The adsorption and desorption of hydrogen and carbon monoxide on bimetallic RePt(111) surfaces

Abstract

Bimetallic surfaces of rhenium on Pt(111) were prepared by vapor depositing rhenium on Pt(111). The adsorption and desorption behavior of CO and H 2 on bimetallic PtRe surfaces were studied using temperature programmed desorption, and compared to the behavior of CO and H 2 on the monometallic Pt(111) and Re(0001) counterparts. Depositing rhenium on a Pt(111) surface decreased the activation energy of desorption of hydrogen, and a surface composed of 0.37 monolayers of rhenium on Pt(111) showed an activation energy of hydrogen desorption that was 2.5 kcal mol less than the 19 kcal mol displayed by the monometallic Pt(111) surface. In contrast, the activation energy of desorption of CO from bimetallic surfaces depended very little on the bimetallic surface composition, and a value of 27 kcal mol was observed for low CO coverages. At saturation exposures of both H 2 and CO, maximum adsorption capacities were obtained for bimetallic surfaces. A surface composed of 0.2 monolayers of rhenium on Pt(111) adsorbed 20% more hydrogen than did Pt(111) alone, while a surface composed of 0.3 monolayers of rhenium on Pt(111) adsorbed 40% more CO than did Pt(111) alone. The results obtained show that surfaces exposing both rhenium and platinum atoms show adsorption/desorption behavior towards hydrogen and CO that is different than the behavior shown by either monometallic platinum or rhenium surfaces. Since the chemisorption behavior cannot be explained as a simple combination of the two metallic components of the surface, it is concluded that an electronic interaction between the two metals at the platinum-rhenium interface modifies the bonding of adsorbates at the mixed metal sites.