FORMATION OF HYDROXYL RADICALS FROM THE REACTION OF WATER AND OXYGEN OVER BASIC METAL-OXIDES

The reaction of water and oxygen to form hydroxyl radicals over the me tal oxide catalysts La2O3, Nd2O3, Sm2O3, Yb2O3, CeO2, and MgO was stud ied al pressures up to several Torr. After reaction over 27 mg of La2O 3 at 900 degrees C, the measured concentration of hydroxyl radicals in the gas phase, detected by laser induced fluorescence spectroscopy, w as equivalent to the expected equilibrium concentration. The reaction becomes kinetically controlled at catalyst loadings below 5 mg. Oxygen incorporation at the surface sites may be the rate limiting step in t he catalytic cycle. The activities of the catalysts decrease from La2O 3, the most active, to CeO2, which is inactive under these reaction co nditions. This order is the same as that found for methyl radical form ation over these oxides, suggesting that the active site on the cataly st surface is the same for both hydroxyl radical formation and methyl radical formation.