INTERACTION OF HYDROGEN WITH SUPPORTED RU CATALYSTS - HIGH-PRESSURE IN-SITU NMR-STUDIES

An in situ H-1 nuclear magnetic resonance (NMR) technique has been emp loyed to study the interaction of hydrogen with silica-supported ruthe nium catalysts in the temperature range 300-473 K and at pressures of 10(-5)-760 Torr. In addition to an upfield NMR peak (called a) occurri ng at approximately -60 ppm and observed at low pressures (P < 100 Tor r), we have noted the emergence of a second peak (called beta) occurri ng at approximately -30 ppm at elevated pressures (P > 100 Torr). Thes e two hydrogen populations represent adsorbed hydrogen interacting wit h Ru metal particles, as indicated by the observed Knight shifts. The a hydrogen species exists in the form of less mobile hydrogen species al, or a mobile hydrogen species am with heats of adsorption determine d by microcalorimetry to be about 70 kJ/mol and 40 kJ/mol, respectivel y. The heat of adsorption of the beta species was determined to be app roximately 10 kJ/mol. Hydrogen adsorption isotherms were obtained from the NMR peak intensities calibrated by a gadolinium-doped lanthanum h ydride internal reference. A higher dispersion of metal particles corr elated with a larger amount of the weakly adsorbed beta hydrogen speci es. The H/Ru(surface) ratio was observed to be in excess of 5 at eleva ted pressures (> 500 Torr). The high H/Ru(surface) was due to the adso rption of large amounts of beta hydrogen. (C) 1994 Academic Press, Inc