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 degrees C, which is promising as a high-temperature CO2 adsorbent for sorption enhanced hydrogen production (SEHP) processes. In contrast to numerous other adsorbents that are severely sintered 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 breakdown 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 degrees C. Moreover, only 6 min is required for complete CO2 desorption at 750 degrees C, indicating that this adsorbent can be practically run with a simple 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.