铁改性水滑石基Pt/BaO/MgFeO催化剂焙烧温度对催化剂结构及NO_x吸附-还原性能的影响

采用共沉淀法和浸渍法制备了贵金属负载均匀的镁铁水滑石基稀燃氮氧化物捕集(LNT)催化剂,并采用多种表征手段研究了焙烧温度对催化剂结构及NO_x吸附-还原反应的影响。结果表明,500-700℃焙烧后催化剂晶相结构稳定,800℃焙烧后催化剂表面出现烧结,Pt颗粒发生团聚;随焙烧温度升高,催化剂的NO_x脱附峰面积先减小后增大,但峰值温度变化不大;与500℃焙烧催化剂相比,800℃焙烧后催化剂表面NO_x吸附物种及吸附路径发生改变,而还原反应产物中氨气/氮气体积比下降,NO_x转化效率由91.7%降为85.2%。

Effect of calcination temperature on the structure and NOx adsorption-reduction performance of Fe modified hydrotalcite-based Pt/BaO/MgFeO catalyst

In this paper, the iron-magnesium hydrotalcite-based catalysts with well dispersed noble metal for the lean NO_x trap (LNT) were prepared by co-precipitation and impregnation methods. The effects of different calcination temperatures on the catalyst structure and the adsorption-reduction performance for NO_x were investigated by analytical techniques. Results show that the crystalline structure of the catalysts remains stable when the calcination temperature is lower than 700℃. The sintering of the catalysts prepared and the conglobation of Pt particles appear on the catalyst surface after calcination at 800℃. With the increase in calcination temperature from 500 to 800℃, the desorption amounts of NO_x increases after an initial decrease, while the corresponding peak temperature show a marginal change. DRIFTs results indicate that the adsorbed NO_x species and the adsorption pathways over the catalyst after calcination at 800℃ differ from those at 500℃. The ratio of NH₃/N₂ released from the reduction of adsorbed NO_x species over the catalyst calcinated at 800℃ decreases in comparison with those calcinated at lower temperatures, which is responsible for the decrease in the NO_x conversion efficiency.