Preparation Of Novel Iron-based Catalysts For Direct Reduction Of NO By Biomass Activated Carbon

Due to the low temperature and the complex composition of flue gas,coke oven flue gas comprehensively considers its safety,stability and maturity,and it faces certain difficulties and challenges in achieving nitrogen oxide emission reduction.The selective catalytic reduction(SCR)is currently the most mature flue gas purification technology and widely used in practical production,however it has higher denitrification temperature window,difficult ammonia storage and transportation and secondary pollution caused by ammonia escape,which is not consistent with the coke oven flue gas denitrification.Therefore,the development of a catalyst with high denitration efficiency,environmental friendliness and low cost for the removal of nitrogen oxides from low temperature coke oven flue gas is a hot research topic.In this paper,coconut shell activated carbon was used as the catalyst carrier,and ferric nitrate was implanted by ultrasonic assisted equal volume impregnation method.The nano zero-valent iron catalyst was prepared by directly using the activated carbon carrier and CO as a reducing agent to reduce it.The experimental data show that the presence of nano-zero-valent iron can greatly reduce the denitration temperature window and improve the low-temperature denitration activity.The NO removal efficiency can reach 100% at 280?.The inactivated nano-zero-valent iron catalyst can completely restore its activity after direct reduction by carbon,howerer,the carrier loss is caused by the no addition of reducing gas.In order to overcome the shortcomings of carbon reduction,it is proposed to use CO as a reducing agent,which minimizes carbon loss,and the prepared catalyst has higher dispersion and better denitration performance.This provides a reference for the preparation conditions of the later catalyst,and the catalyst meets the requirements of green economy and recycling economy,and has a strong economic advantage in replacing the catalyst in the NH3-SCR technology.In order to simplify the preparation of traditional flue gas denitration agents,this study proposes the use of ferric nitrate for activation,one step to complete the carbonization,activation and loading process.The nano-zero-valent iron-iron carbide catalyst supported on biomass activated carbon was prepared for low-temperature flue gas denitrification by using common biomass corncob and sawdust as representatives.The catalyst prepared by this method has a well-developed pore and a smooth outer surface,which provides conditions for the high dispersion of the active component on the porous carbon surface.The flue gas denitration agent also achieves a 100% NO removal efficiency at 280 ?.The reason may be due to the development of mesoporous structure,which provides a channel for the diffusion of flue gas.On the other hand,it may be due to the high activity,good selectivity and certain anti-sintering ability of Fe3 C,avoiding the agglomeration of active components.Based on the experimental data and recent literature reports,the denitrification mechanism of nano-zero-valent iron and nano-zero-valent iron-iron carbide catalystwas analyzed.First,NO is adsorbed by the active site on the surface of the catalyst carrier.Under the action of the active component,the N=O bond breaks to form C(N)and C(O)complexes.The low-valent iron is easily oxidized to the surface of the carrier due to its magnetic properties,thereby being oxidized by C(O)to Fe3O4.If the denitration temperature is further increased,the free C(N)intermediate can be resolved from the carbon surface to form N2,and the C(O)complex is finally precipitated as CO or CO2.When the active site of carbon is exhausted,Fe3O4 is eventually oxidized to Fe2O3,thereby losing the ability to directly catalyze the reduction of NO.Therefore,under low temperature conditions,the low-valent iron in the catalyst has higher activity,and the nano-zero-valent iron and iron carbide as the reducing agent enhance the denitration performance.