Investigations of TiO2 Photocatalysts for the Decomposition of NO in the Flow System: The Role of Pretreatment and Reaction Conditions in the Photocatalytic Efficiency

In order to investigate the photocatalytic stability and/or lifetime of titanium oxide photocatalysts in detail, standard reference photocatalysts (JRC-TIO-2, -3, -4, and -5), of which the surface chemical and physical properties are well known, were studied for the photocatalytic decompositon of NO under a large-scale flow reaction system. In the first stage, the photocatalytic decomposition of NO proceeded with a high efficiency and continuous production of N2, O2, and N2O. However, the reaction efficiency gradually decreased and finally leveled off at constant values. These values were found to be in the order of JRC-TIO-4>-3>-5>-2. Anatase TiO2, with a large surface area and numerous OH groups, was found to exhibit a high efficiency for the decomposition of NO in the flow system. The optimal pretreatment and reaction conditions were observed at a pretreatment temperature around 573 K under a mixture of O2 and Ar. It was confirmed that the surface hydroxyl groups on the photocatalysts play an important role in the decomposition of NO under this flow system.