Synthesis study reveals that subtle modifications in piperidinium templates govern SSZ-39 crystallization rates and composition, indicating key size effects during nucleation.
Key Points
To determine how subtle variations in the architecture of methylated piperidinium organic structure-directing agents impact the crystallization kinetics, framework composition, and nucleation of zeolite SSZ-39.
Synthesized zeolites using four distinct methylated piperidinium hydroxide organic structure-directing agents (OSDAs) differing in methyl and ethyl substituent positions.
Evaluated crystallization rates and material phase outcomes between 3,5- and 2,6-substituted piperidinium derivatives.
Conducted competitive crystallization experiments using mixtures of 2,6-derivatives as well as seed crystal additions to assess nucleation barriers.
Conventional PIPPY (3,5-methyl-N,N-methyl) and 2,6-methyl-N,N-ethyl piperidinium formed SSZ-39 in approximately 24 hours, with the 2,6-ethyl variant yielding a higher silicon-to-aluminum ratio.
3,5-methyl-N,N-ethyl piperidinium hydroxide yielded zeolite SSZ-13 instead of SSZ-39 in under 24 hours.
2,6-methyl-N,N-methyl piperidinium formed SSZ-39 much more slowly, taking three to four days to complete crystallization due to lower nucleation efficiency associated with its slightly smaller size.