Cai Yongqing, Bai Zhaoqiang, Chintalapati Sandhya, Feng Yuan Ping
Charge transfer between metal nanoparticles and the supported TiO$_{2}$ surface is primarily important for catalytic applications as it greatly affects the catalytic activity and the thermal stability of the deposited nanoparticles on the surface. Herein, a systematic spin-polarized density functional calculation is conducted to evaluate the adsorption, diffusion, and charge state of several transition metal monomers on rutile TiO$_{2}$ (110) surface. The role of oxygen vacancy (O$\rm_{v}$) with its accompanying excess electrons in influencing the binding and activation of the monomers is examined. For pristine reduced surface, our hybrid functional calculation shows that only a small portion (around 5%) of the excess electrons distribute on the topmost surface, which are mainly delocalized at the second nearest and third nearest fivefold coordinated Ti (Ti$_{5c}$) atoms. The small amounts of excess electrons populating at the Ti$_{5c}$ atoms can be transferred to strongly electronegative adsorbates like Au and Pt thus enabling a moderate adsorption as reflected in the plots of potential energy surface. This finding helps to clarify the origin of the experimental observation of the adsorption of O$_{2}$ and CO molecules at Ti$_{5c}$ sites. The spatial redistribution of the excess electrons at Ti$_{5c}$ sites around the O$\rm_{v}$ upon the adsorption of monomers is thoroughly examined. Our finding of an accumulation of excess electrons at the Ti$_{5c}$ sites around the monomers may explain the critical role of the perimeter interface of the deposited nanoparticles in promoting the adsorption and activation of reactants observed in experiments.
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http://arxiv.org/abs/1209.0605
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