1. Introduction
Faujasite-type zeolites represented by NaY and HY occupy a dominant position in the global petroleum catalytic industry. HY zeolite is prepared by ammonium exchange and high-temperature calcination of NaY raw powder, replacing sodium ions with protons to form strong acidic framework centers. Different from medium-pore pentasil zeolites and small-pore CHA zeolites, HY possesses open three-dimensional interconnected large-pore structure and huge supercage volume, which allows free diffusion and catalytic reaction of large-size heavy hydrocarbon molecules, showing unique advantages in heavy oil processing and macromolecular catalysis.
The adjustable silicon-aluminum ratio and flexible acid modulation performance enable HY zeolite to be modified into various derivative catalysts such as ultra-stable Y (USY) and rare earth-modified Y (REY). These modified materials effectively solve the problems of poor hydrothermal stability and easy coking deactivation of pristine HY, and have become the mainstream industrial catalysts for fluid catalytic cracking (FCC), residue cracking, aromatic alkylation and isomerization. In recent years, with the development of green chemical industry, HY-based catalysts have also been widely expanded to biomass pyrolysis, waste plastic upgrading and volatile organic compound (VOC) degradation. This paper comprehensively elaborates the structure–activity relationship, modification progress and full-scale industrial applications of HY zeolite.
2. Structural and Physicochemical Characteristics of HY Zeolite
2.1 FAU Topological Pore Structure
HY zeolite belongs to FAU topological structure, with a three-dimensional interconnected microporous system composed of 12-membered ring channels. The pore window size is 0.74 nm × 0.74 nm, and the internal supercage diameter reaches 1.3 nm, which is one of the largest cage structures among conventional industrial zeolites. The cross-connected pore channels in all directions eliminate diffusion dead zones, enabling high-efficiency mass transfer of heavy hydrocarbon macromolecules that cannot enter medium and small-pore zeolites. This structural feature determines the irreplaceable status of HY zeolite in heavy oil catalytic processing.
2.2 Acidic and Structural Properties
Pristine HY zeolite has high density of strong Brønsted acid sites derived from framework Al-O-Si bridging hydroxyl groups, as well as abundant Lewis acid sites generated by extra-framework aluminum defects. The strong acid strength provides high catalytic activity for carbon-carbon bond breaking and carbocation rearrangement reactions. However, high aluminum content also leads to poor hydrothermal stability and rapid coke deposition during high-temperature reactions.
The specific surface area of high-quality HY zeolite exceeds 600 m²/g, with regular micropore structure and good crystal integrity. After high-temperature hydrothermal treatment, the framework of common HY is prone to dealumination and structural collapse, while modified USY and REY zeolites significantly improve structural stability and can adapt to harsh high-temperature regeneration environment of industrial FCC units.
