DFT analysis of CO behaviour on Pt(111)
摘要
Adsorption of reactants on the surface of a catalyst is an important elementary step in surface catalyzed reactions. Adsorption on transition metal catalyst involves complex interactions between reactant molecular orbitals and metal d‐bands. We study the adsorption of CO on Pt(111).At low surface coverage of CO on Pt(111), experiments show an atop site preference while density functional theory (DFT) predicts an fcc hollow site. Further, vibrational analysis predicts a combination of bridge and atop sites. In light of these contrasting reports, we undertake a systematic study of the adsorption process.We perform plane wave pseudo potential based DFT calculations within the Generalized Gradient Approximation (GGA). The system is relaxed from an unbiased initial configuration. We find that the projected density of states (PDOS) and Löwdin charge population analysis provide significant insights into the choice of adsorption site of CO on Pt(111).We validate our simulation setup and parameter set by comparing the bulk modulus (238.2 GPa) and the lattice parameter (3.99 Å) for fcc Platinum using Murnaghan equation of state with experiments (230 GPa and 3.92 Å). From a detailed study of orbital resolved bonding patterns, we attribute the discrepancy in the preferred adsorption site between DFT calculations and experiments to two competing effects: (a) destabilization of atop preferred CO due to back donation of electron density to C by Pt (b) destabilization of fcc preferred CO due to the shift in density distribution peak to higher energies. An interesting hint is the non‐involvement of certain d‐orbitals of metal when CO is fcc bonded. The effect of initial configuration and the exchange‐correlation functional on site preference of CO is explored and discussed in detail.