Murata, Y., Morita, T., Wada, K., and Ohno, H., "NOx Trap Three-Way Catalyst (N-TWC) Concept: TWC with NOx Adsorption Properties at Low Temperatures for Cold-Start Emission Control," SAE Int. J. Fuels Lubr. 8(2):454-459, 2015, doi:10.4271/2015-01-1002.
A new concept for trapping NOx and HC during cold start, the NOx Trap Three-Way Catalyst (N-TWC), is proposed. N-TWC adsorbs NOx at room temperature, and upon reaching activation temperature under suitable air-fuel ratio conditions, it reduces the adsorbed NOx. This allows a reduction in NOx emissions during cold start. N-TWC's reduction mechanism relies on NOx adsorption sites which are shown to be highly dispersed palladium on acid sites in the zeolite. Testing on an actual vehicle equipped with N-TWC confirmed that N-TWC is able to reduce emissions of NOx and HC during cold start, which is a challenge for conventional TWCs.