Direct Reaction Mechanism Research Articles

Ligand effect of PdRu on Pt-enriched surface for glucose complete electro-oxidation to carbon dioxide and abiotic direct glucose fuel cells.

The development of advanced electrocatalysts for the abiotic direct glucose fuel cells (ADGFCs) is critical in the implantable devices in living organisms. The ligand effect in the Pt shell-alloy core nanocatalysts is known to influence the electrocatalytic reaction in interfacial structure. Herein, we reported the synthesis of ternary Pt@PdRu nanoalloy aerogels with ligand effect of PdRu on Pt-enriched surface through electrochemical cycling. Pt@PdRu aerogels with optimized Pt surface electronic structure exhibited high mass activity and specific activity of Pt@PdRu about 450 mA·mgPt-1 and 1.09 mA·cm-2, which were 1.4 and 1.6 times than that of commercial Pt/C. Meanwhile, Pt@PdRu aerogels have higher electrochemical stability comparable to commercial Pt/C. In-situ FTIR spectra results proved that the glucose oxidation reaction on Pt@PdRu aerogels followed the CO-free direct pathway reaction mechanism and part of the products are CO2 by completed oxidation. Furthermore, the ADGFC with Pt@PdRu ultrathin anode catalyst layer showed a much higher power density of 6.2 mW·cm-2 than commercial Pt/C (3.8 mW·cm-2). To simulate the blood fuel cell, the Pt@PdRu integrated membrane electrode assembly was exposed to glucose solution and a steady-state open circuit of approximately 0.6 V was achieved by optimizing the glucose concentration in cell system.

Quantum State-Resolved Nonadiabatic Dynamics of the H+NaF → Na+HF Reaction

The H + NaF reaction is investigated at the quantum state-resolved level using the time-dependent wave-packet method based on a set of accurate diabatic potential energy surfaces. Oscillatory structures in the total reaction probability indicate the presence of the short-lived intermediate complex, attributed to a shallow potential well and exothermicity. Ro-vibrational state-resolved integral cross sections reveal the inverted population distributions of the product. The HF product favors an angular distribution in the forward hemisphere of 30°–60° within the collision energy range from the threshold to 0.50 eV, which is related to the nonlinear approach of the H atom to the NaF molecule. Quantum generalized deflection functions show that the low-J partial waves contribute primarily to the backward scattering, while the high-J partial waves govern the forward scattering. The correlation between the partial wave J and the scattering angle ϑ proves that the reaction follows a predominant direct reaction mechanism.

Due consideration of the breakup and direct reaction mechanisms within (d, p), (d, 2p), (d, xn2p), and (d, xn) reactions

Suitable account of available excitation-function of deuterons interaction with target nuclei components of candidates materials for the ITER fusion reactor, the European DEMO fusion reactor, and the IFMIF-DONES Irradiation Facility has been proved by consistent analysis of the reaction mechanisms involved in the complex deuteron-nucleus interaction. In this work the attention has been focused on the analysis of the deuteron activation cross sections related to the gas accumulation, (d, p), (d, 2p), (d, xn2p), and to the strong neutron emission, (d, xn), interaction processes of interest for the radiation damage and shielding design studies devoted to the structural materials selection. The key role of direct interactions, i.e., breakup, stripping and pick-up processes is stressed out by the comparison of data with theoretical and evaluation predictions.

Multinucleon Transfer Studies of the 70Zn (15 MeV/nucleon) + 64Ni System with Focus on Excitation Energy Distributions

Existing high-resolution experimental data collected with the MAGNEX spectrometer were analyzed to investigate peripheral collisions of medium-mass nuclei from the reaction 70Zn (15 MeV/nucleon) + 64Ni. The main focus of this work was to correlate the observed ejectiles with the excitation energy of their progenitors. Experimental excitation energy distributions were generated and compared with the Deep-Inelastic Transfer (DIT) model. This revealed a dominance of direct reaction mechanisms located at low excitation energies and more complex mechanisms at higher energies. Future efforts include further detailed studies of the excitation energy distributions to elucidate the multinucleon transfer mechanisms and to comprehend the resolution limits achievable with medium-mass nuclei such as 70Zn.

