Fundamental Research On Ceria Based Catalysts For Catalytic Combustion Of Dioxins From Iron Ore Sintering Flue Gas

Controlling emission of pollutants from sintering process is crucial for energy conservation and emission reduction.Catalytic degradation technology can realize the complete mineralization of pollutants,which is a new technology with a good application prospect.It is very important to develop efficient and environmentally friendly catalysts for catalytic combustion dioxins from iron ore sintering process.Therefore,catalytic combustion of dioxins from sintering process over ceria-based catalysts is proposed in this study based on the characteristics of sintering flue gas.In terms of the highly catalytic activity at low temperature with chlorobenzene(CB)acting as a model molecule for dioxins,the emphatically studied issues included the doping of transition metal,controlling of nano-microstructure,the modification of carrier and the promotion of oxide graphene.The stability,the resistance performance of water and sulfur and the denitration activity were investigated.Furthermore,the promotion mechanism by graphene oxide over ceria-based catalysts was revealed.The effect of transition metal vanadium on the catalytic activity of combustion CB over Ce-based catalysts were studied.Among them,Ce-V(2.5)catalysts show good activity at low temperature.The CB conversion is 40%at 150?.The growth direction was regulated by adding alkaline regulator or template additive.Three kinds of nano-microstructure of cubic(CV-1),particles(CV-2)and rods(CV-3)of Ce-V catalysts were obtained,respectively.The comparison of three kinds of nanostructures catalysts was conducted,the order of conversion was CV-3>CV-2>CV-1.The promotion of catalytic activity of CV-3 is due to the formation of Ce VO₄,which can increase the amount of Ce³⁺,adsorbed oxygen O_?and oxygen vacancies on the catalyst surface,and weaken the agglomeration of VO_x on the catalyst surface.Though building of calculation and kinetic analysis model,it is found that the apparent activation energy of chlorobenzene catalytic combustion is 5.60±3.01 k J·mol^-1(CV-1),7.30±3.56 k J·mol^-1(CV-2),and 9.26±3.76 k J·mol^-1(CV-3),respectively.It is consistent with their crystal surface energy.The results indicate that the more unstable the crystal surface of metal oxide is,the stronger of adsorption capacity is,and the higher catalytic activity observe.TiO₂ was introduced into Ce-V catalysts as carried materials by sol-gel method.The optimized proportion of Ce(15)-V(2.5)-Ti catalyst can achieve the catalytic activity of 60%at 150?.The increase of gaseous hourly space velocity(GHSV),the high concentration of reactant and the decrease of oxygen concentration were not conducive to the catalytic degradation process.The stability of Ce-V-Ti catalyst was investigated.The results show that the catalyst is partially inactivated due to temporary chlorine poisoning at about 200 min and recovered around 300 min and then stabilize.The analysis of the mechanism show that the reactants first adsorbed vertically on the surface of the catalyst through nucleophilic substitution,and then activated by Ce component.The activated CB molecules are decomposed by oxygen species,which is released by Ce⁴⁺?Ce³⁺reaction.And then CO₂ and HCl/Cl₂ are generated.The Cl species left the surface of the catalyst through Deacon reaction.Moreover,the oxidation reaction of VO_x in low-price can promote the reduction reaction of Ce.The CB catalytic activity at low temperature over Ce-V catalysts was further enhanced by introducing graphene oxide modification.The effect of different types and addition ratios of graphene oxide on catalytic activity at low temperature were researched.The results show that the appropriate mass percent addition of 0.7%with graphene oxide(BET surface>500 m²/g,diameter 3-10?m)can achieve an excellent catalytic activity.The catalytic activity can achieve 77%at 150?,and 90%at 200?.The main mechanisms of catalytic activity improvement are as follows:(1)After modified by oxide graphene,the active component is more evenly dispersed on the surface,and the precipitation of Ce-O-Ti solid solution is promoted.The proportion of Ce³⁺on the surface of catalysts are increased and the bending energy between oxygen(O_?and O_?)and metal atoms are weakened.Both of them made it easier for the catalysts to provide lattice oxygen during reaction process.(2)The adsorption model changes from vertical adsorption to parallel adsorption,which promote the fracture of benzene ring and weak the dichlorination process.(3)The carboxyl(-COOH)on the graphene oxide surface enhance the formation of?-?bond between catalysts and reactant,which is conductive to the adsorption of CB during catalytic combustion.The resistance performance of water and sulfur and the denitration activity was investigated.By injecting H₂O and SO₂ into the catalytic reaction system,it is found that after modified by graphene oxide,the resistance performance of water and sulfur over Ce-V-Ti catalysts can achieve 60%and 70%at 200?,which increased by 20%and 35%,respectively.A new phase of Ti₅O₉ appears in the catalyst,which increase the amount of oxygen vacancies and was conducive to improving the denitration activity.The denitration activity of Ce-V-Ti/GO catalysts is 80%at 150?The study will be benefit to enrich the basic research of ceria-based catalysts combustion of dioxins at low temperature,laying the foundation for catalytic combustion of dioxins from iron ore sintering flue gas.Also,it can promote the progress and development of pollutant reduction and multi-pollutant collaborative deep purification technology from iron ore sintering flue gas.