Improvement Of The Activity Of Fe-Ti Spinel For The Selective Catalytic Reduction Of NO With NH₃ At Low Temperatures

Nitrogen oxides, greatly contribute to the formation of acid rain, smog and photochemical smog. Due to being a relatively mature with high NOx removal efficiency, selective catalytic reduction (NH3-SCR) is a mainstream technology for NOx abatement. And the most widely used catalyst system is V2O5-WO3/TiO2, which still shows some actual problems, such as the relatively narrow temperature window and the toxicity of vanadium pentoxide to the environment. There are continuing efforts for us to develop novel, highly efficient and environmental-friendly NH3-SCR catalysts.Fe-Ti spinel with high temperature performance and non-toxic, is a potential catalyst for NH3-SCR. Nevertheless, Fe-Ti spinel shows lower activity at relatively low temperature, which restricts its large scale industrial application. This work with Fe-Ti spinel as a target material, combined Fe-Ti spinel with Mn-Fe spinel to widen the operating temperature window specifically and improved the SCR performance of Fe-Ti spinel at low temperature purposefully.The novelties and important conclusions of this work are summarized as flollows:(1) A high temperature SCR catalyst (Fe-Ti spinel) and a low temperature SCR catalyst (Mn-Fe spinel) were combined to remove NOx. As Fe-Ti spinel layer was placed upstream of the Mn-Fe spinel layer, both Fe-Ti spinel and Mn-Fe spinel displayed their strong advantages at their appropriate temperature for the SCR reaction. Therefore, this dual layer catalyst showed excellent SCR activity at a broad temperature window, which was much better than the others. The difference of the SCR performance of the three combination modes mainly depended on the distributions of NH3 consumed to the SCR reaction, the NSCR reaction and the C-O reaction.(2) MnOx was supported on Fe-Ti spinel to remove NOx from coal-fired power plants. As NH3 and NH2 were mainly adsorbed on the support of 10%Mn/Fe-Ti spinel, they were far away from Mn4+ on Mn/Fe-Ti spinel, therefore the over-activation of adsorbed NH2 to NH by Mn4+ can hardly happen on 10%Mn/Fe-Ti spinel resulting in a suppression of N2O formation through the Eley-Rideal mechanism. After the load of MnOx, the regeneration of Fe3+ on Fe-Ti spinel was accelerated due to the rapid electron transfer between Mn4+ and Fe2+, resulting in a remarkable promotion on NH3 activition. Therefore 10%Mn/Fe-Ti spinel showed an excellent SCR performance.