DFT Calculations for the HONO Elimination Process of CL-20 Conformers

The HONO elimination process is regarded to be an important initial decomposition process of energetic nitramines. Four CL-20 conformers based on the ε-CL-20 were obtained by the optimization at the m062x/cc-pvtz level in this study, and the Transition State (TS) and Intrinsic Reaction Coordinate (IRC) calculations were carried out at the same level. In addition, the rate coefficients and activation energy of the HONO elimination process were evaluated using conventional transition state theory (TST) and canonical variational transition state theory (CVT) with Eckart and small-curvature tunneling (SCT) methods to correct the transmission coefficients for the quantum tunneling effect. The calculation results have shown that the HONO elimination process concerning the nitro groups located on six numbered rings is the hardest to happen, and it seems that the longer distance between nitro groups and the adjacent hydrogen atom would result in the higher barrier energy; the HONO elimination process is most likely to happen for the axial positioning of nitro groups located on five numbered rings and most unlikely to happen for the ones located on six numbered rings; CL-20 II and CL-20 IV conformers are the most unstable one and most stable one concerning the reaction difficulty of the HONO elimination process.

Decay Analysis of 197Tl* Compound Nucleus Formed in 16O + 181Ta Reaction at above Barrier Energy Ec.m.~100 MeV

The decay dynamics of 197Tl* compound nucleus has been studied within the framework of the dynamical cluster-decay model (DCM) at above barrier energy Ec.m. ≈ 100 MeV using quadrupole deformed configuration of decay fragments. The influence of various nuclear radius parameters on the decay path and mass distributions has been investigated by analysing the fragmentation potential and preformation probability. It is observed that 197Tl* nucleus exhibits the triple-humped mass distribution, independent of nuclear radius choice. The most preferred fission fragments of both fission modes (symmetric and asymmetric) are identified, which lie in the neighborhood of spherical and deformed magic shell closures. Moreover, the modification in the barrier characteristics, such as interaction barrier and interaction radius, is observed with the variation in the radius parameter of decaying fragments and influences the penetrability and fission cross-sections. Finally, the fission cross-sections are calculated for considered choices of nuclear radii, and the results are compared with the available experimental data.

Cu2O-Ag Tandem Catalysts for Selective Electrochemical Reduction of CO2 to C2 Products

The electrochemical carbon dioxide reduction reaction (CO2RR) to C2 chemicals has received great attention. Here, we report the cuprous oxide (Cu2O) nanocubes cooperated with silver (Ag) nanoparticles via the replacement reaction for a synergetic CO2RR. The Cu2O-Ag tandem catalyst exhibits an impressive Faradaic efficiency (FE) of 72.85% for C2 products with a partial current density of 243.32 mA·cm−2. The electrochemical experiments and density functional theory (DFT) calculations reveal that the introduction of Ag improves the intermediate CO concentration on the catalyst surface and meanwhile reduces the C-C coupling reaction barrier energy, which is favorable for the synthesis of C2 products.

The catalytic activity of PtnCum (n+m=3, m≠3) clusters for methanol dehydrogenation to CO

Based on the density functional theory (DFT), the geometric for the reactants, intermediates, transition states and dehydrogenation products have been optimized. The energy diagrams are drawn out along both the O-adsorption path and H-adsorption path, and the C-H bond scission pathway is energetically more favorable than the O-H bond scission pathway. By calculation, the Pt is the active site in the whole reaction processes, and the barrier energy of the rate-determining step is 11.09 kcal/mol by Pt: Cu=2: 1 which is lower than that of Pt 3 and PtCu 2 . Importantly, it is shown that the complete dehydrogenation product of methanol, CO, can more easily dissociate from PtCu 2 cluster than from Pt 3 cluster. Therefore, Cu doping can promote the catalytic activity of Pt in a certain extent.

Catalyzed Ethanol Chemical Looping Gasification Mechanism on the Perfect and Reduced Fe2O3 Surfaces

Biomass chemical looping gasification (CLG) is a novel gasification technology for hydrogen production, where the oxygen carrier (OC) transfers lattice oxygen to catalytically oxidize fuel into syngas. However, the OC is gradually reduced, showing different reaction activities in the CLG process. Fully understanding the CLG reaction mechanism of fuel molecules on perfect and reduced OC surfaces is necessary, for which the CLG of ethanol using Fe2O3 as the OC was introduced as the probe reaction to perform density functional theory calculations to reveal the decomposition mechanism of ethanol into the synthesis gas (including H2, CH4, ethylene, formaldehyde, acetaldehyde, and CO) on perfect and reduced Fe2O3(001) surfaces. When Fe2O3(001) is reduced to FeO0.375(001), the calculated barrier energy decreases and then increases again, suggesting that the reduction state around FeO(001) favors the catalytic decomposition of ethanol to produce hydrogen, which proves that the degree of reduction has an important effect on the CLG reaction.

Mechanistic Insight into the Hydrogenation of Acetylene on the Pd2/g-C3N4 Catalyst: Effect of Pd Clustering on the Barrier Energy and Selectivity

In this work, the hydrogenation of acetylene on the Pd2/g-C3N4 catalyst is investigated by the Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) calculations. The Pre-reactant (R), transition states (TSs), and the intermediates (IMs), involved in the hydrogenation process, are characterized from the point of view of energy and structure. The calculated energy barrier for the hydrogen transfer to the acetylene and ethylene are 6.77 and 12.28 kcal/mol, respectively which shows that the Pd2/g-C3N4 catalyst has good selectivity for the conversion of acetylene to ethylene rather than ethane. Comparing the values of these energy barriers with those of the hydrogenation of acetylene on the Pd/g-C3N4 catalyst (21.53 and 38.88 kcal/mol, respectively) shows that the increase in the number of the Pd atoms decreases the energy barriers of the hydrogenation reaction and increases the selectivity of the catalyst for the ethylene production.

Kinetics and energetic analysis of the slow dispersive electron transfer from nano-TiO2 to O2 by in situ diffusion reflectance and Laplace transform

In situ diffusion reflectances reveal the trapping-filling effect in the electron transfer from TiO2 to O2 and Laplace transform was developed to derive the broadened apparent barrier energy distribution.