Hydrogen adsorption on Co2+ - and Ni2+- exchanged -US-Y and -ZSM-5. A combined sorption, DR UV–Vis, synchrotron XRD and DFT study

Abstract

Hydrogen adsorption on Co2+ and Ni2+ exchanged Ultrastable-Y (US–Y) and ZSM-5 are investigated experimentally at 298 K and up to 50 bar as well as theoretically. The experimentally calculated initial isosteric heat of H2 adsorption values are between −28 and −32 kJ/mol for Ni2+-ZSM-5, -16 kJ/mol for Co2+-ZSM-5, -23 kJ/mol for Ni2+-US-Y and −18 kJ/mol for Co2+-US-Y. Due to the optimum heat of adsorption values observed on Co2+ and Ni2+ exchanged US-Y and ZSM-5, a reversible volumetric H2 storage capacity of 20 g H2/L is achieved on Ni2+-ZSM-5 at 298 K and 50 bar. The site information of Co2+ and Ni2+ cations are investigated using diffuse reflectance (DR) UV–Vis spectra, synchrotron powder X-ray Diffraction (XRD) as well as theoretical calculations using both periodic and cluster density functional theory (DFT) models for ZSM-5. Majority of Co2+ and Ni2+ cations are found at β and γ-sites in ZSM-5 and at Site III in US-Y.