Reduction of NOx over a NOx-trap catalyst and the regeneration behaviour of adsorbed SO2

A conventional NO-trap catalyst containing platinum, rhodium, barium and lanthanum was conditioned with oxygen at 500 degreesC, preloaded with NO under standard oxidising conditions and then subjected to regeneration with the reductants H-2, CO and C3H6, either alone or as a mixture. Hydrogen is the most efficient reductant in terms of NO conversion efficiency and reductant usage efficiency. There is a temperature optimum for CO between 300 and 400 degreesC and a catalyst loading optimum (mols reductant added)/(mols NOx adsorbed) between 1.5 and 3.0. The behaviour of the catalyst towards sulphur poisoning was examined in supplementary trials with the adsorption of SO2 in the presence or absence of water vapour. When water is not present in both adsorption and reduction steps, very stable sulphates are formed, unattacked by reductants even at 1000 degreesC. Sulfates are more easily reduced when water is present in the reductant mixture.