Reduction of NO, with Propene, Carbon Monoxide or Hydrogen

8 Reduction of NO. with Propene, Carbon Monoxide or Hydrogen 

The oxides of nitrogen (collectively known as NO ) are primary pollutants of the atmosphere. These oxides are emitted into the air during the combustion 

The most practical and convenient method for removing NOj, gases is to reduce them to N2, using unburnt CO, H2, propene or other hydrocarbons in the exhaust gas. This can be achieved using conventional PGM catalysts, using a three-way catalyst (TWO) system, under stoichiometric conditions, where the amount of air supplied is controlled to a level just sufficient for the complete combustion of the fuel [132,489] (see Fig. 6.22). 

The catalyst, developed at Anglo American Research Laboratories (AARL), consists of lwt% An supported on zirconia-stabilised Ce02, Zr02 and Ti02, and contains as promoters 1 wt% CoO , 0.1 wt% Rh, 2wt% ZnO and 2wt% BaO. The catalytically active gold on cobalt oxide clusters are in the range of 40-140 nm (see Fig. 6.23). 

The catalyst was evaluated under simulated gasoline engine emissions for oxidising (0.9% O2) and reducing (0.6% O2) conditions close to stoichiometric. Under oxidising conditions, the catalyst displayed a CO T50 of 348-358 K, an HC T50 of 513 K and as expected no NO reduction. The CO T50 remained unaffected under reducing conditions, whereas the HC T50 increased to 583 K. Complete conversion of NOj, occurred at approximately 603 K, with a T50 of 573 K under reducing conditions. Selectivity for reduction to N2 over N2O is not known. 

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