CHARACTERIZATION OF SILICA CATALYST SUPPORTS BY SINGLE AND MULTIPLE-QUANTUM PROTON NMR-SPECTROSCOPY

Cab-O-Sil HS5, used as the support in silica supported ruthenium (Ru/S iO2) catalysts, was characterized via single and multiple quantum (MQ) H-1 NMR spectroscopy. The samples were studied both in the presence a nd in the absence of ruthenium. Single quantum spin counting of proton s on silica support with and without ruthenium metal indicated that th e total number of hydroxyl groups decreased significantly with increas ing reduction temperature over the range of 350-530 degrees C. Two dif ferent components shown in static H-1 NMR were found to reveal homogen eous and inhomogeneous broadening via spectral hole burning experiment s. H-1 MQ-NMR spin counting, based on the number of MQ coherences obse rved, showed the existence of small clusters of proton spins on the si lica surface. The maximum measured cluster size was 6-7, or less, spin s. Segments of silica resembling the 100 face of cristobalite on the s urface are postulated to be possible sites for the clusters. The clust ers in pure silica became smaller as the reduction temperature increas ed over 500 degrees C. No such change was detected in the presence of ruthenium.