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

Muhammad A. Naeem, Dudari B. Burueva, Paula M. Abdala, Nikolai S. Bushkov, Dragos Stoian, Andrey V. Bukhtiyarov, Igor P. Prosvirin, Valerii I. Bukhtiyarov, Kirill V. Kovtunov, Igor V. Koptyug, Alexey Fedorov, Christoph R. Müller

Результат исследования: Научные публикации в периодических изданияхстатьярецензирование

4 Цитирования (Scopus)

Аннотация

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.

Язык оригиналаанглийский
Страницы (с-по)25299-25307
Число страниц9
ЖурналJournal of Physical Chemistry C
Том124
Номер выпуска46
DOI
СостояниеОпубликовано - 19 ноя 2020

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