PT-195 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) di stance from the atomic planes increases upon coverage with 1/4 monolay er of atomic Li. This should change the response of the surface to inc oming reactants, and might be an important factor in the 'promotion' e ffect of alkalis in catalysis on transition metals. Experimental data on Pt-195 NMR parameters measured on Pt catalysts can, under certain a ssumptions, be analysed to obtain the average E(F) LDOS at a given typ e 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.