Enhanced NOx conversion by coupling NOx storage-reduction with CO adsorption-oxidation over the combined Pd−K/MgAlO and Pd/MgAlO catalysts

• CO adsorption-oxidation was observed in lean-rich cycles for NOx storage-reduction.
• NOx storage-reduction was enhanced by coupling with CO adsorption-oxidation.
• The coupling was achieved by the intimate mixture of Pd-K/MgAlO and Pd/MgAlO.

NOx conversion was enhanced by coupling NOx storage-reduction (NSR) with CO adsorption-oxidation (CAO), which was observed in NSR lean-rich cycle tests with CO as a reductant on catalysts of Mg-Al mixed oxides supported Pd (Pd/MgAlO) and Pd–K (Pd–K/MgAlO). CO was adsorbed on Pd sites in the rich condition and then oxidized by gaseous NOx via Eley–Rideal mechanism during the transition from the rich condition to the lean condition, which results in an enhanced NOx conversion. This is confirmed by different configuration experiments of Pd–K/MgAlO and Pd/MgAlO, acting as NSR and CAO catalysts, respectively. The intimate mixture of Pd–K/MgAlO and Pd/MgAlO showed much higher activity due to the resultant coupling effect of NSR with CAO in comparison with a zone-arranged catalyst system no matter whether Pd–K/MgAlO or Pd/MgAlO was in the front. The coupling also worked in the presence of H2O and CO2 despite that the efficiency were spoiled. This strategy is ease to be implemented and thereby is potential for the practical after-treatment technology for lean-burn and diesel engines.

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