Adsorbed states of CO on dispersed metals: Quantitative analysis with (13)C NMR spectroscopy.
01 January 1988
The (13)C NMR spectra of CO adsorbed on silica-supported Ru and Rh provide quantitative analysis and descriptions of the three adsorbed states; linear- and bridge-bonded CO on metal particles and gem-dicarbonyls on isolated metal atoms. The species adsorbed on the metal particles are immobile at 300K (on the NMR time scale of a few ms) whereas the gem-dicarbonyls are motionally averaged. The ratio of linear to bridging CO on Ru particles is 3.3, and the Ru particles are essentially two-dimensional rafts on the silica, one Ru atom thick. On Rh/silica, this ratio is 1, and the Rh particles are also rafts, but appear to be thicker than Ru, approximately 1 to 2 atoms in depth. The isolated metal atoms are not paramagnetic, which indicates that migration from the metal particles to form dicarbonyls is accompanied by oxidation of the metal.