Abstract
Adsorption of N 2O, NO, and NO 2 on Fe 2O 3 and Fe 3O 4 was studied by means of X-ray photoelectron spectroscopy (XPS) using an AEI ES 100 spectrometer at temperatures from −100 to +250 °C. Adsorption isotherms and isobars of NO and NO 2 have been plotted for Fe 3O 4 and Fe 2O 3. Isotherms are Langmuir curves, and the adsorption isobar of nitrogen dioxide adsorbed on Fe 2O 3 shows a maximum at room temperature. No adsorption of nitrogen monoxide is detected with Fe 2O 3 (the detection limit is about 0.1 monolayer). With adsorbed nitrous oxide a simple peak is recorded in contrast to what is observed in the vapor phase. The N 1s binding energy of adsorbed NO is lower than that of the gaseous species, suggesting that significant electron transfer from the iron oxides to the adsorbed nitrogen oxide occurs; however, this back donation is not observed with adsorbed nitrogen dioxide. Adsorption does not cause changes in the binding energies of Fe 2O 3 core electrons, but shifts the Fe 3p line of Fe 3O 4 toward the higher binding energies, suggesting that Fe 3O 4 is oxidized by the adsorption of nitrogen oxides.
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