H-1-NMR PROCEDURE TO ESTIMATE THE EXTENT OF METAL-SURFACE COVERED BY TIOX OVERLAYERS IN REDUCED RH/TIO2 CATALYSTS

Oxidation at different temperatures of an Rh/TiO2 sample in the SMSI state has been studied by H-1 NMR spectroscopy. In the range 273-473 K electronic perturbation of the metal is progressively eliminated. However, removing of TiO(x) species, which block physically the metal adsorption sites, requires oxidation at 673 K. At this temperature metal particles recover their maximum hydrogen adsorption capacity. From the difference between adsorbed hydrogen in the sample oxidized at 473 and 673 K, a measurement of the metal surface covered by TiO(x) species has been obtained. The influence of reduction pretreatments (temperature and time) on the degree of TiO(x) coverage has been also analyzed.