Insight into the crystallization mechanism of the CON-type zeolite

The crystallization mechanism of the Al- and B-containing CON-type zeolite ([Al,B]-CON) was investigated in details in order to discriminate the different crystallization stages. By the XRD, the XRD peaks corresponding to the CON structures were detected after 4 days of hydrothermal treatment. The results obtained from ICP, Al-27 and B-11 MAS NMR indicated that the CON nuclei contain Al(SiO)(4) species and the crystal growth process proceeds by incorporating B atoms into the CON structure together with the reorganization of the amorphous boroaluminosilicate species. In comparison with the borosilicate CON zeolite, the incorporation of Al into the CON framework gave the additional band at the wavelength of 525 cm(-1) in the FTIR spectrum and this peak arose in the final step of the crystal growth of the CON zeolite. This was also confirmed by the Al-27 MAS NMR analysis in which the peak corresponding to the tetrahedrally coordinated Al atoms gradually shifted from 53 to 57 ppm along with the crystal growth. FTIR analysis of the as-obtained samples indicated that [B]-CON-like species may be formed at the initial stage of the crystallization and the intensity of the bands attributed to the CON structure increased along with the crystal growth. All the characterizations revealed that the crystallization of the CON zeolite consists of three consecutive stages; (1) formation of primary fractal amorphous aggregates, (2) formation of secondary fractal structure by the aggregation and the condensation of the primary aggregates, and (3) crystal growth of the secondary structure to form the CON zeolite.