(4pm) Catalyst and mechanism development for the dehydrogenation of propane to propylene

Multi-scale kinetic modeling, catalyst development, high-throughput experiments, machine learning, process scale-up, selective oxidations, reactor design, in-situ spectroscopic characterization (X-ray, vibrational)

Introduction:

I am a fifth year PhD candidate and GRFP fellow at the University of Wisconsin – Madison studying under Professor Ive Hermans. My thesis research is primarily focused on the development of novel catalysts for the production of propylene. Propylene is an essential commodity chemical undergoing dynamic expansion in production technologies. Previously, propylene was primarily produced through the steam cracking of naphtha, but recently commercialized processes (Dow FCDh, K-Pro, etc.) have focused on the on-purpose dehydrogenation of propane. My research is driven by a fascination with how to translate mechanistic insights derived from careful laboratory studies into materials with enhanced performance. My three research projects have focused on developing catalytic processes for the dehydrogenation of propane directly (DHP) and with oxygen co-feed (ODHP):

1. Recent observations in the literature show that multimetallic ‘high-entropy’ catalytic materials can produce unique stabilizing effects that could be useful for DHP. In my current project I am developing machine learning models to explore a broad space of possible multimetallic platinum-based catalysts for DHP. Because the incorporation of multiple metals significantly complicates the design-space for catalytic materials, we are attempting to use Bayesian Optimization to navigate this multimetallic space efficiently. To fast-track this work I designed and built a parallel-flow fixed-bed reactor for rapid catalyst testing. Next, we synthesized a series of Pt/Al₂O₃ catalysts promoted with Sn, Ga, Fe, Cu, and Ca. After qualifying the reactor through a series of checks testing for transport limitations and dilution effects, we tested 6 rounds of catalysts for this project using a Bayesian Optimization algorithm I wrote. We found novel catalyst formulations that have similar performance to our industrial mimic, suggesting new families of promotors to investigate in tandem for future enhancements.¹

2. Promotors are crucial for the performance of industrially-viable catalysts. A previous publication from our group showed that promotion of V/SiO₂ with co-addition of Ta led to an ODHP catalyst with significantly higher activity and propylene selectivity at isoconversion.² In my second project we utilize differential reactor studies, in situ spectroscopy, and microkinetic modeling to develop a mechanistic understanding of these promotional effects. We find that Ta promotion enhances V reducibility and blocks a pathway for propylene loss that arises from formation of a V-peroxo species. Our mechanistic framework captures the key reactivity of these promoted materials, offering new insights for improved catalyst synthesis and enhanced propylene selectivity.³ We are currently applying these mechanistic insights to new projects that I am leading. For example, I secured grant funding to develop vanadium-based membrane reactors that we believe can enhance the selectivity of our catalyst based on our proposed catalytic cycle.
3. In 2016 boron nitride was shown to be highly active and selective as a catalyst for ODHP. Further research showed that many boron-based materials shared the same reactivity and utilized a mixed surface-and-gas phase mechanism.⁴ In my research I expanded on our understanding of boron-based materials by investigating how propylene is overoxidized over boron-based materials. In-situ X-ray experiments suggested the formation of a boron oxide layer on the catalyst that is implicated in reactivity.⁵ Through a combination of differential reactor studies and microkinetic modeling of the gas-phase chemistry, we demonstrated that, surprisingly, propylene likely overoxidizes in the gas-phase rather than on the surface of the catalytic material. We attempted to use radical mediators to modulate this selectivity but found minimal difference from the background reactivity. Our work identifies avenues key microkinetic pathways future research must focus on to improve propylene selectivity, the industrially-important metric for this chemistry.⁶

Works Cited

(1) Kurumbail, U.; Darji, H.D.; Alvear, M.; Hermans, I. In preparation.

(2) Grant, J. T.; Love, A. M.; Carrero, C. A.; Huang, F.; Panger, J.; Verel, R.; Hermans, I. Improved Supported Metal Oxides for the Oxidative Dehydrogenation of Propane. Top Catal 2016, 59 (17–18), 1545–1553.

(3) Al Abdulghani, A. J.^†; Kurumbail, U.^†; Dong, S.; Altvater, A. R.; Dorn, R.; Cendejas, M. C.; McDermott, W. P.; Agbi, T.O.; Queen, C.M.; Alvear, M.; Rossini, A.J.; Hermans, I.. In preparation. ^†Equal contribution

(4) Venegas, J. M.; Zhang, Z.; Agbi, T. O.; McDermott, W. P.; Alexandrova, A.; Hermans, I. Why Boron Nitride Is Such a Selective Catalyst for the Oxidative Dehydrogenation of Propane. Angewandte Chemie International Edition 2020, 59 (38), 16527–16535.

(5) Cendejas, M. C.; Paredes Mellone, O. A.; Kurumbail, U.; Zhang, Z.; Jansen, J. H.; Ibrahim, F.; Dong, S.; Vinson, J.; Alexandrova, A. N.; Sokaras, D.; Bare, S. R.; Hermans, I. Tracking Active Phase Behavior on Boron Nitride during the Oxidative Dehydrogenation of Propane Using Operando X-Ray Raman Spectroscopy. J. Am. Chem. Soc. 2023, 145 (47), 25686–25694.

(6) Kurumbail, U.; McDermott, W. P.; Lebrón-Rodríguez, E. A.; Hermans, I. From Microkinetic Model to Process: Understanding the Role of the Boron Nitride Surface and Gas Phase Chemistry in the Oxidative Dehydrogenation of Propane. React. Chem. Eng. 2024, 9, 795.