甲烷/丙烷在氧化铁表面还原NO的红外原位研究*

利用漫反射红外傅里叶变换光谱仪(DRIFTS)对甲烷/丙烷在氧化铁表面还原NO的反应进行了原位研究,分析了不同气体在氧化铁表面的吸附特点以及在有O_2条件下甲烷/丙烷还原NO的中间产物生成特性。结果表明,氧化铁对NO有着较好的吸附能力,NO能够以不同桥式硝酸盐与硝基的形式吸附于氧化铁表面。这些吸附物种热稳定性各不相同,并且可能会被氧化铁中的晶格氧氧化产生新的吸附物种,对进一步与还原剂发生选择性催化反应有着重要的作用。甲烷与丙烷在氧化铁表面还原NO的微观反应机理通过一系列路径完成。还原剂吸附于氧化铁表面,与由NO吸附形成的含氮吸附物种相互反应,形成一系列碳氢中间产物,通过进一步反应还原NO;在氧气存在的情况下,O_2会参与碳氢还原剂与含氮吸附物种的竞争反应,并形成R—COO-、CH3COO-等更多活性中间物种,这些活性中间物种通过与NO不断的反应最终还原NO为N2。

In-situ DRIFTS Study on NO Reduction by Methane / Propane over Iron Oxides Surface

NO reduction by methane / propane over iron oxide was studied by using diffuse reflectance infrared Fourier transform spectrometer (DRIFTS). The adsorption characteristics of different gases on the surface of iron oxide and the intermediate production characteristics during the reaction of NO reduction were analyzed. The results show that iron oxides had good adsorption capacity to NO. NO adsorbed on the surface of iron oxides with different bridging nitrates and nitro groups. The thermal stability of these adsorbates is different and may be oxidized by the lattice oxygen of iron oxide to form new adsorbed species, which play an important role in the selective catalytic reaction of NO with the reductant. The micro-reaction mechanism of NO reduction by methane and propane over iron oxides is accomplished through a series of pathways. The reducing agent adsorbs on the surface of iron oxide and reacts with the nitrogen-containing species formed by NO adsorption to form a series of hydrocarbon intermediate products, which reduces NO via a further reaction. In the presence of oxygen, O2 will participate in the competitive reaction of the hydrocarbon reducing agent with the nitrogen-containing adsorbed species, promote the reaction and form more active intermediate species such as R-COO-, CH3COO-, which finally reduce NO to N2.