Study On The Performance And Mechanism Of A New FeTi Composite Bimetal Denitration Catalysts

At present,the air quality has become the focus of public attention.A large number of nitrogen oxides?NO_x:NO,NO₂?emissions are one of the main causes of air pollution,which cause a series of environmental problems,such as photochemical smog,haze,acid rain and ozone hole so on.In general,NO_x emissions from fixed sources?such as coal-fired power plants,etc?and mobile sources?such as automobile exhaust?are the main sources of air pollution.The NH₃ selective catalytic reduction of NO?NH₃-SCR?has been widely considered as the most efficient technology for NO_x removal.The catalysts of V₂O₅-WO₃/Ti O₂ and V₂O₅-Mo O₃/Ti O₂ have excellent SCR reaction activity in the temperature range of 300-400?and good SO₂ resistance,so it are widely used.However,there are some disadvantages,such as narrow operating temperature window,poor catalytic activity at low temperature,expensive active components,poor selectivity of N₂ and secondary pollution.Therefore,there is an urgent market demand for developing low temperature SCR catalyst with wide temperature window,low cost and environmental friendly.Compared with other transition metal oxide based catalysts,iron-based catalysts are the most potential and rational substitutes for vanadium based catalysts.Because of its good catalytic performance,no secondary pollution,no biological toxicity and abundant reserves.It is very important to study the removal of NO_x by Fe and Ti composite oxides at low temperature?100-300°C?for industrial flue gas and diesel engine exhaust gas,because of its low price and rich mineral resources.However,the development of low-temperature catalysts?LTC?for selective catalytic reduction of NO_x is still a challenge,especially the iron-titanium composite oxide catalysts with potential application value,but their activity is poor under low and medium temperature conditions.In view of the above mentioned problems and analysis,this subject takes Fe as the active component and Ti as the auxiliary agent.The iron-titanium catalyst was studied in depth,and a series of different Fe³⁺/Fe²⁺species ratio and Ti-doped catalyst were prepared.The performance of low-temperature NH₃ selective catalytic reduction of NO was investigated.The aim was to find a catalyst with good low-temperature activity and wide temperature window for NO_xremoval.The physical and chemical properties of the catalyst samples were analyzed by a series of characterization methods to reveal the relationship between structure and performance.The research results show that the optimal Fe³⁺/Fe²⁺substance ratio is 1:1,and the most suitable Ti doping amount is 7.5%.At this time,the catalyst reaches the optimal coexistence state of Fe³⁺,Fe²⁺and Ti⁴⁺,and the active species are evenly distributed.The ratio of Fe²⁺/(Fe³⁺+Fe²⁺)in the catalyst reaches the maximum,and the concentration of oxygen vacancies and chemically adsorbed oxygen is increased.It is easier to form highly active species such as gaseous NO₂ on the surface and enhance the strength of Br?nsted acidic sites,which helps the catalyst The reaction happened.The NO_xconversion rate reached 90%at 180?.TPD/TPR and in situ DRIFTS were used to study the adsorption species and their reaction paths.In addition,the effects of different preparation methods on catalyst activity were studied.The catalyst activity was optimal when the co-precipitation method was used.