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In order to gradually reduce automobile exhaust pollution and improve fuel quality, the NOx sensor, which can be monitored in real time in an automobile engine's electronic control system, has become an indispensable part of the automobile lean burn system. In these types of NOx sensors, Au-doped platinum electrodes have received great attention due to their selectivity towards NO. However, the reaction process of NO gas on the Au-doped platinum electrode in the sensor and the possible regulation mechanism is still unclear. In this paper, the density functional theory (DFT) was used to analyze the effect of Au-doped Pt electrodes on the performance of nitrogen oxide sensors in automobiles. Firstly, the adsorption energies of NO molecules on pure Pt and Au/Pt surfaces were compared. The adsorption and dissociation of NO on Pt substrates doped with Au monomers, dimers, and trimers were investigated. These results showed that Au can effectively weaken the adsorption energy of NO molecules on a Pt surface. It was noted that with the increase in the number of Au atoms on the surface of Pt(111), the adsorption capacity of NO molecules on the alloy surface becomes weaker. When observing the transition state of NO decomposition on three different alloy surfaces, the study showed that the activation energy and reaction heat of NO dissociation increased. It further showed that doping with Au increased the activation energy of NO decomposition, thereby effectively inhibiting the decomposition of NO. [ABSTRACT FROM AUTHOR]

The possibility is considered of using values of the thermodynamic functions of transfer of the reagents and reaction products from water to an aqueous–organic solvent to calculate the change in the thermodynamic parameters of reactions in these media. Values of the change in the enthalpy of the dissociation reactions of glycine, β-alanine, L-α-phenylalanine, and glycylglycine in aqueous solutions of ethanol with different alcohol contents are calculated on the basis of the thermodynamic cycle. The calculated values of the enthalpy of the dissociation reactions of glycine and β-alanine are compared to ones obtained experimentally via calorimetry with good convergence of the results. It is found that a change in the enthalpy of the dissociation reactions of amino acids and glycylglycine contributes mainly to a change in the Gibbs energy of these processes in an aqueous ethanol solution. [ABSTRACT FROM AUTHOR]

Values are presented of the change in the enthalpy of dissociation of glycylglycine and glycine in aqueous solutions of dimethylsulfoxide of various compositions, calculated using the enthalpies of resolvation of participants in acid–base interactions in a water–dimethylsulfoxide solvent. A comparison of the calculated values of the enthalpy of dissociation of glycine in water–dimethylsulfoxide solutions and ones obtained experimentally show good convergence of the results. Values of the change in the entropy of the dissociation of glycylglycine and glycine in aqueous solutions of dimethylsulfoxide are calculated and used to show that the enthalpy and entropic contributions to the change in the Gibbs energy of the considered reactions in water–dimethylsulfoxide mixtures largely compensate for each other. [ABSTRACT FROM AUTHOR]

Pure metallic iron is a common component in extraterrestrial samples (e.g., ordinary chondrite, returned lunar samples), and is thought to be an indicator of extremely reducing conditions. However, tiny pure metallic iron (<1 mm) particles are rarely found in Howardite–Eucrite–Diogenite meteorites, and their formation mechanism on Vesta is poorly understood. Sub‐micron sized pure metallic iron particles were identified by transmission electron microscope studies of a melt pocket in the basaltic eucrite meteorite Northwest Africa 11592. Our results demonstrate that the pure metallic iron likely formed through a dissociation reaction of ferrous iron (i.e., 3Fe2+ = Fe0 + 2Fe3+) in pyroxene. Another disproportionation reaction product, ferric iron, was confirmed to be incorporated into Al‐rich clinopyroxene in the melt pocket by electron energy loss spectra analyses. The temperature conditions required for the formation of the melt pocket are estimated to be above 1,310°C, as indicated by the crystallization of nano‐sized hercynite within acicular plagioclase. Such high temperatures on Vesta could only have been reached if an impact occurred during peak thermal metamorphism, early in the asteroid's evolution. This formation mechanism of these pure metallic iron particles could play a role in redox environment of the Vesta. Plain Language Summary: Vesta, the second‐largest asteroid in the main belt and one of the most primitive solar system bodies, is among the few extraterrestrial objects visited by an orbital spacecraft. The Howardite–Eucrite–Diogenite (HED) clan of meteorites has been associated with Vesta for decades, and the Dawn mission provided strong evidence for their genetic relationship. Pure metallic iron (Fe0) particles, an indicator of reducing conditions, are rarely found in HED meteorites, and their origins are not clear. In basaltic eucrite Northwest Africa 11592, abundant sub‐micron sized Fe0 particles embedded in a shock‐induced melt pocket provide new insight into their formation. The presence of Fe3+‐bearing Al‐rich clinopyroxene and nano‐sized hercynite minerals in the melt pocket was also confirmed, which indicates that the Fe0 formed through the dissociation reaction of Fe2+ (i.e., 3Fe2+ = Fe0 + 2Fe3+) present in pyroxene at a temperature above 1,310°C. This formation mechanism provides a possibility that Fe0 particles may have formed as a result of cratering processes, which would have affected the redox conditions on Vesta. Key Points: Evidence for the dissociation reaction of Fe2+, which formed pure metallic iron particles in eucrite meteorite Northwest Africa 11592, was foundAl‐rich clinopyroxene is another carrier of Fe3+ in shocked meteorites, in addition to the high‐pressure phases ringwoodite and bridgmaniteThe disproportionation reaction would occur during cratering on Vesta and may have influenced the redox environment [ABSTRACT FROM AUTHOR]

