Study On The Performance Of Mn-based And Ce-based Catalysts For NH₃ Selective Catalytic Reduction Of NO

With the tightening of NO_xemission limits,the post-treatment of nitrogen oxides has become one of the most important research challenges in the world’s environmental field.At present,selective catalytic reduction of NO_x（NH₃-SCR）is the most effective technology to control NO_xemission.The most practical catalyst in SCR system is vanadium-based catalyst,which must be installed upstream of dust removal and desulfurization to meet its optimal operating temperature of 300～400℃or the catalyst may be poisoned by high concentration dust particles and sulfur-containing ammonium salts.In this case,it is necessary to develop a low-temperature and environment-friendly catalyst,which can not only work effectively downstream,but also avoid the above problems.Aiming at the above problems,this paper designed and studied the SCR activity and H₂O/SO₂resistance of Zr,Ni-Sn modified Ce-based catalysts and Ce modified Mn-based catalysts,and the related reaction mechanism was explored.（1）Zr-modified CeTiO_xmixed oxide catalyst with good NH₃-SCR activity and H₂O/SO₂resistance was synthesized by H₂reduction treatment.The performance test showed that the R-CZT-20/1（Ce:Zr:Ti=20:1:100）catalyst reduced by H₂showed good low-temperature activity,excellent SO₂resistance and good reversibility.The characterization showed that R-CZT-20/1prossessed more surface acid sites and oxygen defects,which promoted the chemical adsorption and activation of NO and NH₃on the catalyst surface.XPS results confirmed that the reduced catalyst enriched Ce³⁺,promoted the electron transfer between Ce³⁺+Ti⁴⁺→Ce⁴⁺+Ti³⁺and produced a large number of oxygen vacancies.In addition,there was a strong synergy between Ce-Zr-Ti,which might be the reason for its excellent SO₂resistance.Among them,the existence of Zr promoted the favorable process.In suit DRIFTS was used to study the reaction mechanism before and after catalyst reduction.（2）In order to further modify CeTiO_xcatalyst,the NSCT（Ni:Sn:Ce:Ti=0.7:0.3:1:2）catalyst co-modified with Ni-Sn was successfully synthesized by ethylene glycol-ethanol solvothermal method.After Ni-Sn co-modification,the redox capacity,the storage capacity of active oxygen and the acid sites of NSCT were obviously improved.The existence of Ce⁴⁺+Ni²⁺＝Ce³⁺+Ni³⁺,Sn⁴⁺+Ni²⁺＝Sn²⁺+Ni³⁺double electron transfer greatly promoted the catalytic performance of NSCT,the NO conversion reached over 90%at 200～400℃,and the activity of NO remained at～91%after 20 h reaction with SO₂.At the same time,the main role of Ni and Sn modification was put forward.Due to the electron transfer from Ni²⁺to Ce⁴⁺,the electron transfer from SO₂to Ce⁴⁺was inhibited,and Sn⁴⁺was easy to get electrons,which would preferentially react with SO₂,so as to inhibit the formation of sulfate species on the active component Ce,which was the main reason that NSCT exhibited excellent SO₂poisoning resistance.According to the research results of In situ DRIFT,the reaction mechanism of the catalyst was put forward.（3）In order to obtain the catalyst with excellent performance at lower temperature,the Ce_0.025-Mn Co Al O_xflaky structure catalyst modified by Ce was successfully synthesized by two-step method,and the activity and SO₂resistance of the catalysts were significantly improved.Ce_0.025-Mn Co Al O_xcould reach 100%NO conversion at 125℃,and at the same time generated less N₂O in the reaction,exhibited good N₂selectivity,and maintained 100%activity in the long-term H₂O and SO₂reaction.Among them,the improvement of catalytic performance was related to the larger specific surface area,better redox capacity and more acid sites of Ce_0.025-Mn Co Al O_x.XPS analysis showed that the electron transfer between Ce³⁺and Mn⁴⁺and Co²⁺+Ce⁴⁺＝Co³⁺+Ce³⁺effectively inhibited the electron transfer from SO₂to active Mn,and prevented the vulcanization of Ce,which effectively protected the active species Mn.This was the main reason that Ce_0.025-Mn Co Al O_xcatalyst possessed excellent SO₂resistance.At last,the related reaction mechanism was put forward by In situ DRIFT.