ENHANCED OXIDATION OF CARBON-MONOXIDE ON PLATINUM IN HCLO4 VIA INTERACTION WITH ACETONITRILE

The influence of acetonitrile on both the adsorption and electro-oxida tion of CO at smooth and rough platinum in 0.1 M HClO4 has been invest igated with the help of on-line electrochemical mass spectrometry (DEM S). It is shown that a small amount of acetonitrile (AN) in solution c atalyzes strikingly the bulk electro-oxidation of CO, The catalytic ef fect is much higher on smooth than on rough platinum surfaces. The cat alytic activity also depends upon the concentration of AN, for a smoot h Pt surface below 0.01 M. However, the electro-oxidation of CO adsorb ates is seriously inhibited by the presence of AN in solution. The int eraction between the surface species derived from AN and CO was studie d in great detail. The results show that the adsorption of CO obviousl y can still proceed by removing parts of preadsorbed AN. On the other hand, the adsorption of AN is completely inhibited on the surface prev iously covered with a monolayer of COad. When both, AN and CO, are pre sent simultaneously in solution, co-adsorbed surface species are forme d at the electrode surface. We think that the enhanced electro-oxidati on of CO is due to a ''third body'' effect modified by a special adsor ption/desorption behaviour of AN.