Gas-phase photocatalytic oxidation of dichlorobutenes

Gas-phase photocatalysis of 1,4-dichlorobut-2-enes and 3,4-dichlorobut-1-en e (DCB) has been studied using TiO2 and 3%WO3/TiO2 supported on SiO2. DCB w as found to oxidize efficiently over these catalysts; however, only low rat es of CO2 formation were observed. With these chlorinated hydrocarbons, the catalysts were found to deactivate over time, probably via the formation o f aldol condensation products of chloroacetaldehyde, which is the predomina nt intermediate observed. The variation in rate and selectivity of the oxid ation reactions with O-2 concentration is reported and a mechanism is propo sed. Using isotope ratio mass spectrometry, the initial step for the DCB re moval has been shown not to be a carbon bond cleavage but is likely to be h ydroxyl radical addition to the carbon-carbon double bond.