Coking resistance of Pt-Sn alloys probed by acetylene chemisorption

Acetylene (C₂H₂) is a reactive molecule with a low C : H stoichiometry that can be used to evaluate aspects of the resistance of metal-based catalysts to the formation of carbonaceous residue (coking). Herein we summarize our results for C₂H₂ chemisorption and thermal reaction on four well-defined, ordered surface alloys of Pt-Sn prepared by Sn vapor deposition on Pt(100) and Pt(111) single crystals under UHV conditions. While chemisorption of C₂H₂ under UHV conditions on Pt is completely irreversible, i.e., thermal decomposition leads to complete conversion of the chemisorbed monolayer into surface carbon, alloying with Sn strongly reduces the amount of carbon thus formed. In addition, the temperature for complete dehydrogenation of the carbonaceous residue formed from acetylene decomposition (polymerization) is increased by up to 100 K, from 760 to 860 K. Both of these phenomena are consistent with observations of increased lifetimes and decreased coking for technical Pt-Sn bimetallic catalysts compared to Pt catalysts used for hydrocarbon conversion reactions.