Research On The NO_X Removal Mechanisms And Preparation Of FeSO₄ SCR Catalyst

The conventional V₂O₅-WO₃/TiO₂ SCR catalyst is expensive, complicated to use and may cause secondary pollution to environment after employment. The aim of this research is to develope Fe-based catalyst to reduce the cost of NOx emission control without compromising NOx removal efficiency. After comparing the existing research, the idea of using FeSO₄ as the SCR catalyst to remove NOx in flue gas has been proposed.The activities and endurances of FeSO₄ under simulated flue gas conditions were first tested in a bench-scale fixed-bed reactor system. The experimental results suggested that FeSO₄-NaY and FeSO₄-ZSM-5 prepared by impregnation method performed well in NOx removal. The NOx removal rates of the prepared catalyst were 20– 35% higher than those of pure FeSO₄, The effective temperature window was largely expanded with the best performance temperature shifted from 440°C to 340°C. SO₂ and H2O in flue gas had no obvious effect on catalyst performance.M?ssbauer spectrometry, XPS and in-situ infrared spectra analysis had been employed to investigate the catalytic mechanism of FeSO₄. It had been found that FeSO₄, Fe(OH)SO₄ and Fe2O(SO₄) were the major components existing in prepared catalyst, with their portions related to carrier type and preparing condition. FeSO₄ combined tighter with the carrier after de-NOx reaction. Fe2O₃ and the chemical bond between Fe and Al had been found. Fe(OH)SO₄ was better than that of Fe2O(SO₄). NH₃ absorbed on FeSO₄-NaY generated the spectra of NH4+ and NH₃, suggesting the Eley-Rideal mechanism. FeSO₄-ZSM-5 absorbed both NH₃ and NO, and the carrier (ZSM-5) itself demonstrated catalytic effect, indicating a different reaction mechanism. SO₄2- from FeSO₄ and the hydroxy from carrier jointly enhanced reaction gas adsorption. Fe provided the active sites for reaction between NH₃ and NO.The preparation of FeSO₄ catalyst module had been attempted by optimized impregnation method. FeSO₄ had been first impregnated on molecular sieve, and then coated on cordierite honeycomb. The effective surface and physical strength of the catalyst had been significantly improved and therefore the industrial application had been enabled. The prepared catalyst module had been tested in a small-scale coal-firing boiler system to verify its reactivity and endurance. The results revealed that, under the condition of NH₃/NO_x=1 and SV=10000/h, the NOx removal rate was above 80% for the temperature range of 280 - 380°C, in spite of flue gas fluctuation. The best NOx removal rate of 95% was achieved under 320°C. No obvious performance lost had been found after 200h continuous test. This preliminary test had proved catalyst's potential for industrial application.The techno-economic analysis suggested that, comparing with the existing commercial catalysts, FeSO₄ had distinctive advantage in large resource, low installaltion and operation cost, and little attention in aftertreatment. In the last part of the thesis, the preparation methods for industrial catalyst module was attempted.