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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.

We examined a filter structure of a SiC-DPF, and found that the reduction in a wall thickness is effective in decreasing a pressure loss. And we made it clear how this reduction in the wall thickness influences the performances of the DPF, that are the filtration efficiency and the accumulated soot mass limit which are important for the DPF. From the results of this study, it can be seen that the filter structure which is suitable for the catalyzed DPF should be controlled in a porosity and the wall thickness in proportion to an amount of catalyst required.