Ambient Oxidation of Ultrasmall Platinum Nanoparticles on Microporous Carbon Catalyst Supports

Ultrasmall platinum nanoparticles on carbon catalyst supports undergo oxidation in ambient air. A systematic survey of carbon supports with controlled pore structures was conducted to isolate the effect of pore structure on particle size and resistance to oxidation. It was found that carbon supports with higher microporosity gave larger metal particles at high metal weight loadings, whereas the particle sizes remained independent of pore size at low weight loadings. It is the large particles that are most stable to oxidation; particles of average size less than 1.4 nm are more than 80% oxidized, while particles greater than 1.8 nm are less than 30% oxidized. The effect of micropores on the stabilization of Pt to oxidation is thus indirect; the larger particles formed in the micropores at high metal loadings do not oxidize. At lower loadings, the pore environment plays no role in stabilizing the Pt nanoparticles to oxidation.