Probing the Adsorption/Desorption of CO<sub>2</sub> on Amine Sorbents by Transient Infrared Studies of Adsorbed CO<sub>2</sub> and C<sub>6</sub>H<sub>6</sub>

CO<sub>2</sub> diffusion limitations and readsorption of desorbed CO<sub>2</sub> during removal from immobilized amine sorbents could significantly reduce the effectiveness of CO<sub>2</sub> capture processes. To decouple CO<sub>2</sub> diffusion from desorption/readsorption on silica and tetraethylenepentamine (TEPA)/silica sorbents, a new transient diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) method was carried out by using benzene as a surrogate probe molecule. Comparison of the infrared intensity profiles of adsorbed CO<sub>2</sub> and Si–OH (which adsorbs benzene) revealed that slow rates of CO<sub>2</sub> uptake and desorption are a result of (i) CO<sub>2</sub> diffusion through an interconnected network produced from CO<sub>2</sub> adsorbed inside of the amine/silica sorbent pores and (ii) readsorption of CO<sub>2</sub> on the amine sites inside of the pores and at the external surface of the sorbents. High rates of CO<sub>2</sub> adsorption/desorption onto/from the immobilized amine sorbents could be achieved by sorbents with low amine density at the external surfaces and pore mouths.