Studies of chemical reactions on well-defined surfaces have considerable potential for providing fundamental knowledge of surface reactivity and guidelines for the understanding of catalytic materials. with the use of low energy election deffraction (LEED)[1,2] surface structures can be diferentiated and the effect of these structures on surface reactivity determined. In addition, the relative case of obtaining surfaces of known composition utilizing Auger electron spectroscopy (AES)[3–5] makes it possible to study metal surfaces with less than 1% impurity and, moreover, to prepare surfaces with known coverages of adatoms such as carbon, oxygen, and sulfur in order to study the effects of these spacies on the activity and selectivity of the surface for given reactants. In some cases, as illustrated of the surface adatoms.