Theoretical study of CO adsorption on Au catalysts under environmental catalytic conditions

Density Functional Theory calculations with both standard GGA and hybrid functionals are performed on Au adatoms, steps, and low index surfaces with coordination numbers (CNs) varying from 3 to 9. The results are used to study adsorption thermodynamics and reactivity of CO on Au nanoparticles. We find that the hybrid functional improves calculated site preferences and predicts CO top site adsorption, regardless of the Au CN, in good agreement with experiments. The calculated adsorption energies vary monotonically with respect to Au CNs, and the results from the hybrid functional are around 20% smaller than the corresponding values from the GGA–PBE functional. A comparison with experimental adsorption energies suggests that these functionals may bound the true CO–Au interaction strength, and seven-coordinated Au atoms may be the active low-coordinated sites on many Au single crystal surfaces. However, thermodynamic analysis on Wulff-like Au particles at ambient temperatures shows that, even though the number of 6-coordinated corner Au atoms is much less than the number of 7-coordinated edge Au atoms and of higher-coordinated Au atoms, they are the dominant sites for CO adsorption on Au nanoparticles with sizes up to 10 nm. In addition, we find that CO adsorption is not influenced by the shape of Au nanoparticles, but the CO oxidation reaction may be.