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Abstract

The commercial, CO₂-intensive, propylene generation process is challenged by a low equilibrium yield, costly separation processes, and severe carbon deposition. The oxidative dehydrogenation (ODH) of propane represents a promising alternative, offering enhanced equilibrium conversion while mitigating coke formation. However, its challenged by excessive propylene overoxidation to undesired carbon oxides. This dissertation explores two innovative catalyst systems to address these challenges: (1) a molten metal-based chemical looping system and (2) a mixed-bed catalyst combining h-BN and Bi₂O₃. Solid chemical looping catalysts have a low oxygen carrying capacity, often less than 1 % in order to avoid cyclic deactivation, arising from changes to the lattice structure in each cycle. The first approach investigates molten metals as chemical looping catalysts. Thermodynamic screening showcases 21 potential candidates, with 14 selected for experimental evaluation. Bi-Sn had the highest conversion, and 50-50 mol% Bi-Sn was supported in a fixed-bed reactor. This resulted in 22 % C₃H₆ yield at 600 °C, compared to a 20 % yield from the reference at the same temperature. The 50-50 mol% Bi-Sn alloy demonstrated superior performance, achieving stable C₃H₆ selectivity (44.3 %) over 37 hours on stream (10 redox cycles). A C₃H₆ yield of 6.3 % was achieved, compared to the traditional V/SiO₂ ODH catalyst, which had a C₃H₆ yield of 5.4 %. Enhanced propylene selectivity was observed using a 50-50 mol% Bi-Sn molten mixture, surpassing the performance of Bi or Sn alone, and leading to reduced carbon oxide formation. This improved selectivity occurred with both co-fed and pre-oxidized catalysts, suggesting the creation of a unique metal oxide selectively generating propylene while minimizing overoxidation to carbon oxides. The second approach examines h-BN and Bi₂O₃ in a mixed-bed system, revealing a 50 % propane conversion with 64 % total light olefin selectivity at 500 °C. A 32 % yield of light olefins was achieved, surpassing that of traditional V/SiO₂ ODH catalysts. However, further improvements and optimizations are necessary to achieve the commercial CATOFIN PDH yield of approximately 50 %. H₂ temperature-programmed reduction analysis indicates a delayed reduction onset, while post-reaction SEM and EDX confirm interfacial interactions between h-BN and Bi₂O₃.