Effects Of Doping Co-Ce Oxides On The Structure And Properties Of Mn/TiO₂Low-temperature DeNOx Catalysts

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(S_1A) and6Ce-6Co-20Mn/TiO₂(S_1D) catalysts presulfurization for1hour were litter changed,denitration efficiency improved. However, After S_2Aand S_2Dcatalysts presulfurization for2hours, the surface area was decreased, pore volume and pore diameter were little change, thedenitration efficiency declined, by contrast, S_2Dhas good stability of sulfur resistant. S_1A and S_1Dmade the concentration of chemical adsorption oxygen increase, N element existedas nitrogen oxide, Co and Ce as CoOx and CeOx, S as SO₄^2-, a small number of SO₄^2-canstrengthen Lewis sites, reduce the accumulation of ammonium sulfates and improve thedenitration efficiency. More “Morning Glory” can be found in the S_1Asurface. Because ofthe acidification of SO₂, the “Morning Glory” disappeared after20Mn/TiO₂catalystspoisoned. With the same presulfurization time, the accumulation of S elements in S_1DandS_2Dwere less than S_1Aand S_2A. 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 S_2Apresulfurization 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. S_2DCatalysts’ sharpening and intensity of binding energy （BE） for Mn2p and Ti2p did not takeobvious change, had less total peak area of SO₄^2-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. SO₄^2-will restrain the formation of CoOx whichhas good catalytic activities.