NO_x storage and reduction performance of Pt-CoO _x-BaO/Al₂O₃ catalysts: Effects of cobalt loading and calcination temperature

The NO_x storage and reduction (NSR) performance of low platinum (0.5 wt%) 0.5Pt-CoO_x-15BaO/Al₂O₃ catalysts with varied Co loadings and calcination temperatures was studied to investigate the promotional effect of CoO_x on the NSR catalysis. The NSR performance was tested under cyclic lean-rich conditions, and was evaluated in terms of NO_x storage capacity (NSC) under the lean condition, the N ₂ selectivity and the amount of nitrogen-containing products (namely, the NO_x reduction capacity (NRC)) under the rich condition. For the catalysts calcined at 800 °C, addition of CoO_x 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-CoO_x-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-CoO_x-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.