Catalytic CO2 Desorption from MEA Solution of Al-FeOOH Composite Catalysts’ Desorption Performance, Structure–Activity Relationship, and New Mechanism

In order to reduce the massive heat duty of amine-based CO2 capture technology, an AlOOH/FeOOH composite catalyst (AF-M/N) was synthesized to speed up the CO2 desorption rates and reduce the heat duty of an aqueous MEA solution. The catalysis of AF-M/M from 1/9 to 9/1 was investigated comprehensively, with characterization of the catalytic desorption with heat duty and desorption factors. Results indicated the special composite catalyst (AF-1/9) possessed optimized catalysis with a relative heat duty of 78.7% and a desorption factor of 0.0037 × 10−3 (mol CO2/L2 kJ min) and relative desorption factor of 194.7%. The structure–activity correlations indicated that the mesopore surface area (MSA), which reached 329 m2/g, and Brϕnsted/Lewis acid ratio (B/L ratio) of 0.11 were the most important factors for enhancing catalysis. Furthermore, molecular simulations were conducted for the catalytic carbamate breakdown mechanism, focusing on the “isomerization” of “carbamate acid” vs. “Zwitterion” as the key step. From the DFT study, the isomerization was most likely to proceed with H2O as catalyst via intermolecular proton transfer instead of intramolecular proton transfer, with an activation energy Ea of 85.9 kJ/mol. With the aid of AlOOH the isomerization was further facilitated due to stabilized Zwitterion, and the Ea decreased to 69.2 kJ/mol. The results not only synthesized a new heterogeneous catalyst but also revealed the map of “isomerization” on a molecular level. Such a discovery indicates that water-assisted proton transfer is advantageous for catalytic carbamate breakdown.