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

1994; IOP Publishing; Volume: 6; Issue: 36 Linguagem: Inglês

10.1088/0953-8984/6/36/001

1361-648X

YuYe J. Tong, G.A. Martin, J. J. van der Klink,

Theoretical and Computational Physics

Theoretical results in the literature for an Rh film indicate that the Fermi level local density of states (EF 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 EF 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 EF LDOS at surface sites increases by 10-15%. At other sites no detectable changes occur.