Designing Zeolites for More Sustainable Natural Gas Utilization and Evaluating Metal-Support Interactions to Enhance Catalyst StabilityKarpe, Sanjana (2024) Designing Zeolites for More Sustainable Natural Gas Utilization and Evaluating Metal-Support Interactions to Enhance Catalyst Stability. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractHeterogeneous catalysis is crucial for sustainable and economical chemical processes. However, despite its long history, catalysts to-date are designed mostly via expensive trial and error, motivating continued interest in rational catalyst design. Towards this goal, this dissertation centers on two primary projects. The first project focused on the design of metal-embedded zeolites for natural gas upgrading via methane dehydro-aromatization to benzene (MDA). Previous studies had shown that this reaction can be “intensified” by the use of microwave-assisted heating. However, while the highly efficient, direct heating of the metal site in a Fe-ZSM-5 catalysts via microwave energy resulted in strongly increased methane conversion, selectivity to the desired aromatics was much reduced due to the creation of intense metal hot spots, which leave the zeolite framework comparatively cold. Thus, we explored the design of SiC@Fe-ZSM-5 core@shell catalysts to reduce intra-catalyst temperature gradients by combining the activity of the metal-embedded zeolite with the high microwave susceptibility of SiC. We found that such rational catalyst structuring can indeed enable distinct temperatures of different catalyst components under microwave conditions, opening new avenues for process design. We furthermore investigated the impact of different forms of coke on the activity of these catalysts. MDA requires high temperatures for methane activation, which results in severe coking and rapid catalyst deactivation. We were able to identify different types of coke formed over the different catalytic sites in the catalyst (metal vs Brønsted acid sites), potentially informing the development of more efficient catalyst regeneration processes. The second, collaborative project focused on a fundamental understanding of metalsupport interactions—a key descriptor for catalyst stability. We developed a novel technique to directly measure force of adhesion between metal nanoparticles and supports and found that alloying metal nanoparticles results in an unexpectedly complex, nonlinear modification of the force of adhesion, which was explained by electron transfer between the two metals in the alloy and the underlying oxide support. Overall, these projects yielded new insights that can aid the rational design of catalysts, and hence improve application of heterogeneous catalysts in terms of their performance in activity, selectivity, and stability. Share
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