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Insights into the enhancement of CO2 adsorption on faujasite with a low Si/Al ratio: Understanding the formation sequence of adsorption complexes
Chemical Engineering Journal ( IF 15.1 ) Pub Date : 2020-09-19 , DOI: 10.1016/j.cej.2020.127056
Kaizhong Yang , Guang Yang , Jingyi Wu

Faujasites (FAUs) with low Si/Al ratios (SARs) show high CO2 adsorption capacities, making them popular adsorbents for CO2 capture. The present study aims to investigate the enhancement mechanisms from the aspect of the formation characteristics of CO2 adsorption complexes. First, we test the CO2 adsorption capacities of two FAU samples (SAR = 1.18 or 1.01). The intensity of the adsorption enhancement for the low-SAR FAU is found to increase, and then decrease, with the growth of CO2 coverage. Subsequently, we perform Monte Carlo simulations with a force field validated by adsorption experiments and molecular structures determined by X-ray diffraction. Various adsorption complexes are validated by the energy distributions and the lowest-energy configurations of the simulations. Five types of CO2 adsorption complexes are classified according to the interacting cations. We study their formation sequences and find that dual-site complexes, preferentially interacted with two Na+ cations in SIII sites (NaIII···CO2···NaIII), are formed earlier than single-site complexes. Multiple CO2 molecules (up to six) may share one single cation at high coverage. Energies calculated for complex NaIII···CO2···NaIII, NaIII···CO2···NaII, and NaII···CO2 are -55.5, -42.7, and -37.8 kJ/mol, respectively. We attribute the adsorption enhancement to a large number of high-energy complexes in the low-SAR FAU. The max numbers of NaIII···CO2···NaIII and NaIII···CO2···NaII are 31 and 46, respectively, for the low-SAR FAU. (16 and 33, for the other FAU). The experimental trend of adsorption enhancement is well explained by the average energies of complexes at different levels of CO2 coverages, in two FAUs.



中文翻译:

低硅铝比提高八面沸石对CO 2吸附的见解:了解吸附复合物的形成顺序

低硅铝比(SAR)的八面沸石(FAU)显示出高的CO 2吸附能力,使其成为捕获CO 2的流行吸附剂。本研究旨在从CO 2吸附复合物的形成特性方面研究增强机理。首先,我们测试了两个FAU样品(SAR = 1.18或1.01)的CO 2吸附能力。发现低SAR FAU的吸附增强强度随CO 2的增加而增加,然后降低覆盖范围。随后,我们使用通过吸附实验和X射线衍射确定的分子结构验证的力场进行蒙特卡洛模拟。通过模拟的能量分布和最低能量配置验证了各种吸附复合物。根据相互作用的阳离子分为五种类型的CO 2吸附复合物。我们研究了它们的形成顺序,发现与SIII位点(Na III ···CO 2 ···Na III)中优先与两个Na +阳离子相互作用的双位点配合物比单位点配合物形成得早。多个CO 2一个分子(最多六个)可以共享一个高覆盖率的阳离子。复杂的Na III ···CO 2 ··Na III,Na III ···CO 2 ·· Na II和Na II ···CO 2的能量计算为-55.5,-42.7和-37.8 kJ /摩尔。我们将吸附增强归因于低SAR FAU中的大量高能配合物。Na III ···CO 2 ···Na III和Na III ···CO 2 ···Na II的最大数目低SAR FAU分别为31和46。(其他FAU为16和33)。在两个FAU中,不同CO 2覆盖水平下复合物的平均能量很好地解释了吸附增强的实验趋势。

更新日期:2020-09-20
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