Siddarth Krishna, Purdue University
"Elucidating Active Site Requirements for Sustainable Catalytic Chemistries"
Catalytic technologies that accelerate desired chemical transformations will play a central role in addressing sustainability challenges of the 21st century, such as producing chemicals from renewable resources and mitigating emissions of harmful pollutants. Rational catalyst design requires a fundamental understanding of how active sites facilitate reaction chemistries, particularly when multiple sites participate in catalysis. In this talk, I highlight three examples of chemistries involving multi-site phenomena; I use kineticmeasurements on materials with widely varying properties to distinguish the roles of each site within reaction mechanisms. First, I discuss the hydrogenolysis of biomass-derived intermediates to high-value chemicals. By varying the ratio and proximity of metal and acid sites, I demonstrate that acid sites facilitate rate-limiting C-O bond rupture, while metal sites hydrogenate reactive intermediates. Next, connections between the structure and reactivity of model silica-alumina catalysts reveal the distinct reactivities of two types of acid sites (Brønsted and Lewis). Finally, I discuss how NOx pollutants in automotive exhaust are eliminated by Cu cations supported on a crystalline aluminosilicate(‘zeolite’) lattice. By combining kinetics with X-ray spectroscopy, I show how Cu+ oxidation rates are influenced by the densities of Cu active sites and chargebalancing Al anions. Both the proximity and mobility of Cu ions influence their reactivity because the mechanism requires dynamic interactions between Cu sites. Taken together, these examples reveal how systematic investigations of multi-site phenomena provide design principles for sustainable catalytic chemistries.
Siddarth is currently a Henson postdoctoral fellow in Chemical Engineering at Purdue University under the supervision of Rajamani Gounder. He received his Ph.D. in Chemical Engineering from UW-Madison under the supervision of James Dumesic and George Huber in 2019, and received his B.S. in Chemical Engineering from UC-Berkeley in 2014. His research interests focus on fundamental catalytic principles to address sustainability challenges including automotive pollution abatement and upgrading of renewable feedstocks. In his free time, he enjoys hiking, frisbee, eating, and social distancing.