Catalytic isomerization and oligomerization of endo-dicyclopentadiene using alkali-treated hierarchical porous HZSM-5

• Hierarchical HZSM-5 was synthesized using alkali treatment.
• Mesopores allow more acidic sites in microchannels that are accessible.
• Hierarchical HZSM-5 is more active than Hβ and Al-MCM-41.
• Highest exo-DCPD yield (50.6%) and selectivity (79.3%) are obtained.
• Highest TCPD yield (36.3%) and catalytic selectivity (84%) are obtained.

Transferring endo-dicyclopentadiene (endo-DCPD) into exo-isomer and exo-tricyclopentadiene (TCPD) has great potential in synthesizing high-density fuels, but microporous acidic zeolites show low activity due to the mass transfer limitation and shape selectivity. Herein, we successfully tuned HZSM-5 into high activity by generating hierarchical pores via alkali treatment. XRD, SEM, TEM, N2 adsorption/desorption and 27Al MAS NMR characterizations confirm that moderate alkali treatment removes the amorphous phase and producess mesopores connecting microchannels, but the framework collapses under rigorous conditions. NH3-TPD and pyridine adsorption IR indicate that the presence of mesopores increases the accessibility of acid sites in microchannles, especially for large molecules. In the isomerization of endo-DCPD, after the generation of hierarchical porosity, the inactive parent HZSM-5 shows a higher exo-DCPD yield than thiose of microporous Hβ and mesoporous Al-MCM-41. In the oligomerization reaction, hierarchical HZSM-5 shows a higher TCPD yield than that of Hβ and the yield is comparable to that of Al-MCM-41. Importantly, this work provides an easy way to produce exo-DCPD and TCPD with maximum yield respectively by adjusting the zeolite treatment and reaction conditions. Z5-70–0.5–1.0 shows the best performance for isomerization whereas Z5-80–0.5–1.0 possessing more mesopores is most suitable for oligomerization. The hierarchical porous zeolite shows excellent coke tolerance, and shows good stability in recycling.

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