Hydrogen Adsorption on Zeolite Na-MAZ and Li-MAZ Clusters

Abstract

Hydrogen adsorption on zeolite Na-MAZ and Li-MAZ clusters was investigated using density functional theory (DFT) with the generalized gradient approximation (GGA) of the Perdew-Burke- Ernzerhof (PBE) exchange-correction functional and the double numerical plus polarization (DNP) basis set. Equilibrium structural parameters, vibration frequencies, and adsorption energies were obtained and compared. The calculated results show that four stable adsorption sites are present on zeolite MAZ. They are designated SIʹ, SIʺ, SIIʹ, and SIIʺ, respectively. The most stable adsorption structure was hydrogen on the SIIʺ site of zeolite Na-MAZ and the hydrogen on the SIʺ and SIIʺ sites of zeolite Li-MAZ were the most stable. We also found that larger adsorption energies indicate longer H―H bond distances and a lower vibration frequency shift. The adsorption ability of zeolite Li-MAZ toward hydrogen is stronger than that of zeolite Na-MAZ. Zeolite Li-MAZ has a higher theoretical hydrogen storage capacity and it may be a potential hydrogen storage material.