Propane dehydrogenation (PDH) is an important industrial process for meeting the growing global demand for propylene, a valuable commodity chemical used for many everyday materials. Traditional thermocatalytic PDH processes face significant challenges, including high energy requirements and catalyst deactivation. Addressing such limitations is imperative for developing more sustainable and energy-efficient PDH processes.

Mechanochemistry is an emerging technology that has the potential to simultaneously address energy input and catalyst activity concerns. Mechanochemistry involves driving a reaction with mechanical energy; a ball mill is used to provide kinetic energy to a reaction vessel which contains milling spheres and a catalyst. Mechanical impacts occur inside the reactor vessel and result in the formation of hotspots, local transient heat delivery, and the creation of extraordinary active sites, possibly inducing catalyst activity improvements and reducing catalyst deactivation rates. This work reports the first known instance of mechanochemical PDH reaction carried out over two different Pt-based catalysts: platinum on carbon (Pt/C) and platinum on alumina (Pt/Al₂O₃).

Propane dehydrogenation and cracking products were produced mechanochemically at ambient pressure and without bulk heating. Pt/Al₂O₃formed the desired propylene product more selectively. The difference in performance of the two catalysts could be explained by the difference in the material properties of the catalyst supports, where the hardness of alumina may contribute to the formation of more intense hotspots. In the first three hours of milling, propane conversion over Pt/Al₂O₃ tends to increase with time, indicating that the catalyst undergoes structural transformations to reach increasingly active forms. In addition, the longevity of the catalyst is explored in detail.

Zili Wu

Dr., Oak Ridge National Laboratory

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