The developments within the ZEOLIghT project focus on the discovery aof nanozeolites by controlling defect sites and structural flexibility. The activities are structured according to three main objectives: fundamental understanding of defects in nanozeolites, studying their flexibility, and engineering zeolites with novel properties for applications where flexibility and defects influence performance.
The synthesis of nanozeolites with tailored properties was achieved through systematic investigations of hydrolysis, condensation, nucleation, and growth processes. This optimization enabled the synthesis of zeolites with various framework structures, using modified precursor suspensions. Both high-solid and highly diluted precursors were employed for the synthesis of pure silica, aluminosilicates, and metal silicates. Metal incorporation into zeolite frameworks demonstrated outstanding stability and catalytic performance in lean methane combustion. A novel Ge-containing zeolite with extreme hydrophobicity and high germanium content (14% Ge) was synthesized, free of defects and no fluorine ions. This resulted in a double-bridge configuration of Ge pairs in zeolites, giving rise to exceptional material stability. Additionally, the impact of template charge density on defect distribution and hydrophilicity of aluminophosphates was demonstrated.
Beyond direct synthesis approaches, post-synthesis treatments highlighted the role of metals in healing silanol defect sites in zeolites. The reactivity of silanol defects was exemplified in Zn-MFI type zeolites, which enhanced hydroxyl radical formation for methane conversion.
In alignment with the second objective, the flexibility of nanozeolites was evaluated by varying alkali cations, intergrowth levels, Al content, and crystal size. The substantial effect of alkali cations (Na⁺, K⁺, Cs⁺) on the flexibility of zeolites was examined, emphasizing their impact on silanol distribution and structural dynamics. These materials showed high efficiency in CO2 separation due to their framework flexibility and controlled particle size, which is critical for diffusion. In addition the amount and distribution of Al within the zeolite framework were found to be crucial for controlled CO2 adsorption. Further attention was given to controlling crystal size and morphology, exemplified by the synthesis of ultra-thin zeolite nanosheets with exceptional water adsorption capacity and mesoporosity, offering excellent flexibility and thermal stability.
The engineered nanozeolites with controlled defect sites and flexibility were tested in various gas separation processes and catalytic applications, particularly those requiring stability under harsh conditions. Zeolites with macropores exhibited reduced coke deposition, enhancing catalyst stability. The simultaneous synthesis, advanced in situ characterization, and application studies facilitated rapid optimization through dynamic feedback loops.
