(456c) Molecular Simulation of Hydrogen Adsorption In Porous Material Made up with Silsesquioxane Units and Metal Catalytic Sites

The adsorptive hydrogen storage of molecular hydrogen on microporous materials is widely studied as an effort for efficient utilization of hydrogen as a pollution free renewable energy source. Porous structures made up with spherosilicate building blocks and consist of metal catalytic sites exhibit promising results for the ability of adsorption of gases.  Experiments are carried out for investigating the hydrogen adsorption ability of these materials. In this study we performed computer simulations to analyze hydrogen adsorption in structures which consist of interconnected silsesquioxane units. This porous material has cubic silicate building blocks (Si₈O₂₀), which are cross-linked by SiCl₂O₂ bridges and decorated with OTiCl₃ catalytic sites and SiMe₃ ends.

The structure for the simulations was developed first using a coarse grain model, followed by an energy optimization and replacing the coarse grains with atoms. The physical properties of the structure such as density, surface area, accessible volume and pore size distribution were compared with experimental vales and they are in good agreement.

Adsorption of hydrogen was modeled by Path Integral Grand Canonical Monte Carlo (PI-GCMC) simulations using standard force fields. From the simulations, hydrogen adsorption isotherms at 300K and 77 K were generated for low pressures up to 10 bars. The energy of adsorption of hydrogen was calculated at each case. Density distribution was developed and analyzed. Classical MD simulations were performed to calculate the self-diffusivity of hydrogen in the porous structure and activation energy was calculated.

Keywords: spherosilicate building blocks, hydrogen adsorption, PI-GCMC simulation, silsesquioxane units, coarse grain model, energy optimization, adsorption isotherm, density distribution, MD simulations, self-diffusivity, activation energy