Adsorption and reactions of 2-iodoethanol on TiO2 have been studied by Fourier transform infrared spectroscopy. ICH2CH2OH possesses two reactive centers of C-I and C-OH. It is found that its decomposition leads to the formation of crotonaldehyde on TiO2. A reaction sequence of ICH2CH2OH --> ICH2CH2O- --> CH3CHO --> CH3CH=CH- CHO is proposed. Although the decomposition routes of C2H5OH and C2H5I, both forming C2H5O- on TiO2, suggest that - OCH2CH2O- may play a role in the crotonaldehyde formation, reaction of HOCH2CH2OH on TiO2 shows that this is not the case. Adsorbed H2O is formed in the ICH2CH2OH decomposition on TiO2; however, it is found that ICH=CH2, possibly generated by ICH2CH2OH dehydration, is not important in the crotonaldehyde formation.