Oxygen penetration into the bulk of palladium

Abstract

The interaction of 02 with polycrystalline Pd was investigated; above 250 °C a significant amount of oxygen is incorporated into the bulk at pressures far below the dissociation pressure of PdO. The rate of uptake into previously unexposed Pd foil was pressure independent, suggesting (1) that penetration into the bulk occurred from an oxygen-saturated surface and (2) that the rate was limited by the process in which chemisorbed oxygen moved out of the surface layer toward the interior of the Pd. The temperature dependence of the uptake rate in this pressure-independent region was characterized by an Arrhenius A factor of 5.2 X 1020 atoms cm'2 min'1 and an activation energy of 17 kcal mol'1 (71 kJ mol'1). After about 100 monolayers of oxygen were incorporated, the uptake rate began to decline and became unobservable after about 350 monolayers were incorporated. Equilibrium oxygen pressures above such extensively oxygen-treated samples were much lower than the reported dissociation pressures of PdO indicating that the palladium-oxygen system under these conditions should be characterized as a solid solution of oxygen in palladium. The role which this incorporation of oxygen may play in catalytic processes is discussed.

Diffusivity and solubility of oxygen in solid palladium

“…Considering the palladium-oxygen system, many investigations have been carried out dealing with the surface adsorption/desorption behaviour of oxygen at low temperatures. Information on the behaviour of oxygen in the bulk of palladium at high temperatures, however, is limited, in part questionable and/or contradictory [1][2][3][4][5][6].…”

“…In literature, only few studies are found that yield statements or data on the solid solubility of oxygen in palladium [1][2][3][4]. Early results stem from gravimetric investigations of the interaction of oxygen with palladium including the oxidation of the metal [1][2][3].…”

“…Early results stem from gravimetric investigations of the interaction of oxygen with palladium including the oxidation of the metal [1][2][3]. The reported rather high values of oxygen solubility were not confirmed by the measurements carried out later by Jehn and Grallath [4].…”

Deactivation of platinum catalysts by oxygen 2. Nature of the catalyst deactivation

“…After the chemisorption of oxygen on the platinum surface, the oxygen atoms are able to diffuse into the platinum lattice. Dissolution of oxygen in the upper layers of metal atoms was also observed in the case of Pd catalysts (31,32), even when conditions under which palladium oxide is unstable were used (33). By the interaction of the platinum lattice and oxygen atoms a solid phase which is unable to catalyze the desired oxidation of sodium-D-gluconate is formed.…”

Proceedings of the 1999 Advanced Turbine Systems Annual Program Review Meeting

“…The dissociation of active surface species of palladium oxide into less active palladium crystals at 900 OC (Farrauto et al 1992;McCarty, Wong and Chang 1993) The absorption of oxygen by palladium, which impairs the catalytic properties of the metal (Campbell, Foyt and White 1977;Ladas, Imbihl and ErtIl989) Signiflcant hysteresis effects in the temperature-dependent formation and dissociation of PdO (Garbowski et al 1994;Briot and Primet 1991;Lieske and Volter 1985;Chen and Ruckenstein 1981) The nonlinear dependence of catalytic activity on catalyst loading and metal particle size (Hicks et al 1990) Metal-support interactions which may alter the catalytic activity (Baldwin and Burch 1990;Baker, Prestridge and McVicker 1984) Variations in reaction sites due to differences in crystalline planes (Wang, Lee and Schmidt 1985;Greenler et al 1985;Corma, Martin and Perez 1983) …”