CHBE 565-International Paper Co Seminar-Prof. Siddarth Krishna, University of Wisconsin (Host: Prof. Elizabeth Rogers) "Tuning the Dynamic Structure and Reactivity of Metal-Zeolites for Sustainable Catalytic Chemistries"
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- Christy Bowser
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Abstract. Catalysts that accelerate chemical reactions will play a central role in enabling new sustainable transformations. Placing metal active sites in the ordered nanopores of aluminosilicate zeolites offers a degree of control over their structures and, moreover, their dynamic evolution during catalysis. First, I will discuss redox reactions facilitated by zeolite-tethered metal cations, where combining reaction kinetics and in situ X-ray absorption spectroscopy enables elucidation of reaction mechanisms. In the reduction of greenhouse gas nitrous oxide (N2O) and toxic nitric oxide (NOx) by ammonia (NH3) over iron-zeolites, we show that the reaction involves rate-limiting oxidation of Fe2+ by N2O, balanced by Fe3+ competitive reduction pathways involving NO and/or NH3. In the selective oxidation of olefins to carbonyl products by bifunctional palladium-copper zeolites (which could replace corrosive homogeneous catalysts), stable catalytic function is achieved only when water vapor is condensed in zeolite pores to create a liquid-like reaction environment. Finally, I will discuss the design of supported metal catalysts for the reversible (de)hydrogenation of N-heterocyclic liquid hydrogen carriers, a strategy for H2 storage in chemical bonds. While reactant-induced metal chelation is a persistent challenge in liquid-phase reactions, we show that encapsulating metal clusters in zeolite pores protects them from sintering during hydrogenation reactions. Taken together, these insights guide the design of active, selective, stable metal-zeolite catalysts for sustainable chemical transformations.
Bio: Siddarth H. Krishna is the Duane H. and Dorothy M. Bluemke Assistant Professor of Chemical and Biological Engineering at the University of Wisconsin-Madison. He obtained his B.S. in Chemical Engineering from UC-Berkeley (2010-2014). He obtained his PhD in Chemical Engineering from UW-Madison (2014-2019) as an NSF Graduate Research Fellow under the supervision of James Dumesic and George Huber. He was then a Henson Postdoctoral Fellow at Purdue (2019-2021) with Rajamani Gounder. Krishna joined UW-Madison as a faculty member in January 2022, where his group combines precise catalyst synthesis, in situ characterization, and reaction kinetics to enable rational catalyst design for sustainable chemical transformations. Krishna is the recipient of an ACS PRF Doctoral New Investigator award (2022), and an award from the NSF DMREF program (2025) leading a collaborative research team studying dynamic catalytic behavior. Krishna has served in leadership roles in the Catalysis Club of Chicago including VP (2023-2024), President (2024-2025), and Director (2025-2027). He also serves on the Early Career Board for Journal of Catalysis.