SURFACE CHARACTERIZATION FROM ADSORBATE KNIGHT-SHIFTS

Recent works on catalyst surface characterisation from adsorbate Knigh t shifts are reviewed. It has been shown how for supported catalysts t he proton NMR gives a better estimate of the metal dispersion than the classical volumetric technique where the amount of hydrogen adsorbed is measured to determine the dispersion. It has also been shown that a dsorption on multiple sites can be probed by the adsorbate Knight shif ts. Again, for bimetallic systems the Knight shifts has been shown to indicate the composition of the surfaces. This has been corroborated b y a microscopic theory using Friedel sum rule. The role of promoters o n active site blocking, the evaluation of kinetic parameters and the e ffect of segregation on the adsorption energy may also be found from N MR Knight shifts. The works reviewed here concern generally hydrogen a s an adsorbate. However, some work using H-2, C-13 and Xe-129 NMR are also discussed. Deuterium NMR helps to find the kinetic parameters in exchange reaction and is complementary to the proton NMR in surface st udies. Similarly, Carbon-13 NMR helps to understand the organic reacti ons on metal surfaces as well as the surface structure of catalysts. X e-129 NMR helps to understand the internal structure of zeolites.