The kinetics of adsorption of CO2 on solid sorbents based on polyethyleneimine/mesoporous silica (PEI/MPS) was studied by following the mass gain during CO2 flow. Linear (PEI-423) and branched (PEI-10k) polymers were studied. The solid sorbents were synthesized by impregnating the PEI into MPS foam. The kinetics of adsorption was fitted with a double-exponential model. In contrast, the desorption process obeyed first-order kinetics. The activation energy of desorption of PEI-423 was lower than that of PEI-10k, presumably because the branched polymer required more energy to expose its nitrogen to CO2. To increase the CO2 sorption capacity, the MPS was treated with nonionic surfactant materials prior to impregnation with PEI. This also lowered the maximum sorption temperature and desorption activation energies.