THE CRITICAL CONDITION FOR CATALYTIC IGNITION - H2/O2 ON PT

The Frank-Kamenetskii condition for catalytic ignition (the sudden transition from a kinetically to a mass transport controlled, exothermic catalytic reaction), is explored experimentally and by simulations for the H-2+1/2O2-->H2O reaction on Pt. At ignition the temperature derivatives of the dissipated chemical power and the heat loss, respectively, are equal [1]. This condition is verified by measurements of the pre-ignition kinetics and calculations taking into account kinetics, heat, and mass transport. The ignition temperature is determined by a competition between hydrogen site blocking on the surface and hydrogen desorption, which makes the ignition temperature increase with increasing H-2/O2 ratio.