Study On Mn-based Cordierite Honeycombed Catalysts For Selective Catalytic Reduction Of NO_x At Low-temperature

Selective catalytic reduction technology is the most effectivemethod to remove NO_Xin the flue gas from stationary sources. Withlow cost of rebuilding and operation, low-temperature SCR technologyhas become the research focus of SCR technology. Currently, the mainobstacles of industrial application of low-temperature SCR technologyare the low activity at low temperature and poor H₂O and SO₂resistanceof catalysts. In order to improve the low-temperature SCR activity ofcordierite monolith De-NO_Xcatalysts, the main research content in thisdissertation included the preparation of the TiO₂washcoats on cordieriteceramic honeycomb and Mn/TiO₂monolith catalysts forlow-temperature SCR, aimed to develop the low temperature SCRcatalysts with high activity and stability during the lowertemperature（≤250℃）, and improved the industrial application of thelow temperature SCR technology.First of all, the preparation method of the TiO₂washcoats wasresearched and the results showed that added urea or hexamethylenetetramine in the TiO₂slurry could increase the loadings of coatings onthe cordierite ceramic honeycomb, the higher loadings and lower losingrate of the coatings could be obtained by adding3wt%urea or0.1wt%hexamethylene tetramine.Second, Mn/TiO₂catalysts with different Mn precursors and Mnloadings were prepared by impregnation method. The results showedthat the Mn/TiO₂from Manganese Nitrate precursor had better lowtemperature activity than the one from Manganese Acetate precursor,and the main reason was possibly due to the high surface Mn atom concentrations and more Lewis acid active sites on the catalysts withManganese Nitrate precursor. Mn/TiO₂catalysts with ManganeseNitrate precursor and65%Mn loadings showed the excellent activity atlow temperature, the NO_Xconversion could be above90%during150℃³00℃.Based on these, the low temperature activity evaluation results ofthe Mn/TiO₂catalysts doped with Fe, Ce, Co, Cu, Cr and V showed thatdoped Fe, Ce, Co, Cu could improve the activity, while doped Cr and Vwould decrease the activity. And the low temperature activity ofMn-Fe/TiO₂catalyst was improved most obviously, the NO_Xconversioncould be above90%at the reaction temperature of125℃.Finally, this paper studied on the effect of the reaction conditionsof H₂O, SO₂, O₂content, ammonia nitrogen ratio and space velocity onthe low temperature activity of Mn-Fe/TiO₂catalyst. The Resultsshowed that H₂O and SO₂had a great influence on the activity ofcatalysts and the effect of H₂O was reversible.