Zhongtian Mao¹, Pablo G. Lustemberg^2*, John R. Rumptz¹, M. Veronica Ganduglia-Pirovano², Charles T. Campbell¹

1 Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA

2 Instituto de Catálisis y Petroleoquímica (ICP-CSIC), C/Marie Curie 2, 28049 Madrid, Spain

* Corresponding authors emails: lustemberg@gmail.com

DOI10.24435/materialscloud:2020.0032/v1 [version v1]

Publication date: Mar 23, 2020

How to cite this record

Zhongtian Mao, Pablo G. Lustemberg, John R. Rumptz, M. Veronica Ganduglia-Pirovano, Charles T. Campbell, Ni Nanoparticles on CeO2(111): Energetics, Electron Transfer and Structure by Ni Adsorption Calorimetry, Spectroscopies and DFT , Materials Cloud Archive 2020.0032/v1 (2020), https://doi.org/10.24435/materialscloud:2020.0032/v1

Description

The morphology, interfacial bonding energetics and charge transfer of Ni clusters and nanoparticles on slightly-reduced CeO2-x(111) surfaces at 100 to 300 K have been studied using single crystal adsorption calorimetry (SCAC), low-energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and density functional theory (DFT). The initial heat of adsorption of Ni vapor decreased with the extent of pre-reduction (x) of the CeO2-x(111), showing that stoichiometric ceria adsorbs Ni more strongly than oxygen vacancies. On CeO1.95(111) at 300 K, the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Ni clusters on stoichiometric steps, followed by the Ni particles spreading onto less favorable terrace sites. At 100 K, the clusters nucleate on terraces due to slower diffusion. Adsorbed Ni monomers are in the +2 oxidation state, and they bind by ~45 kJ/mol more strongly to step sites than terraces. The measured heat of adsorption versus average particle size on terraces is favorably compared to DFT calculations. The Ce 3d XPS lineshape showed an increase in Ce3+/Ce4+ ratio with Ni coverage, providing the number of electrons donated to the ceria per Ni atom. The charge transferred per Ni is initially large but strongly decreases with increasing cluster size for both experiments and DFT, and shows large differences between clusters at steps versus terraces. This charge is localized on the interfacial Ni and Ce atoms in their atomic layers closest to the interface. This knowledge is crucial to understanding the nature of the active sites on the surface of Ni-CeO2 catalysts for which metal-oxide interactions play a very important role in the activation of O-H and C-H bonds. The changes in these interactions with Ni particle size (metal loading) and the extent of reduction of the ceria help to explain how previously reported catalytic activity and selectivity change with these same structural details.

Materials Cloud sections using this data

Files

File name	Size	Description
3x3.terrace.zip MD5md5:7ee60e7cb8d9c7bfd43fc8609427373e	44.8 MiB	DFT calculations corresponding to the models in CeO2(111) terrace.
references.zip MD5md5:079a8d40152e0be37dddca686808231a	252.2 KiB	DFT calculations necessary to obtain the reference values
5x3.steps.zip MD5md5:8a99107af9b427209760923ffba193f3	12.8 MiB	DFT calculations corresponding to the models in in CeO2(111) steps.
README.txt MD5md5:fcb1cbe308a8ada849cf6d1e56853d23	1.1 KiB	README

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External references

Keywords

Ni charge transfer Ni on CeO2 terrace and steps Ni heat of adsorption