Photooxidation of ethanol on Fe-Ti oxide particulates

Previous studies have indicated that metal oxide particulates such as fly ash can display significant activity toward photooxidation of oxygenates in the troposphere. In some cases the reaction rates approach those characteristic-of purely homogeneous mechanisms. Oxides of Fe and Ti appear to play the most important role, but the state of aggregation of these metals remains poorly characterized on tropospheric particulates. The present work seeks to elucidate certain aspects of the reaction mechanism by relating kinetic measurements on synthetic Fe-Ti oxides to surface composition and oxidation state. In the case of ethanol photooxidation, increasing the ratio of Ti to Fe generally tends to increase the rate and steer selectivity away from acetaldehyde formation toward CO2 production. However, both activity and selectivity correlate only modestly with surface composition and with surface oxidation state. Instead, structural effects play a key role in governing the reaction path.