Laser diagnostics of radicals in catalytic reactions

Abstract

OH radicals emitted from a Pt foil surface during the reaction between H 2 and O 2 have been studied by laser-induced fluorescence. The experiments were performed in a flow system with a O 2/H 2 mixing ratio of 6/1 and Ar as the carrier gas. The total pressure and Pt-sample temperature ranges were 0.01 - 2 torr and 850 – 1150 K, respectively. Some preliminary results are reported. The OH yield increases linearly with pressure up to about 0.3 torr, where collisional quenching starts to be significant. Assuming Arrhenius behaviour an apparent desorption energy of OH of (50 ± 5) kcal/mole was obtained. The OH rotational population gives a temperature of only (525 ± 50) K at a sample temperature of (975 ± 50) K. The most likely source of OH is the thermally activated desorption of OH radicals formed by recombination of H and 0 atoms on the surface (forward reaction), but contributions from H 2O decomposition (backward reaction H 2O + O → 2OH) on the surface cannot be excluded.