NSLS-II Friday Lunchtime Seminar

"Effect of Metal (Pt, Ir) Nuclearity in the Subnanometer Regime on CO Oxidation Activity"

Presented by Ayman M. Karim, Department of Chemical Engineering, Virginia Polytechnic Institute and State University

Friday, February 21, 2020, 12:00 pm — NSLS-II Bldg. 743 Room 156

Supported noble metal catalysts are extensively used in industry and their catalytic performance is strongly affected by particle size and shape. In the last decade, supported single atoms and clusters in the subnanometer size regime have attracted a lot of interest since they maximize the metal utilization and have also shown extraordinary catalytic properties for many reactions. However, to tailor the catalyst properties for specific reactions and determine possible limitations, there is a need to understand, on the atomic scale, the origin of reactivity in the subnanometer regime. In this seminar, I will present my group's efforts in understanding the role of metal nuclearity and electronic properties in catalyzing CO oxidation as a model reaction. Using a suite of advanced characterization techniques (aberration-corrected electron microscopy, microcalorimetry, in-situ and in-operando DRIFTS, XPS, EXAFS and HERFD-XANES) complemented by DFT calculations and detailed kinetics measurements, the catalyst structural and electronic properties are identified and correlated with the reaction kinetics. In the talk, CO oxidation on Ir and Pt single atoms and subnanometer clusters supported on MgAl2O4 and CeO2, respectively, will be presented. We identified the active Ir and Pt single atom complexes and show that the reaction follows a combination of Eley-Rideal and Mars-van Krevelen mechanisms. Moreover, we show that despite considered a non-reducible support, CO oxidation on MgAl2O4 supported Ir subnanometer clusters follows a similar mechanism as on a reducible oxide where O2 is activated at the metal-support interface. Finally, the role of metal-support interaction in O2 activation and effect of CO binding strength on the catalytic activity will be discussed.

Hosted by: Ignace Jarrige

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