Devasia George, Nandanwar Sachin U, Krishnamurty Sailaja
Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune, 411008, India.
Catalysis and Inorganic Chemistry Division, CSIR-National Chemical Laboratory, Pune, 411 008, India.
Phys Chem Chem Phys. 2025 Apr 9;27(15):7846-7857. doi: 10.1039/d4cp04193c.
Separation of N from a N/O gas mixture is critical for various industrial/medical applications. Temperature/pressure swing adsorption is the top-notch industrial technology used for this separation, where zeolites are the materials used for adsorption. Zeolite X/Y with Li as an extra-framework cation is the best-known sorbent for N gas molecules. However, the present net zero emission scenario has made lithium a critical element, making it imperative to implement its alternative in various other technologies. In this context, the present work is a computational evaluation to identify a cation that can replace Li for preferential adsorption of N over O. The DFT study, based on parameters such as selective adsorption energies of N over O and IR stretching frequencies of the adsorbed N and O molecules, identifies Mg, Ca, Sr, Co and Zn as potential cations. These cations have preferential adsorption for N over O by 10 kJ mol or more. However, BOMD simulations reveal that only Mg, Ca, Co and Zn keep the N molecule bound at 300 K and the O molecule gets desorbed from these frameworks. The desorption temperature of N on Ca and Zn is 350 K and on Mg is 400 K. These observations are corroborated by electronic charges on cations and molecular orbitals. Significantly, Ca is identified to adsorb up to 2 N molecules, making it an ideal candidate for N/O separation in place of Li. To validate this, we have carried out an experimental study that showed a good N adsorption capacity of 2.1 mmol g for Ca.
从氮/氧气体混合物中分离出氮对于各种工业/医疗应用至关重要。变温/变压吸附是用于这种分离的一流工业技术，其中沸石是用于吸附的材料。以锂作为骨架外阳离子的X型/Y型沸石是最著名的氮气分子吸附剂。然而，当前的净零排放情景使锂成为关键元素，因此必须在各种其他技术中采用其替代品。在此背景下，本工作是一项计算评估，旨在确定一种能够替代锂以实现对氮优先于氧进行吸附的阳离子。基于氮相对于氧的选择性吸附能以及吸附的氮和氧分子的红外伸缩频率等参数的密度泛函理论研究，确定镁、钙、锶、钴和锌为潜在阳离子。这些阳离子对氮的优先吸附比对氧的优先吸附高10 kJ/mol或更多。然而，玻恩-奥本海默分子动力学模拟表明，只有镁、钙、钴和锌能在300 K时保持氮分子的吸附，而氧分子则从这些骨架上解吸。氮在钙和锌上的解吸温度为350 K，在镁上为400 K。这些观察结果得到了阳离子上的电荷和分子轨道的证实。值得注意的是，钙被确定最多可吸附2个氮分子，使其成为替代锂进行氮/氧分离的理想候选物。为了验证这一点，我们进行了一项实验研究，结果表明钙的氮吸附容量良好，为2.1 mmol/g。
