From geopolymers to zeolites: Synthesis and characterization of foamed FAU-X monoliths

A FAU-X-rich porous monolith has been obtained by means of an unconventional two-stage method consisting of the production of a foamed geopolymeric precursor and its subsequent conversion by means of a hydrothermal method. The influence of the conversion process parameters, such as NaOH concentration (0.1-2 M), treatment temperature (40-80 degrees C) and time (24-72 h) on the FAU-X crystallization was studied. Collected data revealed that the highest yield in terms of zeolite content and FAU-X/LTA ratio was obtained performing the hydro -thermal treatment with a 0.5 M NaOH solution at 60 degrees C. The crystallization kinetics of FAU-X inside the geo-polymer precursor was investigated by means of Synchrotron Radiation X-Ray Diffraction Quantitative Phase Analysis (SR-XRD-QPA). Results showed that the crystallization starts after an induction time of about 3 days, and the weight percentage of the zeolite in the sample raises up to about 78% after 20 days of treatment. The highest yield in terms of zeolite content, about 80% of FAU-X and 6% of LTA, was reached at 20 days. Finally, Scanning Electron Microscopy (SEM) analysis showed the presence of well-defined octahedral crystals either on the pore surface or in the bulk of the sample starting from 3 days of hydrothermal treatment.

Automated summary

A FAU-X-rich porous monolith was prepared using an unconventional two-stage method involving foamed geopolymeric precursor production and subsequent hydrothermal conversion. The influence of conversion process parameters on FAU-X crystallization was investigated, and the highest yield was obtained at 60°C with a 0.5 M NaOH solution. Crystallization kinetics of FAU-X within the geopolymer precursor were studied using synchrotron radiation X-ray diffraction quantitative phase analysis (SR-XRD-QPA). Scanning electron microscopy (SEM) analysis showed the presence of well-defined octahedral crystals after 3 days of hydrothermal treatment.