UV-induced Reduction of Molybdenum Ions on the Surface
of Alumina in the Presence of Carbon Monoxide
and Nitrogen Oxide

I. R. Subbotina, A. L. Tarasov, B. N. Shelimov, and V. B. Kazansky

Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 117913 Russia

Received April 10, 1998

Abstract—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 Mo⁴⁺. The average oxidation states of molybdenum ions
in photoreduced samples 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/Al₂O₃. The Mo⁴⁺ ions are assumed to be
formed from the surface monomolybdates, whereas the Mo⁵⁺ ions are formed from polymolybdates, whose
fraction substantially increases with an increase in the concentration of the supported molybdenum. The heating
of photoreduced samples in a vacuum at 300°C results in a substantial decrease in the concentration of Mo⁴⁺
and in an increase in the concentration of Mo⁵⁺ due to the metathesis Mo⁴⁺+ Mo⁶⁺2Mo⁵⁺ in polymolyb-
date structures. The composition of Mo⁴⁺(CO)_x complexes in photoreduced MoO₃/Al₂O₃ is studied by IR spec-
troscopy. When MoO₃/Al₂O₃ is UV-irradiated in the presence of the CO + NO mixtures, the photocatalytic
reduction of NO yields N₂O and CO₂.

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