Interaction of CO and NO with the spinel CuCr2O4 (100) surface: A DFT study

Abstract The characteristics of CO and NO molecules at Cu 2+ and Cr 3+ ion sites on the CuCr 2 O 4 (100) surface have been studied by first principles calculations based on spin‐polarized density functional theory (DFT). The calculated results show that adsorption energies for X‐down(C, N) adsorption vary in the order: Cu 2+ ‐CO>Cr 3+ ‐NO≈Cr 3+ ‐CO>Cu 2+ ‐NO. CO molecules are preferentially adsorbed at Cu sites, whereas NO molecules adsorb favorably at Cu 2+ and Cr 3+ ion sites. The C‐O and N‐O stretching frequencies are red‐shifted upon adsorption. Combining the analysis of frontier molecular orbitals and Mulliken charge, for CO and NO X‐down adsorption systems, the 5σ orbitals donate electrons and the 2π * orbitals obtain back‐donated electrons. Although for NO with O‐down adsorption systems, the NO‐2π * orbitals obtain back‐donated electrons from substrates without 5σ‐donation. Coadsorption calculations show the CO/NO mixture adsorb selectively at the Cu 2+ ion site but simultaneously at the Cr 3+ ion site, respectively. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008