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HC-SCR is more convenient when compared to urea-SCR, since for HC-SCR, diesel fuel can be used as the reductant which is already available onboard the vehicle. However, the DeNOX efficiency for HC-SCR is lower than that of urea-SCR in both low and high temperature windows. In an attempt to improve the DeNOX efficiency of HC-SCR, the effect of hydrogen were evaluated for the fresh and aged catalyst over 2 wt.% Ag/Al₂O₃ using a Euro-4 diesel engine. In this engine bench test, diesel fuel as the reductant was injected directly into the exhaust gas stream and the hydrogen was supplied from a hydrogen bomb. The engine was operated at 2,500 rpm and BMEP 4 bar. The engine-out NOX was around 180 ppm-200 ppm. H₂/NOX and HC₁/NOX ratios were 5, 10, 20, and 3, 6, 9, respectively. The HC-SCR inlet exhaust gas temperatures were around 215°C, 245°C, and 275°C. The catalyst volumes used in this test were 2.5L and 5L for both fresh and aged catalysts.

The oxidation of soot (carbon black) which is assisted by Pt/CeO2 catalyst is studied using a flow reactor system simulating the condition of diesel exhaust. In this study, the temperature programmed oxidation (TPO) scheme is mainly used for different NO and O2 concentrations and soot oxidation rate is evaluated by monitoring both CO and CO2 concentrations. Pt/CeO2 catalyst lowers the temperature of the peak CO/CO2 concentrations significantly when there is either NO or O2. Oxidation starts at 200°C and the peak CO2 concentration is observed at 360°C, which depends on the amount of catalyst and NO concentration. The effect of catalyst on NO2 recycling is also investigated. For this purpose, two different types of sample have been prepared. For the mixed case, 10mg of carbon black is mixed with 50mg of Pt/CeO2 catalyst under conditions of loose contact. For the unmixed case, the catalyst layer is placed on top of soot layer without mixing.

Today's diesel PM reduction systems are mainly based on catalyzed particulate filter(CPF) systems. However, most of their reaction kinetics remain unresolved. Among others, the soot oxidation rate over catalyst is particularly important in the evaluation of the performance of the catalysts and the efficient control of CPF regeneration. This study, therefore, investigated the oxidation rate of carbon black (Printex-U) over various Pt supported catalysts using a flow reactor setup simulating diesel exhaust conditions. Compared to non-catalyzed soot oxidation, the oxidation rate of carbon black over Pt catalysts was to an extent shifted towards low temperatures. This activity enhancement of soot oxidation over a catalyst can be attributed principally to NO to NO2 conversion because NO2 oxidizes soot with much lower activation energy (Ea=60kJ/mol) than O2 (Ea=177kJ/mol).

Plasma-catalyst (Ag, Au/Al2O3) systems were applied to NOx reduction in a model lean-burn engine exhaust gas. Also, DeNOx test of real diesel exhaust gas was performed by plasma-Ag/Al2O3 system. In the case of model exhaust gas, the catalytic activity for NOx reduction was enhanced by the assistance of plasma in the wide temperature range. The NOx conversion efficiency of plasma-Ag/Al2O3 was 40∼90% under the condition of C3 H6 3200ppm (C1/NOx = 5.96) and 10% O2 over the temperature range of 250∼400°C. The plasma-Au/Al2 O3 system showed remarkable low temperature NOx reduction activity at 100∼250°C. The real engine full flow test was performed for 70% of the full load and at engine speed of 1500rpm. NOx removal of 46% from the diesel exhaust gas was achieved by the plasma-Ag/Al2O3 catalyst system at 364°C(C1/NOx = 6). In the case of higher C1/NOx = 10, the NOx conversion increased up to 73% at 381°C. Also, DeNOx engine tests were performed for full load of 1500, 2000 and 2500rpm.

Two features to facilitate chemical reactions at low temperature, non-thermal plasma and the weak dependency of photocatalyst on temperature, have been exploited by many researchers to effectively decompose hydrocarbon emissions emitted until the light-off of a three-way catalyst in spark ignition engines. To develop a realizable emissions reduction reactor, as part of such effort, this study investigates for the three model gases, propylene, n-butane and acetylene: 1) the conversion efficiency of the emissions reduction reactor, which utilizes the effect of dissociation, ionization-by-collision of the non-thermal plasma and the photocatalytic effect of TiO2, and 2) the concentrations of the products such as acetaldehyde, acetic acid, polymerized hydrocarbons and NO2. The operating parameters to obtain the plasma energy density ranging from 7.8 to 908 J/L were varied.

NOx reduction by a plasma/catalyst system was tested with modeled gas and real exhaust gas. Ag/Al2O3 was used as the catalyst. The oxidation of NO to NO2 by the plasma was increased as HC concentration and input energy density increase. The presence of H2O in the reactant gas led to the production of acid by plasma. The catalytic activity for NOx reduction was enhanced by the assistance of plasma especially in the lower temperature region. This activity was a little suppressed in the presence of H2O, but the acid was not detected in the effluent gas treated by the plasma/catalyst system. The NOx conversion to N2 was evaluated by a gas chromatography in the model gas with helium as the balance gas. The result in helium balance gas showed the selectivity to N2 depended on the catalyst temperature and was also enhanced by the assistance of plasma. The 50% of NOx removal from the diesel exhaust gas was achieved by the plasma /catalyst system.