2-Propanol dehydration on TiO2(110):: The effect of bridge-bonded oxygen vacancy blocking

On 100 K rutile TiO2(1 10) 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)(2)CHOH 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. (C) 2007 Elsevier B.V. All rights reserved.