Direct Synthesis of Highly Siliceous Faujasite-type Zeolite Enabled by Low Charge Density Organic Structure-directing Agents

Ultrastable Y (USY) zeolites (Faujasite-type, FAU ) with high SiO 2 /Al 2 O 3 ratios (SARs) have been widely applied in fluidized catalytic cracking and hydrocracking processes. However, their preparation typically involves labor-intensive post-treatments that inevitably introduce defects, extra-framework species, and compositional gradients. Herein, we report the direct synthesis of FAU -type zeolite with a record-high SAR up to 21.28, which shows superior catalytic performance in the catalytic cracking of cumene and straight-run diesel. This was achieved by using a highly siliceous initial gel and seed, together with low charge-density organic structure-directing agents (OSDAs) of tetramethylammonium (TMA + ) and tetrabutylammonium (TBA + ) cations, while minimizing the use of high charge-density inorganic Na + cations. Comprehensive NMR analyses, including two-dimensional (2D) heteronuclear correlation (HETCOR) experiments ( 1 H– 13 C, 1 H– 27 Al, 1 H– 29 Si), and synchrotron radiation X-ray diffraction-based Rietveld refinements, revealed that (1) TMA + and TBA + preferentially interact with Si species over Al species in the initial gel, promoting Si incorporation into the FAU structure’s long-range order; and (2) TMA + cations were tightly confined within the sodalite ( sod ) cages, while TBA + cations occupied the faujasite ( fau ) supercages, adopting folded butyl chain configurations. The encapsulation of low charge-density OSDA cations, coupled with the exclusion of high charge-density Na + cations, resulted in a highly siliceous Y zeolite with a SAR of 21.28. The synthesized Y zeolite exhibited improved durability and enhanced activity in cumene cracking and comparable selectivity for the target products [liquefied petroleum gas (LPG) and gasoline] while reducing coke formation by 28% in straight-run diesel catalytic cracking compared to conventional USY zeolites.