In-situ investigation of microstructural evolution of γ-AlOOH to Al2O3 using electron atomic pair distribution function (ePDF)

• The transition from γ-AlOOH to alumina were examined in-situ and ex-situ. • The changes in Al 3+ coordination during the phase transitions from γ-AlOOH to alumina were investigated by selected area electron diffraction (SAED), electron atomic pair distribution function (ePDF) analysis and electron energy loss spectroscopy (EELS). • The calcination conditions markedly influence the kinetics of the phase transitions from γ-AlOOH to alumina rather than the thermodynamics. Alumina (Al 2 O 3 ) is renowned for its excellent catalytic and electrochemical properties, but its structural complexity and microstructure variability are crucial to its performance. Understanding the interatomic distances and coordination states in alumina remains a significant challenge in synthesizing high-performance alumina catalysts. This study employs a series of ex-situ and in-situ characterization methods to investigate the changes in Al 3+ coordination and the distances between Al-O and Al-Al atomic pairs during the phase transitions from γ-AlOOH to alumina. The experiments employed electron energy loss spectroscopy , selected area electron diffraction based pair distribution function for qualitative and quantitative analysis. The results show that as the temperature increases, the transition from γ-AlOOH to γ-Al 2 O 3 and δ-Al 2 O 3 leads to an increase in tetrahedrally coordinated Al 3+ concentration, but the differences in the calcination conditions markedly influence kinetics of the phase transition. Despite the occurrence of a phase transition, a substantial boehmite-like component persists within the aluminas, gradually diminishing at elevated temperatures. These findings significantly advance our comprehension of alumina as a catalyst support, facilitating the advancement of precise synthesis and catalyst preparation techniques, which are pivotal for its functional applications.