Experimental and Theoretical Study on the Nature of Adsorbed Oxygen Species on Shaped Ceria Nanoparticles

Abstract

Ceria is widely used in heterogeneous catalysis owing to its redox properties. Engineering the shape of ceria particles offers a powerful tool to develop materials with enhanced catalytic properties. In this study, we provide evidence for the shape-dependent dioxygen adsorption and activation of ceria nanoparticles with (111) and (100) facets by in situ Raman spectroscopy and relate these properties to unique adsorption sites employing density functional theory. Temperature- and gas-phase-dependent experiments demonstrate facilitated formation of peroxide, superoxide, and weakly bound dioxygen species on the (100) facets as rationalized by calculated vibrational frequencies of O2 2–, O2 –, and O2 species on CeO2–x (100) surfaces. Our results show that localization of the excess charge, driving the Ce4+ → Ce3+ reduction, significantly affects the stretching vibrations. Our approach provides a powerful basis for future developments of ceria-based catalysts by bridging the materials gap between idealized and real catalytic systems.

Infrared spectroscopy data- and physics-driven machine learning for characterizing surface microstructure of complex materials

“…First-principles models most often consider only one active site on a crystallographic plane, closely mimicking ultra-high vacuum single crystal experiments. The disparity between single crystal experiments, and associated calculations, and real-world materials is known as the materials gap [3][4][5] . Our ability to close the materials gap demands methods to quantify the types of surface sites of complex materials, along with their dynamic behavior under operando (working) conditions.…”

Shining Light on Indium Oxide Gas Sensors at Work: A Combined Operando Raman/UV-Vis/FT-IR Spectroscopic Study

“…We illustrate its potential in combined operando Raman/UV-Vis/FT-IR spectroscopic experiments on In2O3 gas sensors during EtOH and CO gas sensing. For example, in experiments during CO sensing (500 ppm), resistance measurements can be correlated with (i) simultaneous FT-IR gas phase spectra showing changes in the gas-phase composition (CO, CO2, H2O); (ii) Raman spectra revealing information on adsorbates (carbonate, formate) and hydroxy species, while in contrast to ceria no super-/peroxide species are observed [4], and (iii) UV-Vis spectra indicating In2O3 reduction by increased Vis absorption. Very recent experiments on SnO2 and CeO2 gas sensors demonstrate the general applicability of the combined operando approach.…”

Revealing the Li2O2 Nucleation Mechanisms on CeO2 Catalysts for Lithium‐Oxygen Batteries

“…Since the calculated formation energy of the oxygen vacancy in the subsurface is~0.28 eV lower than the surface one, the absence of superoxo and peroxo formation at this particular facet is assigned to a subsurface diffusion of O vacancies. However, Schilling et al [22] show through in situ Raman spectroscopy that in contrast to single crystals, the (111), truncated nanoparticles possess both surface and subsurface oxygen vacancies, and peroxides species do form at 35°C. [22] Therefore, both vacancy configurations should be considered in the (111) facet if aiming to describe the effect of CeO 2 nanoparticles in the context of the LOB.…”

“…The O 2 reduction leads to the oxidation of a Ce + 3 to Ce + 4 (see Figure 2), in agreement with previous reported calculations. [22] The adsorption energies of the more stable situations in the (110) and (100) surfaces areÀ 1.30 andÀ 2.03 eV, respectively, in contrast to the SSOV (111) one where O 2 presents a physical adsorption with a bond height of 1.83 Å and a d OÀ O bond length of 1.26 Å, close to the one of the neutral O 2 , 1.23 Å. Furthermore, in this last case, the two Ce + 3 remains at the surface, and the O 2 is not reduced, confirming previous results by Sauer and coworkers.…”

“…[19] It has been shown that the catalytic performance of ceria nanoparticles depends on its morphology and that the redox activity varies on the different exposed CeO 2 facets. [20][21][22] Even in the context of the LOB, it has been reported that NPs with filmlike morphology exhibits higher capacity than octahedral and spherical ones. [23] However, no details are given regarding the different crystalline facets that are exposed in the reported NPs, and the higher capacity is explained in terms of higher surface area.…”