Gas-phase oxidation of 2-propanol over Au/TiO sub(2) 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 N sub(2) 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 TiO sub(2) above 500K the acid-base catalyzed dehydration yielding propene and water, the dehydrogenation to acetone and H sub(2), 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 H sub(2)O at temperatures below 400K, whereas the selective oxidation to acetone at higher temperatures above 500K was also observed on pure TiO sub(2). Also the dehydration of 2-propanol to propene and H sub(2)O and, to a minor extent, the total oxidation to CO sub(2) and H sub(2)O were catalyzed by Au/TiO sub(2). Therefore, the Au/TiO sub(2) 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 TiO sub(2) pointing to a Mars-van Krevelen mechanism based on an enhanced reducibility of TiO sub(2).