The adsorption of PAMAM G4OH dendrimer and dendrimer-stabilized platinum nanoparticles onto alumina supports has been investigated using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. The presence of dendrimers on the Al2O3 surface is indicated by the appearance of several characteristic vibrational bands. The positions and relative intensities of amide I and II bands suggest that dendrimer conformation is effected by the presence of the encapsulated platinum nanoparticle. Aqueous phase carbon monoxide adsorption onto supported encapsulated Pt nanoparticles results in the appearance of a prominent vibrational peak associated with terminally adsorbed CO. The adsorbed CO can be removed by purging the CO from the liquid with either dissolved O-2 or N-2. The mechanism for this removal is likely via a reaction of CO with adsorbed OH formed from water dissociation. Comparisons with a traditional supported 1% Pt/gamma-Al2O3 catalyst indicate that the surrounded dendrimer does not hinder the adsorption of CO on the Pt when liquid water is present. However, under dry conditions the dendrimer completely blocks the occurrence of any CO adsorption.