Intergrowth of Zeolites LTA and FAU/EMT in Nanosized Particles Synthesized from Organic-Free Gels

The effect of process and composition parameters of inorganic aluminosilicate gels on the particle size of zeolite LTA were studied. The samples were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The crystallization domain of zeolite LTA around synthesis gel with composition 1.8 SiO₂:1 Al₂O₃:12 Na₂O:214 H₂O was found to be narrow, with slight changes in composition leading to the crystallization of other zeolite phases, without a significant decrease in LTA particle size. Slightly increasing the Si/Al ratio of the synthesis gel results in the crystallization of a second population of nanosized crystals (down to 50 nm), which were revealed to be mostly FAU/EMT crystals from transmission electron microscopy imaging. FAU/EMT was found to exist as separate crystals or intergrown with LTA in the same particle, providing the first evidence of FAU/EMT and LTA intergrowth at this scale. Based on structural study using high resolution transmission electron microscopy imaging and comparison to simulations, we propose that the connection at the interface between LTA and Faujasite could be either by inversion or mirror symmetries across double six-membered rings, and both cases have been observed.