Modification of chemisorption properties by electronegative adatoms: H 2 and CO on chlorided, sulfided, and phosphided Ni(100)

Abstract

The effect of preadsorbed electronegative atoms Cl, S and P on the adsorption-desorption behavior of CO and H 2 on Ni(100) has been studied using thermal desorption, LEED and AES. It is found that the presence of the electronegative atoms causes a reduction of the adsorption rate, the adsorption bond strength and the capacity of the Ni(100) surface for CO and H 2 adsorption. The poisoning effect becomes stronger with increasing electronegativity of the preadsorbed atoms. In the case of CO adsorption the most tightly bound β 2 -state is suppressed most significantly. The variation of the initial sticking coefficient of CO as a function of the adlayer precoverage shows that at low Cl and S coverages the effective number of the influenced Ni surface atoms is more than four. The observed reduction of CO and H 2 adsorption and the difference in the poisoning effect of Cl, S and P is generally interpreted in terms of the changes in the surface electron density in the presence of electronegative atoms.