<title>Fluorescence imaging technique applied to high-temperature catalysis</title>

Abstract

We have used the planar laser induced fluorescence, PLIF, technique to study the OH concentration distributions outside a catalytic surface at different pressures and gas compositions. In the experiments a flow of hydrogen and oxygen at a total pressure of 0.2 - 1 Torr is directed towards a platinum foil, which is resistively heated to 1300 K. OH radicals are formed on the catalyst surface as an intermediate in the 2H<SUB>2</SUB> + O<SUB>2</SUB> yields 2H<SUB>2</SUB>O reaction. A small fraction of the OH radicals desorb to the gas phase, instead of reacting with adsorbed H atoms to form H<SUB>2</SUB>O. These desorbed radicals are detected with the PLIF technique in a region 1 - 6 mm from the surface, i.e., spatial distribution patterns are obtained. The recorded fluorescence patterns are corrected for laser beam intensity variations. The corrected patterns are used to determine the relative OH concentration distributions outside the surface at different pressures and gas compositions. The recorded fluorescence patterns from different transitions are used to determine rotational temperature distributions. The measurements are compared with results from a computer model that simulates the laminar stagnation point flow of hydrogen and oxygen on the catalyst. The model includes both gas phase reactions and surface reactions. The relative amount of OH radicals as function of the distance from the platinum foil and gas temperatures with the simulated temperature profiles we found that the gas phase temperature can not be calculated assuming continuity in the temperature over the gas-surface boundary.