Influence of supported gold particles on the surface reactions of ethanol on TiO2

• TiO2-supported gold favors the dehydrogenation of ethanol to acetaldehyde.
• Ethanol is converted mainly to butene and water on the bare TiO2 support.
• Au atoms tune the reactions of ethanol on TiO2, providing sites for H recombination.

The adsorption and reactions of ethanol on the surfaces of TiO2 and TiO2-supported gold samples were investigated by infrared (IR) spectroscopy and mass spectrometry. IR spectra measured as the samples were treated in flowing ethanol at room temperature indicate that the alcohol was adsorbed both molecularly and dissociatively in the form of ethoxy species bonded to Ti4+ sites. Our results suggest that the presence of neighboring gold particles facilitates cleavage of the β-CH bond of the ethoxy species at increasing temperature, leading to the formation of acetaldehyde linearly bonded to Ti4+ sites, which is readily desorbed. In the process, hydrogen adatoms are recombined on gold particles to give H2. In absence of gold, Ti4+ sites abstract hydrogen atoms from the ethoxy species to give titanium hydride species, which react with hydroxyl groups to produce water and leave oxygen vacancies on the TiO2 surface. Acetaldehyde is formed in the process and it is adsorbed in a bidentate configuration on the oxygen vacancies, where it undergoes reductive coupling to give butene. Our data show that the ability of gold particles to abstract and recombine hydrogen atoms prevents the formation of oxygen vacancies on the support and, in consequence, hinders the subsequent reactions of the produced acetaldehyde.

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