The reaction of ethanol has been studied on the surface of rutile TiO(2)(110) by Temperature Programmed Desorption (TPD), online mass spectrometry under UV excitation and photoelectron spectroscopy while the adsorption energies of the molecular and dissociative modes of ethanol were computed using the DFT/GGA method. The most stable configuration is the dissociative adsorption in line with experimental results at room temperature. At 0.5 ML coverage the adsorption energy was found equal to 80 kJ mol(-1) for the dissociative mode (ethoxide, CH(3)CH(2)O(a) + H(a)) followed by the molecular mode (67 kJ mol(-1)). The orientation of the ethoxides along the [001] or [110] direction had minor effect on the adsorption energy although affected differently the Ti and O surface atomic positions. TPD after ethanol adsorption at 300 K indicated two main reactions: dehydration to ethylene and dehydrogenation to acetaldehyde. Pre-dosing the surface with ethanol at 300 K followed by exposure to UV resulted in the formation of acetaldehyde and hydrogen. The amount of acetaldehyde could be directly linked to the presence of gas phase O(2) in the vacuum chamber. The order of this photo-catalytic reaction with respect to O(2) was found to be 0.5. Part of acetaldehyde further reacted with O(2) under UV excitation to give surface acetate species. Because the rate of photo-oxidation of acetates (acetic acid) was slower than that of ethoxides (ethanol), the surface ended up by being covered with large amounts of acetates. A reaction mechanism for acetaldehyde, hydrogen and acetate formation under UV excitation is proposed.

The review focus is on hydrogen production from renewables using photocatalysis. In particular we focus on the role of synergism on the reaction rate. Among the most studied examples for this phenomenon are catalysts based on TiO 2 . TiO 2 exists in two common phases: anatase and rutile, with the latter more thermodynamically stable. For hydrogen production the photocatalyst is often composed of nano-size precious metals deposited on TiO 2 (such as Pt, Pd, or Au). It has been observed by many researchers over a decade that M/TiO 2 rutile is far less active than M/TiO 2 anatase. Yet, the presence of the two phases together results in considerable enhancement of the reaction rate when compared to M/TiO 2 anatase alone. The main reason for this is the increase of the charge carriers' lifetime allowing for electron transfer to hydrogen ions and hole transfer to oxygen ions (and/or the sacrificial agent used). In this work we review the few proposed models, so far, explaining the way by which this charge transfer occurs across both phases.

TiO 2 and TiO 2 -based materials are prototypes for photo-catalytic reactions as they have been shown for many decades to be active for total oxidation of hydrocarbons to clean the environment. In the last decade or so there has been a shift in the objectives for photoreactions mainly towards hydrogen production from renewables. Here we review the fundamentals behind the reactivity of model TiO 2 surfaces with simple organic compounds in the dark and under photo-irradiation, then we consider the case of ethanol photo-reaction to hydrogen at its fundamental and applied levels. The review starts with an overview of the bulk and surface structures of rutile TiO 2 , as it is the most studied phase in surface science despite its lower activity for hydrogen production compared to the anatase phase. We then focus on the gold/TiO 2 system where both phases (anatase and rutile) of TiO 2 have received more attention. In the gold/TiO 2 system emphasis is mainly devoted to understanding the effect of particle dimensions on the electronic conduction as well as the oxidation state of Au particles. The most recent observation using environmental X-ray Photoelectron Spectroscopy indicated the absence of charge transfer from the support to the metal. The photoreaction of ethanol is presented in more detail. The rate for hydrogen production on Au/TiO 2 catalysts does not change if TiO 2 particles are of macro-size or nano-size once normalised by surface area. Also, it was clearly seen that Au/TiO 2 anatase is about two orders of magnitudes higher compared to a similar system where TiO 2 is in the rutile phase. The mechanism for hydrogen production is presented and discussed on the metal/semiconductor systems. Of particular interest is the observation of synergistic effect between the anatase and rutile nanoparticles and one explanation involving electron transfer from one phase to the other is invoked.

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