¹⁹⁵Pt NMR observation of local density of states enhancement on alkali-promoted Pt catalyst surfaces

Theoretical results in the literature for an Rh film indicate that the Fermi level local density of states (E_F LDOS) at a fixed (small) distance from the atomic planes increases upon coverage with 1/4 monolayer of atomic Li. This should change the response of the surface to incoming reactants, and might be an important factor in the 'promotion' effect of alkalis in catalysis on transition metals. Experimental data on ¹⁹⁵Pt NMR parameters measured on Pt catalysts can, under certain assumptions, be analysed to obtain the average E_F LDOS at a given type of Pt site (surface, subsurface, bulk). Such an analysis is applied here to Pt catalysts promoted with alkali salts. It is shown that the average E_F LDOS at surface sites increases by 10-15%. At other sites no detectable changes occur.