Photoreaction of ethanol on Au/TiO2 anatase: comparing the micro to nanoparticle size activities of the support for hydrogen production

The work presents the dark and photocatalytic reactions of ethanol over Auparticles deposited on TiO2anatasenano (=10 nm) and micro (ca. 0.15 µm) particle catalysts. The Auparticles are of uniform and similar dimension (mean particlesize = ca. 5 and 7 nm on the micro– and nano-sized TiO2, respectively). XPS Au4f indicated that in both cases Auparticles are present in their metallic state with no evidence of charge transfer to (or from) the semiconductor. Under dark conditions, ethanol adsorption leads to stable ethoxide species (from in situ Infrared analysis) up to ca. 550 K at which point conversion to acetaldehyde by dehydrogenation and ethylene by dehydration occurs (from temperature programmed desorption (TPD) analysis). Liquid slurry photoreaction indicated the production of hydrogen with a rate ˜2 L/kgCatal min on 2 wt.% Au/TiO2anatase nanoparticles under UV photo irradiation of comparable intensity to solar radiation. While the reaction rate per unit mass was lower on the micro-sized Au/TiO2, it simply scaled up to an equivalent rate for the nano-sized Au/TiO2 catalyst when normalised by unit area, indicating the absence of a particlesize effect of the semiconductor on the electron transfer reaction within the range 10–150 nm).