The reactivity of ordered metal layers on single crystal surfaces of other metals: Au on Pt(100) and Pt on Au(100)

Gold was deposited on Pt(100) and platinum was deposited onto a Au(100) single crystal surface. The variation of the reactivity of these surfaces with coverage of the adsorbate metal was studied using the cyclohexene dehydrogenation to benzene as a test reaction. The reactions were carried out with 6 × 10 −8 Torr (8.0 × 10 −6 Pa) cyclohexene in hydrogen with a partial pressure of 1 × 10 −6 Torr (1.3 × 10 −4 Pa) at 373 K. It was found that the reactivity of a Pt(100) surface is enhanced about six-fold by the deposition of just one monolayer of gold that itself is not measurably active under these reaction conditions. When the gold coverage exceeds one monolayer the reactivity decreases. The deposition of platinum onto a Au(100) single crystal surface causes an increase in the reactivity until a broad maximum is reached at about 1.5–2 layers of platinum. At this maximum the reactivity is six times larger than that of a Pt(100) single crystal surface. Beyond three to four layers, the reactivity decreases slowly with increasing platinum coverage and approaches the reactivity of the clean Pt(100) single crystal surface.