Theoretical Kinetics Predictions for Reactions on the NHO Potential Energy Surface.

Recent modeling studies of ammonia oxidation, which are motivated by the prospective role of ammonia as a zero-carbon fuel, have indicated significant discrepancies among the existing literature mechanisms. In this study, high-level theoretical kinetics predictions have been obtained for reactions on the NHO potential energy surface, including the NH + O, HNO + H, and NH + OH reactions. These reactions have previously been highlighted as important reactions in NH oxidation with high sensitivity and high uncertainty.

Re-Examination of the NO + O Reaction.

The reaction of NO with O is a key step in consumption of nitrous oxide in thermal processes. It has two product channels, NO + NO (R2) and N + O (R3). The rate constant for R2 has been measured both in the forward and the reverse direction at elevated temperature and is well established.

Probing High-Temperature Amine Chemistry: Is the Reaction NH + NH ⇄ NH + H Important?

The reaction NH + NH ⇄ NH + H (R1) has been identified as a key step to explain experimental results for pyrolysis and oxidation of ammonia. However, no direct experimental or theoretical evidence for the reaction has been reported. In the present work, the reaction was studied by ab initio theory and by reinterpretation of experimental data.

On the Rate Constant for NH+HO and Third-Body Collision Efficiencies for NH+H(+M) and NH+NH(+M).

In low-temperature flash photolysis of NH/O/N mixtures, the NH consumption rate and the product distribution is controlled by the reactions NH + HO → products (R1), NH + H (+M) → NH (+M) (R2), and NH + NH (+M) → NH (+M) (R3). In the present work, published flash photolysis experiments by, among others, Cheskis and co-workers, are re-interpreted using recent direct measurements of NH + H (+N) and NH + NH (+N) from Altinay and Macdonald. To facilitate analysis of the FP data, relative third-body collision efficiencies compared to N for R2 and R3 were calculated for O and NH as well as for other selected molecules.

Ab initio calculations and kinetic modeling of thermal conversion of methyl chloride: implications for gasification of biomass.

Limitations in current hot gas cleaning methods for chlorine species from biomass gasification may be a challenge for end use such as gas turbines, engines, and fuel cells, all requiring very low levels of chlorine. During devolatilization of biomass, chlorine is released partly as methyl chloride. In the present work, the thermal conversion of CH3Cl under gasification conditions was investigated.

Inhibition and Promotion of Pyrolysis by Hydrogen Sulfide (HS) and Sulfanyl Radical (SH).

This study resolves the interaction of sulfanyl radical (SH) with aliphatic (C-C) hydrocarbons, using CBS-QB3 based calculations. We obtained the C-H dissociation enthalpies and located the weakest link in each hydrocarbon. Subsequent computations revealed that, H abstraction by SH from the weakest C-H sites in alkenes and alkynes, except for ethylene, appears noticeably exothermic.

Rate constant and thermochemistry for K + O2 + N2 = KO2 + N2.

The addition reaction of potassium atoms with oxygen has been studied using the collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) method. KCl vapor was photolyzed with 266 nm pulses and the absorbance by K atoms at 766.5 nm was measured at various delay times with a narrow line width diode laser.

Temperature and Pressure Dependence of the Reaction S + CS (+M) → CS2 (+M).

Experimental data for the unimolecular decomposition of CS2 from the literature are analyzed by unimolecular rate theory with the goal of obtaining rate constants for the reverse reaction S + CS (+M) → CS2 (+M) over wide temperature and pressure ranges. The results constitute an important input for the kinetic modeling of CS2 oxidation. CS2 dissociation proceeds as a spin-forbidden process whose detailed properties are still not well understood.

Glyoxal Oxidation Mechanism: Implications for the Reactions HCO + O2 and OCHCHO + HO2.

A detailed mechanism for the thermal decomposition and oxidation of the flame intermediate glyoxal (OCHCHO) has been assembled from available theoretical and experimental literature data. The modeling capabilities of this extensive mechanism have been tested by simulating experimental HCO profiles measured at intermediate and high temperatures in previous glyoxal photolysis and pyrolysis studies. Additionally, new experiments on glyoxal pyrolysis and oxidation have been performed with glyoxal and glyoxal/oxygen mixtures in Ar behind shock waves at temperatures of 1285-1760 K at two different total density ranges.

Oxidation of reduced sulfur species: carbon disulfide.

A detailed chemical kinetic model for oxidation of CS2 has been developed, on the basis of ab initio calculations for key reactions, including CS2 + O2 and CS + O2, and data from literature. The mechanism has been evaluated against experimental results from static reactors, flow reactors, and shock tubes. The CS2 + O2 reaction forms OCS + SO, with the lowest energy path involving crossing from the triplet to the singlet surface.

Rate constant and branching fraction for the NH2 + NO2 reaction.

The NH2 + NO2 reaction has been studied experimentally and theoretically. On the basis of laser photolysis/LIF experiments, the total rate constant was determined over the temperature range 295-625 K as k1,exp(T) = 9.5 × 10(-7)(T/K)(-2.

Predicted thermochemistry and unimolecular kinetics of nitrous sulfide.

The geometry of N(2)S was obtained at the CCSD(T)/aug-cc-pV(T + d)Z level of theory and energies with coupled-cluster single double triple (CCSD(T)) and basis sets up to aug-cc-pV(6 + d)Z. After correction for anharmonic zero-point energy, core-valence correlation, correlation up to CCSDT(Q) and relativistic effects, D(0) for the N-S bond is estimated as 71.9 kJ mol(-1), and the corresponding thermochemistry for N(2)S is Δ(f)H(0)(∘)=205.

Reactions of SO3 with the O/H radical pool under combustion conditions.

The reactions of SO3 with H, O, and OH radicals have been investigated by ab initio calculations. For the SO3 + H reaction (1), the lowest energy pathway involves initial formation of HSO3 and rearrangement to HOSO2, followed by dissociation to OH + SO2. The reaction is fast, with k(1) = 8.

Thermal dissociation of SO3 at 1000-1400 K.

The thermal dissociation of SO3 has been studied for the first time in the 1000-1400 K range. The experiments were conducted in a laminar flow reactor at atmospheric pressure, with nitrogen as the bath gas. On the basis of the flow reactor data, a rate constant for SO3 + N2 --> SO2 + O + N2 (R1b) of 5.

Formation and destruction of CH2O in the exhaust system of a gas engine.

A computational study of chemical reactions occurring in the exhaust system of natural gas engines has been conducted, emphasizing the formation and destruction of formaldehyde. The modeling was based on a detailed reaction mechanism, developed for describing oxidation of C1-C2 hydrocarbons and formaldehyde. The mechanism was validated against data from laboratory flow reactors and from the exhaust system of a full-scale gas engine.