Gas-Phase Hydroxyl Radical Generation by the Surface Reactions over Basic Metal Oxides

Hydroxyl radical desorption in the heterogeneous catalytic reactions of water or hydrogen with oxygen was examined by laser-induced fluorescence spectroscopy. The catalytic activities of Pt, Al<INF>2</INF>O<INF>3</INF>, and basic metal oxides (MgO, CaO, SrO, BaO) supported on Al<INF>2</INF>O<INF>3</INF> were studied in the pressure range 0.1−10 Torr and the temperature range 1100−1300 K. In the case of OH generation from water, the catalytic activities of Pt and all oxides except Al<INF>2</INF>O<INF>3</INF> were very high and the OH concentration reached the equilibrium value within a residence time of 4 ms. In the case of hydrogen oxidation, differences in the catalytic behavior were clearly observed. The surface reaction mechanisms and the effects of Al<INF>2</INF>O<INF>3</INF> and MgO on gas-phase ignition are discussed.