The inhibition of the hydrogen + oxygen reaction by formaldehyde

Abstract

The inhibiting action of HCHO on the first and second limits of the H2+02 reaction has been studied in KClcoated vessels at 540°C. The e5ciency of inhibition is almost inversely proportional to the mole fraction of 0 2 , and is less dependent on the mole fraction of H2. This indicates that the main primary termination process is thereaction H+HCH0( 14) which competes with the reaction H+02(2); a smaller contribution results from the reaction of OH+HCHO(lS) competing with OH+H2(1), or from O+HCHO = OHSHCO(13) competing with O+H2 = OH+H(3). The efficiency of inhibition is independent of diameter showing that the HCO radicals are not destroyed at the surface ; this is confirmed by the fact that the fraction of HCO radicals undergoing chaintermination reactions is effectively independent of mixture composition and of pressure over the range 4-100 mrr~ Hg. Evidence against the reactions HCO = H+CO and HC0+02 = C02+0H is provided, and it is concluded that chain termination ultimately results either from the reaction HC0+02 = CO+HO2, or from the reaction HCO+02 = HCO3, the HCO3 radicals being destroyed at the surface. The results permit the evaluation of the ratios k14/k2 and kls/kl(or k13/k3) and from estimates of k14, a value of k2 can be obtained which agrees with earlier estimates.

Ab Initio Chemical Kinetics for the CH3 + O(3P) Reaction and Related Isomerization–Decomposition of CH3O and CH2OH Radicals

“…For the CH 2 O + H reaction, direct H atom abstraction producing CHO + H 2 , several kinetic experiments have been carried out in different temperature ranges in the past decade. − In 1999, Baulch et al recommended the rate constant expression for the temperature range 300–1700 K, k = 2.1 × 10 –16 T 1.62 exp­[−1090/ T ] cm 3 molecule –1 s –1 , derived by Choudhury and Lin from a nonlinear least-squares analysis of their high-temperature shock tube data with the low-temperature data of Baldwin and Cowe, Westenberg and deHaas, Ridley et al, and Klemm . Dóbé et al reported a rate constant at 298 K, (3.98 ± 0.83) × 10 –14 cm 3 molecule –1 s –1 , measured by the discharge flow technique.…”

Reaction Rate Constant of CH2O + H = HCO + H2Revisited: A Combined Study of Direct Shock Tube Measurement and Transition State Theory Calculation

“…The authors acknowledge based on past experience that the relatively more accurate polarization configuration interaction computed barrier of 12.7 kcal/mol was probably too high by up to several kilocalories/mole. Harding and Schatz also performed TST calculations using generalized valence bond configuration interaction derived parameters, having to reduce the computed barrier height to 4.9 kcal/mol in order to reconcile the computed rates with available experimental data for the title reaction. ,, …”

“…Harding and Schatz also performed TST calculations using generalized valence bond configuration interaction derived parameters, having to reduce the computed barrier height to 4.9 kcal/mol in order to reconcile the computed rates with available experimental data for the title reaction. 17,30,31 More recently, Irdam et al in the 1990s recomputed the potential energy surface of this system with a multireference configuration interaction scheme, 20 employing a moderately sized pVDZ basis set. The authors obtained a barrier height of 12.8 kcal/mol, still too high to fit experimental data, by about a factor of 2.…”

Inhibition of the hydrogen + oxygen reaction by ethylene. Part 1.—Kinetic results

“…(b) By assuming that removal of H atoms is the important primary inhibition process but that Q decreases as the pressure is lowered. Further observations on the way in which Q varies with pressure may be obtained by a study of the inhibiting action of C2H4 at the first limit which, as shown with HCHO 15 and C2H& 4 enables the pressure range to be extended. Simple equations for the inhibition of the first limit may be derived by making the following assumptions: where k H is the velocity constant for the surface destruction of H atoms and Ql is the fraction of radicals produced from C2H4 which are destroyed without propagating the chain at first limit pressures PI.…”