SO_4~(2-)功能化处理对Fe_2O_3催化剂上氨选择性催化还原NO_x性能的促进机理研究

采用沉淀法制备了Fe(OH)_3和Fe_2O_3。通过硫酸化处理得到SO_4~(2-)/Fe(OH)_3和SO_4~(2-)/Fe_2O_3两种催化剂,并将其应用于氨选择性催化还原NO_x(NH_3-SCR)反应,研究了SO_4~(2-)功能化处理对Fe_2O_3催化剂上NH_3-SCR脱硝性能的促进机理。结果表明,与纯的Fe_2O_3相比,硫酸化处理得到的催化剂上SCR活性得到显著提升;其中,SO_4~(2-)/Fe(OH)_3表现出更加优异的催化性能,在250-450℃时NO_x转化率高于80%,且具有优异的稳定性和抗H_2O+SO_2性能。XRD、Raman、TG、FT-IR、H_2-TPR、NH_3-TPD和in situ DRIFTS等表征结果显示,硫酸功能化处理能抑制Fe_2O_3的晶粒生长,同时SO_4~(2-)与Fe~(3+)结合形成硫酸盐复合物,提高了催化剂表面酸性位点的数量和酸强度,抑制了Fe_2O_3上的氨氧化反应,从而提高了其脱硝催化性能。

Promoting effect of SO42- functionalization on the performance of Fe2O3 catalyst in the selective catalytic reduction of NOx with NH3

Fe(OH)₃ and Fe₂O₃ were first prepared by a precipitation method and then sulfated to obtain the SO₄^2--functionalized SO₄^2-/Fe(OH)₃ and SO₄^2-/Fe₂O₃ catalysts for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR); the promoting effect of SO₄^2- functionalization on the performance of Fe₂O₃ catalyst in NH₃-SCR was then investigated. The results indicate that the SCR activity of the SO₄^2--functionalized Fe₂O₃ catalysts is significantly improved in comparison with that of unmodified Fe₂O₃. In particular, the SO₄^2-/Fe(OH)₃ catalyst exhibits excellent performance in NH₃-SCR, with the NO_x conversion of over 80% at 250-450 ℃; besides, it also display high catalytic stability and resistance towards H₂O + SO₂. A series of characterization results including XRD, Raman spectroscopy, TG analysis, FT-IR spectroscopy, H₂-TPR, NH₃-TPD and in situ DRIFTS reveal that the functionalization with sulfuric acid can inhibit the growth of Fe₂O₃ grains; moreover, SO₄^2- combines with Fe³⁺ to form the sulfate complex, leading to an increase in the number of surface acid sites and the acid strength, which can inhibit the ammonia over-oxidation on Fe₂O₃ and enhance the deNO_x performance of Fe₂O₃.