ZSM-35 zeolite (also known as ferrierite or FER-type zeolite) is a highly effective catalyst for the conversion of n-paraffins (normal alkanes) due to its unique structural and acidic properties. Its FER-type framework, characterized by intersecting 8- and 10-membered ring channels, provides exceptional shape-selective catalysis, making it ideal for targeted hydrocarbon transformations.

Key Advantages of ZSM-35 in n-Paraffin Conversion

1. Shape-Selective Pore Structure
   • The 8-membered ring channels (0.43 × 0.55 nm) restrict the diffusion of larger, branched hydrocarbons while allowing linear n-paraffins to enter and react.
   • This selectivity enables preferential conversion of n-paraffins over isoparaffins, minimizing unwanted side reactions.
2. Moderate Acidity
   • ZSM-35 exhibits balanced Brønsted and Lewis acid sites, facilitating cracking, isomerization, and aromatization reactions without excessive coke formation.
   • Its acidity can be fine-tuned via ion exchange (e.g., with H⁺, Mg²⁺, or rare-earth cations) to optimize activity and selectivity.
3. High Thermal/Hydrothermal Stability
   • Resistant to deactivation under harsh conditions (high temperatures, steam exposure), ensuring long-term stability in industrial processes like fluid catalytic cracking (FCC) or hydrocracking.

Applications in n-Paraffin Conversion

1. Isomerization of Light n-Paraffins (C₅–C₇)
   • Converts n-pentane, n-hexane, and n-heptane into their branched isomers (e.g., isopentane, isohexane), improving gasoline octane numbers.
   • Competitive with traditional Pt/Al₂O₃ catalysts but operates under milder conditions with lower hydrogen consumption.
2. Skeletal Isomerization of Long-Chain n-Paraffins (C₁₀–C₂₀)
   • Produces branched-chain paraffins (e.g., from n-dodecane to 2-methylundecane), valuable as lubricant base oils or diesel additives with enhanced cold-flow properties.
3. Aromatization of n-Paraffins (C₆–C₁₂)
   • Converts n-hexane to benzene or n-heptane to toluene via cyclization and dehydrogenation, useful for producing high-value aromatics.
4. Hydrocracking of Heavy n-Paraffins
   • Breaks down long-chain n-paraffins into lighter fractions (e.g., diesel, jet fuel) with improved cetane numbers and reduced pour points.

Catalyst Optimization Strategies

1. Ion Exchange Modification
   • Replacing Na⁺ with H⁺ enhances acidity for cracking reactions.
   • Incorporating Mg²⁺ or Ce³⁺ improves hydrothermal stability and reduces coke formation.
2. Phosphorus Modification
   • Phosphorus loading (e.g., P/ZSM-35) tunes acid site density and strength, optimizing isomerization selectivity while suppressing cracking.
3. Steam Treatment
   • Controlled steaming adjusts pore size and acidity, enhancing selectivity for specific products (e.g., mono-branched isomers).
4. Bimetallic/Promoter Addition
   • Adding Pt or Pd improves dehydrogenation activity for aromatization.
   • Incorporating Zn or Ga enhances cracking/isomerization performance.

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