Comparison of phosgene formation from adsorption of carbon tetrachloride on oxygen modified Ir(111) and oxygen modified Ir(110)

The production of phosgene was observed when a pure carbon tetrachloride mo lecular beam was impinged on the oxygen modified Ir (111) and Ir(110) surfa ces. Although the mechanism of phosgene formation is believed to be identic al on the two surfaces, important differences in reactivity were observed. The phosgene production of oxygen modified Ir(111) was greater than the oxy gen modified Ir(110) surface. Oxygen atoms are more tightly bound to the Ir (110) surface making it less reactive for the production of phosgene. Forma tion of the surface oxide on Ir(110) (which begins to occur if the surface is heated above 550 K) reduces adsorption of carbon tetrachloride, which ne cessarily decreases phosgene formation. The Ir(110) surface may also cause a more rapid decomposition of the adsorbed CCl2 intermediate. Phosgene prod uction on oxygen modified Ir(110) also demonstrated a maximum at 500 K, whe reas phosgene production on oxygen modified Ir(111) decreased with increasi ng temperature. (C) 2001 American Vacuum Society.