Study On The Effect And Mechanism Of Alkali Metals On Denitration Of VW/Ti Catalyst Under Fast SCR Atmosphere

The selective catalytic reduction（SCR）used in the denitrification industry of power station boiler exhaust gas is widely used because of its high activity,wide temperature window and few by-products.With the continuous improvement of national economic level,the protection of the atmospheric environment in China is getting stronger and stronger,and the requirements for denitration of the exhaust gas from moving source and fixed source are getting stricter and stricter.And the core of the selective catalytic reduction technology-SCR catalysts,vulnerable to energy such as coal,oil,especially the biomass of the toxicity of alkali metals,alkali metal can destroy the activity of catalyst acid sites,alkali metal salt formation of fly ash can clog catalyst channel,make the SCR catalyst activity fell sharply,seriously affect the normal operation of denitration system,cannot reach discharge standards.How to effectively improve the anti-alkali metal capability of SCR denitrification system is of great significance for the efficient and stable denitrification of industrial tail gas.Fast SCR reaction,as one of the research hotspots in recent years,has better reaction performance and faster reaction rate,which is a potential application direction.However,the fast SCR reaction characteristics in the presence of alkali metals are still unknown.This paper mainly studies the reaction performance of fast SCR reaction of catalyst after alkali metal poisoning and deposition,analyzes the reasons and mechanism,and discusses how to run fast SCR reaction stably and efficiently in alkaline flue gas.In this study,the VW/Ti catalyst of commercial formulation was firstly used as the research object.By comparing the fast SCR reaction with the standard SCR reaction of the VW/Ti catalyst with the alkali-containing flue gas,it was proved that the fast SCR reaction had better NOx conversion and N₂ selectivity.Three of the two SCR reactions-NO,NO₂ and NH₃-were studied.The NH₃-tpd of the same alkali metal poisoning catalyst indicates that the adsorption performance of NH₃ is the same,but the reaction stages of NH₃ in the two SCR reactions are different.NO cannot cause NH₃reaction order to change,but NO₂-TPD proves that NO₂ adsorption makes gaseous NH₃participate in the reaction,which is different from the traditional standard SCR mechanism that requires NH₃ adsorption.Finally,the standard SCR reaction was carried out on the alkali metal poisoning catalyst pre-adsorbed NO₂,and it was found that the adsorbed NO₂ could improve the activity of the standard SCR,which also proved the correctness of the new"E-R"reaction mechanism.Due to the involvement of alkali metals and NO₂,The reaction mechanism of fast SCR changes,and the factors affecting its reactivity are also different from those of standard SCR.When the composition of inlet NOx is NO:NO₂=1:1,the reactivity of fresh catalyst is the highest.After alkali poisoning,NO₂>NO in NOx is more active.However,the increase of the amount of vanadium in the active component of the catalyst,the addition of tungsten in the auxiliary component and the increase of the acid site will all improve the activity of the fast SCR reaction in the alkaline flue gas,which is similar to the standard SCR reaction.Under sulfur and water bearing conditions,the rapid SCR reaction of alkaline flue gas has higher and more stable activity than the standard SCR reaction.