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

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.