Synthesis of ordered Ca- and Li-doped mesoporous silicas for H2 and CO2 adsorption at ambient temperature and pressure

Abstract

Ca- and Li-doped mesoporous silicas have been prepared successfully using cetyltrimethylammonium bromide (CTAB) surfactant in basic media. Sol-gel synthesis and hydrothermal treatment produced highly ordered mesoporous Ca and Li loaded silica particles. The MCM-41 type mesostructures, the porosity, the pore sizes as well as the surface area of Ca- and Li-silicas have been thoroughly investigated using small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N2 sorption analysis. Samples prepared with varying amounts of Li and Ca loading have been further analyzed using inductive coupled plasma-atomic emission spectroscopy (ICP-AES) and field-emission scanning electron microscopy (FESEM) with an energy dispersive spectral attachment (EDS), which confirmed quite a large amount of Ca while the amount of Li was not enough. Additionally, H2 and CO2 gas uptake studies of these metal-loaded silicas have been carried out using a thermogravimetric analyzer (TGA) at normal temperature (25 °C) and pressure (1 atm). H2 uptake of up to 10 mmol g-1 by Ca-doped silica was recorded. CO2 and H2 selectivity were tested with both pure metal-MCM-41 and amine loaded silica using pure N2 gas and a mixed flow of CO2/N2 and H2/N2. The effect of temperature on CO2 uptake was also studied using Ca-MCM-41 materials.