Research Of Catalytic Denitrification Using Zinc-based Metal Organic Framework MOF-5

Nitrogen oxides（NO_x）can cause serious environmental problems such as acid rain,photochemical smog,and ozone hole,which greatly damage human health and the ecological environment.Therefore,it is of great significance to study NO_x treatment technology.At present,NH₃-SCR is the mainstream technology for denitration,but there are problems such as easy leakage of NH₃,corrosion of equipment and high transportation costs.CO is one of the common gases in flue gas.Using CO as reductant for selective catalytic reduction denitrification（CO-SCR）could realize“using waste to treat waste”.The denitration catalyst is the core of CO-SCR.Zinc-based metal organic frameworks MOF-5 is novel porous materials with huge specific surface area and high thermal stability,which has potential as SCR denitration catalyst.In this study,zinc-based metal organic framework materials were used as the object to investigate the effect of MOF-5 synthesis conditions and metal doping modification on its denitrification performance in the presence of SO₂.At the same time,the denitrification mechanism was elucidated.The main results were as follows:1.MOF-5 with better denitration activity was selected as the research object of SCR catalyst.the synthesis conditions were optimized to obtain MOF-5 catalyst with regular crystal form and large specific surface area;after pretreatment at 250℃for 1 h in slightly reducing（CO）atmosphere,the denitrification rate of MOF-5 could reach 87%at 240℃.2.The one-step solvothermal method was selected as the modification method through characterization analysis and denitration activity test;The Me_1/12-MOF-5 catalyst was prepared by controlling the doping ratio Me:Zn=1:12（Me=Co,Cu,Ni,Mn and Fe）.The order of denitration activity was:Ni_1/12-MOF-5>Cu_1/12-MOF-5>Co_1/12-MOF-5>MOF-5≈Mn_1/12-MOF-5>Fe_1/12-MOF-5.3.In the Ni_x-MOF-5 catalyst,Ni partially replaced Zn in the Zn-O bond,and formed the Ni-O bond with O,which provided more active sites for the denitration reaction.It could adsorb reactant CO and NO molecules to form the active adsorption species(Zn²⁺（NO）₂、Zn²⁺（CO）_n、Ni²⁺（NO）₂and Ni²⁺（CO）_n)to promote CO-NO reaction.With the increase of Ni doping ratio,the denitration rate of the catalyst increased and then decreased.Among Ni_x-MOF-5,the denitration rate of Ni_1/12-MOF-5 was the highest,reached 94%at 240℃.4.The doping of Cu could increase the concentration of adsorbed oxygen and improve the redox ability of the catalyst;Cu in Cu_x-MOF-5existed as Cu⁺and Cu²⁺species,which formed the synergistic catalysis with the active site Zn of MOF-5.And the interaction between Cu and Zn generated surface synergistic oxygen vacancies,forming the redox reversible cycle(Cu⁺（?）Cu²⁺).It could promote the transfer and exchange of electrons between the active components,thereby enhancing the catalyst activity;the denitration rate of Cu_1/6-MOF-5 could reach 95%at 200℃.In the presence of SO₂（800 ppm）,the denitrification rate of Cu_1/6-MOF-5reached 87%at 200℃.