NOx storage and reduction performance of Pt–CoOx–BaO/Al2O3 catalysts: Effects of cobalt loading and calcination temperature

The NOx storage and reduction (NSR) performance of low platinum (0.5 wt%) 0.5Pt–CoOx–15BaO/Al2O3 catalysts with varied Co loadings and calcination temperatures was studied to investigate the promotional effect of CoOx on the NSR catalysis. The NSR performance was tested under cyclic lean–rich conditions, and was evaluated in terms of NOx storage capacity (NSC) under the lean condition, the N2 selectivity and the amount of nitrogen-containing products (namely, the NOx reduction capacity (NRC)) under the rich condition. For the catalysts calcined at 800 °C, addition of CoOx to the 0.5Pt–15BaO/Al2O3 catalyst enhanced the NSC but lowered significantly the NRC, which made the NRC/NSC ratios dropped significantly from 0.82 for the reference 0.5Pt–15BaO/Al2O3 catalyst to around 0.50 for the catalysts containing 1 and 5 wt% Co, and to 0.37 for the catalyst containing 10 wt% Co. Moreover, the N2 selectivity remained at around 50% for the 0.5Pt–CoOx–15BaO/Al2O3 catalysts when the Co loading was kept low (0–5 wt%), and decreased significantly to 30% when the Co loading was 10 wt%. The calcination temperature of the 0.5Pt–CoOx–15BaO/Al2O3 sample containing 5 wt% Co was varied in the range of 350–800 °C to improve the NSR performance. The catalyst calcined at 550 °C was found to produce the highest NRC/NSC ratio (0.80) and N2 selectivity (76.1%) under the rich condition. The maximum efficiency for NSR catalysis of this catalyst seemed to be associated with the amount of binary Pt–Co oxides.