Research Information System
Microporous and Mesoporous Materials, vol.391, 2025 (SCI-Expanded, Scopus)
The role of Al-Si spinel crystallization during high-temperature calcination of kaolin and halloysite was investigated to optimize the direct synthesis of zeolites 4A and 13X without additional silica or structure-directing agents. Differential thermogravimetry (DTG) and in situ synchrotron X-ray diffraction (SR-XRD) tracked dehydroxylation and Al-Si spinel crystallization, revealing complete dehydroxylation at 575 °C for kaolin and 500 °C for halloysite, with spinel crystallization occurring in a range of 900–940 °C for both clays. Calcination promoted the formation of Al-Si spinel and amorphous silica, increasing the Si/Al ratio and enabling control of zeolite composition and porosity. Calcination conditions determined the zeolite type, evolving from pure 4A to a mixture of 4A/13X, and finally pure 13X. The presence of Al-Si spinel in 13X enhanced mesoporosity, introducing voids and channels between micropores and contributing to high BET surface areas (>500 m2/g) with a dual micro/mesoporous structure. This study establishes a direct link between calcination parameters and zeolite properties, highlighting Al-Si spinel's role in phase transitions and porosity development. These findings provide valuable insights for optimizing industrial applications such as adsorption and catalysis.