A study of the kinetics of the interactions of O2 and N2O with a Cu(111) surface and of the reaction of CO with adsorbed oxygen using aes, LEED and ellipsometry

Abstract

The interactions of O2 and N2O in the low pressure range with a Cu(111) surface and of CO with adsorbed oxygen have been studied with ellipsometry, Auger electron spectroscopy and LEED. The adsorption of O2 was investigated in the 10−6–10−4 Torr range and at crystal temperatures ranging from 23 to 400°C. O2 chemisorbs dissociatively with an initial reaction probability of about 10−3 and an apparent activation energy of 2–4 kcal/mol, which depends on the substrate temperature, up to a saturation coverage of 0.45. The probability of decomposition of N{ib2}O is 10−5 at 300°C, and the activation energy is 10.4 kcal/mol for 250 < T < 400°C. The oxygen coverage saturates at θ = 0.45 as well. For both oxidation reactions the kinetics can be described with a precursor state model. With LEED no superstructures were observed. The probability of the reaction of CO with adsorbed oxygen is 4 × 10−5 at 250°C and is initially independent of the oxygen coverage. The reaction is assumed to proceed via a Langmuir-Hinshelwood mechanism. The activation energy for the reaction COad + Oad → CO2 is 18–20 kcal/mol.