Methane oxidation over noble metal gauzes: An LIF study

The contributions of homogeneous and heterogeneous reactions to high-temper ature catalytic methane oxidation were studied over three different gauze c atalysts (Pt, Pt-10%Rh, and Ni) using laser-induced fluorescence (LIF) spec troscopy to measure OH concentrations in the boundary layers downstream of the gauzes. OH concentrations were found to decrease in the order Ni > Pt-1 0%Rh > Pt, which could be correlated with the catalytic activity of the met als with Pt being the most active oxidation catalyst, followed by Pt-10%Rh, and then Ni, which is essentially inert in excess oxygen. The experimental LIF results were compared to one-dimensional reaction-diffusion simulation s, confirming that the differences in the measured OH concentrations can be explained by the different degrees of catalytic methane conversion by the three gauze catalysts. No evidence for a direct interaction of homogeneous and heterogeneous reaction pathways through the radical pool was observed. Rather, the heterogeneous and the homogeneous reactions appeared to be spat ially decoupled. (C) 2000 by The Combustion Institute.