密度泛函理论研究Al在丝光沸石骨架中的取代位置和NH<sub>3</sub>的吸附

郭海燕; 任君; 冯刚; 李昌盛; 彭兴; 曹端林

密度泛函理论研究Al在丝光沸石骨架中的取代位置和NH₃的吸附

1.
中北大学化工与环境学院, 山西太原 030051;
2.
上海中石化技术研究所, 上海 201208

基金项目: Supported by the National Science Foundation of China (21371159), the Natural Science Foundation of Shanxi Province (2009011014) and Shenzhen Strategic Emerging Industries Special Fund Program of China (GGJS20120619101655715).

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中图分类号: O643
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出版历程
- 收稿日期: 2013-10-31
- 修回日期: 2014-01-07
- 刊出日期: 2014-05-30

Distribution of Al and adsorption of NH₃ in mordenite：A computational study

1.
College of Chemical Engineering and Environment, North University of China, Taiyuan 030051, China;
2.
Shanghai Research Institute of Petrochemical Technology SINOPEC, Shanghai 201208, China

Funds: Supported by the National Science Foundation of China (21371159), the Natural Science Foundation of Shanxi Province (2009011014) and Shenzhen Strategic Emerging Industries Special Fund Program of China (GGJS20120619101655715).

摘要

摘要: 采用色散校正密度泛函方法（DFT-D2）计算了Al同晶取代进入H-[Al]MOR丝光沸石骨架中可能的位置及其对NH₃分子吸附表征Brönsted酸性。热力学上，Al优先取代位是T2O5位，接着是T4O2、T1O7和T3O1位，能量差仅在0.03~0.07 eV，表明Al可能分布在四种非等价晶体T位。同时，电荷平衡质子的位置影响Al取代位的稳定性，数据表明电荷平衡质子与O5位结合的可能性最大。另外，用DFT和 DFT-D2方法计算了NH₃分子在每一个Al取代的T位的吸附能，通过比较，DFT低估了NH₃吸附能0.41 eV，表明色散校正DFT-D2方法对于NH₃吸附是很有必要的，T2O5位的Brönsted酸性最强。
- 丝光沸石 /
- Al同晶取代 /
- NH₃吸附 /
- DFT-D2
Abstract: Dispersion corrected density functional theory (DFT-D2) were employed to investigate the distribution of Al in the framework of H-[Al]MOR and the strengths of Brönsted acid sites by NH₃ adsorption. Thermodynamically, the most favorable site for distribution of Al is T2O5, followed by T4O2, T1O7 and T3O1, which are a little higher in energy when Al is incorporated. It was found that the energy differences for Al in different T sites are 0.03~ 0.07 eV, indicating that the Al atoms might distribute in all kinds of four non-equivalent crystallographic tetrahedral sites of MOR. Moreover, it is also suggested that the location of protons plays an important role in the stability of the Al substitution site. In addition, we also computed the adsorption energies for NH₃ adsorbed at each crystallographic position of H-[Al]MOR by DFT and DFT-D2, respectively. By comparison, the DFT method always underestimates the substitution energy by 0.41 eV for the adsorption of NH₃, indicating that the dispersion correction is necessary to calculate the adsorption of NH₃ in H-[Al]MOR. The results show that the Brönsted acid site at T2O5 is stronger than the other acid sites, and the adsorption of NH₃ on the Lewis acid sites is clearly weaker than on the Brönsted acid sites.
- mordenite /
- Al distribution /
- NH₃ adsorption /
- DFT-D2

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参考文献(34)

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