Résumé
By means of the results obtained by 129Xe n.m.r. spectroscopy for the local distribution of CO chemisorbed on the very small platinum particles (six atoms on average) supported on NaY zeolite, it has been possible to determine precisely the effects of back-donation from the metal to CO and of dipole–dipole coupling between chemisorbed CO on the variation of vCO with surface coverage. The effect of dipolar coupling predominates when the coverage rises from one CO molecule per particle to saturation, but back-donation increases at the same time. The latter could be due to the small size of the particle and/or to the acidic nature of the support.