A Theoretical Investigation of Cu⁺ , Ni²⁺ and Co²⁺ -Exchanged Zeolites for Hydrogen Storage

This study investigates the H₂ adsorption on Cu⁺ , Ni²⁺ and Co²⁺ -exchanged SSZ-13 (CHA) and SSZ-39 (AEI) using periodic DFT computations. The most stable Cu⁺ position was found to be the 6-membered-ring window for both zeolites. Similarly, for the investigated Ni²⁺ and Co²⁺ loadings on 6-membered-ring windows, the third nearest neighbor Al positions, i. e., Al-O-Si-O-Si-O-Al coordination, was found to be the most stable position. H₂ adsorption was investigated for all the Cu⁺ , Ni²⁺ and Co²⁺ centers. AEI and CHA resulted in similar H₂ -Cu interactions for the Al and B substituted structures. H₂ adsorption on Cu⁺ located in the 8-membered-ring gave the highest adsorption energy for both frameworks. Replacing Al with B in the framework increased the electron back donation from Cu⁺ (3d) orbitals to H₂ antibonding orbital (σ_H2 ^* ). The H₂ adsorption energies on the Ni²⁺ and Co²⁺ -exchanged zeolites were found to be between -15 and -44 kJ/mol. Higher energy values were observed on the AEI framework, especially when two Al atoms have the Al-O-Si-O-Al configuration. Lesser interaction of the d-orbitals in the case of the Co²⁺ and Ni²⁺ cations resulted in heat of H₂ adsorption close to optimum values required for H₂ storage on porous materials.