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The method of converting NOx with urea SCR is an effective solution for complying with the stringent NOx emission legislations of the future, particularly in the case of heavy duty diesel vehicles. In order to broaden the freedom of SCR catalyst design and volume design, a honeycomb structure formed with metal ion exchanged zeolite (NCH: New Concept Honeycomb) and for comparison a wash-coat type structure (conventional catalyst) were prepared. The possible range of catalyst volume reduction in NCH was investigated by comparative measurement of NH₃ adsorption distribution, consumption behavior of adsorbed NH₃ within the structures, and of space velocity and NO₂/NOx dependence of NOx conversion efficiency. In addition, from NEDC evaluation in an engine bench, it was found that combining urea injection logic suitable for NCH results in equal or higher NOx conversion efficiency and NH₃ slip characteristics with only 1/2 the volume of conventional catalyst structure.

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.

Diesel emission regulation becomes stringent more and more regarding both particulate matter (PM) and NOx in the worldwide. SCR coated DPF system is considered as one of the promising options for future diesel exhaust after-treatment because it has several benefits such as the downsizing of the system, quick light-off of the catalytic function due to mounting closed-couple position. To integrate the SCR converter into the DPF, it is necessary to design the DPF substrate's porosity higher and pore size larger than conventional DPF to improve SCR catalyst coating capability. However to make the porosity higher will lose the robustness in general. Against these problems, it was studied to improve the high porosity DPF performances by applying the new technology to modify the thermal shock resistance property.