Properties For Catalytic Reduction Of NO_x Over Iron Oxide

Nitrogen oxide (NO_x) is an environmental pollutant because it contributed to catalytic destruction of stratospheric ozone and does harm to human beings. Mixed metal oxides are one of the catalysts that wipe NO_x off. Because of its special crystal structure and high oxidation-reduction catalytic activity, it will be of applied prospect.A serial of cordierite-based complex oxides of Fe(O),FeNi(O) and FeNiZr(O) was prepared by impregnation and their catalytic activity in selective catalytic reduction were systematically investigated using method of temperature progress while urea as reductant. The catalytic reactions were conducted in fixed-bed fluxion reactor. Loading of active component, calcination temperature of catalyst and velocity were also investigated. The results revealed that the calcination temperature, loading and the velocity had important effects on catalytic activity. The catalytic activity of iron in selective reduction of NO_x was low. To be specific, the efficiency was 34.2% while calcinations temperature was 600℃, loading of iron was 6wt%, and it deactivated dramatically with the rising of velocity; When modifying the catalysts of Fe(O), the added La,Ce,Mn,Co,Ni affected the catalytic property of these catalysts. The catalytic activity was improved remarkably by the addition of Ni and the conversion of NO_x, increased up to 58.1% at the reaction temperature of 250℃. A remarkably increase in the conversion of NO_x, was observed when Zr used for promoter and the maximum conversion exceed to 80%.The structure, reduction property, surface morphology and surface elements of the catalysts were analyzed by XRD,SEM,BET,TPR,XPS method. The results indicated that the surfacial elements of the catalysts existed in the form of oxides; the aggregating status of active Fe species changed with the addition of Ni, and its diameter decreased sharply, surface area increased dramatically. The addition of Zr enhanced the dispersion of Fe on the support so that the surface active species were increased and the catalytic activity is enhanced. Meanwhile the added Zr also lowered the reaction activation energy, made the active Fe species more reducible, accelerated its reduction rate, and the catalytical activity was improved.