1. Introduction
Faujasite (FAU) zeolites have always been the most important porous materials in petrochemical industry and environmental adsorption engineering. NaY zeolite is the original sodium-form FAU molecular sieve synthesized by conventional hydrothermal methods. Different from proton-type HY zeolite with strong solid acidity, the framework negative charges of NaY are completely compensated by Na⁺ ions, resulting in negligible Brønsted acidity and excellent structural stability in alkaline environments. Therefore, NaY cannot be directly used as a high-efficiency cracking acid catalyst, but it serves as the only high-quality precursor for preparing various modified Y-type catalysts including HY, USY and rare-earth modified REY.
In addition to precursor preparation, NaY itself has unique application values. Its uniform large-pore structure, high pore volume and rich exchangeable sodium ions endow it with outstanding adsorption capacity, selective separation performance and ion exchange performance. It is widely used in industrial gas separation, organic waste gas adsorption, heavy metal wastewater treatment and detergent auxiliary fields. In recent years, with the development of green environmental protection and high-end catalytic materials, modified NaY zeolites have been gradually developed into high-efficiency composite adsorbents and supported catalyst carriers. This review systematically summarizes the structural advantages, synthesis technologies, modification methods and multi-field industrial applications of NaY zeolite.
2. Structural and Physicochemical Properties of NaY Zeolite
2.1 FAU Topological Structure
NaY zeolite belongs to the cubic FAU crystal system, possessing a highly regular three-dimensional interconnected microporous network. The basic structural units are sodalite cages (β-cages), which are connected through double six-rings (D6R) to form large ellipsoidal supercages (α-cages). Each supercage is interconnected with four adjacent supercages through 12-membered ring pore windows, forming an open and unobstructed three-dimensional pore system.
Key structural parameters of NaY zeolite: 12-MR pore opening of 0.74 nm × 0.74 nm, supercage inner diameter up to 1.3 nm, high specific surface area exceeding 600 m²/g, and large micropore volume. Compared with medium-pore ZSM-series and small-pore SAPO/CHA zeolites, NaY has stronger macromolecular mass transfer and accommodation ability, which can adsorb and accommodate large organic molecules that are difficult to diffuse in other microporous materials.
2.2 Unique Physicochemical Characteristics
High ion-exchange performance: A large number of exchangeable Na⁺ ions are distributed in the supercages and on the framework surface of NaY zeolite. These sodium ions can be easily replaced by H⁺, rare earth ions, transition metal ions and other cations, which is the fundamental reason why NaY can be modified into various high-performance functional materials.
Neutral surface and weak alkalinity: Different from acidic HY zeolite, saturated Na⁺ compensation eliminates framework acidity. NaY exhibits stable weak alkalinity, resisting acid dissolution and structural damage in mild alkaline environments, and is suitable for alkaline adsorption and reaction systems.
Excellent structural stability: Well-crystallized NaY zeolite has high thermal stability, maintaining complete crystal structure above 750 °C. Its original framework structure is more stable than protonated HY under high-temperature and hydrothermal conditions, effectively avoiding dealumination and structural collapse.
Non-acidic catalytic property: Pure NaY has almost no Brønsted acid sites, so it cannot initiate carbocation cracking reactions. This feature makes NaY avoid excessive coking and side cracking, and is suitable as adsorbent and catalyst carrier rather than acid catalyst.
