Amine-based CO₂ capture sorbents: A potential CO₂ hydrogenation catalyst

Mechanism of CO₂ adsorption on amine loaded SBA-15 sorbents with varying amine coverage has been assessed using thermogravimetric analysis (TGA) and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). TGA study showed that sorbent adsorption capacities increased by 122-153% with CO₂ concentrations (5-80%) in the gas at 50/75°C. The DRIFTS studies indicate that low amine loaded sorbents exhibit higher uptakes with an increase in CO₂ concentrations which is attributed to the mode of CO₂ adsorption i.e. 1:1 CO₂ to amine forming carbamic acid. At higher amine loadings CO₂ is adsorbed following the 1:2 CO₂ to amine forming carbamate-ammonium ions pair resulting in lower adsorption capacities per amine site. The studies also showed an increase in carbamic acid formation with pressure from 100 to 500kPa at low amine loadings and both carbamic acid and carbamates at higher amine loadings. The paper provides insights into the mechanistic understanding of CO₂ adsorption behaviour of the varyingly covered amines on the SBA-15 support with a change in concentration and pressure of CO₂. The current work presents the conditions to alter the CO₂ adsorption mechanism on amine sites with potential application in CO₂ conversion to chemicals.