P-Derived Organic Cations as Structure-Directing Agents: Synthesis of a High-Silica Zeolite (ITQ-27) with a Two-Dimensional 12-Ring Channel System

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks
as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite,
ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on
synchrotron powder diffraction data (λ = 0.8702 Å) after the unit cell and space group were determined
from tilt electron diffraction experiments on individual microcrystals. The material crystallizes in space group
Fmmm, where a = 27.7508(5) Å, b = 25.2969(7) Å, and c = 13.7923(4) Å. The final model, refined by
Rietveld methods, comprises seven unique T-sites forming a framework with straight 12-MR channels that
are connected by 14-MR openings between them. (Corresponding 12-ring pore dimension is 6.94 Å ×
6.20 Å.) Since access from one 14-MR opening to the next is through the 12-MR channel, the structure is
best described as a two-dimensional, 12-MR framework.