Abstract
Palladium ultrafine powders were prepared by a hydrogen plasma-metal reaction method. After exposure of the prepared powders to air, gas evolution characteristics were examined by a temperature programmed desorp-tion method. Main evolved gases detected with a quadrupole mass spectrometer were H2O, CO and CO2. H2O and CO2 evolution peaks were appeared at temperatures of approximately 420 and 620 K. CO evolution peaks were appeared at temperatures of approximately 440, 510, 610 and 770 K. From the results of gas evolution behaviour after exposure to specific gases such as O2, CO and H2O, the origins of those peaks were discussed. The result was interpreted as follows; Palladium oxide (PdO), hydroxide (or its precursor) and impurity carbon existed on the surface. The evolution of H2O, CO and CO2 were due to the desorption of adsorbed species on the surface of the above compounds and the production by surface reactions.
