Tailoring hierarchically structured SiO2 spheres for high pressure CO2 adsorption

Abstract

The synthesis, characterization, and experimental validation of hierarchically structured, millimeter-sized SiO₂ spheres with high CO₂ uptake capacities have been systematically explored. The solvents employed during synthesis (aniline, benzyl alcohol and butanol) of the silica structures from alkoxisilanes strongly influence the physicochemical properties by controlling hydrolysis and condensation rates. The new sorbents possess specific surface areas up to 660 m² g⁻¹ and a hierarchically ordered mesoporous/macroporous pore structure. The SiO₂ spheres showed lower heat of adsorption of CO₂ (8–17 kJ mol⁻¹) compared to the benchmark zeolite 13X, facilitating the desorption of CO₂ in temperature swing adsorption applications. Moreover, the CO₂ adsorption isotherms of SiO₂ spheres are less steep compared to those of zeolite 13X resulting in an increased CO₂ uptake capacity in pressure swing adsorption processes. Addition of Zr⁴⁺ cations to SiO₂ increases the CO₂ uptake by generating Lewis acid–base sites. Because the presence of Zr⁴⁺ in the structure also dramatically enhances the abrasion resistance of the sorbents, additional coagulation steps, required for the benchmark sorbents, are not necessary.