Methane oxidation over noble metal gauzes: an LIF study

The contributions of homogeneous and heterogeneous reactions to high-temperature catalytic methane oxidation were studied over three different gauze catalysts (Pt, Pt-10%Rh, and Ni) using laser-induced fluorescence (LIF) spectroscopy to measure OH · concentrations in the boundary layers downstream of the gauzes. OH · concentrations were found to decrease in the order Ni > Pt-10%Rh > Pt, which could be correlated with the catalytic activity of the metals 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 simulations, 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 spatially decoupled.