Abstract
The uptake of hydrogen by titania-supported Ni, NiFe, and Pt samples was investigated at room temperature following reduction at 770 K. The hydrogen uptake was low for each sample (e.g., zero for Pt TiO 2 ) as determined by adsorption measurements. After the samples were subsequently equilibrated with gaseous hydrogen at ca. 40 kPa for extended periods of time (ca. 15–20 h), hydrogen desorption measurements were determined. Significant amounts of hydrogen strongly held by the samples were observed in this manner. Metal particle sizes estimated from these hydrogen uptakes were in good agreement with particle sizes determined by X-ray line broadening and transmission electron microscopy. The hysteresis between the adsorption and desorption measurements was indicative of slow hydrogen adsorption. Titania-supported Pt samples were also observed to adsorb CO weakly, and Ni(CO) 4 was formed slowly when Ni TiO 2 was exposed to CO at room temperature. These data are discussed in terms of the presence of titanium species (TiO x ) on the surfaces of the metal particles, and the possible migration of hydrogen from metal particles to adjacent regions of the titania support.
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