HYDROGEN ADSORPTION ON SILICA-SUPPORTED PLATINUM STUDIED BY H-1-NMR SPECTROSCOPY

H-1 NMR spectra resulting from the adsorption of hydrogen on a silica- supported platinum catalyst have been recorded quantitatively over a w ide coverage range to produce an NMR adsorption isotherm as well as th e isotherm determined volumetrically. The coverage dependence of the c hemisorbed hydrogen resonance frequency has been analysed in terms of a three-state model that includes terms for strongly and weakly chemis orbed hydrogen as well as gas-phase hydrogen, all in fast exchange and , hence, in dynamic equilibrium. This analysis yields values for the N MR frequency of the strongly bound hydrogen of -48(+/-2) ppm and of +3 7(+/-10) ppm for the weakly bound hydrogen. The model accurately descr ibes the observed coverage dependence of the chemisorbed hydrogen reso nance over the wide coverage range studied.