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 2 O 3, and basic metal oxides (MgO, CaO, SrO, BaO) supported on Al 2 O 3 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 2 O 3 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 2 O 3 and MgO on gas-phase ignition are discussed.