Recyclable hydrazine-passivated NiBx/Ni heterostructured catalyst for enhanced hydrogenation of polystyrene pyrolysis oil

Authors: PARK, JUNG HYUN - University Of Illinois; ZABOROWSKI, ELIAH - University Of Illinois; LU, HONG - University Of Illinois; Sharma, Brajendra; KUMAR, NALIN - Uhv Technologies Inc; RAJAGOPALAN, NANDAKISHORE - University Of Illinois; KIM, JAEMIN - University Of Illinois

Submitted to: ACS Applied Materials and Interfaces
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2025
Publication Date: 4/3/2025
Citation: Park, J., Zaborowski, E., Lu, H., Sharma, B.K., Kumar, N., Rajagopalan, N., Kim, J. 2025. Recyclable hydrazine-passivated NiBx/Ni heterostructured catalyst for enhanced hydrogenation of polystyrene pyrolysis oil. ACS Applied Materials and Interfaces. https://doi.org/10.1021/acsami.5c02622.
DOI: https://doi.org/10.1021/acsami.5c02622

Interpretive Summary: Ethylbenzene is an important industrial chemical component, especially in the automotive and aviation fuel industries. The current methods of production are energy-intensive. An alternate greener route for ethylbenzene production is the thermal degradation of polystyrene (PS) waste into styrene, followed by its hydrogenation and distillation toward ethylbenzene production. Hydrogenation typically requires precious metal catalysts making the process costly and difficult to scale up. In the present work, a nickel-based catalyst has been shown to not only improve the hydrogenation of styrene to ethylbenzene but also tackle the oxidation problems typically encountered with this kind of catalyst. This study highlights the potential use of this nickel-based catalyst for low-cost operation in industrial hydrogenation applications. This approach could be used to produce biofuels as well. This will improve the economic viability of biofuel production and thereby help farmers by increasing the value of waste biomass generated on the farms.

Technical Abstract: While nickel boride (Ni2B) is an excellent hydrogenation catalyst, it suffers from oxidation in air environments. Here, we report a hydrazine-passivated nickel boride/nickel (NiBx/Ni) heterostructured catalyst to tackle the oxidation problem and improve hydrogenation performance from styrene to ethylbenzene using real polystyrene (PS) pyrolysis oil. The hydrazine passivation on the catalyst surface not only prevents oxidation but reduces cationic Ni and B, which enhances the overall catalytic efficacy. The turnover frequency (TOF) for styrene to ethylbenzene conversion was calculated to be 24.9 mmol/h·g with 99.9% alkene selectivity. This represents a 38.3% improvement over the control Ni2B catalyst (18.0 mmol/h·g). This outstanding performance of the NiBx/Ni catalyst was attributed to the increased charge density on both Ni and B atomic structures induced by a strong hydrazine reductant, where the performance was further compared with other ligands such as ethanolamine and ethylamine. An enhanced magnetic property of NiBx/Ni was observed, resulting from the nanocrystalline structure alongside the Ni(111) easy axis. The used NiBx/Ni catalyst, recovered from the solution using a neodymium magnet, was tested for five consecutive cycles, demonstrating no significant activity loss (4% loss). This study highlights the potential use of the NiBx/Ni catalyst for low-cost operation in industrial hydrogenation applications.