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

摘要

The characteristics of CO and NO molecules at Cu2+ and Cr3+ ion sites on the CuCr2O4 (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: Cu2+-CO>Cr3+- NO approximate to Cr3+-CO>Cu2+-NO. CO molecules are preferentially adsorbed at Cu sites, whereas NO molecules adsorb favorably at Cu2+ and Cr3+ 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-clown adsorption systems, the 5 sigma orbitals donate electrons and the 2 pi* orbitals obtain back-donated electrons. Although for NO with O-down adsorption systems, the NO-2 pi* orbitals obtain back-donated electrons from substrates without 5 sigma-donation. Coadsorption calculations show the CO/NO mixture adsorb selectively at the Cu2+ ion site but simultaneously at the Cr3+ ion site, respectively. (C) 2008 Wiley Periodicals, Inc.