锰锆复合氧化物CO催化还原NO性能研究

采用柠檬酸络合法制备了锰锆复合氧化物催化剂,用XRD、H_2-TPR、XPS和SEM等技术进行了表征,研究了其CO催化还原NO性能。结果表明,MnO_x主要以Mn_3O_4物相存在,Zr占比的增加会促进Mn_3O_4物相的分散,引起Mn_3O_4平均晶粒粒径减小;Mn主要有Mn~(2+)、Mn~(3+)、Mn~(4+)离子价态形式,添加Cu和Ce后,(Mn~(3+)+Mn~(4+))含量和表面吸附氧(OA)含量增加,H_2-TPR还原峰温度向低温区偏移,有利于催化活性的提升。Mn-Zr-O复合氧化物的CO催化还原NO活性较低,加入Cu后的Mn-Cu-Zr-O复合氧化物其CO催化还原NO的活性得到改善,而添加Ce后所制备的Mn-Cu-Ce-Zr-O复合氧化物的催化活性进一步提高;在350℃下、反应空速为18000 h~(-1)时,Mn-Cu-Ce-Zr-O复合氧化物表现出较好的CO催化还原NO活性,CO转化率达到了89.17%,NO转化率达到了91.70%。

Performance of manganese-zirconium composite oxide in the catalytic reduction of NO by CO

A series of manganese-zirconium composite oxides were prepared by citric acid complexing method and characterized by XRD, H₂-TPR, XPS and SEM; their performance in the catalytic reduction of NO by CO was investigated. The results show that Mn₃O₄ is the main phase for MnO_x in the Mn-Zr composite oxide; an increase in the Zr content can promote the dispersion of Mn₃O₄ and reduce the average grain size of Mn₃O₄. Mn may exist in the form of Mn²⁺, Mn³⁺ and Mn⁴⁺ ions; the content of (Mn³⁺ + Mn⁴⁺) and the quantity of surface adsorbed oxygen (OA) increase after the addition of Cu and Ce, which is beneficial to enhancing the catalytic activity. The pristine Mn-Zr-O composite shows a relatively low activity in the catalytic reduction of NO by CO; after adding Cu, the Mn-Cu-Zr-O composite exhibits much higher activity than Mn-Zr-O; moreover, the activity of Mn-Cu-Ce-Zr-O composite is even enhanced by adding Ce. For the catalytic reduction of NO by CO over the Mn-Cu-Ce-Zr-O composite at 350℃ and with a space velocity of 18000 h^-1, the CO conversion and NO conversion are 89.17% and 91.70%, respectively.