Spatially resolved laser-induced fluorescence imaging of OH produced in the oxidation of hydrogen on platinum

Abstract

The laser-induced fluorescence technique has been used to study OH radicals desorbed from a polycrystalline Pt foil in the H 2 + O 2 reaction. The experiments were performed under steady-state reaction conditions in the pressure range 10–100 mTorr at a catalyst temperature of 1300 K. Concentration profiles of OH radicals as a function of the distance from the catalyst were measured by imaging the fluorescence light with a diode array detector. The measurements in this pressure range support our earlier conclusion that the detected OH radicals are produced by catalytic reactions on the surface (S. Ljungström et al., Surf. Sci. 216, 63 (1989)). No evidence was found for the catalytic promotion of gas-phase reactions, as has been observed in studies of similar reactions with catalytically stabilized thermal burners at higher pressures. Analysis of the measured concentration profiles shows that the desorbed OH radicals can best be descricbed by a cos θ distribution. The effects of gas-phase collisional processes have been investigated by evaluation of the local rotational distribution of the desorbed OH radicals.