Chemisorption Of Molecular Oxygen Research Articles

Studies of Ni—Cu catalysts with parallel chemisorption of O 2 and decomposition of N 2O

Chemisorption of molecular oxygen and decomposition of nitrous oxide on Ni—Cu powders and (Ni—Cu)/γ-Al 2O 3 catalysts were studied. O 2 is chemisorbed on Ni—Cu alloys similarly to on Ni powder. Decomposition of N 3O depends on the composition of the Ni—Cu alloy surface; it proceeds similarly on nickel or on copper for Cu surface concentrations, expressed as Cu surface atomic fractions, below and above ~0.5, respectively. Chemisorption of O 2 and decomposition of N 2O may be used for the determination of metal surface area and for monitoring the surface composition of Ni—Cu alloys, respectively.

Adsorption of germanium and of oxygen on cleaved InP(110) surfaces: Auger electron spectroscopy and measurements of work function and of surface photovoltage

The deposition of germanium as well as the chemisorption of molecular oxygen cause the formation of depletion layers on cleave InP(110) surfaces initially exhibiting flat bands, and on p- as well as on n-type doped samples the Fermi level is finally pinned (1.11±0.02) eV above the valence-band top Evs. From the surface band bending vs Ge coverage curves the energies of the chemisorption-induced surface states, i.e., their effective occupation levels, were evaluated as Evs +1.08 eV for the surface donors and Evs +1.15 eV for the surface acceptors. Chemisorbed oxygen, in contrast to germanium, introduces no surface dipoles on InP(110) and is thus incorporated rather than adsorbed. Both the unstimulated and the photon-stimulated interactions of unexcited molecular oxygen with InP(110) surfaces result in a phosphorous loss. After exposures of 1013 L of oxygen in the dark and when simultaneously illuminated by the light of a xenon-arc lamp the phosphorous loss is equivalent to a depletion of one and 1.65 InP layers, respectively, while the oxygen uptake amounts to 0.6 and 1.35 monolayers, respectively. Thus, an indium-oxide layer forms on InP(110) which finding is in agreement with the nonexistent chemisorption dipoles.

Can desorption be described by the local density formalism?

The local spin density approximation, commonly used in modern chemisorption calculations, sometimes provides a spurious description of desorption. Adsorbates can desorb with fractional charge, leading to qualitatively incorrect binding energy curves and induced dipole moments at large distances. However, the true binding-energy curves exhibit a universal nature which allows them to be simply predicted, as exemplified by atomic and molecular chemisorption of oxygen on Pt(111). The exact density functional explanation for the desorption limit is also presented.

Desorption d'oxydes de niobium a partir de la solution solide niobium-oxygene, sous 3 × 10 −7 Torr A 3 × 10 −5 Torr d'oxygene, entre 1700 K et 2350 K

We have studied the desorption of oxygen from homogeneous niobium-oxygen solid solutions under a pressure of 3 × 10 −7 to 3 × 10 −5 Torr of oxygen between 1700 K and 2350 K. The products of this desorption process are NbO and NbO 2, which we have demonstrated are formed by a superficial reaction after chemisorption of molecular oxygen on to two distinct sites. Two models for the process are discussed: in the first, the speeds of desorption are assumed to be a function of the surface coverage. This model suggests that the binding energy of the adsorbed oxygen atoms should vary with the coverage. In the second model the bulk concentration is assumed to be variable. It is shown that at low concentration this model is related theoretically to the first. Good agreement with experiment was found for this model in the steady state throughout the whole homogeneity range of the solid solutions. In the transient state, however, the model only applies to thin samples.

Valence band studies of the copper + oxygen system

An experimental reinvestigation (UPS and XPS) of the chemisorption of molecular oxygen on copper is described. Ultra-violet (HeI and HeII) photoelectron spectra of the oxidised surfaces are reported: XPS intensity data were used to monitor the uptake of oxygen, enabling an apparent discrepancy between previously published studies to be resolved. The spectra suggest that surface reconstruction occurs at ordinary temperatures even for very small oxygen uptakes.