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Research article - Peer-reviewed, 2019

In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(II) carbene complex during an undirected C–H acetoxylation reaction

Yuan, Ning; Wendt, Ola F.; Persson, Ingmar; Majeed, Maitham H.; Bajnoczi, Eva G.; Persson, Axel R.; Wallenberg, L. Reine; Inge, A. Ken; Heidenreich, Niclas; Stock, Norbert; Zou, Xiaodong

Abstract

In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(ii) catalyzed undirected C-H acetoxylation reaction in the presence of an oxidant. A Pd(ii) N-heterocyclic carbene complex -stacked onto reduced graphene oxide (rGO) was used as the catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(ii) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(ii) are replaced by other ligands with a mean bond distance to Pd matching Pd-C/N/O. Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(iv) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(iv) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(ii)-Pd(iv)-Pd(ii) reaction mechanism.

Keywords

X-ray absorption spectroscopy (XAS); reaction mechanisms; palladium(II)

Published in

Catalysis science & technology
2019, volume: 9, number: 8, pages: 2025-2031

Authors' information

Yuan, Ning
Swedish University of Agricultural Sciences, Department of Molecular Sciences
Yuan, Ning
Stockholm University
Majeed, Maitham H.
Lund University
Bajnóczi, Éva (Bajnóczi, Éva)
Swedish University of Agricultural Sciences, Department of Molecular Sciences
Persson, Axel R.
Lund University
Wallenberg, L. Reine
Lund University
Inge, A. Ken
Stockholm University
Heidenreich, Niclas
Kiel University (CAU)
Stock, Norbert
Kiel University (CAU)
Zou, Xiaodong
Stockholm University
Wendt, Ola F.
Lund University
Swedish University of Agricultural Sciences, Department of Molecular Sciences

UKÄ Subject classification

Inorganic Chemistry

Publication Identifiers

DOI: https://doi.org/10.1039/C8CY02430H

URI (permanent link to this page)

https://res.slu.se/id/publ/99638