Nitrogen production efficiency for acetaldehyde and propionaldehyde in lean NO_x reduction over anatase titania

The nitrogen formation efficiencies, defined as the number of nitrogen molecules formed for every reductant molecule consumed were determined for acetaldehyde and propionaldehyde in the reduction of NO₂ under lean conditions over anaiase TiO₂. The efficiency increased with increasing NO₂/reductant in the feed, reaching 0.61 ± 0.05 for NO₂/'acetaldehyde between 1.5 and 3.0 and 0.85 ± 0.08 for NO₂/propionaldehyde between 3.8 and 5.7. Simultaneously, the CO/CO₂ ratio as well as the small concentration of N₂O in the product stream increased. The results suggested that at higher NO ₂/reductant ratios, the reaction between the reductant and adsorbed NO₂ accounted for a large majority of the reaction. The results were consistent with the IR results, which showed that surface nitro groups reacted readily with acetaldehyde. The implications of these results on the NO ₂ reduction mechanism were discussed.