Silica-supported bimetallic catalysts were prepared by decomposing the mole
cular clusters Pt2Au4(C=(CBu)-Bu-t)(8) and Pt2Cu4(C dropC(t)Bu)(8). The res
ulting catalysts were characterized with hydrogen, oxygen, and carbon monox
ide chemisorptions. These indicated that CO chemisorption is the preferred
method for evaluating metal dispersion. Chemisorption results also suggeste
d that different types of substrate binding sites may be present on the bim
etallic particles and that a significant fraction of the available platinum
atoms may not be capable of activating hydrogen, Catalytic activity was ev
aluated with the toluene hydrogenation reaction. The new catalysts were fou
nd to be relatively inactive for this reaction at 60 degreesC, despite havi
ng high platinum dispersions. Apparent activation energies for toluene hydr
ogenation were evaluated with Arrhenius plots. Although activities were low
at 60 degreesC, the cluster-derived catalysts had smaller apparent activat
ion energies than a traditionally prepared Pt/silica catalyst. Trends in hy
drogen chemisorption and toluene hydrogenation are discussed in terms of po
ssible electronic, particle size, and ensemble size effects.