The complex-formation dynamics of O + H(D)2+ (v = 0,1; j = 0) reactions on 12A'' and 12A′

The reactions O + H(D)2+ are studied based on the ground state potential energy surface (PES) 12A″ and the first excited PES 12A′. Both two potential energy surfaces comprise deep wells during the minimum energy reaction path. The average lifetimes of the complex-formation of the title reactions as a function of translational energy are calculated. The results indicated that the average lifetime of the complex-formation decreases with the increasing of collision energy for the two potential energy surfaces. There are two kinds of reaction mechanisms, one is direct reaction mechanism; another is indirect one. The indirect mechanism is dominated for all the collision energies studied. However, with the increasing of the collision energy, the direct reaction mechanism becomes more and more pronounced. Besides, the influences of reagent vibrational excitation and isotopic effect on the scalar properties and vector properties are studied in detail respectively in this work. The reagent vibrational excitation enhances the number of the direct reactive trajectories remarkably on 12A″, though it has nearly no influence on the average lifetime of the complex formation. In strong contrast, the reagent vibrational excitation suppresses the number of indirect reactive trajectories and reduces the average lifetime of the complex formation on the 12A′. The isotopic substitution has no influence on the scalar properties; however, it affects the vector properties strongly.

Interfacial reaction mechanism and high temperature stability of heat-resistant steel and SiC under a vacuum environment

The physical and chemical stabilities of SiC and heat-resistant steel were assessed by the diffusion couple method under vacuum at 1200 °C, which is a commonly used condition in magnesium metallurgy. High-temperature visualization instruments were used and Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic analyses were performed to verify the relevant mechanism. The reaction between SiC and heat-resistant steel can be divided into two stages: solid–solid and solid–liquid reactions. The solid–solid interfacial reaction produces graphite, which hinders the interfacial reaction. The interfacial reaction simultaneously generates silicides (NiSi, Ni2Si, and Ni3Si) with low melting points and transforms the reaction interface into a solid–liquid interface. The formation of the liquid phase promotes the dissolution and diffusion of carbon, leading to the accelerated corrosion of SiC and low-temperature melting of steel. Supersaturated carbon precipitates in the melt in the form of nanowires or nanotubes are catalyzed by Fe/Ni. Herein, a general model describing the direct interfacial reaction mechanism of SiC and heat-resistant steel is proposed to explain the reaction process under vacuum.

New 26P(p, γ)27S Thermonuclear Reaction Rate and Its Astrophysical Implications in the rp-process

Accurate nuclear reaction rates for 26P(p, γ)27S are pivotal for a comprehensive understanding of the rp-process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of 26P(p, γ)27S because of the lack of nuclear mass and energy level structure information for 27S. We reevaluate this reaction rate using the experimentally constrained 27S mass, together with the shell model predicted level structure. It is found that the 26P(p, γ)27S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, and 1.777 MeV above the proton threshold in 27S. The new rate is overall smaller than the other previous rates from the Hauser–Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new 27S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in the rp-process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of 27S/26P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path 26P(p, γ)27S(β +,ν)27P is not as important as previously thought for producing 27P. The adoption of the new reaction rates for 26P(p, γ)27S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements.

Investigation on the photocatalytic property of direct Z-type van der Waals g-C3N4/AlN heterojunction and its mechanism

Using hybrid density functional method, the electronic, interfacial and optical characters of the g-C3N4/AlN heterojunction as well as the effect of electric field and biaxial strain on its photocatalytic performance were systematically studied. The g-C3N4/AlN is a direct band gap semiconductor (2.71 eV) with stagger band alignment structure and exhibits direct Z-scheme photocatalytic reaction mechanism. Under the external electric field and biaxial strain, the staggered band feature of the heterostructure is retained and its VBM potential and CBM potential still have strong oxidation and reduction capabilities, which can meet the redox potential conditions of photocatalytic water-splitting. Meanwhile, the band gap gradually decreases with the increase of electric field strength ranged from −0.5 V/Å to 0.5 V/Å and 1% compressible strain tunes the heterostructure from direct band gap to indirect band gap. Our work provides a theoretical basis for the design of g-C3N4-based heterojunctions with high photocatalytic performance.

