Adsorption and reaction of unsaturated hydrocarbons on Sn/Pt alloys

Alloying Sn with Pt can strongly modify the catalytic properties of Pt catalysts for many reactions. Surface science experiments, particularly those involving the use of temperature programed desorption (TPD) and vibrational spectroscopy, accompanied by theoretical calculations, have revealed the surface chemistry that underpins these modifications. Much of this fundamental information comes from investigations of Pt-Sn ordered surface alloys, mainly for the surface (2×2) and (√3 × √3) R3°)alloys formed for Sn/Pt(111), regarding the adsorption and reaction of a range of unsaturated hydrocarbons including alkenes, dienes, aromatics, alkynes, and α,β-unsaturated aldehydes. Alloying Sn with Pt generally reduces the adsorption energy of unsaturated hydrocarbon molecules, promotes reversible molecular desorption in TPD, and strongly decreases further dehydrogenation. In some cases, coupling reactions can be observed such as acetylene cyclotrimerization. Details on how Sn affects initial sticking coefficients, monolayer saturation coverages, and the nature of chemisorption bonding are also available from surface science studies of unsaturated hydrocarbons on Pt-Sn alloys.