Synthesis, characterization, and framework heteroatom localization in ITQ-21.
ITQ-21 has been synthesized in a wide range of compositions. By rationally modifying the synthesis variables and zeolite composition, it is possible to fine-tune the crystallite size from nanocrystals (<80 nm) up to microns and to avoid the competition of other phases such as CIT-5, SSZ-24, or a laminar phase that can also be synthesized with the same organic structure directing agent. By means of XRD and (19)F MAS NMR, Ge and Si have been localized among the different crystallographic positions, and it is shown that Ge preferentially occupies T1 positions at the D4R cages, avoiding formation of Ge-O-Ge pairs. However, at high Ge loadings (Si/Ge = 1.7), a new (19)F MAS NMR signal at -14 ppm has been observed and assigned to the presence of Ge-O-Ge in Ge-rich D4R cages. Energetic configurations obtained by theoretical calculations fully agree with experimental observations, with the following increasing order in energy for Ge substitution: T1 < T2 < Ge-O-Ge in T1 < T3.
Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Avda. de los Naranjos s/n, 46022 Valencia, Spain.
Teresa
T
Blasco
Avelino
A
Corma
Maria José
MJ
Díaz-Cabañas
Fernando
F
Rey
Jordi
J
Rius
German
G
Sastre
José A
JA
Vidal-Moya