The selective role of the orbital angular momentum on the reaction stereo-dynamics

This paper reports on the characterization of the stereo-dynamic controlling three different chemi-ionization reactions, recent objective of our study, since they participate to the balance of phenomena occurring in plasma, interstellar medium, planetary atmospheres, flames and lasers. The optical potential, obtained by a phenomenological method and defined in the whole space of the relative configurations of reagents, has been formulated in an accurate and internally consistent way for three different systems. Some cuts of the multidimensional potential, that asymptotically correlate with a specific fine level of the open shell atom and/or with a defined orientation of the molecular reagent, have been exploited in the present study to emphasize crucial features of the collision dynamics along selected entrance channels of the reactions. Consistently, basic quantities determining the topology of the reaction stereo-dynamics have been properly defined, emphasizing in the three cases relevant changes in the microscopic reaction evolution. Much attention focused on the selectivity of the orbital angular momentum, affecting each collision event at any chosen collision energy. It controls the relative weight of two different reaction mechanisms. The direct reaction mechanism is driven by short-range chemical forces, promoting, by direct electron transfer between reagents, a prototypical elementary oxidation reaction. The indirect mechanism, controlled by the combination of long-range chemical and physical forces, can be triggered by a virtual photon exchanged between reagents, promoting a sort of photo-ionization process. Obtained results and emphasized differences appear to be of general interest for many other elementary processes, more difficult to characterize at this level of detail.Graphic abstract

Direct Synthesis of Silicon Compounds—From the Beginning to Green Chemistry Revolution

This paper discusses the historical beginnings and the current state of knowledge of the synthesis of organosilicon compounds and chlorine derivatives of silicon. The key importance of these compounds for modern industry, including the semiconductor industry (photovoltaic cells, microprocessors, memory chips and many other electronic elements) is highlighted. Significant environmental threats related to the production of these compounds and the research challenges aimed at their elimination are discussed. The complexity of the catalytic mechanism of direct reaction of silicon with CH3Cl and alcohols is presented in an accessible way. In the last part of the work, the directions of the development of direct synthesis technology in line with the principles of green chemistry are indicated.

An examination of the reaction pathways of XO + O → X + O2 (X = Br and I)

Kinetics and mechanism of potentially important atmospheric ozone depletion reactions XO + O → X + O2 (X = Br and I) have been explored at the ab initio level. Several minimum energy geometries and transition states are identified at the MP2 level using correlation consistent triple zeta and effective core potential basis sets and energetics are obtained at the QCISD(T)//MP2 level of theory. Possible reaction pathways are discussed on the basis of IRC calculations and changes of geometries along the reaction paths. A direct reaction mechanism as well as reaction path via transition states and equilibrium geometries are identified. For both the reactions, early transition states have been detected just after the reactions start. In case of BrO + O reaction, we obtained a transition state of Br.OO type before the product formation, whereas in case of IO + O reaction, an equilibrium geometry of I.OO type has been detected leading to the product formation. Similar to I.OO, for ClO + O reaction an equilibrium geometry of Cl.OO type was reported in literature for product formation. This anomaly for TS-Br.OO may be due the artifact of MP2 optimization method. A multi-reference approach is expected to reveal the correct picture. A detailed dynamical study of this transition state may lead to clear bond-breaking and bond-forming information, which may be helpful to predict the true reaction pathway. Heats of reaction are found to be consistent with experimental data. Bond dissociation energies of the ground state intermediate isomers to various dissociation asymptotes are also reported. This is the first theoretical report for the possible reaction pathways and may be served as a reference for future investigation using higher methodology.

Simulation of the RIBRAS Facility with GEANT4

A Geant4 simulation code was developed to perform realistic simulations of the RIBRAS facility. A second order expansion of a finite solenoid field was included to describe the beam optics with a good precision. A systematic study of coil currents for several magnetic rigidities and focal points was performed. Parameterizations of the coil currents for single and dual mode operations were obtained. Dedicated routines were developed to simulate the mechanism of direct reactions involving two and three particles in the final state. The present simulations were employed to investigate the feasibility of a Solenoidal Spectrometer with the RIBRAS facility. Our first results indicate that the concept can be applied in the RIBRAS system under certain conditions. Forthcoming studies both from simulations and experiment are already under development.

