Experimental Study On Selective Catalytic Reduction Of NO By Fe-La-Mn/γ-Al₂O₃at Low Temperature

Nitrogen oxides （NO_x）, as a major source of air pollution, do serious damages to theenvironment and human health. This paper introduces the source of NO_x, its damage, thegeneration mechanism and control standard. The control method of NO_xis discussed. Theselective catalytic reduction （SCR） of NO with NH₃is one of the most typical and effectivemethods to cut down the emission of NO from stationary sources. The paper mainlydiscusses the overseas and domestic research status of catalysts. The research objective isto find a kind of SCR catalysts which is efficient at low temperature, and to study theproperty.A series of Mn/Al₂O₃, La-Mn/Al₂O₃and Fe-La-Mn/Al₂O₃catalysts were prepared byimpregnation method. Under the condition of simulation flue gas in the laboratory, it wasresearched that the effect of active component and their load mass on the catalytic activity.The experiment results showed that NO conversions over catalysts increased with theincreasing of experimental temperature. The NO conversion over La-Mn/Al₂O₃wasobviously improved after La doped. The addition of Fe further increased the NOconversion. The catalyst of Fe_0.04La_0.03Mn_0.06/Al₂O₃with the load mass of MnO₂=6%,La₂O₃=3%and Fe₂O₃=4%exhibited relatively high catalytic activity and yielded98%NO conversion at260℃with a space velocity of15,000h-1. The simulated flue gas wascomposed of1000ppm NO,1100ppm NH₃,5%O₂,8%H₂O （when used）,100ppm SO₂（when used） and N₂as balance gas.On the base of the results of activity test, the influences of gas hourly space velocity（GHSV） and NH₃/NO on the NO conversion were examined. The poisoning effect of H₂Oand SO₂was also discussed. The experimental results revealed that SCR activity slightlydeclined in the presence of H₂O and the poisoning effect was recoverable, while thesynthetic effect of H₂O and SO₂was much more intense and unrecoverable. In comparisonwith La_0.03Mn_0.06/Al₂O₃, the addition of Fe could enhance the resistance of catalysts to H₂Oand SO₂, and the78%NO conversion was still obtained when8%H₂O and100ppm SO₂were introduced.The catalysts were characterized by means of N₂adsorption measurement, X-raydiffraction （XRD） and X-ray photoelectron spectroscopy （XPS）. A further discussion aboutthe physicochemical property of the catalyst was made. The results showed that the dopingof La enhanced the dispersion and oxidation states of Mn on the surface of Al₂O₃. On the surface of Fe_0.04La_0.03Mn_0.06/Al₂O₃catalyst, La was highly dispersed and mixed oxidationstate of Mn existed, while iron ions were only in Fe³⁺state.At last, the mechanism of selective catalytic reduction over these catalysts was alsodiscussed. In this experiment, metal oxides loaded on the support were the catalytic centerswhich served as electron transfer during NO reduction. The electron transfer between Mn3+and Fe³⁺might also exist and the mixture oxidation states of Mn on the surface ofFe_0.04La_0.03Mn_0.06/Al₂O₃catalyst contributed to the SCR activity.Through this research, the catalyst loaded MnO₂、La₂O₃and Fe₂O₃were developed.The catalyst showed both high catalytic activity at low temperature and high resistance toH₂O and SO₂.