ADSORPTION AND THERMAL-DECOMPOSITION OF ETHYLENE ON CLEAN AND CARBON MONOXIDE-COVERED IR(110) SURFACES

The adsorption and the thermal decomposition of ethylene have been investigated on clean and CO-covered Ir(110) surfaces at temperatures ranging from 170 to 600 K. HREELS, TDS and UPS methods are used. Adsorption on a clean surface at 170 K is found to lead to the formation of ethylidyne (≡C-CH3) whereas on a surface with a saturated CO coverage small amounts of ethylene are adsorbed molecularly at the same temperature forming a di-σ-bond. After heating, ethylidyne decomposes to CxH fragments (x = 1, 2), the process taking place at lower temperatures than on the (111) iridium surface. The presence of carbon monoxide on the surface enhances the temperature stability of the ethylidyne species by about 50° compared to that on a clean surface and hinders the formation of fragments. The stabilizing effect of carbon monoxide also concerns the decomposition products of ethylidyne. © 1990 Elsevier Science Publishers B.V. (North-Holland).