Synthesis Of Bimetallic MOF-74 And Its Catalytic Performance For Co Reduction Of NO

Nitrogen oxide（NO_x）and carbon monoxide（CO）are among the most harmful air pollutants,have caused great harm to the eco-environment and human health.The selective catalytic reduction of NO_x by carbon monoxide（CO-SCR）has proven to be a cost-effective and environmentally friendly technique which can eliminate NO_x and CO simultaneously,and transform them into harmless CO₂ and N₂.However,its denitration efficiency cannot meet the actual industrial application demands.Though the platinum group metals（PGMs）have been considered as one of the efficient catalysts for NO reduction with CO,the disadvantages of high expense,low capacity and low-temperature inactivity still limit their widely practical application.Metal-organic frameworks（MOFs）as a novel functional material has been widely used in SCR reaction due to its large specific surface area,abundant metal active sites and controllable pore structure,and has achieved satisfactory denitration efficiency.Among them,MOF-74 has a unique infinite grid structure which can stably contain different metal ions,and has a strong fault-tolerance property for mixing other metals in the same lattice system,which not only provides more active components,but also enhances the synergy between different metals.Therefore,developing superior bimetallic MOFs SCR catalyst at low-temperature（below250°C）is of great interesting.In this paper,bimetallic NiMn-MOF-74 and Ag-Ni-MOF-74catalysts were prepared by adjusting the ratio of mixed metals Ni/Mn and Ni/Ag.The synergy effect of different metal ratios on the structure and SCR performance of the catalysts were investigated,and the physical and chemical properties and reaction mechanism of the catalysts were explored by a series of characterization methods.The main research results are as follows:（1）Bimetallic Ni_1-x-x Mn_x-MOF-74 micro-flower catalyst were fabricated using a one-step hydrothermal method.Compared with the monometallic Ni-MOF-74 catalyst,the addition of Mn increased the specific surface area of the catalyst and produced a large number of active sites,induced more Lewis acid sites and increased the ratio of active Mn⁴⁺and surface adsorbed oxygen.Ni_0.65Mn_0.35-MOF-74 exhibited an excellent low temperature activity,which achieved a maximum NO conversion of 100%in the temperature range of 175-300℃with a nearly 100%N₂ selectivity at 200°C.And it has good thermal stability,resistance to SO₂ and H₂O at 225℃,which could be stable at 80%NO removal rate for a long time.In situ FT-IR was used to investigate the adsorption and transformation process of various species on the surface of Ni_0.65Mn_0.35-MOF-74 catalyst.It was proposed that the mechanism of CO-SCR reaction over NiMn-MOF-74 following L-H mechanism.（2）The high-dispersion bimetallic Ag_x-Ni-MOF-74 micron-needle structure catalyst was prepared by a post-synthesis modification method.Compared with the bimetallic NiMn-MOF-74 catalyst,the low-temperature CO-SCR catalytic activity of the Ag_x-Ni-MOF-74 catalyst was further enhanced.The NO conversion of Ag₁-Ni-MOF-74 was over 50%at 80℃,and reached100%at 200℃.The introduction of Ag not only increases the surface adsorption oxygen and oxygen vacancy,but also increases the specific surface area of the catalyst,improving the adsorption and activation of NO and CO,and thus enhancing the low-temperature CO-SCR activity.