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 C2 H2 under UHV conditions on Pt is completely irreversible, i.e., thermal dec omposition leads to complete conversion of the chemisorbed monolayer into s urface carbon, alloying with Sn strongly reduces the amount of carbon thus formed. In addition, the temperature for complete dehydrogenation of the ca rbonaceous residue formed from acetylene decomposition (polymerization) is increased by up to 100 K, from 760 to 860 K. Both of these phenomena are co nsistent with observations of increased lifetimes and decreased coking for technical Pt-Sn bimetallic catalysts compared to Pt catalysts used for hydr ocarbon conversion reactions.