Preparation And Properties Of Denitration Catalysts With CO As Reductant

A large amount of nitrogen oxides（NO_x）are present in the flue gas of coal-fired industries,which is one of the atmospheric pollutants.Its excessive emissions will seriously threaten the environment and human health.Selective catalytic reduction（SCR）is a widely used method in flue gas treatment to achieve effective removal of NO_x.In the existing denitration catalyst system,ammonia（NH₃）is generally used as a reducing agent.However,ammonia is a dangerous chemical,which has strict requirements for storage and transportation.Chemical storage accidents are liable to occur due to improper storage or transportation.At the same time,the added reducing agent increases the denitration cost.Therefore,finding a suitable reducing agent to replace NH₃ is a hot spot of current research.As a harmful gas component present in the flue gas,carbon monoxide（CO）also has a reducing ability.It can be used as a reducing agent in the denitration system to simultaneously remove NO_x and CO.In this paper,TiO₂ was used as the support material to prepare the monolithic denitration catalysts by integral extrusion molding method.The CO gas was used as the reducing agent to study the SCR denitration efficiency and mechanism of different catalysts.The transition metals of Fe,Cr and Mn were combined with Cu to obtain composite oxide catalysts.The denitrification efficiency of different catalysts,the effect ofO₂ and CO/NO_x concentration ratio on the denitration efficiency of flue gas were investigated.The results indicated that the Cr-Cu composite oxide displayed the best denitration efficiency.The denitration efficiency increased with increasing temperature.When the temperature reached 500°C,the denitrification efficiency was the highest,which has reached 80.1%.With the increase of Cr content,the denitration efficiency of Cu-Cr composite oxide increased,and the best denitration efficiency（81.3%）was obtained when the Cr content reached 2.5 wt%.WhenO₂ was present in the simulated flue gas,the denitrification activity of the catalyst decreased.With the increase of temperature,the influence ofO₂gradually decreased.When the temperature exceeded 400°C,the difference in efficiency between the two cases was less than 4%.In the CO/NO_x concentration ratio test,it was found that when the ratio was less than 1.2,the NO_x conversion was too low to be completely removed.When the ratio was greater than 1.2,the denitration activity was basically unchanged.The denitration effect of Ni/TiO₂ catalyst was studied.The results show that Cr has a significant effect on the denitrification activity of Ni/TiO₂.The denitration efficiency of the catalyst increased gradually with increasing temperature.Among them,the2.3Cr-4.9Ni/TiO₂ catalyst showed higher catalytic efficiency,and the denitration efficiency reached 85.9%at 500°C.The analysis results of Cr-Ni/TiO₂ catalysts show that the specific surface area and pore volume of the catalyst were increased after the addition of the Cr element,thereby contributing to the adsorption and passage of the reaction gas.Cr could promote the conversion of Ni²⁺to Ni³⁺in nickel oxide and make the catalyst more easier to be reduced,thereby increasing its denitration activity.The effect of rare earth element Ce on the denitrification performance of Cr-Ni/TiO₂composite oxide catalyst and its reaction mechanism were tested and analyzed.The results show that the presence of rare earth element Ce increases the reduction abilities of the catalyst,resulting in more formation of Ni³⁺and surface adsorbed oxygen,thereby its catalytic activity was improved.The 1.1Ce-2.3Cr-4.5Ni/TiO₂catalyst has the highest denitration efficiency,reaching 97.6%at 500°C.The study on the denitration mechanism of the catalyst showed that the CO-SCR reaction was mainly carried out in two steps,including oxidation of CO and adsorption of NO.There was a synergistic effect between Ni and Cr elements,and Ni-O-Cr was formed as an active site,and its existence provides an important prerequisite for the SCR reaction.