Paper SS-TuA9
Understanding the Enhanced Activity for Methanol Reaction on Titania-supported Au Clusters

Tuesday, November 1, 2011, 4:40 pm, Room 109

The growth and chemical activity of Au clusters deposited on rutile TiO₂(110) were studied by scanning tunneling microscopy, temperature programmed desorption and density functional theory calculations. Methanol reaction on 0.25 ML Au clusters produces formaldehyde as the major product at 535 K with methanol desorption observed at the same temperature; water and hydrogen evolution are detected below room temperature, as well as methyl radical evolution at 575 K. On the titania surface itself, methanol reaction also produces methyl radial around 600 K. Formaldehyde production reaches its maximum value between 0.25 and 2 ML but decreases dramatically as the coverage is increased to 5 ML. This behavior suggests that formaldehyde is produced at the Au-titania interface since formaldehyde production does not occur at pure Au sites. STM experiments confirm that the 0.25 ML Au coverage has the greatest number of Au-titania interfacial sites at the perimeter of the clusters. For higher coverages of 2 and 5 ML, cluster coalesence diminishes the number of Au-titania sites, and this is consistent with the decreased formaldehyde yield at higher Au coverages. When the titania surface is reoxidized with ¹⁸O₂ prior to Au deposition and exposure to methanol, lattice oxygen is incorporated into the water that is evolved at low temperature. We propose that the role of the titania support is to facilitate the formation of the reactive methoxy intermediate via abstraction of the hydroxyl hydrogen in methanol by lattice oxygen. Density function theory calculations also indicate that methoxy is the intermediate formed at the Au-titania interface after O-H bond scission is induced by lattice oxygen.