Structure-Directing Roles and Interactions of Fluoride and Organocations with Siliceous Zeolite Frameworks

Abstract

Interactions of fluoride anions and organocations with crystalline silicate frameworks are shown to depend subtly on the architectures of the organic species, which significantly influence the crystalline structures that result. One- and two-dimensional (2D) (1)H, (19)F, and (29)Si nuclear magnetic resonance (NMR) spectroscopy measurements establish distinct intermolecular interactions among F(-) anions, imidazolium structure-directing agents (SDA(+)), and crystalline silicate frameworks for as-synthesized siliceous zeolites ITW and MTT. Different types and positions of hydrophobic alkyl ligands on the imidazolium SDA(+) species under otherwise identical zeolite synthesis compositions and conditions lead to significantly different interactions between the F(-) and SDA(+) ions and the respective silicate frameworks. For as-synthesized zeolite ITW, F(-) anions are established to reside in the double-four-ring (D4R) cages and interact strongly and selectively with D4R silicate framework sites, as manifested by their strong (19)F-(29)Si dipolar couplings. By comparison, for as-synthesized zeolite MTT, F(-) anions reside within the 10-ring channels and interact relatively weakly with the silicate framework as ion pairs with the SDA(+) ions. Such differences manifest the importance of interactions between the imidazolium and F(-) ions, which account for their structure-directing influences on the topologies of the resulting silicate frameworks. Furthermore, 2D (29)Si{(29)Si} double-quantum NMR measurements establish (29)Si-O-(29)Si site connectivities within the as-synthesized zeolites ITW and MTT that, in conjunction with synchrotron X-ray diffraction analyses, establish insights on complicated order and disorder within their framework structures.

Synthesis and Structure Determination of Large‐Pore Zeolite SCM‐14

“…[38,39] The goniometer tilt range is from À68.88 to 65.88 (exposure time 0.5 s), and in total 737 ED patterns were recorded with as tep of 0.28.T he reciprocal space reconstruction and reflection intensity extraction were carried out using the RED software. 13 Cs olid-state MAS NMR spectra were recorded aV arian Model VNMRS-400WB spectrometer with a7 .5 mm probe at 100.54 MHz and as pinning rate of 5kHz. Liquid 13 CNMR spectra were recorded on aB ruker AV-400 spectrometer.…”

In situ synthesis of CuSAPO-34/cordierite and its selective catalytic reduction of nitrogen oxides in vehicle exhaust: The effect of HF

“…It has been known that hydrofluoric acid (HF) functions as the mineralizati on structure directing agent for the crystallization of the molecular sieves [15][16][17][18]. When SAPO-34 molecular sieves are synthesized with morpholi ne as template, the addition of HF into the crystallization liquid can obviously promote the dissolution of the aluminum source and shorten the growth time of the crystal nucleus [19].…”

Breaking Structural Energy Constraints: Hydrothermal Crystallization of High‐Silica Germanosilicates by a Building‐Unit Self‐Growth Approach

“…The F − ions may act as mineralizing agents and catalysts for the formation of Si‐O‐Si bonds during the nucleation, crystallization, and growth of zeolite crystals . In some cases, F − ions play unique structure‐directing roles through strong interactions with the zeolite . When IM‐20‐A was crystallized in the absence of F − ions, only a material with extremely low framework crystallinity was obtained, and an excess of H 2 O or less OSDA both have highly negative influences on the synthesis of highly crystalline IM‐20‐R (Figure S9 and Table S7 in the Supporting Information).…”