Study of reaction mechanism of the reduction of nitric oxide by hydrocarbon in excess oxygen over a platinum catalyst via the investigation of surface species

Abstract

In this thesis, the reaction mechanism of the selective catalytic reduction of nitric oxide by hydrocarbon over Pt/Al₂O₃ catalyst under excess oxygen is proposed via the investigation of surface species produced on the catalyst surface. With propene as a model reductant, an experimental set of three continuous steps consisting of reaction step, temperature programmed desorption step and temperature programmed oxidation step was carried out. It can be observed that there are at least three types of surface species occurred on Pt/Al₂O₃ catalyst. The observation of the reactivity of surface to various oxidizing gases and the investigation of the nature of surface species after the addition of sulfur dioxide in the reactant gas mixture indicate that a few mechanisms are simultaneously proceeded at the same reaction condition. Hence, it is difficult to control the required reaction mechanism pathway over this catalyst. However, at low operating temperature where propene oxidation is not completed, the only partially oxidized hydrocarbon compounds, which decompose themselves at high temperatures, distinctly play an important role in such reaction. Unfortunately, the investigation of surface species can not effectively apply with the above reaction using propene as a reductant instead of propene due to the obtained surface species behaving as the spectator species.