Unexpected highly reversible topotactic CO2 sorption/desorption capacity for potassium dititanate

Potassium dititanate (K2Ti2O5) was revealed to possess an unexpected highly reversible CO2 sorption/desorption capacity at ca. 750 oC, which is promising as high–temperature CO2 adsorbent for sorption enhanced hydrogen production (SEHP) processes. In contrast to many other adsorbents which sinter severely during cycles at high–temperatures, the CO2 sorption/desorption cycles over K2Ti2O5 exhibited a contrast particle size “break–down” process. The large K2Ti2O5 particles gradually break–down into K2Ti2O5 nanofibers after 20 cycles, leading to a very stable CO2 sorption/desorption performance with very rapid kinetics. A reversible CO2 capture capacity as high as 7.2 wt% was achieved at 750 oC. What’s more, only 6 min is required for complete CO2 desorption at 750 oC, indicating this adsorbent can be practically run with a simply pressure swing sorption scheme. Surprisingly, an interesting structure switching phenomenon between K2Ti2O5 and K2Ti4O9 caused by CO2 sorption and desorption was revealed. A detailed mechanism was proposed based on XRD, FTIR, SEM, HR-TEM, and SAED analyses, and was further verified by density functional theory calculation. Considering its relatively high CO2 capture capacity, superior cycling stability, and excellent regeneration ability, we believe K2Ti2O5 offers significant potential as a practical novel high–temperature CO2 adsorbent