Research On Iron-based Catalyst For NO_x Removal In Flue Gas

Selective catalytic reduction of NOxby ammonia (NH3-SCR) is an efficienttechnology to abate NOxin the flue gas from stationary sources. For severalshortcomings of vanadium-based catalysts need to be addressed, including the narrowtemperature window, the low N2selectivity at high temperatures, losing SCR activity bySO2poisoned, and the secondary pollution to the environment， a series ofenvironmentally friendly iron based catalysts were investigated for NH3-SCR reactionin this paper. For the SCR activities of Fe2O3catalysts dropped sharply in the hightemperature, the method of sulfate was adopted and prepared a series of sulfateiron-based catalyst, furthermore, investigated the coordicating role between Fe3+andSO42-and the effects of the sulphate ions position for NH3-SCR. Through improving thesupport, Fe2O3·SO42-/TiO2-ZrO2catalyst was developed and discussed for NH3-SCR.The main results were in the following:(1) γ-Fe2O3catalyst showed higher catalytic activity than α-Fe2O3in150~300oC,however, γ-Fe2O3catalyst easily transforms to α-Fe2O3and the SCR activities of thesetwo catalysts decreased sharply in300~500oC.(2) Varying Fe3+and SO42-contents remarkably affected the SCR activities of sulfatediron-based catalysts, and it was found that Fe3S5Zr catalyst had the highest NOxconversion which was above90%in all sulfated iron-based catalysts in350~450oC. Itwas concluded that the coordinate impacts between Fe3+and SO42-on theoxidation-reduction property and the storage capacity of NH3and NOxinfluenced theSCR activity.(3) By changing the sulfating process,(FeS)/Zr, Fe/(SZr) and S(Fe/Zr) catalysts wereprepared, on which sulphate ions’ position were various. Compared with the (FeS)/Zrcatalyst, Fe/(SZr) catalyst showed much higher de-NOxefficiency in the temperaturerange of300~450oC. Due to the differences of sulfate process, the forms of Fe3+andSO42-were different on different catalysts, which resulted in the large distinction in theoxidation-reduction ability, the acidities of Lewis and Br nsted and the NH3adsorptionspecies that were important for the SCR activity for abating NOx.(4) Fe2O3·SO42-/TiO2-ZrO2catalyst with the TiO2/ZrO2weight ratio of1:4showedhigher activity and N2selectivity and better SO2poisoning resistance than Fe2O3·SO42-/ZrO2catalyst in300~500oC. Doping TiO2into ZrO2, the phase structureand surface adsorption property of catalyst were effectively improved, which was key tothe SCR reaction.