Direct mass spectrometric observation and reaction mechanism of gas-phase initial intermediates during CL-20 decomposition

The formation and decay of initial intermediates of energetic materials (EMs) such as polynitropolyaza-caged CL-20 are responsible for the initiation of decomposition reaction network, which acts as a key mechanistic step during combustion and detonation. However, direct in situ measurements of these species have not been reported previously, and their formation mechanism remains unclear. Herein, we present direct probing of gas phase decomposition intermediates, particularly reactive initial products with parent molecule's caged skeletons from CL-20, by using in situ atmospheric pressure photoionization high-resolution mass spectrometry. The detected intermediates mainly include NO2-elimination products (C6H5O10N11, C6H6O8N10, etc.), O-elimination product (C6H6O11N12), and NO-elimination products (C6H6O11N11, etc.). Bimolecular reaction pathways involving initial intermediate C6H6O10N11 and NO2/NO are proposed and evaluated to account for the formation of initial products.

Dynamic study of the D + DAu reaction based on a new ground potential energy surface

Based on the ground potential energy surface (PES) (2A') constructed by Yuan and coworkers, the D + DAu reactive scattering was investigated using the time-dependent wave packet method. It was found that the total reaction probabilities and integral cross section of the D + DAu reaction are smaller than those of the H + HAu reaction, due to smaller zero point energy and weaker tunneling effect. The abstract and exchange reaction channel exhibit different reaction mechanisms, a direct reaction mechanism in the abstract channel and long lifetime indirect mechanism in the exchange channel, respectively. During the reaction, the collision energy could be efficiently transferred to vibration of the D2 product in the abstract reaction channel and rotation of the DAu product in the exchange channel.

Simultaneous analysis of elastic scattering and fusion in He6+Zn64 : A transition in direct reaction mechanisms, striking threshold anomalies, and halo effects

Using the extended optical model, a simultaneous analysis is carried out of elastic scattering and fusion reactions induced by the neutron halo $^{6}\mathrm{He}$ projectile on a $^{64}\mathrm{Zn}$ target. Dynamic polarization potentials ${U}_{F}$, ${U}_{D}$ are introduced which can be associated to fusion and direct couplings, respectively. Appropriate fitting parameters leading to dispersive potentials are found which provide a good simultaneous description of the data. An unexpected local maximum is uncovered in the energy dependence of the total reaction cross sections, indicating a transition in the involved direct reaction processes, and a possible underlying mechanism is discussed. ${U}_{F}$ is found to follow the normal threshold anomaly but with an unusually large threshold energy. ${U}_{D}$, on the other hand, exhibits a breakup threshold anomaly, but with a strikingly high value of the peak energy, which can be associated to the above-mentioned transition. The results also are discussed within the context of possible halo effects.

Studying the Conversion Mechanism to Broaden Cathode Options in Aqueous Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) are regarded as alternatives to Li-ion batteries benefiting from both improved safety and environmental impact. The widespread application of ZIBs, however, is compromised by the lack of high-performance cathodes. Currently, only the intercalation mechanism is widely reported in aqueous ZIBs, which significantly limits cathode options. Beyond Zn-ion intercalation, we comprehensively study the conversion mechanism for Zn2+ storage and its diffusion pathway in a CuI cathode, indicating that CuI occurs a direct conversion reaction without Zn2+ intercalation due to the high energy barrier for Zn2+ intercalation and migration. Importantly, this direct conversion reaction mechanism can be readily generalized to other high-capacity cathodes, such as Cu2 S (336.7 mA h g-1 ) and Cu2 O (374.5 mA h g-1 ), indicating its practical universality. Our work enriches the Zn-ion storage mechanism and significantly broadens the cathode horizons towards next-generation ZIBs.

Studying the Conversion Mechanism to Broaden Cathode Options in Aqueous Zinc‐Ion Batteries

AbstractAqueous Zn‐ion batteries (ZIBs) are regarded as alternatives to Li‐ion batteries benefiting from both improved safety and environmental impact. The widespread application of ZIBs, however, is compromised by the lack of high‐performance cathodes. Currently, only the intercalation mechanism is widely reported in aqueous ZIBs, which significantly limits cathode options. Beyond Zn‐ion intercalation, we comprehensively study the conversion mechanism for Zn2+ storage and its diffusion pathway in a CuI cathode, indicating that CuI occurs a direct conversion reaction without Zn2+ intercalation due to the high energy barrier for Zn2+ intercalation and migration. Importantly, this direct conversion reaction mechanism can be readily generalized to other high‐capacity cathodes, such as Cu2S (336.7 mA h g−1) and Cu2O (374.5 mA h g−1), indicating its practical universality. Our work enriches the Zn‐ion storage mechanism and significantly broadens the cathode horizons towards next‐generation ZIBs.

