Correlation between the Knight shift of chemisorbed CO and the Fermi level local density of states at clean platinum catalyst surfaces

We have investigated the ¹⁹⁵Pt and ¹³C nuclear magnetic resonance (NMR) spectroscopy of clean-surface platinum catalysts and of CO chemisorbed onto Pt catalyst surfaces. We use Knight shift, relaxation, and J-coupling data to deduce information about the Fermi level local density of states (E(f)-LDOS) at catalyst surfaces. There is a linear correlation between the Knight shifts of chemisorbed CO and the clean surface E(f)-LDOS of platinum onto which the CO is bound, as determined by ¹³C and ¹⁹⁵Pt NMR. The correlation amounts to ~12 ppm/Ry^-1·atom^-1, the same as that which can be deduced for CO on palladium, as well as from the electrode potential dependence of ¹³C Knight shifts and infrared vibrational frequencies, ν(CO), and the relationship between ν(CO) and the E(f)-LDOS at clean platinum surfaces. The ability to now directly relate metal and adsorbate electronic properties opens up new avenues for investigating metal-ligand interactions in heterogeneous catalysis and electrocatalysis.