A comparison of CO adsorption on Pt(2 1 1), Ni(2 1 1), and Pd(2 1 1) surfaces using density functional theory

Adsorption of CO on Pt(2 1 1), Ni(2 1 1), and Pd(2 1 1) surfaces has been investigated by density functional theory (DFT) method (periodic DMol3) with full geometry optimization. Adsorption energies and structures of CO on these surfaces are studied by considering multiple possible adsorption sites, and comparing them with the experimental data at low coverage. There are several striking differences in site-preference and adsorption structures (tilt angle, C–O bond length, metal–C distance) among the three surfaces. For Pt(2 1 1), CO adsorbs preferentially on step edge, and the same site-preference as inferred experiments is obtained, i.e. step atop followed by step bridge and then the terrace sites. For Ni(2 1 1) and Pd(2 1 1), differences in adsorption energy among step and terrace sites become smaller than Pt(2 1 1) (small or no adsorption energy preference for step sites), and the CO molecules on step edge tilt downward considerably from the (2 1 1) normal to the (1 0 0) normal.