Ce-Li-LSX制氧分子筛增强吸附机理的DFT研究

Density functional theory study on enhanced adsorption mechanism of Ce-Li-LSX zeolite

基于密度泛函理论(DFT),对N_(2)和O_(2)在构建的Ce-Li-LSX和Li-LSX2种分子筛模型上的吸附行为进行研究。研究结果表明:用Ce^(3+)替换Li-LSX分子筛SI’位置的Li^(+)后,N_(2)和O_(2)在Ce-Li-LSX上的吸附能较在Li-LSX上的吸附能分别提高了40.8%和12.8%,且Li^(+)有向超笼中心移动趋势。通过吸附剂-吸附质模型的电子性质研究发现,由于SI’位置Ce^(3+)的加入,Ce^(3+)与相邻沸石框架上氧原子之间形成配位键,改变了沸石框架原子中的电荷分布,原子间电荷通过Ce^(3+)-O_(40)-Al_(11)-(O_(39)和O_(41))和Ce^(3+)-O_(40)-Si_(11)-(O_(18)和O_(37))影响路径传递至超笼中Li^(+)周围的沸石框架氧原子,使得沸石框架氧原子对Li^(+)屏蔽作用减弱。在2种作用的耦合条件下,Ce-Li-LSX对N_(2)和O_(2)具有增强吸附效果。

The adsorption behavior of N_(2) and O_(2) on Ce-Li-LSX and Li-LSX zeolite models was studied by density functional theory(DFT).The results show that after Ce^(3+) is used to replace Li^(+) at SI’ position of Li-LSX zeolite,the adsorption capacity of N_(2) and O_(2) on Ce-Li-LSX are 40.8% and 12.8% higher than that on Li-LSX respectively,and Li^(+) tends to move towards the center of the supercage.By studying the electronic properties of the adsorbentadsorbent model,due to the addition of SI’ position Ce^(3+),Ce^(3+) changes the charge distribution in zeolite frame atoms by forming covalent bonds with oxygen atoms on the adjacent zeolite frame.Interatomic charge is transferred to zeolite frame oxygen atoms around Li^(+) in the supercage through the influence path of Ce^(3+) -O_(40-)Al_(11)-(O_(39) and O_(41))and Ce^(3+) -O_(40)-Si_(11)-(O_(18) and O_(37)),and the shielding effect of the oxygen atoms on the zeolite frame on the adsorption of Li^(+) in the zeolite supercage is weakened.Under the coupling conditions of the two effects,Ce-LiLSX has enhanced the adsorption effect of N_(2) and O_(2).