2-Propanol dehydration on TiO2(1 1 0): The effect of bridge-bonded oxygen vacancy blocking

On 100 K rutile TiO2(1 1 0) surfaces with 3.5 ± 0.5% surface bridge-bonded oxygen vacancies (BBOV's), propene formation by dehydration of 2-propanol was monitored by temperature programmed desorption (TPD). The BBOV's were either filled or unfilled when the 2-propanol was dosed. Propene desorption rates exhibit two local maxima, nominally at 350 (LT) and 570 K (HT). The former is not altered by filling BBOV's while the latter is reduced by factors of 2.5 and 5 when the vacancies are pre-filled with water (H-OH) and alcohol (R-OH), respectively. The HT process is attributed to a reaction of 2-propoxy groups located on surface BBO's. To account for much of the HT C3H6 yield when BBOV's are filled before (CH3)2CHOH dosing, we propose a model whereby, during TPD, vacancies form and are filled with 2-propoxy. The factor of two difference between titrating BBOV's with H2O and alcohols is attributed to stoichiometry; twice as many OH groups form on surface BBO rows when H2O is used so twice as many vacancies are created when OH recombines.