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

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. © 1979.