Adsorption properties of oxidized gallium-modified zeolite ZSM-5 from diffuse-reflectance IR-spectroscopic and quantum-chemical data: II. Interaction with carbon monoxide and water

Diffuse-reflectance IR spectroscopy was used to study the adsorption and subsequent high-temperature transformations of water and carbon monoxide molecules on the oxidation-treated gallium-modified zeolite Ga/HZSM-5. The results were correlated with the corresponding quantum-chemical calculation data. Usually, it is thought that the oxo ions [Ga=O]+ are formed in the oxidation of Ga/HZSM-5. Based on the experimental and calculated data, the possible reactions of the gallium oxo ions with the above molecules are considered. The oxo ions were found highly reactive, and it is likely that polynuclear gallium oxide nanoclusters were formed in the oxidation of the gallium-substituted zeolite Ga/HZSM-5. The Ga+ ions, which appeared in the course of Ga/HZSM-5 reduction, were partially oxidized by water at 573 K; in turn, this could initiate the formation of polynuclear nanoclusters. It was found that ∼25% of the Ga+ ions were oxidized in the interaction with water to liberate molecular hydrogen. The thermal reduction of a nitrous oxide-preoxidized Ga/HZSM-5 sample with carbon monoxide was studied, and a conclusion on dissimilar states of oxygen bound to gallium was drawn.