Progress and perspectives on ZSM-22-based catalysts for long-chain n-alkane hydroisomerization

Hydroisomerization of long-chain n-alkanes holds significant value in pour point reduction and quality enhancement of fuels, the development of premium lubricants, and the industrial advancement of biofuels. Among various catalysts, ZSM-22 zeolite has emerged as an ideal support due to its unique pore structure and tunable acidity. This review summarizes the latest research progress on ZSM-22-based bifunctional catalysts. Studies have shown that two main strategies are commonly employed to enhance isomerization performance: optimizing the hydrogenation/dehydrogenation functionality of metal sites and tailoring the physicochemical properties of the zeolite. High-quality metal function contributes to an ideal bifunctional catalytic mechanism, which can be achieved by precisely controlling the dispersion, location, and exposed crystal facets of noble metals (e.g., Pt, Pd). While non-noble metals (e.g., Ni) can show hydroisomerization performance rivaling noble metals, their development relies on constructing bimetallic sites and carefully balanced metal-support interactions. In terms of ZSM-22 functional modification, reducing crystal size and constructing hierarchical pore structures are effective in mitigating the diffusion limitations imposed by its micropores on alkanes and olefinic intermediates. Meanwhile, acidity modulation can be achieved via framework heteroatom incorporation, ion exchange, surface acid site passivation, and partial pore blockage. Additionally, co-crystallization and composite zeolite strategies offer promising pathways for further enhancing the isomerization performance of ZSM-22-based catalysts. This review aims to provide both theoretical insights and technical guidance for the development of efficient catalysts for long-chain n-alkane hydroisomerization, offering value to researchers new to this field.