DDR framework topology

As one would have expected based on its structure, aluminum-free deca-dodecasil 3R readily adsorbs small molecules like CO2, N2O and NH3 [20]. On the other hand, alkanes and alkenes with three or four carbon atoms show only retarded adsorption at 296 K, while 1,3-butadiene is readily adsorbed under these conditions. This peculiar behavior has been attributed to the more elliptical cross section of the diolefin due to the presence of sp -hybridized carbon atoms. The former obviously has a better fit to the elliptical windows in the DDR structure than the circular cross section of saturated hydrocarbons [20]. In the following, the synthesis of materials with the DDR framework topology will be described in more detail. 

So far, essentially two templates have been reported to promote the crystallization of materials with the DDR framework topology, viz. 1-aminoadamantane (ADA) and methyltropiniumiodide. Their structures are depicted in Fig. 1. Both are relatively bulky molecules which, after hydrothermal synthesis, are encapsulated inside the large cavities of the DDR structure and have to be removed by calcination in an oxygen-containing atmosphere at temperatures of at least 813 K. Materials which have been prepared using 1-aminoadamantane are denoted as deca-dodecasil 3R [20,22] or Sigma-1 [18], while zeolite ZSM-58 is prepared using methyltropiniumiodide [16,17,19]. 

Fig. 1. Templates reported in the literature for the synthesis of zeolites with the DDR framework topology...

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