In order to gradually reduce automobile exhaust pollution and improve fuel quality, the NOx sensor, which can be monitored in real time in an automobile engine’s electronic control system, has become an indispensable part of the automobile lean burn system. In these types of NOx sensors, Au-doped platinum electrodes have received great attention due to their selectivity towards NO. However, the reaction process of NO gas on the Au-doped platinum electrode in the sensor and the possible regulation mechanism is still unclear. In this paper, the density functional theory (DFT) was used to analyze the effect of Au-doped Pt electrodes on the performance of nitrogen oxide sensors in automobiles. Firstly, the adsorption energies of NO molecules on pure Pt and Au/Pt surfaces were compared. The adsorption and dissociation of NO on Pt substrates doped with Au monomers, dimers, and trimers were investigated. These results showed that Au can effectively weaken the adsorption energy of NO molecules on a Pt surface. It was noted that with the increase in the number of Au atoms on the surface of Pt(111), the adsorption capacity of NO molecules on the alloy surface becomes weaker. When observing the transition state of NO decomposition on three different alloy surfaces, the study showed that the activation energy and reaction heat of NO dissociation increased. It further showed that doping with Au increased the activation energy of NO decomposition, thereby effectively inhibiting the decomposition of NO.

High-energetic materials belong to two main classes: propellants and explosives. The still rather unexplored family of 1,3,5,2,4,6-trioxatriazinanes, N 3 O 3 R 3 , has a representative of each class. We have selected three compounds, R = H, R = CH 3 and R = NO 2 , this last compound being known as TNTOTA, "trinitro-trioxa-triazinane". Of these compounds we have studied the conformational analysis, the nitrogen inversion, the heats of formation, and the dissociation reaction into the three monomers. In addition, the corresponding 1,3,2,4-dioxadiazetidines (N 2 O 2 R 2 ) have also been studied., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

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Methane hydrate is one of the most promising future energy resources for humankind. In recent years, due to its vast existence in permafrost regions and deep ocean beds, increasing attention has been paid to the extraction, transportation and utilization of methane hydrate. The current study proposed core-scale numerical investigation models for the complex multiphase dissociation flows of methane hydrate inside porous media, which is a continuation and an extension of previous numerical investigations. The current numerical model focuses on the depressurization process and thermal boundary effects and discusses the parametric effects of the core-scale internal flows and controlling factors of the dissociation boundaries. The new findings with respect to the dissociation front movement and water–ice equilibrium effects during the dissociation process are also analyzed in this study. Ice formation and boundary heat conduction limitations are found to be critical for the smooth production of methane gas. Based on these results, trade off and production strategies for depressurization methods and thermal stimulation methods are also discussed in detail. It is hoped that this study will be useful for related core-scale analysis and possible engineering system designs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stabilities of AlH 3 -based composite high-energy systems were studied theoretically. • AlH 3 is more sensitive to temperature changes than its surface alumina film. • Non-decomposition adsorption occurred between CH 3 OC 2 H 5 /CH 3 N 3 and the alumina layer. • CH 3 OC 2 H 5 was stably adsorbed on the AlH 3 surface, and no reaction took place. • The adsorption of CH 3 N 3 on AlH 3 resulted in a surface hydrogen transfer reaction. The stability of aluminum hydride(AlH 3) based high-energy propellants is important for its large-scale application. In this work, to explore the stability mechanism of systems composed of AlH 3 and a binder containing C O C or –N 3 groups, molecular dynamics simulations were carried out to explore the thermal expansion properties of AlH 3 , and density functional theory calculations were employed to study the micro-interactions between molecules containing C O C or –N 3 groups and AlH 3. More specifically, CH 3 OC 2 H 5 and CH 3 N 3 were used to model polyethylene glycol and glycidyl azide polyether, respectively. It is found that AlH 3 is more sensitive to temperature changes than its oxide layer. Upon contact between the alumina layer and CH 3 OC 2 H 5 or CH 3 N 3 , these compounds exist stably on the α-Al 2 O 3 (0001) and γ-Al 2 O 3 (1 1 0) surfaces. Upon direct contact with the α-AlH 3 (0 1 0) surface, CH 3 OC 2 H 5 is relatively stable, while CH 3 N 3 can trigger the surface hydrogen transfer reaction due to the low energy barrier(5.0 kcal/mol). The current work provides a theoretical basis for understanding the sensitivity of AlH 3 and binders containing C O C or –N 3 groups, and is useful in the research and development of superior composite energetic propellants. [ABSTRACT FROM AUTHOR]

