Supplementary materials A the rate equation development from Eley–Rideal model of heterogeneous catalytic carbamate formation based on CO<sub>2</sub>–MEA absorptions with CaCO<sub>3</sub>, MgCO<sub>3</sub> and BaCO<sub>3</sub>

The mechanism was proposed of heterogeneous catalytic CO<sub>2</sub> absorptions with primary/secondary amines involving ‘catalytic carbamate formation’. Compared with the non-catalytic ‘Zwitterion mechanism’, this Eley–Rideal model was proposed for CO<sub>2</sub> + RR′NH with MCO<sub>3</sub> (M = Ca, Mg, and Ba) with four elementary reaction steps: (B1) amine adsorption, (B2) Zwitterion formation, (B3) carbamate formation, and (B4) carbamate desorption. The rate law if determining step of each elementary step was generated based on ‘steady-state approximation’. Furthermore, the solid chemicals were characterized by SEM and BET, and this rate model was verified with 39 sets of experimental datasets of catalytic CO<sub>2</sub>–MEA absorptions with the existence of 0–25 g CaCO<sub>3</sub>, MgCO<sub>3</sub> and BaCO<sub>3</sub>. The results indicated that the rate-determining step was B1 as amine adsorption onto solid surface, which was pseudo-1st-order for MEA. This was the first time that the Eley–Rideal model had been adopted onto the reactions of CO<sub>2</sub> + primary/secondary amines over alkaline earth metal carbonate (MCO<sub>3</sub>).