Structure of Ag ON Rh and its effect on the adsorption of D 2 and CO

Abstract

Ag vapor deposited on Rh(100) is investigated as a possible model for the corresponding bimetallic cluster catalyst. Ag overlayer growth follows the Frank-Van der Merwe mechanism at 300 K and the Stranski-Krastanov mechanism at 640 K. The first Ag overlayer grows epitaxially with the Rh(100) surface and forms two-dimensional islands. The second layer reconstructs forming a pseudohexagonal lattice structure with a 19% greater Ag atom density than the first layer. Neither alloy formation nor dissolution of Ag into the Rh crystal lattice is observed. The presence of Ag decreases the capacity of the Rh(100) surface for both D 2 and CO chemisorption. In both cases, loss of adsorption sites on the Rh surface is attributed to physical site blocking by islands of Ag. Very weakly bound CO adsorption sites are observed which are attributed to CO bonding to Ag atoms in the first Ag overlayer. The Ag/Rh(100) system is found to be very similar to the analogous SiO 2 supported catalyst.