摘要
本文通过制备一系列Ba/Al2O3催化剂,探讨进一步加入Pt、Fe对催化剂结构、NOx储存能力及耐硫中毒能力的影响。结果表明:Ba/Al2O3催化剂存在着两种不同的Ba物种,即与载体紧密接触的高分散的Ba物种以及体相BaAl2O4尖晶石相。Fe的加入抑制Ba物种的分散,加剧BaAl2O4晶粒的聚集长大,而Pt的加入促进Ba物种的分散,其原因可能是负载Pt时体相BaAl2O4发生水解,使得焙烧后Ba物种再度分散。Pt及Fe的加入均使得NOx储存量有所增加,但二者增加的机制不同,Fe可能促进NOx向Ba位的传递与转移;而Pt则主要由于其对NO具有较强的氧化能力而促进样品对NO的捕获,Pt较Fe更有效地提高样品对NOx的储存量。Fe的加入一定程度上降低Pt与Ba物种的接触几率并削弱其相互作用,使PtFe共存样品的NOx储存量较仅含Pt不含Fe的样品要小。此外,Pt的加入促进SO2的吸附,硫化样品中BaSO4颗粒也较大,与之相反,Fe的加入明显地抑制硫化样品中BaSO4晶粒的聚集和长大,抗硫作用明显。
A series of Ba/Al2O3 catalysts were prepared by impregnation method,and the effect of the addition of Pt and Fe on the catalyst structure,NOx storage capacity（NSC） and sulfur-resistance ability was investigated. Two types of barium species are found in Ba/Al2O3 catalyst,namely the highly dispersed barium species which strongly interacted with the alumina support,and the bulk BaAl2O4 spinel phase. The addition of Fe inhibits the dispersion of the barium species,leading to the agglomeration of the bulk BaAl2O4,whereas the addition of Pt promotes their dispersion,mainly by the hydrolysis of the BaAl2O4 phase during the impregnation of Pt. This hydrolyzed phase undergoes redistribution after calcination,and the barium species are re-dispersed. Both the addition of Fe and Pt increases the NOx storage capacity,but the implying mechanisms are different. Fe probably forms the NOx-adsorbed species with relatively high mobility,which in turn accelerates the transferring of NOx to the barium sites,while the function of Pt to NSC could be ascribed to its high oxidizing and trapping ability to NO. Pt is more efficient than Fe for increasing the NSC of the samples. The coexistence of Pt and Fe decreases the NSC,as compared with the sample only containing Pt,which may be due to the fact that the addition of Fe has decreased the contacting probability and weaken the interaction between Pt and Ba to some extent. However,the addition of Fe prominently suppresses the growth of BaSO4 crystal,showing.strong sulfur-resisting ability,while the addition of Pt promotes the SO2 adsorption,and large BaSO4 crystals are found in the sulphated sample.
基金
教育部高等学校博士学科点专项科研基金(20040056028).
