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The diesel oxidation catalysts (DOC) having high purification performance to the exhaust gas at low temperatures were investigated. In this paper two main technological improvements from conventional DOC are shown. First is forming Pt/Pd composite particles in order to suppress sintering of precious metal under high thermal aging condition. This generating Pt/Pd composite and the effect were exemplified by TEM-EDS and XRD analysis. Second is adjusting electric charge of Pt/Pd surface to reduce interaction between Pt/Pd and carbon monoxide (CO) by modifying the support material components. Adjusting electric charge of Pt/Pd surface by applying new support material could cancel CO poisoning at Pt/Pd surface. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) studies suggested that improved support material is more suitable for CO oxidation at a low temperature based on the concept.

Among the platinum group metals (PGMs), rhodium (Rh) is known as an exceedingly valuable element for automotive catalysts due to its powerful catalytic function. Because Rh is a costly material, it is paramount to enhance its catalytic function in three-way catalysts (TWCs). This work reports results on the palladium (Pd)-Rh combination which assists the catalytic function of Rh. XPS and XRD are used to observe the Rh characteristics, and engine dynamometer and vehicle testing are conducted to measure catalytic performance and quantify the emission benefits of the Pd-Rh interaction in TWCs. It is well known that Pd-Rh forms a core-shell structured alloy with Rh in its core. This alloy exerts a large negative impact on NOx performance. However, it is inferred from our analyses that highly-dispersed Pd and Rh particles within a certain Pd/Rh atomic ratio prevent this deterioration phenomenon.

Previously air-fuel ratio control using a λ O2 sensor had two problems which resulted from the binary output characteristics: (1) Insufficient convergence performance after A/F disturbance, resulting in worsening of emissions in transient states, and (2) A narrow A/F control range, resulting in worsening of emissions due to mean A/F shift in the front A/F. However, we have executed a paradigm shift to mean A/F control focused on the O2 storage ability of the catalyst and on the conversion characteristics, and carried out the following improvements. (1) Using a catalyst O2 storage model, we analyzed the interaction among front A/F feedback, O2 storage behavior, the rear. O2 signal, and emissions. Based on the results of this analysis, we designed an optimal O2 storage capacity (OSC) using a new catalyst with improved O2 storage ability, and verified that the first problem was resolved. (2) Previously, it was difficult to design front λ O2 control due to its strong non-linearity.

Extensive research and development has been performed to develop the NOx-adsorber catalytic system, which would make Mitsubishi vehicles powered by the gasoline direct-injection (GDI™) engines comply with European Stage 4 emissions regulations. This NOx-adsorber catalytic system is a three-brick configuration, consisting of a three-way catalyst in the front (the front catalyst) and the rear catalytic converter, composed of a new NOx-adsorber catalyst and a conventional three-way catalyst (TWC). In the present research work, a special effort has been made to define the required performance of the front catalyst, particularly with HC reduction efficiency at the cold start, the steady-state leaner A/F and the transient phase of the A/F from leaner to stoichiometric. For HC reduction, it has been found that platinum (Pt) had the highest HC efficiency.

Practical application of leanburn gasoline engines for passenger cars has been increasing in recent years. The leanburn gasoline engine is operated under high air fuel (A/F) ratio to improve fuel economy. However, reduction of NOx from the exhaust under oxygen-rich condition is very difficult to achieve. The Three Way Catalyst (TWC) designed for conventional gasoline engines cannot be applied to the leanburn gasoline engine because of low NOx conversion under lean conditions. To achieve better fuel economy and lower emissions, a breakthrough in NOx control technology for oxygen-rich conditions is needed. To address this need, a new type of catalyst technology using Iridium was developed. This new catalyst can constantly reduce NOx from exhaust under lean conditions using hydrocarbons as reducing agents. This is accomplished without formation of N2O. In addition, the newly developed catalyst has a tolerance for sulfur poisoning and exhibits reasonable heat stability.