Chemisorption palladium hydrides

The dissolution of hydrogen in palladium to form a- and (i-phase palladium hydrides has been assumed to present problems in determining the surface area of palladium catalysts by hydrogen chemisorption, but under normal chemisorption conditions this is probably not a factor. The a-phase Pd-H forms initially by the migration of hydrogen atoms from the surface into the interstitial volume of the palladium crystals. Hydrogen pressures near atmospheric are... 

Pd hydride formation was routinely determined by chemisorption and calorimetric measurements and heats of formation of the g-phase hydride were consistently near 10 kcal/mole H2 absorbed, independent of support and crystallite size, which is in good agreement with literature values for bulk palladium. 

K mol kJ (theory). The conclusion was that atoms escape from the surface of solid palladium modifier (the E parameter was measured at temperatures lower than the melting point for Pd) as a result of desorption of single atoms and, thereafter, the mechanism of their retention on palladium on the stage during pyrolysis reduces to dissociative chemisorption. The analyte atoms are adsorbed on the modifier surface in the course of low-temperature decomposition of nitrates or in the process of sample introduction into the furnace in the form of hydrides (see Table 5.4). 

Results for palladium were less reliable because of the possibility of hydride formation. For this reason, chemisorption was conducted at a higher temperature (100 C) to minimise the dissolution of Hj in the metal [10],... 

---