Acetylene, ethylene, and arene chemistry of palladium surfaces

The chemisorption behavior of acetylene, ethylene, and benzene on the low Miller index planes of palladium is described. This behavior is very sensitive to the surface composition, particularly to sulfur and phosphorus adatoms. Most complex was the acetylene chemistry where decomposition to carbon, reversible desorption, reversible C-H bond scission, trimerization to benzene, and hydrogenation to ethylene were five readily characterizable, competing reactions. In this context of acetylene chemistry, the palladium surfaces behave quite differently from those of nickel and platinum under ultrahigh vacuum conditions. Also, unlike nickel and platinum, palladium under ultrahigh vacuum conditions effected hydrogenation reactions such as the conversion of acetylene to ethylene.