日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Development and characterization of Fe/zeolites for NH₃ selective catalytic reduction (NH₃-SCR) of NO_x emitted from diesel vehicles were conducted. The NO_x reduction activity of fresh samples was dependent on the Fe loading method and the type of zeolite (pore structures and Si/Al₂ ratios). Amajor factor affecting fresh activity was the number of ion-exchanged Fe sites which can be quantified using temperature-programmed desorption of NO₂. A hydrothermal stability was improved by using larger zeolite crystal size and by sequential ion-exchange of rare earth metals. It was because dealumination which leads to a loss of the ion-exchange Fe was inhibited. Standard SCR (NO₂/NO_x=0%) reaction was investigated by means of in situ FT-IR, transient and steady-state reaction studies. The ratedetermining step is the oxidation of NO to NO₂, and this step is inhibited by coexisting gaseous NH₃.Finally, overall SCR scheme including Fast SCR (NO₂/NO_x=50%) and NO₂-SCR (NO₂/NO_x=100%) was presented as a function of the NO₂/NO_x ratio and temperature.