CO 2 adsorption on Cr(1 1 0) and Cr 2O 3(0 0 0 1)/Cr(1 1 0)

Abstract

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(1 1 0), and one of its surface oxides, Cr 2O 3(0 0 0 1)/Cr(1 1 0). The kinetics and dynamics of CO 2 adsorption have been studied by low energy electron diffraction (LEED), Aug er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E i = 0.1–1.1 eV and adsorption temperatures of T s = 92–135 K. The Cr(1 1 0) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E d = 33.3 kJ/mol, first order pre-exponential 1 × 10 13 s −1). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks ( E d = 39.5 and 30.5 kJ/mol). The initial adsorption probability, S 0, is independent of T s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(1 1 0) with increasing E i, with S 0 smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S( Θ), at low E i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E i with coverage (adsorbate-assisted adsorption). CO 2 physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E d has been obtained by means of a Redhead analysis of the TDS curves.