Tracing the reaction steps involving oxygen and IR observable species in ethanol photocatalytic oxidation on TiO2.

The rate-determining step of ethanol photocatalytic oxidation was identified to be the adsorption of O(2) by an infrared (IR) spectroscopy coupled with mass spectrometry method. Dosing O(2) during reaction showed that adsorption of O(2) controls the accumulation of photogenerated electrons and the formation of acetate (CH(3)COO(-)(ad)), acyl species (CH(3)CO(ad)), acetaldehyde (CH(3)CHO(ad)), CO(2), and H(2)O. Accumulation of CH(3)COO(-)(ad) on the TiO(2) surface slowed down the conversion of ethanol to CO(2) and H(2)O. Removal of CH(3)COO(-)(ad) from the TiO(2) surface holds the key to accelerating the rate of ethanol photocatalytic oxidation. This study bridges the gap between results of nanosecond and millisecond transient absorption studies and those of minute scale photocatalytic oxidation studies.