The adsorption and dissociation reactions of hydrogen sulfide (H 2 S) on the Pt atom anchored graphene (Pt-graphene) surfaces were investigated by first-principles calculations. It is found that the atomic S has stronger interaction with the Pt atom, while the SH and H 2 S species are weakly bound on the Pt-graphene surfaces. The adsorption of S-based species can regulate the electronic structure and magnetic properties of Pt-graphene systems. Besides, the calculated results show that the formation of SH and H from the H 2 S (H 2 S → SH + H) is rather easy and further the hydrogenation reaction generates the hydrogen molecular (H 2 ), as well as leaving the SH anchors on the Pt atom (SH + H + H → SH + H 2 ). Moreover, the preadsorbed S atom with the presence of H atoms can be converted into other species (SH or H 2 S) and thus inhibit the sulfur deposition on the Pt-graphene surfaces, which is expected to prevent the sulfur poisoning on graphene-based anode materials and boost the efficiency of fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: By performing density functional theory calculations, this work clarifies the sites and energetics of both the non-dissociative and dissociated adsorptions of CH3SH on clean Au(111) and Au(111) with intrinsic defects. It was found that the adsorption on defect-free Au(111) is most stable for non-dissociative CH3SH. Its direct molecular dissociation to form CH3S/Au and H/Au is barred by an activation barrier of 0.9eV. However, the presence of neighboring Auad can assist the dissociation reaction to form CH3S–Auad–H by lowering the energy barrier to 0.6eV. As for the dissociated CH3S, the surface geometry of two CH3S joined by a Auad is the most favorable one. [Copyright &y& Elsevier]

The potential energy surfaces (PES) of unimolecular dissociation reactions for di-ethyl beryllium and di-t-butyl beryllium are investigated by B3LYP, CCSD(T), and G3B3 approaches. Possible reaction pathways through either the radical or transition state (TS) of the molecules are considered. The geometries, vibrational frequencies and relative energies for various stationary points are determined. From the study of energetics, the TS pathways arising from concerted molecular eliminations are indicated to be the main dissociation pathways for both molecules. The PES differences of the dissociation reactions are investigated. The activation energies and rate constants will be helpful for investigating the predictive ability of the reaction in further theoretical and experimental research. [ABSTRACT FROM AUTHOR]

Abstract: To go further in the comprehension of hydrogen desorption mechanisms from PECVD (Plasma Enhanced Chemical Vapour Deposited) silicon nitride, a method to determine the chemical composition of amorphous silicon nitride films using fast and non destructive characterization techniques has been developed. In particular, Silyph name="sbnd" />H, Sincentrations are calculated from Fourier transform infra red spectroscopy, ellipsometry and mass measurement. Next, different PECVD silicon nitride films were annealed at 600°C during 2min. Results show that hydrogen desorption from PECVD silicon nitride depends on film mass density and main chemical reactions leading to hydrogen desorption are identified thanks to the determination of Sincentrations. [Copyright &y& Elsevier]

Abstract: Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature (T gas) value. In our opinion, the resulting T gas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N2H+ to N2 + leads to a calculated T gas of 4550 to 4900K, depending on the computational data used. The COH+ to CO+ system yields a similar temperature, which is not surprising considering the similar energies and structures of COH+ and N2H+. The dissociation of H2CO+ to HCO+ leads to a much lower T gas (<1000 to 2000K). Finally, the dissociation of H2COH+ to HCOH+ generates a T gas value between those from the other H x CO+ ions studied here. All of these measured T gas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO+ and COH+, and H2CO+ and HCOH+, which have virtually the same m/z values and need to be considered in the interpretation of results. [Copyright &y& Elsevier]

