Correlation between the Knight Shift of Chemisorbed CO and the Fermi Level Local Density of States at Clean Platinum Catalyst Surfaces

Abstract

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 (Ef-LDOS) at catalyst surfaces. There is a linear correlation between the Knight shifts of chemisorbed CO and the clean surface Ef-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, νCO, and the relationship between νCO and the Ef-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.