UV-induced reduction of molybdenum ions on the surface of alumina in the presence of carbon monoxide and nitrogen oxide

The UV irradiation of the MoO3/Al2O3 catalyst in the CO atmosphere at room temperature results in the reduction of the surface Mo6+ ions to Mo5+ and M O4+. The average oxidation states of molybdenum ions in photoreduced sample s and ESR data suggest that Mo4+ ions dominate in 0.1% MoO3/Al2O3 samples, whereas Mo4+ and Mo5+ are formed in nearly the same amounts in 1% MoO3/Al2O 3. The Mo4+ ions are assumed to be formed from the surface monomolybdates, whereas the Mo5+ ions are formed from polymolybdates, whose fraction substa ntially increases with an increase in the concentration of the supported mo lybdenum. The heating of photoreduced samples in a vacuum at 300 degrees C results in a substantial decrease in the concentration of Mo4+ and in an in crease in the concentration of Mo5+ due to the metathesis Mo4+ + Mo6+ --> 2 Mo(5+) in polymolybdate structures. The composition of Mo4+(CO)(x) complexe s in photoreduced MoO3/Al2O3 is studied by IR spectroscopy. When MoO3/Al2O3 is UV-irradiated in the presence of the CO + NO mixtures, the photocatalyt ic reduction of NO yields N2O and CO2.