Gas-phase oxidation of 2-propanol over Au/TiO2 catalysts to probe metal-support interactions

2-Propanol and oxygen were converted over titania and gold nanoparticles supported on titania to investigate the reactivity of the support, the influence of the metal and the role of metal-support interactions. The catalysts were characterized by N2 physisorption and transmission electron microscopy. In addition to deriving the degrees of conversion and the yields as a function of temperature, temperature-programmed desorption and diffuse reflectance infrared spectroscopy were applied in fixed-bed reactors under continuous flow conditions. Over pure TiO2 above 500K the acid-base catalyzed dehydration yielding propene and water, the dehydrogenation to acetone and H2, and the oxidative dehydrogenation to acetone and water were found to occur. The additional presence of Au nanoparticles induced the selective oxidation to acetone and H2O at temperatures below 400K, whereas the selective oxidation to acetone at higher temperatures above 500K was also observed on pure TiO2. Also the dehydration of 2-propanol to propene and H2O and, to a minor extent, the total oxidation to CO2 and H2O were catalyzed by Au/TiO2. Therefore, the Au/TiO2 catalyst shows bifunctional properties in oxygen activation needed for the selective oxidation of 2-propanol. 2-propoxide species were detected by IR spectroscopy, which are identified as intermediate species in 2-propanol conversion, whereas strongly bound acetates and carbonates acted as catalyst poison for the selective low-temperature oxidation route, but not for the high-temperature route. Selective low-temperature oxidation is assumed to occur at the perimeter of the Au nanoparticles, which also enhance the high-temperature oxidation route on TiO2 pointing to a Mars-van Krevelen mechanism based on an enhanced reducibility of TiO2.