In heterogeneous catalysis, the interaction between the reactant molecules (adsorbate) and the surface of the active center (metal crystals such as Ni, Ru, Rh, etc.) are important in the performance of the catalyst. The structure of the active metal crystals changes with the size. As the size increases, they move from platonic to archimedean to bulk solid. The structure and properties of them changes accordingly. While platonic solid looks same from any vertex (has only one surface), in archimedean solids has two different faces. Properties of these faces, such as the crystal lattice structure and surface defects (e.g., steps, holes, vacancies, ad atoms, dislocations and terraces), usually influence the specific structure of the reactant molecules when they are chemically bound to the metal crystals.

We are trying to develop catalysts for the manufacturing of ethanol from green fuel using syngas. We have to study the adsorption of CO and H2 and their activation energy in subsequent dissociation. In this process we need to study the reaction mechanism, find the rate limiting features and learn how the surface features affect it. This has motivated us to study CO chemisorptions on Ni, Ru and Rh.

In this paper we estimate the adsorption energy of CO on Ni, Ru and Rh surfaces using DFT methods. The CPMD program is used for our DFT calculations. We consider both regular surfaces as well as surfaces with different defects. First, we perform a geometry optimization for the 3D lattice structure and surface of Ni, Ru and Rh. After that, we estimated the adsorption energy of CO on several surfaces of the Ni, Ru and Rh crystals. The number of surface layers is increased till a constant energy per atom is obtained. The surface free energy is obtained from the difference of energies of surface structure and similar number of atoms from the bulk structure. A change in average surface energies is calculated for surface defects like vacancies and dislocations. Finally, we determine the fractal dimension of the surfaces using wavelet analysis methods, and establish how the surface properties, such as adsorption energies, depend on the fractal dimensions.