Enhancement of carbon dioxide adsorption performance on mesoporous alumina modified with alkaline earth metals

The mesoporous alumina-supported alkaline earth metal 5 M/MA (MA= mesoporous alumina, M=Mg, Ca, Sr, and Ba) and xMg/MA (x=1, 3, 5, and 7 wt%) adsorbents were synthesized via evaporation-induced self-assembly (EISA) and impregnation method. The adsorption properties of CO2 were evaluated by thermal gravimetric analyzer to focus on exploring the dynamic adsorption process of the prepared adsorbents. Loading alkaline earth metals mainly enhanced the basic sites of these adsorbents, and the alkaline sites played an extremely critical role in determining the amount of CO2 adsorbed. Of all the adsorbents prepared, 5Mg/MA exhibited the highest adsorption uptake (1.08 mmol/g), a 2.16-fold enhancement compared to MA (0.50 mmol/g). In-situ DRIFTS indicated that CO2 primarily existed in the form of carbonate species, and the analysis of adsorption kinetics elucidated that the adsorption process was predominantly chemisorbed, with external diffusion being the main process of adsorption. Simultaneously, based on DFT calculations, it has been found that Mg-loaded MA has a higher affinity for CO2 compared to MA, which providing a good explanation for the experimental results. Furthermore, the 5 Mg/MA adsorbent not only exhibited excellent adsorption capacity, but also maintained excellent cyclic stability after 10 adsorption and desorption cycle runs, making it a highly favorable option for capturing CO2. [Display omitted] •The addition of alkaline earth metals primarily increased basic sites.•In-situ DRIFTS revealed that CO2 was primarily present as carbonate species.•5Mg/MA exhibited excellent adsorption performance and recycling stability.•Adsorption kinetics analysis manifested 5Mg/MA was predominantly chemisorbed.•DFT validated Mg/MA has a higher affinity for CO2 compared to MA.