Reactivity of Graphene-Supported Pt Nanocluster Arrays

Nanocluster arrays on graphene (Gr) are intriguing model systems for catalysis. We studied the adsorption and oxidation of CO on Pt/Gr/Rh(111) with synchrotron-based high-resolution X-ray photoelectron spectroscopy. On the nanoclusters, CO is found to adsorb at three different sites: namely, on-top, bridge, and step. The C Is spectra exhibit remarkable similarities to those on the stepped Pt(355) surface. Similar to the case for stepped Pt surfaces, a clear preference for the adsorption on the step sites is found, while the preference for the adsorption on the on-top site over the bridge site on the terraces is much less pronounced in comparison to that on Pt single crystals. Temperature-programmed X-ray photoelectron spectroscopy revealed an enhanced binding energy for the cluster step sites, similar to the situation on stepped Pt surfaces. The oxidation of CO on graphene-supported Pt nanoclusters follows a pseudo-first-order rate law. Applying an Arrhenius analysis, we found an activation energy of 13 +/- 4 kJ/mol, which is much smaller than that on Pt(111), due to the more reactive step and kink sites on the nanoclusters.