A theoretical study of CO adsorption on Pt, Ru and Pt–M (M=Ru, Sn, Ge) clusters

The adsorption of CO on pure Pt, Ru, and on mixed Pt–M metal surfaces (M=Ru, Sn, Ge) has been studied with the relativistic density-functional self-consistent field Xα method. PtnM10−n clusters simulated the metal (111) surfaces. Adsorption energies, metalC and CO bond lengths, force constants and stretching frequencies were calculated. The calculated properties agree with available experimental findings. The presence of M atoms weakens the PtC bond, and generally slightly lowers the CO stretching frequency of adsorbed carbon monoxide. The role of ruthenium and tin in promoting dissociation of water to form adsorbed OH was also examined in calculations on (Pt–M)–OH2, –OH and –H clusters. Substitution of ruthenium and tin for platinum is found to alter the dissociation energy of H2O. The results indicate that the promoting effect of alloying atoms involves both modification of PtCO binding and water activation. CO frequency shifts induced by an applied potential are also discussed. The vibrational tuning rate with potential V on Ru(001) is about 5 cm−1 V−1 larger than that on Pt(111).