Reactions of U+ with H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Theory.

The kinetic energy-dependent reactions of the atomic actinide uranium cation (U+) with H2, D2, and HD were examined by guided ion beam tandem mass spectrometry. An average 0 K bond dissociation energy of D0(U+ - H) = 2.48 ± 0.06 eV is obtained by analysis of the endothermic product ion cross sections. Quantum chemistry calculations were performed for comparison with experimental thermochemistry, including high-level CASSCF-CASPT2-RASSI calculations of the spin-orbit corrections. CCSD(T) and the CASSCF levels show excellent agreement with experiment, whereas B3LYP and PBE0 slightly overestimate and the M06 approach badly underestimates the bond energy for UH+. Theory was also used to investigate the electronic structures of the reaction intermediates and potential energy surfaces. The experimental product branching ratio for the reaction of U+ with HD indicates that these reactions occur primarily via a direct reaction mechanism, despite the presence of a deep-well for UH2+ formation according to theory. The reactivity and hydride bond energy for U+ are compared with those for transition metal, lanthanide, and actinide cations, and periodic trends are discussed. These comparisons suggest that the 5f electrons on uranium are largely core and uninvolved in the reactive chemistry.

Theoretical investigation on the reaction mechanism of ozone with chlorine, bromine and iodine atoms

Theoretical investigation on the reaction mechanism of X + O3 → XO + O2 (X = Cl, Br and I) reactions have been performed at the ab initio level using correlation consistent and effective core potential basis sets. The geometry and frequency of the reactants, products, equilibrium geometries and transition states are obtained using MP2 level of theory and energetics are calculated at the CCSD(T) and QCISD(T) methods. Heat of reactions are found to be consistent with the experimental data. Possible reaction pathways are discussed. In case of reactions of ozone with chlorine and brome, it starts producing a nonplanar trioxide (OOOX) transition state with acute dihedral angle. It then proceeds via nonplanar equilibrium geometry and transition state. Finally dissociates to XO + O2 from a planar O2·OX equilibrium geometry. For the reaction with iodine, initial transition state and equilibrium geometry with acute dihedral angle are disappeared. The reaction proceeds through planar intermediates and finally dissociated to IO + O2 via O2·OI isomer. There exists a flat plateau on the potential energy surface in the intermediate region for all the cases. Finding of O2·OX equilibrium geometry strengthens the suggestion of previous investigations and for the possibility of direct reaction mechanism. High level theoretical investigation including reaction dynamics on these reactions can reveal the actual reaction mechanism.

Direct and sequential four-body recombination rates at low temperatures

We investigate four-body nuclear reactions in stellar environments contributing to creation of light nuclei, exemplified by $^9$Be and $^{12}$C. The originally assumed process is radiative capture, where nuclear clusters combine into the excited final nucleus and photon emission populates the stable nuclear ground states. Instead, we consider nuclear four-body recombination reactions where a spectator nuclear particle replaces the photon. We first develop the elaborate formalism for both, direct and sequential capture processes, where the decaying three-body resonance is formed without and with population of an intermediate two-body resonance, respectively. To facilitate both calculations and practical applications we parameterize the involved cross sections as done successfully in previous computations of reaction rates. We consider the lowest-lying nuclear states with their dominant contributions at low stellar temperatures. We calculate and compare reaction and production rates for different processes. The direct reaction mechanism dominates by many orders of magnitude at low temperature, where the sequential stepping stones are energetically too expensive to use. At somewhat higher temperatures these two different nuclear four-body mechanisms become comparable. Comparison to radiative three-body capture reveals already formally, but also numerically, that four-body nuclear recombination must dominate for sufficiently high nuclear densities. Numerical values are given for all these rates as function of temperature and density. The relative importance is exhibited.