No abstract

No abstract

The chemical kinetics of ammonia borane (AB) in glyme solution is studied using quantum mechanics (QM) based calculations along with experimental results available in the literature. The primary objective of this study is to propose a detailed reaction mechanism that explains the formation of species observed during AB decomposition for temperatures ranging from 323 to 368 K. The quantum mechanics investigation uses transition state theory to identify the relevant reaction pathways. Intrinsic reaction coordinate calculations use the identified transition-state structure to link the reactants to the products. These calculations were performed using the Gaussian 09 program package, including the solvation model based on density (SMD) with acetonitrile as the solvent. Thermodynamic properties of species at equilibrium or at transition states were computed using the G4(MP2) compound method. Sensitivity analysis was performed using a species conservation model to identify reactions and species that play a critical role. This study confirms the previous experimental observation regarding the initiation of decomposition of AB in glyme. It also elucidates the role of DADB, ammonium borohydride salt ([BH 4 ] − [NH 4 ] + ) and BH 2 NH 2 in hydrogen release and intermediates formed during initial phase of AB decomposition. This work shows how QM calculations along with experimental results can contribute to our understanding of the complex chemical kinetics involved during AB dehydrogenation. K E Y W O R D Sammonia borane, hydrogen release, QM calculations, reaction pathways 568

No abstract

The primary objectives of this study are to identify the initiation steps of perchloric acid (HClO 4 ) decomposition and to validate and provide insights into the reaction pathways of O 2 formation. To this end, we have performed quantum chemical calculations using the Gaussian 09 program package to identify new reaction pathways and species formed during decomposition. The thermodynamic quantities of the species, such as Gibbs free energy and enthalpy, are calculated using a double-hybrid density functional theory method, B2PLYP, with Jensen's basis set, aug-pc2. For heavy atoms, such as chlorine, the basis set is augmented by adding 2 d functions with a stride factor of 2.5. To incorporate the solvation effect, the conductor-like polarizable continuum model, which is an implicit solvation model, is used. Numerical simulations using a control−volume analysis of an experiment are also performed using the proposed mechanism. In these simulations, rates of the reactions are calculated using transition state theory, incorporating diffusion effects on the rate constants. In order to consider the nonideal behavior of a concentrated HClO 4 solution, activity coefficients are used to calculate the effective concentration of acid in solution. The activity coefficient of HClO 4 plays a critical role in the calculation of the induction period involved in the HClO 4 decomposition. A comparison of numerically predicted O 2 evolution and duration of the induction period with experimental data shows that the numerical simulation using the proposed mechanism predicts both the three-stage decomposition characteristics and the induction period observed during HClO 4 decomposition, thus validating the proposed mechanism.

No abstract