-SCR Reaction Performance with Fe/Zeolite Based Catalytic Honeycomb Substrate
Stringent NOx emission legislation accelerates the study of NOx aftertreatment. Urea-SCR system which is one of promising NOx 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, NOx 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 NOx 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 NOx 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 NOx conversion performance of the conventional structure.