OPTIMIZATION OF THE VOLUMETRIC HYDROGEN CHEMISORPTION TECHNIQUE FOR DISPERSIONS OF RU SIO2 CATALYSTS/

Metal dispersions of silica-supported ruthenium catalysts determined b y the standard volumetric chemisorption technique were found to be ina ccurate due to irreversible spillover of hydrogen to the support. Dire ct evidence was obtained via in situ H-1 NMR for an irreversibly bound component of the hydrogen that migrated from the metal to the support on a time scale of tens of minutes or longer at room temperature. It was also shown in this work that hydrogen saturated the surface of the metal particles on a shorter time scale, on the order of minutes. Bas ed on H-1 NMR, optimum conditions for the volumetric chemisorption met hod were determined in order to alleviate the interference of spillove r with measurements of hydrogen uptake on the metal. Ruthenium dispers ions obtained from the optimized volumetric chemisorption technique we re more accurate and agreed well with the results of the H-1 NMR metho d. (C) 1995 Academic Press, Inc.