Differentiating the Role of Organic Additives to Assemble Open Framework Aluminosilicate Zeolites Using INS Spectroscopy
Presently there is little clarity concerning how organic additives control structure formation in the synthesis of zeolite catalysts and their chemistry. Such ambiguity is a major obstacle towards the synthesis design for new bespoke zeolites with intended applications. Herein, we have applied inelastic neutron scattering (INS) spectroscopy to experimentally probe the organic-framework interactions that are crucial to the structure direction process. With this technique we have studied the dynamics of 18-crown-6 ether, which can be used as an additive to direct the formation of four zeolites: Na-X, EMC-2, RHO and ZK-5. We observe significant softening of the 18-crown-6 ether molecule’s dynamics upon occlusion within a zeolite host, with a strong influence on both the circular and radial vibrational modes. Furthermore, there is a strong correlation between the efficacy of the organic additive and the strength of the organic-framework interactions, which are a consequence of both the framework cavity size and geometry. We propose that the approach used herein should be used to study other zeolites, and hence gain a more comprehensive view of structure directing organic-framework interactions.