Hydrogen adsorption on silica-supported platinum studied by 1H NMR spectroscopy

Abstract

¹ H NMR spectra resulting from the adsorption of hydrogen on a silica-supported platinum catalyst have been recorded quantitatively over a wide coverage range to produce an NMR adsrption isotherm as well as the isotherm determined volumetrically. The coverage dependence of the chemisorbed hydrogen resonance frequency has been analysed in term of a three-state model that includes terms for strongly and weakly chemisorbed hydrogen as well as gas-phase hydrogen, all in fast exchange and, hence, in dynamic equilibrium. This analysis yields values for the NMR frequency of the strongly bound hydrogen of –48(±2) ppm and of +37(±10) ppm for the weakly bound hydrogen. The model accurately describes the observed coverage dependence of the chemisorbed hydrogen resonance over the wide coverage range studied.