Effect of Au nanoparticles on the activity of TiO2 for ethanol upgrading reactions

This article analyses the role of gold nanoparticles supported on TiO2 for the gas-phase ethanol condensation. Previously, the original P25 surface was modified for increasing the Au-Ti interaction, in order to minimize the thermal deactivation. Catalysts were tested both in absence and presence of hydrogen (523-673 K, WHSV = 7.9 h(-1) y(EtOH) = 0.32; y(H2) = 0-0.1; 0.1 MPa). Parent TiO2 is mainly selective for dehydration reactions yielding diethyl ether (favoured at low temperatures) and ethylene (favoured at higher temperatures). The presence of Au in the catalyst promotes dehydrogenation pathways, yielding acetaldehyde, as well as condensation products (mainly butanol, with selectivities close to 10%). According to DRIFT spectroscopy results, the strong ethanol adsorption on the TiO2 surface justifies the low yields and the high relevance of side-reactions produced by inter- or intra-molecular dehydration routes (diethyl ether, and ethylene formation). The gold addition minimizes this adsorption and enhances the main route by a double role: an improvement in the dehydrogenation rate (yielding more acetaldehyde) and an enhancement in the hydrogenation steps.