THE INTERACTION OF COADSORBED CL AND CO ON NI(110)

The influence of preadsorbed chlorine on the adsorption behavior of CO on Ni(110) has been studied using AES, photoemission and work functio n measurements. It is found that the presence of chlorine causes a dra stic reduction of the CO adsorption rate and capacity on the Ni(110) s urface. Cl presaturation of the Ni(110) surface completely blocks the CO sticking. Conversely, chlorine displaces preadsorbed CO. At constan t total coverage, increasing Cl precoverage causes the 1 pi level of c oadsorbed CO to shift to higher binding energy, while the 5 sigma leve l slightly moves towards lower binding energy. These findings together with the decrease in the average dipole moment of CO induced by coads orbed chlorine indicate the reduced CO-Ni coupling and are in line wit h the poisonous character of electronegative surface additives in hete rogeneous catalysis.