Efficient carbon integration of CO₂ in propane aromatization over acidic zeolites

Aromatics, as extremely crucial basic chemicals in the modern industrial system, are widely used in many fields such as energy, medicine, materials and the daily chemical industry. However, the traditional petroleum-based production routes, such as naphtha cracking and catalytic reforming, are facing the dual pressures of tight petroleum resources and carbon emissions. Meanwhile, CO2, as a typical greenhouse gas, its efficient and value-added utilization offers dual benefits in both environment and economic development, but is limited by its thermodynamic stability, and there are still challenges in producing aromatics with high selectivity through hydrogenation pathways. Propane, as a major component of natural gas and shale gas, generates a large amount of small-molecule alkane byproducts due to imbalanced carbon-hydrogen ratios during direct aromatization, limiting aromatic selectivity. Compared to C4~C6 alkanes, propane possesses a higher C-H bond energy, requiring more rigorous reaction conditions for activation. So far, there has been no report on the coupling conversion of CO2 and propane to aromatics catalyzed by acidic zeolites.

Recently, a research team led by Researcher Wenliang Zhu from the Dalian Institute of Chemical Physics and Professor Jiaxu Liu from Dalian University of Technology reported a new route for the efficient production of aromatics via the coupling of CO2 and propane over H-ZSM-5. In this process, CO2 regulates the hydrogen transfer process by combining with olefins, breaking through the carbon-hydrogen balance limitation of traditional aromatization reactions. Additionally, the study directly demonstrates that carbon atoms in CO2 can participate in product formation, significantly improving carbon utilization efficiency. This research achievement was published in Chinese Journal of Catalysis (10.1016/S1872-2067(25)64680-8).

The researchers systematically compared the conversion behaviors of propane under Ar/CO2 atmospheres. Experiments showed that the introduction of CO2 significantly improved the selectivity of aromatics. Under the conditions of 723 K, 3.0 MPa, and C3H8/CO2=1:120, propane conversion reached 48.8%, and aromatic selectivity increased to 60.2%, an improvement of approximately 30% compared to the Ar atmosphere. By regulating the acid amount of the zeolite, it was found that an increase in acid amount promoted the formation of aromatics while inhibiting small-molecule alkane byproducts, indicating that the propane aromatization process under a CO2 atmosphere is a Brønsted acid-catalyzed process distinct from the traditional hydrogen transfer mechanism.

Through in situ DB-FTIR, 13C isotope labeling experiments, TPSR, and probe molecule experiments, it was demonstrated that olefins and lactones are key intermediate species, and carbon atoms in CO2 directly participate in the formation of aromatics. A new coupling conversion mechanism of CO2 and propane over acidic zeolite: Propane was first cracked, dehydrogenated and oligomerized over zeolite to produce various low-carbon olefins. The olefins can react with CO2 to produce lactones and finally be converted into aromatics. At the same time, olefins can also undergo hydrogen transfer reactions to generate aromatics and corresponding alkanes.

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