Nuclear Magnetic Resonance Study of the Platinum - Rhodium Bimetallic Clusters.

We report the study of supported Pt-Rh bimetallic catalysts by ^{195}Pt NMR and by ^{13}C NMR of adsorbed CO. The metal particles are 5A-50A in diameter. Study of the dependence of the ^{13} CO resonance position as a function of Pt/Rh ratio and particle size shows that Rh is segregated to the surface. Study of the ^{195}Pt NMR shows that the center of the particles consists of Pt only. By ^{195}Pt-^ {13}CO double resonance we measure CO frequencies for those CO molecules which are bonded to Pt. We found thereby that the electronic structure of the bimetallic particle surfaces probed by CO NMR is independent of whether CO is bonded to Pt or Rh.