Abstract
Here different Ethanol-To-Hydrocarbons (ETH) reaction pathways on the external surface and in the channels of HZSM-5 were revealed by comparing the catalytic performance of ZSM-5 samples with different distributions of acidic type and location: including (1) SiO2(Ⅱ)-NaZSM-5 with only internal Lewis (L) acidity, (2) NaZSM-5 with both internal and external L acidity, (3) SiO2(Ⅱ)-HZSM-5 with only internal Brönsted (B) & L acidity, and (4) HZSM-5 with B & L acidity on both external and internal surface. The primary product was the ethylene from ethanol dehydration over NaZSM-5, SiO2(Ⅱ)-NaZSM-5 and SiO2(Ⅱ)-HZSM-5, which exhibited the much low selectivities of C3+ hydrocarbons. However, except C2 aliphatics, plenty of C3+ aliphatics and aromatics were generated over the HZSM-5 which showed a higher ethanol conversion. These results indicate the B acid sites on external surface are responsible for a high-efficiency conversion of ethanol/ethylene into C3+ hydrocarbons via double-cycle process, which cannot likely occur on the acidic internal-surface in micropores due to both the much low dimerization reactivity of ethylene and the severe space-restriction effect there. Both internal and external L acid sites are only involved in the catalytic ethanol dehydration, which is also catalyzed by internal and external B acidity. These reaction pathways on the external surface of HZSM-5 were further confirmed by the ETH reaction results over two mesoporous materials (i.e., γ-Al2O3 with only L acidity and B2O3-γ-Al2O3 with both L and B acidity).
Published Version
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