Chemistry at Surfaces

CO oxidation on Au(111) in the presence of H2O

Gold nanoparticles are remarkably active for CO oxidation in the presence of water. We have used density functional theory to study this reaction on Au(111) in an effort to gain insight as to how this reaction proceeds at the surfaces of Au nanoparticles, which consist mostly of {111} planes. Our calculations reveal that surface hydroxyls easily form via the reaction H2O+½O2→2OH, and that these hydroxyls in turn significantly reduce the barrier for CO oxidation:




Both of the above reactions occur with an energy barrier of only ~0.10 eV. Without H2O+½O2→2OH, however, the barrier for CO oxidation is significantly greater (0.33 eV). These two reactions are a likely reason that H2O activates CO oxidation on Au nanoparticles. These reactions also help explain the experimental findings of the Mullins Group [UT Department of Chemical Engineering], as a recent experimental-theoretical Mullins-Henkelman collaboration demonstrates (for the full story, click here).


CO3 formation and decomposition

Carbonate is known to form on Ag(110) in the reaction CO2+½O2→CO3. Given its similarity with silver, an interesting question is whether or not CO3 forms on Au(110). This has not been reported experimentally. We have modeled CO3 formation and decomposition on Ag and Au (110) and (111) surfaces with density functional theory. Our calculations reveal that CO3 likely forms on Au(110), and to a lesser extent on Au(111):




References

L. Xu, D. Mei, and G. Henkelman, Adaptive kinetic Monte Carlo simulation of methanol decomposition on Cu(100) J. Chem. Phys. 131, 244520 (2009).

R. A. Ojifinni, J. Gong, N. S. Froemming, D. Flaherty, M. Pan, G. Henkelman, and C. B. Mullins, Carbonate formation and decomposition on atomic oxygen precovered Au(111) J. Am. Chem. Soc. 130, 11250 (2008).

R. A. Ojifinni, N. S. Froemming, J. Gong, M. Pan, T. S. Kim, J. M. White, G. Henkelman, and C. B. Mullins, Water-enhanced low-temperature CO oxidation and isotope effects on atomic oxygen covered Au(111) J. Am. Chem. Soc. 130, 6801 (2008).

G. Henkelman, A. Arnaldsson, and H. Jónsson, Theoretical calculations of CH4 and H2 associative desorption from Ni(111): Could subsurface hydrogen play an important role?, J. Chem. Phys. 124, 044706 (2006).

G. Henkelman and H. Jónsson, Theoretical calculations of dissociative adsorption of CH4 on an Ir(111) Surface, Phys. Rev. Lett. 86, 664 (2001).