Vibrational Properties of CO Adsorbed on Au Single Atom Catalysts on TiO2(101), ZrO2(101), CeO2(111), and LaFeO3(001) Surfaces: A DFT Study

The nature and local environment of Au single atoms supported and stabilized on four different oxides is studied by means of DFT +U calculations using CO as probe molecule and its stretching frequency, omega(e), as a fingerprint of the site where the Au atom is bound. Four oxides are considered, anatase TiO2, tetragonal ZrO2, cubic CeO2, and a perovskite LaFeO3. In this latter case a recently reported experimental study has detected a stretching mode for CO adsorbed on Au-1/LaFeO3 of 2215 cm(-1), with a large blue shift, Delta omega(CO)= 72 cm(-1) with respect to free CO. In order to identify the Au adsorption site that can give rise to this large blue-shift we have considered five cases: (a) Au replacing a lattice cation, (Au)(subM); (b) Au replacing a lattice O anion, (Au)(subO); (c) Au adsorbed on the surface, (Au)(ads); (d) Au bound to an extra O atom on the surface, (AuO)(ads), or (e) Au bound to two extra O atoms on the surface, (AuO2)(ads). It turns out that the correct reproduction of Delta omega for CO adsorbed on positively charged gold, Au delta+, is challenging for DFT. Therefore, we have performed a comparative study of Au delta+-CO molecular compounds for which omega(e)(CO) is known experimentally using various kinds of DFT functionals and accurate CCSD and CCSD(T) quantum chemistry methods. Also based on this comparison we propose a tentative assignment for the observed frequency of CO adsorbed on Au-1/LaFeO3 single atom catalyst. [GRAPHICS] .

Automated summary

The nature and local environment of Au single atoms supported on four different oxides were studied using DFT +U calculations, with CO as a probe molecule. The stretching frequency of CO, omega(e), was used as a fingerprint to determine the binding site of the Au atom. By considering various scenarios for Au adsorption sites, it was found that reproducing the blue-shift in the stretching frequency of CO adsorbed on positively charged gold, Au delta+, was challenging for DFT methods. A comparative study using different DFT functionals and accurate quantum chemistry methods was performed to propose a tentative assignment for the observed frequency of CO adsorbed on Au-1/LaFeO3 single atom catalyst.