The reactions of ethanol on TiO2 and Au/TiO2 anatase catalysts

The surface reactions of ethanol over TiO2 and Au/TiO2 nanoparticle catalysts were systematically investigated by temperature programmed desorption (TPD) and infra-red (IR) spectroscopic studies, in order to understand the effect of adding gold on the surface chemistry. Transmission Electron Microscopy (TEM) indicated that Au particles were mostly less than 10 nm in size; TiO2 was of pure anatase form (XRD) of about 15–20 nm in size. Ethanol TPD on H2-reduced TiO2 showed that most reaction products desorbed in one single desorption domain at ca. 660 K. The main reaction product was ethylene (with a carbon selectivity of about 70%); other minor products were acetaldehyde, butene, and crotonaldehyde in decreasing order of yield. Ethanol TPD over H2-reduced Au/TiO2 was considerably different. First, a large fraction of the reaction products desorbed around 600 K; second the main desorption product was observed to be benzene. Infrared spectroscopy indicated that at room temperature both ethanol (1262 cm−1, 1310 cm−1, and 1398 cm−1; due to O–H bending, CH2 wagging, and CH3 symmetric deformation modes, respectively) and ethoxide species (1047 cm−1, 1073 cm−1, 1093 cm−1, and 1122 cm−1; due to the stretching modes of CO and CC) are present with the former disappearing faster than the latter. In addition bands at 1634 and 1658 cm−1 attributed to ν(C–O), ν(Cdouble bond; length as m-dashC) and ρ(CH3) of adsorbed crotonaldehyde are seen when the ethanol dosed surface was flashed to 570 K. A scheme for the formation of the reaction products on TiO2 and Au/TiO2 is proposed in which benzene is formed on Au/TiO2 by successive condensation reactions.