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Efficient Ammonia Synthesis over a Core-shell Ru/CeO2 Catalyst with Tunable CeO2 Size: DFT Calculation and XAS Spectroscopy Studies

Abstract

In the present work, Ru@CeO2 catalysts similar in core-shell morphology but different in nanoparticle sizes (95, 150 and 225 nm) were obtained by varying the hydrothermal time for the preparation of colloid carbon spheres to be used as templates. The surface areas of these catalysts are in the range of 111–146 m2/g. After in situ H2 treatment at 450 °C for 4 h, the Ru@CeO2-9 catalyst with the nanoparticle size of 225 nm has an ammonia synthesis rate of 13504 μmol/gNH3.h at 1 MPa (N2:H2 = 1:3) and 425 °C. The results of XAS, Raman and XPS investigations reveal that the active sites in the form of Ru-hydride and Ru0 clusters of the Ru@CeO2 catalysts for ammonia synthesis. Moreover, H2 treatment results in strengthening of ruthenium–ceria interaction, which is beneficial for ammonia formation. It is demonstrated that the size of nanoparticle has a strong effect on the strength of ruthenium–ceria interaction, which influences the reduction degree of ruthenium and cerium as well as the amount of generated Ru-hydride species. The outcomes of DFT calculation provide evidence that the strength of ruthenium–cerium interaction is associated with N2 adsorption energy. In comparison with Ru/CeO2-CP synthesized by co-precipitation method, the core–shell structure of Ru@CeO2 affords larger surface area, stronger metal-support interaction and more reductive species, and the consequence is higher ammonia synthesis rate.

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Publication details

The article was accepted on 28 Nov 2018 and first published on 30 Nov 2018


Article type: Research Article
DOI: 10.1039/C8QI01244J
Citation: Inorg. Chem. Front., 2018, Accepted Manuscript
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    Efficient Ammonia Synthesis over a Core-shell Ru/CeO2 Catalyst with Tunable CeO2 Size: DFT Calculation and XAS Spectroscopy Studies

    X. Wang, X. Peng, Y. Zhang, J. Ni, C. Au and L. Jiang, Inorg. Chem. Front., 2018, Accepted Manuscript , DOI: 10.1039/C8QI01244J

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