A theoretical investigation on Pt3Sn(1 0 2) surface alloy and CO-Pt3Sn(1 0 2) system |
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Authors: | Asl?han Sü mer,A. Erhan Aksoylu |
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Affiliation: | Department of Chemical Engineering, Bo?aziçi University, 34342 Bebek Istanbul, Turkey |
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Abstract: | The adsorption properties of CO on experimentally verified stepped Pt3Sn(1 0 2) surface were investigated using quantum mechanical calculations. The two possible terminations of Pt3Sn(1 0 2) were generated and on these terminations all types of possible adsorption sites were determined. The adsorption energies and geometries of the CO molecule for all those sites were calculated. The most favorable sites for adsorption were determined as the short bridge site on the terrace of pure-Pt row of the mixed-atom-ending termination, atop site at the step-edge of the pure row of pure-Pt-ending termination and atop site at the step-edge of the pure-Pt row of the mixed-atom-ending termination. The results were compared with those for similar sites on the flat Pt3Sn(1 1 0) surface considering the fact that Pt3Sn(1 0 2) has terraces with (1 1 0) orientation. The LDOS analysis of bare sites clearly shows that there are significant differences between the electronic properties of Pt atoms at stepped Pt3Sn(1 0 2) surface and the electronic properties of Pt atoms at flat (1 1 0) surface, which leads to changes in the CO bonding energies of these Pt atoms. Adsorption on Pt3Sn(1 0 2) surface is in general stronger compared to that on Pt3Sn(1 1 0) surface. The difference in adsorption strength of similar sites on these two surface terminations is a result of stepped structure of Pt3Sn(1 0 2). The local density of states (LDOS) of the adsorbent Pt and C of adsorbed CO was utilized. The LDOS of the surface metal atoms with CO-adsorbed atop and of their bare state were compared to see the effect of CO chemisorption on the electron density distribution of the corresponding Pt atom. The downward shift in energy peak in the LDOS curves as well as changes in the electron densities of the corresponding energy levels indicate the orbital mixing between CO molecular orbitals and metal d-states. The present study showed that the adsorption strength of the sites has a direct relation with their LDOS profiles. |
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Keywords: | CO adsorption Pt3Sn CO adsorption on Pt3Sn(1 0 2) Stepped alloy surfaces Pt-Sn alloys DFT calculations |
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