Fluoride- and Seed-Free Synthesis of Pure-Silica Zeolite Adsorbent and Matrix Using OSDA-Mismatch Approach

Abstract

The pure-silica zeolite plays a crucially important role in the gas separation of alkane/alkene, the low-k dielectric material, and the robust matrix for confining metal species during catalysis. However, the environmentally friendly synthesis of pure-silica zeolites is still challenging since (1) the toxic fluoride or dealuminum seeds are inevitably utilized through the hydrothermal synthesis and (2) it will also take a longer crystallization time. Herein, we present an efficient method called the OSDA-mismatch approach for the fluoride- and seed-free synthesis of pure-silica zeolites using <b>Si-SOD</b> (enriched 4-rings) as the sole silica source. This approach allows for the rapid and green synthesis of 15 pure-silica zeolites (<b>CHA</b>, <b>*BEA</b>, <b>EUO</b>, <b>SFF</b>, <b>STF</b>, <b>-SVR</b>, <b>*-SVY</b>, <b>DOH</b>, <b>MTN</b>, <b>NON</b>, <b>*MRE</b>, <b>MEL</b>, <b>MFI</b>, <b>MTW</b>, and <b>*STO</b>). Furthermore, distinct crystallization mechanisms of two significant pure-silica <b>CHA-</b> and <b>*BEA</b>-type zeolites (denoted as <b>Si-CHA</b> and <b>Si-BEA</b>) are investigated in detail by advanced characterization techniques such as FIB, 3D ED, 4D-STEM, HRTEM, Raman, and ²⁹Si MAS NMR. More importantly, <b>Si-CHA</b> displays promising propane/propylene separation performance even better than the one synthesized in the presence of toxic HF. In addition, the incorporation of Zn species within <b>Si-BEA</b> fabricated by this approach also renders superior performance on propane dehydrogenation.