A study of metals promoted CaO-based CO2 sorbents for high temperature application by combining experimental and DFT calculations

The CaO-based sorbents are promising candidates for CO2 capture through calcium looping for high temperature applications, but have a problem of rapid deactivation over multiple carbonation/calcination cycles. Synthesizing metals promoted CaO-based sorbents is regarded as one of the most efficient method to overcome loss-incapacity problem. A clear understanding of underlying mechanisms, through which the metal-promoters influence initial sorbent properties and/or rejuvenate deactivated sorbents, can help rationalize the design. In this study, a comprehensive study on metals promoted sorbents was performed by combining experimental and DFT calculations. First, the sorption capacity and stability of various promoted sorbents prepared by a sol-gel auto-combustion route was investigated in fixed bed reactor. Except Na, sorbents promoted with Al, Mg, and Zr exhibit outstanding performance during long-term cycles. Next, by DFT calculations we explore the effect of metal-promoters on the chemical reactivity and resisting sintering of sorbents. Results showed that Al and Mg could slightly weaken the adsorption energy, but Zr and Na could enhance obviously the adsorption energy, especially for Zr, the adsorption energy as strong as 2.38 eV. The more adsorption energy is more favorable for the enhancement of carbonate extent. In addition, the strong bonding interaction between O atom from Ca4O4 and Al, Zr and Mg sites of promoted surface was observed, which inhibited the migration and growth of CaO nanoclusters.