SAXS and USAXS Investigation on Nanometer-Scaled Precursors in Organic-Mediated Zeolite Crystallization from Gelating Systems

The formation of precursor particles in the crystallization of zeolites from gelating systems has been studied using X-ray scattering at small angles. The crystallization of Si−MFI using trimethylene-bis( N -hexyl, N -methyl-piperidinium) as the structure-directing agent shows the formation of two categories of precursors: gel particles and nanometer-scaled primary units. The size of the primary units for the crystallization of Si−MFI is found to be 2.8 nm both for gelating and nongelating systems using different structure-directing agents. Zeolites Si−BEA and Si−MTW have been prepared using the same organic (trimethylene-bis( N -benzyl, N -methyl-piperidinium)) at different concentrations. Primary units with a size of 2.6 nm are found to be present in the synthesis of Si−BEA, while their size is 1.5 nm in the synthesis mixture directing to Si−MTW. Our data suggest that the nanometer-scaled primary units are specific for the zeolite topology formed.