The NH ₃ -SCR Reaction Performance with Fe/Zeolite Based Catalytic Honeycomb Substrate

Stringent NO_x emission legislation accelerates the study of NO_x aftertreatment. Urea-SCR system which is one of promising NO_x reduction measures has been widely studied and been put to practical use not only for heavy duty vehicles but also passenger cars. As SCR catalyst, although use of zeolite ion-exchanged with transition metals (M/zeolite) has been under intense investigation, in particular, NO_x conversion performance at low temperatures are still a challenging problem. Increasing the number of active sites is one of countermeasures to solve the problem.

In this study, a catalytic honeycomb substrate mainly comprised of M/zeolite (NCH structure) and a conventional wash coated type catalyst(conventional structure) were prepared, respectively. To clarify the advantage of NCH structure, a relationship between NH₃ adsorption and NO_x conversion of the NCH structure and of the conventional structure were evaluated in both synthetic gas bench and engine bench. As a result, it was found that NCH structure has possibility to increase controllability of NH₃ breakthrough due to its higher NH₃ adsorptive capability and that NO_x conversion performance of the NCH structure is always superior to the conventional structure at a given NH₃ adsorption ratio. Especially at low temperatures, the NCH structure exhibits approximately 1.6 times NO_x conversion performance of the conventional structure.