Synthesis And Properties Of CeO₂-MnO_x Low Temperature Denitration Catalyst

With the rapid economic development,a series of increasingly prominent atmospheric environmental problems have emerged.NO_x emitted from fixed sources?such as coal-fired power plants?and mobile sources?such as automobile exhaust?as one of the major pollutants in the atmosphere.Therefore,it is an urgent task to control the NO_x emission.One of the most effective denitration techniques is the selective catalytic reduction?SCR?,and the catalyst is the key of this technique.At present,the V₂O₅-WO₃/TiO₂ catalyst is a mature denitration catalyst for commercial application.However,the poor activity in low temperature,the biological toxicity of vanadium and the tendency of TiO₂ to change from anatase to rutile at high temperature in actual working conditions are problems,which result in the application of this commercial catalyst in more fields is limited.So,it is of great importance to devote a novel environment-friendly denitration with an outstanding catalytic performance at low temperature?<300°C?.On the one hand,MnO_x catalyst has excellent low temperature catalyst activity,on the other hand,CeO₂ is non-toxic,cheap,and with excellent oxygen storage and release capacity.Therefore,the CeO₂-MnO_x catalyst is recognized as a promising low temperature NH₃-SCR catalyst.While poor N₂ selectivity and poor H₂O and SO₂ resistance are two main problems for the catalyst to use for the industrial application.With the purpose of improving the N₂ selectivity and water and H₂O and SO₂ resistance of the catalyst by changing the physicochemical properties of the catalyst,we modified the CeO₂-MnO_x catalyst by elements in-corporation and solvents modulation,respectively.The results obtained are as follows:?1?The CeO₂-MnO_x?Ce-Mn?catalyst and a series of CeO₂-MnO_x catalysts incorporated by Ti⁴⁺and/or Sn⁴⁺were synthesized by inverse co-precipitation method with ammonia,and the performance of these catalysts for low temperature selective catalytic reduction nitrogen by ammonia?NH₃-SCR?was studied.The results show that after co-incorporated by Ti⁴⁺and Sn⁴⁺,the catalytic performance of the CeO₂-MnO_x-TiO₂-SnO₂?Ce-Mn-Ti-Sn?catalyst gets enhanced.Ce-Mn-Ti-Sn catalyst displayed the optimal catalytic performance with an enhancement of 30%NO_x conversion compared with Ce-Mn in the range of 225-275°C.Moreover,the N₂O?by-product?formation was inhibited remarkably compared to Ce-Mn?152 ppm?,and there was no N₂O?0 ppm?detected even at 250°C.This is linked to the synergistic effect of Ti⁴⁺and Sn⁴⁺which further results in moderate weakening of redox property,enhancement of acidic strength,more generation of acid sites,as well as large amount of Ce³⁺,oxygen vacancies,and absorbed oxygen species for the Ce-Mn-Ti-Sn catalyst.?2?A series of supported MnO_x/CeO₂?Mn/Ce?catalysts were prepared by modulating the solvents?deionized water?DW?,anhydrous ethanol?AE?,acetic acid?AA?,and oxalic acid?OA?solution?with the purpose of improving the low-temperature NH₃-SCR performance,broadening the operating temperature window,and enhancing the H₂O+SO₂ resistance,the performance of these catalysts for low temperature selective catalytic reduction nitrogen by ammonia?NH₃-SCR?was studied.The obtained results indicate that MnO_x/CeO₂catalyst prepared with oxalic acid solution as a solvent exhibits the best catalytic performance among these catalysts,which shows above 80%NO conversion during a wide operating temperature range of 100-250°C and an excellent H₂O+SO₂ resistance for low-temperature NH₃-SCR reaction.This is related to that oxalic acid solution can promote the dispersion of MnO_x and enhance the electron interaction between MnO_x and CeO₂,which are beneficial to improving the physicochemical property of MnO_x/CeO₂ catalyst,and further contribute to the enhancement of catalytic performance and good H₂O+SO₂ resistance.