Probing the surface of a heterogeneous catalyst: Double resonance of carbon monoxide chemisorbed on highly dispersed platinum

Spin Echo Double Resonance (SEDOR) is observed at 77 K for small Pt particles on which l3CO was chemisorbed. The samples are Pt supported on eta-alumina with Pt dispersions (fraction of the atoms that are on the surface) of 26% and 76%. After cleaning, the samples are exposed to CO enriched to 90% l3C• The l3C NMR is observed indirectly through its effect on the 195Pt spin echo. SEDOR allows the NMR of the surface Pt nuclei to be observed underneath the resonance of the nonsurface nuclei from which the surface nuclei are ordinarily unresolved. The position (1.096 kG/MHz) and width (500 G at 80 kG) of the 195pt SEDOR signal confirms the assignment by Rhodes et al. of a peak in the 195pt NMR line shapes to the surface layer of platinum atoms. No surface nuclei are detected at any other locations in the 195pt NMR line shape. Though the 195pt NMR line shapes for the two dispersions are very different, the SEDOR line shapes are identical. SEDOR shows that the bonding of the CO is to the clean Pt surface through the carbon and that the Pt-C J coupling is similar to that in Pt carbonyls.U of I OnlyThesi