Density Functional Theory Study Of Sufur,Nitrate And Carbon Adsorption On Mg-MOF-74

Coal is the main component of my country’s energy structure,and its direct combustion will produce a large amount of SO₂,NO,CO₂,and CO,which seriously threatens the ecological environment and human health.As a general method for treating the above gases,adsorption method has been widely concerned because of its wide application conditions,low energy consumption and simple operation.Mg-MOF-74 can effectively adsorb gas molecules due to its abundant metal sites,high specific surface area and other significant advantages,and has good application prospects and competitive advantages.However,this material has not been applied on a large scale,and it is difficult to accurately probe the adsorption mechanism and properties experimentally.In this paper,on the one hand,Mg-MOF-74 was synthesized,and its adsorption and co-adsorption performance for SO₂,NO,and CO were tested by fixed-bed adsorption experiments.On the other hand,based on density functional theory（DFT）,by identifying the key adsorption sites and adsorption modes,calculating the charge density and density of states,the single adsorption,co-adsorption of SO₂,NO,CO on Mg-MOF-74,and the effect of CO₂on the adsorption of SO₂,NO and CO has been deeply explored,which can provide a theoretical basis for the adsorption process of SO₂,NO,CO and CO₂.It has important research significance.The main research conclusions are as follows.（1）Experiments showed that the saturated adsorption capacities of adsorbent Mg-MOF-74 for single adsorption of SO₂,NO and CO were 0.233 mmol/g,0.109mmol/g and 0.034 mmol/g,respectively.In the co-adsorption system,the interaction between the gases is different due to the different adsorption sequences.When SO₂and NO are adsorbed at the same time,there is a competitive effect,which leads to the decrease of their respective adsorption effects.Pre-adsorbed NO increases the amount of SO₂adsorption through the interaction,pre-adsorbed SO₂weakens the adsorption of NO due to its strong ability to occupy adsorption sites;when SO₂and CO are adsorbed at the same time,the two gases have opposite adsorption effects.Pre-adsorption of SO₂will reduce the saturated adsorption capacity of CO;there is a competitive effect on the simultaneous adsorption of NO and CO.Pre-adsorbed NO has little effect on CO adsorption.There is a competitive adsorption mechanism among SO₂,NO and CO,and their respective saturated adsorption capacity decreases to different degrees during co-adsorption.（2）Based on DFT,the adsorption properties of adsorbent Mg-MOF-74 for adsorbing SO₂,NO,and CO alone were investigated.The results showed that the bare metal sites were the main sites for gas adsorption,and the three gases were adsorbed and activated in the form of terminal sites.The O-terminal adsorption of SO₂is more likely to occur than the S-terminal adsorption.Both the N-terminal and O-terminal adsorption of NO can occur,and the C-terminal and O-terminal adsorption of CO are difficult to occur.The interaction between metal sites and gas leads to the significant weakening of S-O,N-O and C-O bonds,which promotes the splitting of gas molecules.The charge transferred from the adsorbent to the gas molecules is proportional to the elongation of the gas molecular bonds.（3）The adsorption properties of SO₂＆NO,SO₂＆CO,NO＆CO,SO₂＆NO＆CO on the adsorbent Mg-MOF-74 were investigated based on DFT.The results showed that the charge transfer between SO₂and NO increased the stability of the co-adsorption system;CO promoted the pre-adsorbed SO₂Molecular structure changes and electron-gaining ability;CO has weak competitive adsorption ability to pre-adsorbed NO;when SO₂＆NO＆CO are adsorbed at the same time,the adsorption effect of adsorbent on various molecules is weakened.（4）The effect of CO₂on the adsorption of SO₂,NO,and CO was explored based on DFT,and the results showed that:CO₂could not compete with the adsorption sites of pre-adsorbed gases and could not further activate SO₂,but could promote the activation of NO in a small amount and CO at the adjacent metal sites.In the SO₂＆NO＆CO₂co-adsorption system,the adsorption of SO₂is inhibited,NO adsorption was not significantly affected.In the SO₂＆NO＆CO＆CO₂co-adsorption system,the adsorption effect of SO₂was weakened,NO and CO were further activated.