Abstract: The drawback of lean operation with hydrocarbon fuels is a reduced power output. Lean operation of hydrocarbon engines has additional drawbacks. Lean mixtures are hard to ignite, despite the mixture being above the low fire (point) limit of the fuel. This results in misfire, which increases un-burned hydrocarbon emissions, reduces performance and wastes fuel. Hydrogen can be used in conjunction with compact liquid fuels such as gasoline; alcohol or diesel provided each is stored separately. Mixing hydrogen with other hydrocarbon fuels reduces all of these drawbacks. Hydrogen’s low ignition energy limit and high burning speed makes the hydrogen/hydrocarbon mixture easier to ignite, reducing misfire and thereby improving emissions, performance and fuel economy. Regarding power output, hydrogen augments the mixture’s energy density at lean mixtures by increasing the hydrogen-to-carbon ratio, and thereby improves torque at wide-open throttle conditions. This paper involves the simulation program for determining the mole fraction of each of the exhaust species when the hydrogen is burnt along with diesel and the results are presented. The proportion of hydrogen in the hydrogen–diesel blend affecting the mole fraction of the exhaust species is also simulated. Experimental investigations were carried out, in hydrogen–diesel dual fuel mode, which showed a good agreement between the predicted and experimental results. The program code developed is valid for any combination of dual fuels. [Copyright &y& Elsevier]

Abstract: Common polyatomic ions (ArO+, NO+, H2O+, H3O+, Ar2 +, ArN+, OH+, ArH+, O2 +) in inductively coupled plasma-mass spectrometry (ICP-MS) are identified using high mass resolution and studied using kinetic gas temperatures (T gas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the T gas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal. [Copyright &y& Elsevier]

Abstract: Reaction of ground-state Ag2+ (2Σg+, 4d20 σ(5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of either the second ethene or first propene ligand to the Ag2+ ion. The measured rate constants exhibit a negative temperature dependence and relatively high reaction efficiency suggesting that the dissociation reactions are exothermic. Electronic structure calculations were preformed using density functional theory (DFT) at the B3LYP level in order to generate potential transition state structures for the dissociation reactions. Phase space theory (PST) was used to model the experimental rate data. Good agreement was found between experiment, DFT calculations and PST results for both systems. In both reactions, the negative temperature dependence is due to two factors: The reactions are only mildly exothermic and the product density of states increases more slowly with energy than the reactant density of states. The second factor is due to an atom being one of the products. No evidence for tight transition states was found for either reaction. [Copyright &y& Elsevier]

[Display omitted] • H 2 dissociation on transition metal (TM = Ni, Pd) single atom, dimer and trimer doped on Au substrate have been studied. • The H 2 dissociation in the form of Ni, Pd trimer exhibited the best catalytic performance. • The H 2 dissociation process follow the BEP relation on different structural units. Elucidating the effect of different structural units in the catalyst on catalytic performance was very important for the development of the excellent heterogeneous catalyst. This work used density functional theory (DFT) approach to investigate H 2 dissociation over transition metal (TM = Ni, Pd) single atom, dimer and trimer doped on Au substrate. The influence of different structural units toward the catalytic performance was elucidated. The results showed that the catalytic performance of Ni, Pd trimer was stronger than those of Ni, Pd single atom and dimer. Therefore, it was proposed that for the H 2 dissociation, the structural units in the form of Ni, Pd trimer exhibited the best catalytic performance. It was also obtained that the H 2 dissociation process followed the BEP relation on different structural units. This work provides insights about structural units for the reasonable design of the excellent heterogeneous catalysts toward dissociation reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO can be stably adsorbed on the Pt-Au bimetallic surface doped in the form of Pd trimer. • Through the exploration of CO decomposition transition states on three different Pt-Au(1 1 1) surfaces, it is concluded that the aggregation of Pt weakens the bond energy between C O. It is very important to elucidate how different structural units in a catalyst affect its performance in order to develop excellent heterogeneous catalysts. In this study, density functional theory (DFT) is used to investigate CO adsorption by transition metal (TM = Ni and Pt) monoatoms, dimers and trimers doped on Au substrates. The effects of different structural units on CO adsorption are analyzed. The results show that the Pt trimer has a stronger CO adsorption capacity than the other gold-based bimetallic catalysts. The effects of different Pt structural units on the C O bond in CO molecules are investigated. An exploration of the transition states in CO decomposition on three different Pt-Au(1 1 1) surfaces leads to the conclusion that Pt aggregation weakens the C O bond. [ABSTRACT FROM AUTHOR]