Catalysis of radical recombination in flames by iron

Abstract

Flame photometric measurements of H and OH radical concentrations in fuel‐rich laminar atmospheric‐pressure H₂/O₂/N₂ flames with and without added iron have been made by the Li/Na comparison method. The observed catalysis of radical recombination by iron is quantitatively interpreted in terms of the following homogeneous gas‐phase reaction cycle, with associated forward and backward rate coefficients in milliliter · molecule · second units: $$\begin{array}{cc}{\mathrm{FeOH\; +\; H\rightleftharpoons FeO\; +\; H}}_2:& k_f{\text{= 5 × 10}}^{\text{−11}}\text{exp(−800/T),}\\ & k_b{\text{= 1.1 × 10}}^{\text{−9}}\text{exp(−6200/T);}\\ {\mathrm{FeO\; +\; H}}_2{\mathrm{O\rightleftharpoons Fe(OH)}}_2:& k_f{\text{= 9 × 10}}^{\text{−12}},\\ & k_b{\text{= 1.0 × 10}}^{13}\text{exp(−35 500/T);}\\ {\mathrm{Fe(OH)}}_2{\mathrm{+\; H\rightleftharpoons FeOH\; +\; H}}_2\mathrm{O:}& k_f{\text{= 1.1 × 10}}^{\text{−10}}\text{exp(−300/T),}\\ & k_b{\text{= 1.1 × 10}}^{\text{−11}}\text{exp(−12 000/T).}\end{array}$$ The interpretation also includes contributions from the effectively balanced reaction Fe+H₂O⇄FeOH+H; equilibrium constant = 66 exp(−16 100/T).