Top-down strategy for direct synthesis of high silica Y zeolite molecular sieve

Fluidized catalytic cracking (FCC) and hydrocracking are currently the most important secondary processing processes of crude oil in the petroleum refining industry, as well as the core process of heavy oil lightening. The Y-type zeolite with high silicon to aluminum ratio with FAU topology is the main active component of current industrial cracking catalysts, and its industrial consumption ranks first in the world for solid catalysts. The inherent low silicon framework characteristics of conventional synthetic Y zeolite and the resulting structural instability have become the main bottleneck for the direct application of materials. Industrial practice and basic research have shown that increasing the silica-to-aluminum ratio of the Y zeolite framework is the best way to improve acid properties, increase stability, and further enhance the reaction performance of the catalyst. At present, the Y zeolite with high silicon to aluminum ratio widely used in industry is mainly obtained by conventionally synthesized low silicon Y zeolite through post-treatment methods such as dealumination or dealumination and silicon supplementation. The post-treatment process is not only complicated, but also energy-consuming and time-consuming. There will also be a dealumination gradient on the surface and inside of the crystal, causing uneven distribution of acid centers. In contrast, the directly synthesized high-silica Y zeolite has a perfect structure and uniform aluminum distribution. It is an ideal catalytic material and a goal pursued by the industry and researchers. However, in the past 60 years, the framework silica-to-aluminum ratio (SiO2/Al2O3) of Y zeolite has always been difficult to break through the limit of 5-9. The direct synthesis of high silica Y zeolite has always been a huge challenge in the field of molecular sieve synthesis.