A shock-tube study of ammonia pyrolysis

Abstract

The pyrolysis of NH3 was studied behind reflected shock waves at temperatures 2500–3000 K, using mass spectrometric analysis of dynamically sampled gas. The initial mixtures contained 0.14% to 6% NH3, with Kr as diluent, at total gas concentrations of about 2 × 10−6 mol cm−3. Concentration profiles of NH3, NH2, NH, and N2 were measured. It was found that the apparent rate coefficient for overall removal of NH3 is increased by increasing the initial NH3 concentration, but is decreased by addition of H2. Addition of H2 also suppressed NH, but left the NH2 concentration relatively unchanged. A close correlation was found between NH2 concentration and N2 formation rate, indicating that NH2 participates in the reaction which produces N2.The experimental results are consistent with a chain mechanism in which NH3 is removed by unimolecular decomposition and by attack by H, NH, and NH2. Computer analysis yields a rate constant of 1.2 × 1016 exp (−91 000 cal mol−1/RT) cm3 mol−1 s−1 for the unimolecular process.

Kinetics of the NH reaction with H2 and reassessment of HNO formation from NH + CO2, H2O

“…for reaction (1) in the 2600-2800 K range [21] and from the reverse reaction [35,36] also at higher temperatures.…”

Thermal decomposition of ammonia in shock waves

“…This is shown in Figure 8, which also shows the kII reported by other investigators. The present values of kII are found to be a little larger than those of Dove and Nip [14]. Since the data of (H)ss/(M) were scattered, as seen in Figure 7, and the activation energy of kI is high, the uncertainty of the temperature dependence of kII is considerably large.…”

Exploring NH (X3Σ−)+D (2S)→N (4S)+HD (X1Σg+) reaction with time-dependent wave packet method

“…NH + H reaction plays an important role in the atmospheric chemistry and combustion of nitrogen-containing species [13][14][15]. In particular, the ground state hydrogen abstraction reaction, NH (X 3 − ) + H ( 2 S) → N ( 4 S) + H 2 (X 1 g + ), is among the series of radical reactions involved in the pyrolysis of ammonia (NH 3 ) and is supposed to play a vital role in the decay of imidogen (NH) [16][17][18]. Taking account of isotope substitution which gives important insights into a reaction without changing the system dramatically, we study the NH (X 3 − ) + D ( 2 S) → N ( 4 S) + HD (X 1 g + ) reaction in this work.…”