1. Introduction

Catalytic cracking is a cornerstone of modern petroleum refining, converting heavy hydrocarbons into high-value products like gasoline, diesel, and light olefins. Traditional catalysts, such as Y zeolites and ZSM-5, face limitations in coke resistance and selectivity for small-molecule products. ZSM-35 zeolite, with its FER-type framework composed of intersecting 8-membered and 10-membered rings, offers a promising alternative due to its:

• Precise pore dimensions (0.5–0.6 nm) enabling shape-selective catalysis.
• Moderate acidity (Si/Al ratio: 15–70) balancing activity and stability.
• High thermal stability (>700°C) and water resistance.

This review synthesizes recent advancements in ZSM-35’s catalytic cracking performance, emphasizing structural-property relationships and industrial relevance.

2. Pore Structure and Shape-Selective Catalysis

2.1 Unique Pore Architecture

ZSM-35’s FER framework features two perpendicular channels:

• 10-membered ring channels (0.42 × 0.54 nm): Allow diffusion of linear hydrocarbons (C₅–C₁₂).
• 8-membered ring channels (0.35 × 0.48 nm): Restrict bulky molecules, promoting crack reactions of linear alkanes into lighter fragments.

This dual-pore system enhances selectivity for light olefins (C₂–C₄) and branched isomers (e.g., isobutane) while suppressing coke precursors like polyaromatic hydrocarbons.

2.2 Diffusion Advantages

Compared to ZSM-5 (10-membered ring channels only), ZSM-35’s intersecting pores reduce residence time of reaction intermediates, minimizing secondary cracking and coke deposition. For instance, in diesel catalytic cracking, ZSM-35 achieves:

• 20–30% higher light olefin yield than ZSM-5.
• 50% lower coke accumulation under identical conditions.

3. Acid Site Distribution and Catalytic Activity

3.1 Brønsted vs. Lewis Acid Sites

ZSM-35’s acidity arises from framework aluminum (Brønsted acid, B-acid) and extra-framework metal ions (Lewis acid, L-acid). B-acid sites are critical for cracking reactions, while excessive L-acid sites promote coke formation.

• Optimal B/L ratio: Modifications like phosphoric acid treatment reduce L-acid density, enhancing selectivity. For example, phosphorus-modified ZSM-35 shows:
  • 90% increase in propylene selectivity in naphtha cracking.
  • 40% reduction in coke yield compared to unmodified samples.

3.2 Si/Al Ratio Effects

Higher Si/Al ratios (e.g., Si/Al = 70) decrease acid site density but improve thermal stability and anti-coking performance. In diesel cracking:

• Si/Al = 30: High initial activity but rapid deactivation (coke rate: 9.83 wt%).
• Si/Al = 70: Lower activity but prolonged lifetime (coke rate: 2.35 wt%).

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