Unveiling the temperature-dependent reaction dynamics of Li3BO3: Formation and carbonation mechanisms via in situ synchrotron XRD

Tri-lithium borate (Li 3 BO 3 ) has emerged as a promising CO 2 sorbent for intermediate-high temperature applications, particularly in post-combustion carbon capture processes. Its high CO 2 uptake capacity, along with improved kinetic performance when modified with additives, makes it a compelling alternative to conventional lithium-based sorbents. Upon carbonation, Li 3 BO 3 reacts to form lithium carbonate (Li 2 CO 3 ) and lithium borates, such as Li 6 B 4 O 9 and LiBO 2 , with reaction kinetics strongly dependent on CO 2 partial pressure and temperature. However, the fundamental high-temperature reaction dynamics governing Li 3 BO 3 formation and carbonation remain largely unexplored. This study employs time-resolved in situ synchrotron X-ray diffraction (XRD) to unveil the phase transformations and reaction pathway occurring during Li 3 BO 3 synthesis and its reaction with CO 2 . Structural evolution during the heating of a mechanically milled H 3 BO 3 -Li 2 CO 3 mixture from room temperature to 600 °C reveals a successful transformation to Li 3 BO 3 via a multi-step mechanism. In situ high-temperature synchrotron XRD measurements coupled with Rietveld refinement demonstrate that the carbonation mechanism of Li 3 BO 3 is significantly influenced by CO 2 partial pressure. Under 10% of CO 2 , Li 6 B 4 O 9 and Li 2 CO 3 are identified from 400 °C, followed by the formation of Li (2+x) C (1 − x ) B x O 3 solid solution between 530 °C and 580 °C. In contrast, under pure CO 2 , Li 6 B 4 O 9 forms at 350 °C, with LiBO 2 appearing at higher temperatures. Notably, the temperature range of Li (2+x) C (1 − x ) B x O 3 stabilization shifts toward higher temperatures under pure CO 2 conditions. Understanding these transformations is essential for optimizing the performance and stability of Li 3 BO 3 in CO 2 capture applications and serves as a basis for future additive optimization, contributing to the broader development of high-temperature sorbent materials.