Chemisorption on cobalt surfaces: The effect of subsurface rhenium atoms from quantum chemical cluster model calculations

We have calculated chemisorption energies for different sorbates on cluster models for a number of sites on pure and subsurface rhenium-doped cobalt surfaces. Bonding energies follow the trend water < CO < propyl < methyl < hydrogen < hydroxyl, and are in good agreement with experimental results where available. The results indicate that for single-bond radicals (hydrogen, alkyl, hydroxyl), rhenium inclusion stabilizes the chemisorbed species. Further, the stabilization leads to a greater number of sites being energetically close to the most stable ones, possibly enhancing surface mobility of chemisorbed species. Hydrogen is less stabilized by rhenium substitution compared to propyl, indicating a possible mechanism for the greater yield of long-chained hydrocarbons afforded by rhenium-doped catalysts. For carbon monoxide, the results are less conclusive as rhenium substitution does not influence chemisorption energies so strongly.