|AVS 58th Annual International Symposium and Exhibition|
|Surface Science Division||Tuesday Sessions|
|Session:||Chemisorption & Surface Reactions|
|Presenter:||S. Hong, University of Central Florida|
|Authors:||S. Hong, University of Central Florida
D.A. Chen, University of South Carolina
T.S. Rahman, University of Central Florida
|Correspondent:||Click to Email|
We have performed density functional theory calculations to understand the reaction pathway selection for methanol decomposition on clean and Au13 deposited TiO2(110) surface. We find that when methanol adsorbs on the clean and reduced TiO2(110) surface, it decomposes spontaneously into methoxy, which adsorbs on the O-vac site and desorbs as methyl leaving behind O-br on the TiO2(110) surface. On the stoichiometric TiO2(110) surface, we find that while methanol decomposition has a small activation energy of 0.2 eV, methoxy decomposition (i.e. formaldehyde formation) is not possible because of high activation energy of 3 eV. Nevertheless, once the surface is oxidized formaldehyde formation becomes spontaneous, through C-H bond scission by surface oxygen species. These results confirm the experimental results of methyl formation on the reduced and formaldehyde formation on the oxidized TiO2(110) surface. Turning to the case of partially reduced Au/TiO2(110) surface, our DFT calculations show that the adsorption of methanol and its intermediate methoxy does not occur on gold sites but on TiO2 sites Methoxy, in fact, forms at the Au-titania interface as a result of O-H bond scission by lattice oxygen (O-br), and its optimized tilted structure makes C-H bond scission -- through H abstraction by lattice oxygen near the interface site -- much easier than that for a vertical, non-tilted structure of methoxy in a non-interfacial site. Moreover, depending on the reduction level of the TiO2(110) surface, the adsorption site preference for methanol and methoxy species on the Au/TiO2(110) surface is: O-vac > interfacial Ti-cus > stoichiometric Ti-cus site. This hierarchy implies that the major product will switch from methyl on the fully-reduced surface, to formaldehyde on the partially-reduced or oxidized Au/TiO2(110) surface. This conclusion is in full agreement with experiment.
This work is supported in part by US-DOE under Grant No. DEFG02-07ER15842.