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Effects of Doping Co-Ce Oxides on the Structure and Properties of Mn/TiO2Low-temperature DeNOx Catalysts

Author: FengYunSang
Tutor: LiuShaoGuang
School: Jiangsu University of Science and Technology
Course: Materials Science
Keywords: Low-temperature denitrification SCR catalysts Co-Ce-MnOx/TiO2 anti-SO2poisoning
CLC: TQ426
Type: Master's thesis
Year: 2013
Downloads: 3
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Abstract


Nitrogen oxide （NOx） is one of the main air pollutants. In order to solve the issue ofNOx pollution, SCR is considered to be a potential technique. Many problems such asblocking, eroding, polluting （poisoning caused by alkali elements） and construction costoften generated in medium temperature. SCR DeNOx process reacted in low-temperaturewill become the future development direction. Among many low-temperature catalysts，Mn-based catalysts have been researched widely because of its good low temperatureactivity.In this paper，a series of MnOx/TiO2catalysts were prepared by extrusion moldingtechnology and DeNOx experiments were tested in the simulated flue gas condition. Theeffect of sulfur-poisoning resistance on low-temperature catalysts were researched afterpresulfurization. A series of characterizations including SEM, EDS, BET and XPS has beencarried out to analyze catalysts’ internal structure, surface elements situation and the dualeffect of SO2.At125℃temperature, experimental results showed that the denitration efficiency ofthe TiO<sup>2-supported catalyst loading20%MnOx reached72.6%.When loading6%Co and6%Ce metal oxides into20Mn/TiO2catalyst separately，the denitration efficiency reached85.5%and88%. When loading6%Co and6%Ce oxides together, the catalytic performancereached the highest, up to90.7%. It was found that “Morning Glory” substances wereobserved on the surface of20Mn/TiO2catalysts，which were conductive to the denitrationefficiency in connection with manganese-containing oxide.The conclusions drawn from XPS analysis were Mn existed as MnO2and Mn2O3,oxygen existed as lattice oxygen and chemical adsorption oxygen; More Mn3+was oxidizedinto Mn4+, the chemical adsorption oxygen was increased after the doping of Co and Ceelements, which make the catalytic performance enhanced; Ce co-existence in the form ofCe2O3and CeO2.Co2p XPS results illustrated that CoTiOx was the dominant phase in the6Ce-6Co-20Mn/TiO2catalysts before SCR reaction, but translated into CoO and Co3O4phase after SCR reaction. However, the phase of Co3O4has higher oxidative activity.The surface area, pore volume and pore diameter of20Mn/TiO2(S1A) and6Ce-6Co-20Mn/TiO2(S1D) catalysts presulfurization for1hour were litter changed,denitration efficiency improved. However, After S2Aand S2Dcatalysts presulfurization for2hours, the surface area was decreased, pore volume and pore diameter were little change, thedenitration efficiency declined, by contrast, S2Dhas good stability of sulfur resistant. S1A and S1Dmade the concentration of chemical adsorption oxygen increase, N element existedas nitrogen oxide, Co and Ce as CoOx and CeOx, S as SO42-, a small number of SO42-canstrengthen Lewis sites, reduce the accumulation of ammonium sulfates and improve thedenitration efficiency. More “Morning Glory” can be found in the S1Asurface. Because ofthe acidification of SO2, the “Morning Glory” disappeared after20Mn/TiO2catalystspoisoned. With the same presulfurization time, the accumulation of S elements in S1DandS2Dwere less than S1Aand S2A. It concluded as well that the facilitation role of introduce Coand Ce into the catalysts was to inhibit the formation of sulfates.The sharpening and intensity of binding energy （BE） for Mn2p and Ti2p had changedafter S2Apresulfurization for two hours. The chemical adsorption oxygen （531.2ev） wasdecreased, O1s was shifted to higher BE, S existed as （NH4）2SO4and NH4HSO4,Theformation of NH4+by N1s existed in the （NH4）2SO4and NH4HSO4. While the formation the20Mn/TiO2catalysts poisoned mainly results from the formation of certain ammoniumsulfate and Mn （SO4）2species deposited on catalyst surface, blocking the active sites. S2DCatalysts’ sharpening and intensity of binding energy （BE） for Mn2p and Ti2p did not takeobvious change, had less total peak area of SO42-and NH4+, the potential of blockingminimized and stability of sulfur resistant improved. During the progress of sulphurating,Ce4+was converted into Ce3+，large amount of metal sulfate Ce2（SO4）3was also formed. Thespin-orbit peak of Co2p is relatively weak. SO42-will restrain the formation of CoOx whichhas good catalytic activities.

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CLC: > Industrial Technology > Chemical Industry > Reagents and the production of pure chemicals > Catalyst ( catalyst )
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