Mg3MnxAl1-xCO3类水滑石衍生NSR催化剂的制备及其性能评价

采用共沉淀法合成了三元类水滑石Mg_3Mn_xAl_(1-x)CO_3,通过高温煅烧得到其衍生氧化物Mg_3Mn_xAl_(1-x)O_m,再经浸渍负载Pt或BaO后制得新型NO_x存储/再还原(NSR)催化剂。XRD及SEM表征结果显示,当Mn与Al的摩尔比(Mn/Al)大于1时所制备的Mg_3Mn_xAl_(1-x)O_m有杂晶相出现且发生团聚,结合NO_x存储性能评价结果,确定最优Mn/Al为1。BaO负载不利于NO_x的存储,而当Pt负载量为1%(w)时NO_x存储性能最优,250℃条件下的存储量由负载前的0.52 mmol/g提升至0.61 mmol/g。CO_2与NO_x之间存在较强的竞争吸附。负载1%Pt催化剂的NSR性能评价结果表明,8个稀燃-富燃循环后NO_x的去除率为68%,表明催化剂的还原性能仍需加强。

Preparation and performance evaluation of Mg3MnxAl1-xCO3 hydrotalcite-like derivative oxides as NOx storage and reduction catalysts

Ternary hydrotalcite-like Mg₃Mn_xAl_1-xCO₃ was synthesized by coprecipitation method. Its derivative oxides Mg₃Mn_xAl_1-xO_m were obtained by calcination at high temperature,and then supported with Pt or BaO by impregnation to prepare a new type of NO_x storage and reduction （NSR）catalysts. The characterization results obtained by XRD and SEM showed that when the molar ratio of Mn to Al （Mn/Al）was higher than 1,the prepared Mg₃Mn_xAl_1-xO_m had hetero-crystalline phase and agglomerated. Combining with the evaluation results of NO_x storage performance,the optimum Mn/Al was determined to be 1. BaO loading was not conducive to NO_x storage,and the catalyst loading 1%（w）Pt showed the best NO_x storage capacity of 0.61 mmol/g at 250 ℃,which is higher than 0.52 mmol/g before loading. There was a strong competitive adsorption behavior between CO₂ and NO_x. The evaluation results of NSR capability of catalyst loading 1% Pt showed that after 8 lean burn-rich burn cycles,the removal rate of NO_x was only 68%,indicating that the reductive capability of the catalyst still needed to be enhanced.