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Researchers propose electric field-assisted NSR process for lean NOx reduction at low temperatures

Researchers at Waseda University in Japan, with a colleague from Isuzu Central Research, are proposing electric field-assisted lean NOx reduction for lean-burn engines. An open-access paper on their work is published in the RSC journal Chemical Communications.

Lean-burn engines offer lower CO2 emissions, higher thermal efficiency, and better fuel economy than stoichiometric combustion engines. However, classical three-way catalysts (TWCs) are ineffective at reducing NOx in lean burn engines because of the presence of residual oxygen in the exhaust gases. To overcome this difficulty, NOx storage reduction (NSR) technology has attracted attention as a viable approach to remove NOx from lean-burn engine exhaust.

AN NSR catalyst combines nobles metal active sites with alkali or alkaline earth metal oxides as NOx storage sites. Under lean burn conditions, NO is oxidized by O2 and is stored on the NSR catalyst surface in the form of nitrate (NO3-). NOx released from the surface in rich conditions )oxygen-deprived) is reduced to nitrogen (N2) by reductants such as hydrogen (H2), carbon monoxide and hydrocarbons.

… conventional NSR technology requires complex cyclic operation with frequent switching between lean and rich states, resulting in unavoidably lower fuel efficiency.

For this study, a new catalytic NSR process is proposed to reduce the adsorbed NOx and to improve engine efficiency using H2 in a lean burn state without switching to a rich combustion state after NOx adsorption. This new concept is designated as electric field-assisted lean NOx reduction, as an electric field is applied to the NSR catalyst during lean NOx reduction.

With the introduction of this technology, surplus electricity in the vehicle is useful for exhaust gas purification, which is part of energy management. Furthermore, the application of an electric field activates the reduction function of the supplied H2 and simultaneously promotes hydrogen transfer. This effect promotes NOx reduction, even at low temperatures.

—Shigemoto et al.


. Assumed reaction model for electric field-assisted lean NOx reduction over 3wt%Pt-16wt%BaO/CeO2. Shigemoto et al.

Tests with a 3wt%Pt-16wt%BaO/CeO2 catalyst demonstrate markedly higher NOx conversion to N2 (13.1% vs. 2.9% without an electric field).


  • A. Shigemoto, Y. Inoda, C. Ukai, T. Higo, K. Oka and Y. Sekine (2024) “Electric field-assisted NSR process for lean NOx reduction at low temperatures” Chem. Commun. doi: 10.1039/D3CC05189G.


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