A Critical Revisit of Zeolites for CO2 Desorption in Primary Amine Solution Argues Its Genuine Catalytic Function

Zeolites are the most widely reported solid materials that are used in primary amine-containing postcombustion CO2 capture processes for quicker solvent regeneration at a lower energy consumption. Catalytic solvolysis of the carbamate intermediate, assisted by the Brönsted acid sites (BAS), is commonly accepted as an explanation. However, there is little, if any, attention given to the regeneration of BAS in such basic amine-rich solution. Herein, we revisit the role of zeolite for CO2 desorption in primary amine solution at room to moderately elevated temperature ranges. We noticed indeed an accelerating effect on the CO2 desorption rate in the presence of BAS. Both their numbers as well as their accessibility for the amine-CO2 adduct (i.e., carbamate) (direct) or amine (indirect pathway) are important. However, we also noticed, using spectroscopic techniques and by zeolite reuse, a very strong chemical interaction between BAS and the regenerated amine. This suggests that BAS recovery to close the catalytic cycle is difficult and that zeolites can hardly be considered as genuine catalysts, but rather, this study concludes a merely stoichiometric effect of the zeolites for the overall desorption process, and this is in contrast to reference oxides such as TiO­(OH)2.