Honda announced it’s new second generation i-CTDi engine today, featuring a new NOx catalytic converter which significantly reduces NOx emissions to meet stringent U.S. Environmental Protection Agency (EPA) Tier II Bin 5 emissions requirements.

The new NOx catalytic converter converts toxic nitrogen oxide (NOx) into harmless nitrogen (N2) through a two-layer structure. In the first layer, some of the NOx reacts with hydrogen (H2) to produce ammonia (NH3). Ammonia is stored, then used in the second layer to reduce NOx into N2.

The development of the new NOx filter was done on the Super Clean Tier II Bin 5 diesel engine research vehicle – which is an European market Honda Accord (shown above).


  1. During lean burn operation, the NOx adsorbent in the lower layer adsorbs NOx from the exhaust gas.
  2. As needed, the engine management system adjusts the engine air-fuel ratio to rich-burn, wherein the NOx in the NOx adsorption layer reacts with hydrogen (H2) obtained from the exhaust gas to produce ammonia (NH3). The adsorbent material in the upper layer temporarily adsorbs the NH3.
  3. When the engine returns to lean-burn operation, NH3 adsorbed in the upper layer reacts with NOx in the exhaust gas and reduces it to harmless nitrogen (N2).

Source: Honda Motor Co., Ltd.