High-efficiency and cost-effective adsorbents are crucial to dry capture of carbon dioxide (CO2). The polyethyleneimine (PEI) was co-impregnated with tetraethylenepentamine (TEPA) on γ-alumina (Al2O3) to synthesize the adsorbent and enhance the capture process. The influence of amine loading and operating parameters on CO2 adsorption was investigated, and the process parameters were modeled. The results depict that the optimal loading is 50 % when functionalized either PEI or TEPA individually, which is 3.7 and 4.6 times higher than γ–Al2O3. The CO2 capacity of γ–Al2O3 functionalized with multiple amines (30 %PEI+20 %TEPA) is 2.65 mmol/g, due to the synergies of the two amines to increase the chance of CO2 binding to the sites. Regeneration performance illustrates that the adsorbent remains at 90.2 % of the initial capacity after seven tests. The maximal capacity of 2.70 mmol/g occurs at 70 °C. Modeling results indicate the kinetics can be evaluated by the Avrami model (R2 > 0.990) with the activation energy of 5.65 kJ/mol. The process is controlled by physical–chemical adsorption, influenced by intraparticle diffusion, as described by the deactivation model. Finally, a comparison and assessment were conducted for their techno-economic performances, and the pathway to applications was also proposed in engineering practice.