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

Abstract

This study investigates the H-2 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. H-2 adsorption was investigated for all the Cu+, Ni2+ and Co2+ centers. AEI and CHA resulted in similar H-2-Cu interactions for the Al and B substituted structures. H-2 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 H-2 antibonding orbital (sigma(H2)*). The H-2 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 H-2 adsorption close to optimum values required for H-2 storage on porous materials.