Deterioration Effect of Three-way Catalyst on Nitrous Oxide Emission

To find a clue to reduction techniques for Nitrous Oxide (N₂O) emission from three-way catalyst equipped vehicles, four test samples of three-way catalysts with typical noble metal compositions were fabricated by way of experiment and their N₂O formation characteristics have been experimentally studied. Then, these catalyst samples were conditioned artificially by aging with real automotive exhaust gas and the N₂O formation characteristics after aging has been also observed.

As results, catalyst temperature zones and concentration levels of N₂O formation varies greatly by the catalyst composition. In general, a catalyst with lower metal content showed lower N₂O mass emission at both fresh and after aging conditions. The tendency of the increase in N₂O mass emission due to the deterioration is also different among the tested catalyst samples.

It was also clarified that the main cause of N₂O increase with aged catalyst was the shift of maximum N₂O formation temperature zone to the higher regions. Catalyst deterioration effects on N₂O emission of a vehicle were predicted using model gas experiment and catalyst temperature distribution of a passenger vehicle driven on a chassis dynamometer with various test procedures.