Iridium-based materials are among the most active bifunctional catalysts in heterogeneous catalysis and electrocatalysis. We have investigated the properties of atomically defined Ir/CeO2(111) model systems supported on Cu(111) and Ru(0001) by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, near ambient pressure X-ray photoelectron spectroscopy (NAP XPS), scanning tunneling microscopy, and temperature programmed desorption. Electronic metal-support interactions in the Ir/CeO2(111) system are accompanied by charge transfer and partial reduction of CeO2(111). The magnitude of the charge transfer depends strongly on the Ir coverage. The Ir/CeO2(111) system is stable against sintering upon annealing to 600 K in ultrahigh vacuum (UHV). Annealing of Ir/CeO2(111) in UHV triggers the reverse oxygen spillover above 450 K. The interaction of hydrogen with Ir/CeO2(111) involves hydrogen spillover and reversible spillover between 100 and 400 K accompanied by the formation of water above 190 K. Formation of water coupled with the strong reduction of CeO2(111) represents the dominant reaction channel upon annealing in H2 above 450 K. The interaction of Ir/CeO2(111) with oxygen has been investigated at moderate and NAP conditions. Additionally, the formation and stability of iridium oxide prepared by deposition of Ir in oxygen atmosphere was investigated upon annealing in UHV and under exposure to H2. The oxidation of Ir nanoparticles under NAP conditions yields stable IrOx nanoparticles. The stability of Ir and IrOx nanoparticles under oxidizing conditions is hampered, however, by encapsulation by cerium oxide above 450 K and additionally by copper and ruthenium oxides under NAP conditions.
Charge transfer and spillover phenomena in ceria-supported iridium catalysts: A model study
Present address: CEMNAT, Faculty of Chemistry and Technology, University of Pardubice, Nam. Cs. Legii 565, 53002 Pardubice, Czech Republic.
Note: The paper is part of the JCP Special Topic Collection on Catalytic Properties of Model Supported Nanoparticles.
Yaroslava Lykhach, Jan Kubát, Armin Neitzel, Nataliya Tsud, Mykhailo Vorokhta, Tomáš Skála, Filip Dvořák, Yuliia Kosto, Kevin C. Prince, Vladimír Matolín, Viktor Johánek, Josef Mysliveček, Jörg Libuda; Charge transfer and spillover phenomena in ceria-supported iridium catalysts: A model study. J. Chem. Phys. 28 November 2019; 151 (20): 204703. https://doi.org/10.1063/1.5126031
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