(395ak) Gas Adsorption Simulation in Porous Material Made up with Silsesquioxane Units and Metal Catalytic Sites

Porous structures made up with spherosilicate building blocks and consist of metal catalytic sites exhibit favorable properties for the ability of adsorption of gases.  Inspired by the experimental work, we modeled these amorphous structures and performed adsorption simulations for hydrogen, carbon dioxide and methane. This porous material has cubic silicate building blocks (silsesquioxane units: Si₈O₂₀), which are cross-linked by SiCl₂O_2, SiClO₃ and SiO₄ bridges and decorated with OTiCl₃ catalytic sites and SiMe₃ ends.

The structures 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 gases was simulated by Grand Canonical Monte Carlo (GCMC) method. For CO₂ and methane United atom model and TraPPE fore fields were used to model the adsorbate molecules. For adsorption of hydrogen, UFF force fields were used and Feynman-Hibbs effective potential (FH) method was used to account for the quantum effects. Adsorption isotherms at 300K and 77 K were generated for a pressures range up to 100 bars. Energy of adsorption was calculated at each case. Analyzing the pair correlation functions was useful in identifying gas adsorption sites.