaction. This result is due to the formation of a strong hydrogen-bonded complex in the trans isomer, which is dominated by the enthalpy factor rather than the entropy factor. The results predict that the catalytic effect of FA on the O2 + OH˙CHOH reaction is important when the concentration of FA is not included in the calculations; however, it has no effect under tropospheric conditions, when the FA concentration is included in the calculation. As a result, the total effective reaction rate constants are smaller. This work provides experimental/theoretical confirmation of Franco et al. who predicted that methanediol is the precursor for the FA formation, resolving an open problem in the kinetics of the gas phase reaction. O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) probably explain other diol systems, which can help explain the formation of other atmospheric acids that affect aerosol formation and cloud evolution.

Hydrogen evolution reaction of Ben + H2O (n = 5-9) based on density functional theory.

The structural evolution of Ben clusters with n = 5-9, the adsorption energy created by the Ben@H2O (n = 5-9) complex, and the mechanism of the hydrogen evolution reaction of Ben + H2O (n = 5-9) were all studied using DFT calculations based on the PBE0-D3/Def2TZVP level. Excluding the Be7 cluster, the global minimum structures of beryllium clusters with n = 5-9 showed a higher point group pair formation. Be7 clusters' high point group symmetry is unstable. Be9@H2O released the greatest energy during the complex's creation (-1.45 eV). Exothermic hydrogen evolution occurs in Ben + H2O (n = 5-9), and all transition states, intermediate stages, and products have energies lower than the equilibrium constant (EC). More energy is released when an O-H bond in the Ben@H2O (n = 5-9) complex is broken, and the energy release results in a change in the cluster structure, which is more pronounced in the Be7 + H2O reaction. Interestingly, there are eight transition states in the Be6 + H2O hydrogen evolution reaction, with the second O-H bond break requiring more energy than the first. There are only three transition states in the Be8 + H2O hydrogen evolution reaction, and the reaction energy is the greatest (-4.13 eV).

Full-dimensional neural network potential energy surface and dynamics of the CH2OO + H2O reaction.

An accurate global full-dimensional machine learning-based potential energy surface (PES) of the simplest Criegee intermediate (CH2OO) reaction with water monomer was developed based on the high level of extensive CCSD(T)-F12a/aug-cc-pVTZ calculations. This analytical global PES not only covers the regions of reactants to hydroxymethyl hydroperoxide (HMHP) intermediates, but also different end product channels, which facilities both the reliable and efficient kinetics and dynamics calculations. The rate coefficients calculated by the transition state theory with the interface to the full-dimensional PES agree well with the experimental results, indicating the accuracy of the current PES. Extensive quasi-classical trajectory (QCT) calculations were performed both from the bimolecular reaction CH2OO + H2O and from HMHP intermediate on the new PES. The product branching ratios of hydroxymethoxy radical (HOCH2O, HMO) + OH radical, formaldehyde (CH2O) + H2O2 and formic acid (HCOOH) + H2O were calculated. The reaction yields dominantly HMO + OH, because of the barrierless pathway from HMHP to this channel. The computed dynamical results for this product channel show the total available energy was deposited into the internal rovibrational excitation of HMO, and the energy release in OH and translational energy is limited. The large amount of OH radical found in the current study implies that the CH2OO + H2O reaction can provide crucially OH yield in Earth's atmosphere.