共沉淀法制备的MnOx-CeO2在含NO气氛中氧化碳烟的研究

摘要

用共沉淀法制备的复合氧化物MnOx-CeO2,其程序升温氧化(TPO)结果显示,1 000 mL·m-3 NO和10％O2条件下MnOx-CeO2对应的碳烟起燃温度Ti为250～303℃,远低于无催化剂时的Ti(402℃)及CeO2的Ti(334℃);也低于无NO下MnOx-CeO2的Ti(346～360℃);与MnOx的Ti(290℃)相当,但MnOx-CeO2的Tm(413～441℃)仍比MnOx的Tm(441℃)稍低.明显地,NO促进了碳烟的氧化,MnOx-CeO2比CeO2和MnOx的活性都要高.NO-TPD、FT-IR及原位DRIFTs表明,MnOx-CeO2表面对NO吸附能力强,更易促进NO氧化和NOx储存,从而有利于碳烟的氧化.可能的机理为,富氧条件下气相O2推动催化剂中氧物种(如超氧O2ˉ,化学弱吸附氧Oˉ与晶格氧O2-)的形成(含相互转化)与迁移,推进了NO或NO2-的氧化;储存的NOx在低温下生成硝酸根离子,在高温时则释放出高活性的NO2*和Oˉ,促进碳烟氧化,其中间产物包括C-NO2复合物与C(O)复合物.%Mn0x-Ce02 with various Mn/Ce ratios were prepared by co-precipitation method, and the results of temperature programmed oxidation (TPO) test revealed that, when exposed to 1 000 mL·m-3 NO and 10% O2, ignition temperature Ti for soot oxidation in presence of Mn0x;-CeO2 ranged in 250~303℃, much lower than the Ti (402℃) without catalyst, the Ti (334 ℃) in presence of CeO2 and the Ti (346-360 X) in presence of MnOx-CeO2 without NO, which also corresponded ~to the case of MnOx approximately. However, the combustion temperature at maximum rate Ti (413~441℃) of MnOx-CeO2was lower than that of MnOx (441 ℃). Apparently, NO promoted the oxidation of soot, and MnOx-CeO2 exhibited higher activity than CeO2 and MnOx alone. NO-TPD, FTIR and in situ DRIFTs showed that Mn0x-CeO2 was greatly adsorptive to NO, enhancing NO oxidation and NOx storage capacity, as well as the oxidation of soot. The possible mechanism could be that gaseous O2 in rich O2 condition accelerated the formation (including transformation) and mobility of oxygen species in catalyst (such as super oxygen O2-,weakly chemisorbed oxygen O-,and lattice oxygen O2-), facilitating the oxidation of NO and NO2-; The NOx was stored in the form of N03- at low temperatures, and NO3- easily decomposed into high-activity NO2* and O- at higher temperatures, thus soot oxidation was promoted. The intermediate products included composite C-NO2 and composite C(0) complex.