Reactions of small gold cluster cations with propylene, methane, and hydrogen: permissive and competitive coadsorption effects

Coadsorption effects of molecular hydrogen and small hydrocarbons, CH 4 and C 3 H 6 , on free Au 3 + and Au 5 + were investigated in an octopole ion trap under multi-collision conditions. For hydrogen and methane the observations indicate that both molecules coadsorb on the same adsorption site, i.e., the same atom of the cluster. This type of molecular adsorption on free clusters is termed permissive coadsorption, in contrast to competitive coadsorption, in which two molecules compete for the same adsorption site. The latter case was observed for hydrogen and propylene: already trace amounts of propylene were able to completely saturate the clusters preventing the coadsorption of H 2 . The size dependent adsorbate coverage is discussed and implications on the cluster structure are deduced from time and temperature dependent reaction measurements.