The Study Of Low-temperature SCR Performance Of Mn-Ce/TiO₂ Catalysts With Preferential Exposure Of Anatase TiO₂{001} Facets

Selective catalytic reduction（SCR）is the most widely used flue gas denitrification technology.At present,commercial SCR uses vanadium-titanium catalysts,the active temperature window（300-400°C）is relatively high and narrow,which needs to be arranged in the high temperature and high dust area during flue gas denitrification of coal-fired power plant,and there are problems such as wear and blockage during long-term operation.Due to the limitation of active temperature window,it can not meet the denitration demand of cement kiln and sintering flue gas.Therefore,the development of low-temperature（<300°C）SCR technology is a major requirement for NO_x emission control of industrial sources.However,low temperature SCR catalyst is difficult to overcome the problem of SO₂ poisoning,which is a key bottleneck in the commercialization of low temperature SCR technology.The support of low temperature SCR catalyst is generally anatase TiO₂.Based on the experiments,the influence of the anatase TiO₂ support crystal surface characteristics on the denitration activity and sulfur resistance of Mn-Ce/TiO₂ catalyst were studied.The main results are as follows:（1）Anatase TiO₂ preferentially exposed to the{001}facets（TiO₂-NS）and anatase TiO₂preferentially exposed to the{101}facets（TiO₂-NP）were synthesized by hydrothermal methods with different crystal surface guiding agents,and Mn-Ce/TiO₂-NS and Mn-Ce/TiO₂-NP low-temperature SCR catalysts were prepared by the impregnation method.The results showed that the preferential exposure of TiO₂{001}facets could inhibit the agglomeration of particles during the preparation of the catalyst,and the Mn-Ce/TiO₂-NS catalyst had more active oxygen,more Ce³⁺and Mn⁴⁺concentration and stronger acidity,which promoted the SCR reaction,so that the Mn-Ce/TiO₂-NS catalyst had good denitration performance.（2）The toxic effect of SO₂ on Mn-Ce/TiO₂ catalyst is irreversible.The formation of（NH₄）₂SO₄ or/and NH₄HSO₄ and the sulfation of Mn O_x and Ce O_x on the catalyst surface were the two reasons for the deactivation of the Mn-Ce/TiO₂ catalyst,and further research results showed that the main reason for the toxic effects of SO₂ was that SO₂ reacted with the active species of manganese and cerium to form corresponding metal sulfates on the catalyst.（3）The preferential exposure of the anatase TiO₂{001}facets can improve the sulfur resistance of the Mn-Ce/TiO₂ catalyst.The reason is that the high exposure of the anatase TiO₂{001}facets can effectively inhibit the formation of（NH₄）₂SO₄ and NH₄HSO₄ on the catalyst surface,and the more reactive{001}facets made it easier for the support TiO₂-NS to generate Ti（SO₄）₂ in a sulfur-containing atmosphere,which protected Mn O_x and Ce O_x to a certain extent,so that the Mn-Ce/TiO₂-NS catalyst still had high denitration efficiency when exposed to an SO₂-containing atmosphere for a long time.