Cu-ZSM-5分子筛吸附NOx的密度泛函理论研究

用密度泛函理论(DFT)方法对Cu+在ZSM—5分子筛孔道内的位置进行了系统地研究,并在此基础上对NOx(NO,N2O,NO2)分子在Cu—ZSM—5不同孔道内的吸附进行了考察。采用包含完整直孔道、正弦孔道以及两孔道交叉处的22T模型,确定了Cu+在ZSM—5分子筛内的三种可能位置:直孔道内、孔道交叉处和正弦孔道内。研究结果表明,Cu+与2—3个骨架氧原子形成配位键负载于ZSM—5分子筛内;三种结构模型中,Cu+在孔道交叉处的构型最稳定。对Cu—ZSM—5吸附NOx的研究表明,NOx与分子筛均可通过形成Cu—N键而发生较强的相互作用,从而不同程度地削弱了NOx分子中的N—O键,使N—O键长增长。在Cu—ZSM—5的三种结构模型上,NO,N2O,NO2分子的吸附情况有所不同,其中NO,NO2在Cu+位于直孔道的模型上的吸附均引起铜向孔道交叉处迁移,形成的吸附复合物与Cu+位于孔道交叉处的吸附复合物几乎收敛于同一构型。表明由于孔道交叉处空间较大,使NO,NO2更容易达到稳定的平衡状态。吸附复合物总能量数据表明进一步的反应很有可能发生在Cu—ZSM—5分子筛的孔道交叉处。

DFT Investigation of NOχ Interaction with Cu+ Ion-exchanged Zeolites

A systematically theoretical research on Cu+—exchanged zeolite catalyst(Cu—ZSM—5) was performed. First of all, a whole geometric configuration includes integrated straight and sinusoidal channel of ZSM—5 model was building. Then a thorough examination was made of the effects of placing Cu + in each of potential cationexchange sites available in the zeolitesan after an Al instead of Si atom at T12 site. Observed result shown that there are three classical Cu exchanged sites in the cluster, which are located at straight and sinusoidal channel and there intersection site, respectively. Then equilibrium geometries was optimized. After that a exhaustive study of NO, NO 2 and N 2O absorption on the optimized Cu—ZSM—5 model was performed through analyzing the equilibrium structure parameters, adsorption energies and Mulliken charge distribution. Obtained result shown that Cu—ZSM—5 has excellent interaction with NO x , all adsorbates N—O bonds are weaken by this activity, and the adsorption energy in all cluster are among (30—60) kcal/mol. All of the theoretical research using Density Functional Theory (DFT) at B3LYP/6—31G level. Then the further Quantum Chemical Study would provide theoretical basis for the guidance of seeking particularly valuable catalyst and optimal catalysis conditions.