TY - JOUR

T1 - Deciphering the Nature of Ru Sites in Reductively Exsolved Oxides with Electronic and Geometric Metal-Support Interactions

AU - Naeem, Muhammad A.

AU - Burueva, Dudari B.

AU - Abdala, Paula M.

AU - Bushkov, Nikolai S.

AU - Stoian, Dragos

AU - Bukhtiyarov, Andrey V.

AU - Prosvirin, Igor P.

AU - Bukhtiyarov, Valerii I.

AU - Kovtunov, Kirill V.

AU - Koptyug, Igor V.

AU - Fedorov, Alexey

AU - Müller, Christoph R.

N1 - Funding Information: The authors acknowledge the Scientific Center for Optical and Electron Microscopy (ScopeM) at ETH Zürich for the use of their electron microscopy facilities and Dr. A. Kierzkowska (ETH Zürich) for performing TEM analysis. ESRF and the Swiss Norwegian Beamlines (SNBL at ESRF) are gratefully acknowledged for providing access to the synchrotron facility. Financial support from the Competence Center of Energy and Mobility (CCEM), Swiss National Science Foundation R’Equip grant (4879135), Swiss Grid, Stiftung Claude & Giuliana, and the Swiss National Science Foundation (200020_156015) is greatly appreciated. V.I.B. and I.V.K. thank RSF (grant no: 19-13-00172) for the support of the catalyst characterization via XPS. D.B.B. and K.V.K. thank RFBR (19-29-10003 and 19-43-540004) and the Russian Ministry of Science and Higher Education (AAAA-A16-116121510087-5) for financial support. Publisher Copyright: © 2020 American Chemical Society. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/11/19

Y1 - 2020/11/19

N2 - The reductive exsolution of metallic Ru from fluorite-type solid solutions Ln2Ru0.2Ce1.8O7 (Ln = Sm, Nd, La) leads to materials with metal-support interactions that influence the electronic state and the catalytic activity of Ru. In situ X-ray absorption spectroscopy at the Ru K-edge identified that with increasing temperature, the exsolution of Ru from Sm2Ru0.2Ce1.8O7 in a H2 atmosphere proceeds via an intermediate Ruδ+ state, that is, Ru4+→Ruδ+→Ru0. X-ray photoelectron spectroscopy (XPS) established that, in parallel (H2 atmosphere at ca. 500 °C), also Ce4+ ions reduce to Ce3+, which is accompanied by an electron transfer from the reduced host oxide to the exsolved Ru0 clusters, creating Ruδ- states. Low-temperature diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) using CO as a probe molecule reveals a red shift of the CO adsorption bands by ca. 18 cm-1 when increasing the temperature during the H2 treatment from 300 to 500 °C, consistent with an increased π-backdonation from more electron-rich Ru species to CO. However, at a lower reduction temperature of ca. 100 °C, a blue-shifted CO band is observed that is explained by a Lewis-acidic Ruδ+-CO adduct. Nuclear magnetic resonance (NMR) signal enhancement in parahydrogen-induced polarization experiments was used as a structure-sensitive probe and revealed a decreasing propene hydrogenation rate with increasing exsolution temperature, accompanied by a notable enhancement of propane hyperpolarization (ca. 3-fold higher at 500 °C than at 300 °C). These data suggest that the exsolved, subnanometer-sized Ru species are more active in propene hydrogenation but less selective for the pairwise addition of p-H2 to propene than Ruδ- sites engaged in a strong metal-support interaction.

AB - The reductive exsolution of metallic Ru from fluorite-type solid solutions Ln2Ru0.2Ce1.8O7 (Ln = Sm, Nd, La) leads to materials with metal-support interactions that influence the electronic state and the catalytic activity of Ru. In situ X-ray absorption spectroscopy at the Ru K-edge identified that with increasing temperature, the exsolution of Ru from Sm2Ru0.2Ce1.8O7 in a H2 atmosphere proceeds via an intermediate Ruδ+ state, that is, Ru4+→Ruδ+→Ru0. X-ray photoelectron spectroscopy (XPS) established that, in parallel (H2 atmosphere at ca. 500 °C), also Ce4+ ions reduce to Ce3+, which is accompanied by an electron transfer from the reduced host oxide to the exsolved Ru0 clusters, creating Ruδ- states. Low-temperature diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) using CO as a probe molecule reveals a red shift of the CO adsorption bands by ca. 18 cm-1 when increasing the temperature during the H2 treatment from 300 to 500 °C, consistent with an increased π-backdonation from more electron-rich Ru species to CO. However, at a lower reduction temperature of ca. 100 °C, a blue-shifted CO band is observed that is explained by a Lewis-acidic Ruδ+-CO adduct. Nuclear magnetic resonance (NMR) signal enhancement in parahydrogen-induced polarization experiments was used as a structure-sensitive probe and revealed a decreasing propene hydrogenation rate with increasing exsolution temperature, accompanied by a notable enhancement of propane hyperpolarization (ca. 3-fold higher at 500 °C than at 300 °C). These data suggest that the exsolved, subnanometer-sized Ru species are more active in propene hydrogenation but less selective for the pairwise addition of p-H2 to propene than Ruδ- sites engaged in a strong metal-support interaction.

KW - PARAHYDROGEN-INDUCED POLARIZATION

KW - CO-ADSORPTION

KW - IN-SITU

KW - HETEROGENEOUS HYDROGENATION

KW - RUTHENIUM NANOPARTICLES

KW - GOLD NANOPARTICLES

KW - AMMONIA-SYNTHESIS

KW - SOLID-SOLUTIONS

KW - CATALYSTS

KW - TIO2

UR - http://www.scopus.com/inward/record.url?scp=85096621238&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.0c07203

DO - 10.1021/acs.jpcc.0c07203

M3 - Article

AN - SCOPUS:85096621238

VL - 124

SP - 25299

EP - 25307

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 46

ER -