Li Yingwei, Yang Ralph T
Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
J Phys Chem B. 2006 Aug 31;110(34):17175-81. doi: 10.1021/jp0634508.
Low silica type X zeolites (LSX, Si/Al = 1) fully exchanged by alkali-metal cations (Li(+), Na(+), and K(+)) were studied for their hydrogen storage capacities. Hydrogen adsorption isotherms were measured separately at 77 K and <1 atm, and at 298 K and <10 MPa. It was found that the hydrogen adsorption capacity of LSX zeolite depended strongly on the cationic radius and the density of the cations that are located on the exposed sites. The interaction energies between H(2) and the cations follow the order Li(+) > Na(+) > K(+), as predicted based on the ionic radii. Oxygen anions on zeolite framework were minor adsorption sites. Li-LSX had an H(2) capacity of 1.5 wt % at 77 K and 1 atm, and a capacity of 0.6 wt % at 298 K and 10 MPa, among the highest of known sorbents. The hydrogen capacity in LSX zeolite by bridged hydrogen spillover was also investigated. A simple and effective technique was employed to build carbon bridges between the H(2) dissociation catalyst and the zeolite to facilitate spillover of hydrogen atoms. Thus, the hydrogen storage capacity of Li-LSX zeolite was enhanced to 1.6 wt % (by a factor of 2.6) at 298 K and 10 MPa. This is by far the highest hydrogen storage capacity obtained on a zeolite material at room temperature. Furthermore, the adsorption rates were fast, and the storages were shown to be fully reversible and rechargeable. Further optimization of the bridge building technique would lead to an additional enhancement of hydrogen storage.
研究了用碱金属阳离子（Li⁺、Na⁺和K⁺）完全交换的低硅X型沸石（LSX，Si/Al = 1）的储氢能力。分别在77 K和<1 atm以及298 K和<10 MPa下测量了氢吸附等温线。发现LSX沸石的氢吸附容量强烈依赖于阳离子半径以及位于暴露位点上的阳离子密度。基于离子半径预测，H₂与阳离子之间的相互作用能顺序为Li⁺>Na⁺>K⁺。沸石骨架上的氧阴离子是次要的吸附位点。Li-LSX在77 K和1 atm下的H₂容量为1.5 wt%，在298 K和10 MPa下的容量为0.6 wt%，是已知吸附剂中最高的之一。还研究了通过桥连氢溢流在LSX沸石中的储氢能力。采用了一种简单有效的技术在H₂解离催化剂和沸石之间构建碳桥，以促进氢原子的溢流。因此，Li-LSX沸石在298 K和10 MPa下的储氢容量提高到了1.6 wt%（提高了2.6倍）。这是迄今为止在沸石材料上室温下获得的最高储氢容量。此外，吸附速率很快，并且储氢显示出完全可逆和可再充电。桥连构建技术的进一步优化将导致储氢能力的进一步提高。
