CO adsorption on PdGa(1 0 0), (1 1 1) and (1¯1¯1¯) surfaces: a DFT study

Abstract

CO adsorption on (1 0 0), (1 1 1) and (1¯ 1¯ 1)¯ planes is analyzed using density functional theory (DFT) calculations. Changes in the electronic structure of these surfaces and CO bond after adsorption are also addressed here. CO is located on Pd atop geometry with a tilted configuration of 7.8◦ in the (1 0 0) plane, while in the (1 1 1) and (1¯ 1¯ 1)¯ are perpendicular to the surface. No direct interaction of CO with Ga is detected. The overlap population (OP) of Pd-Pd and Pd-Ga bond decreases as the new Pd-CO bond is formed. In all cases, the C-O bond length changes less than 1% compared to the vacuum but its strength decrease about 50% as determined by the changes in the OP. The effect of CO is limited to its first Pd neighbor. Analysis of orbital interaction reveals that Pd-CO bond mainly involves s-s and s-p orbitals with less participation of Pd 4d orbitals. Computed CO vibration frequencies after adsorption shows a red shift from vacuum towards 1972.9, 1990.4 and 1988.6 cm−1 on (1 0 0), (1 1 1) and (1¯ 1¯ 1)¯ planes respectively, following the same trend that experimental data on the PdGa intermetallic compound.