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In Situ XAS Investigation of the Deactivation and Reactivation Mechanisms of a Heterogeneous Palladium(II) catalyst during the Cycloisomerization of Acetylenic Acids
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0003-2758-4811
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Organic Chemistry.ORCID iD: 0000-0001-9329-0091
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2019 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The cause and mechanism of deactivation of a well-studied heterogeneous palladium(II) catalyst in the intramolecular lactonization of acetylenic acids to γ-alkylidene lactones have been investigated. It was shown that the deactivation was driven by the formation of reduced palladium species following the addition of the base triethylamine. In this work, X-ray absorption spectroscopy (XAS) was used to identify the palladium species and follow their evolution over the course of the reaction. It was also found that the choice of substrates has significant influences on the Pd species under the same reaction conditions. With these insights into the deactivation mechanism derived from XAS, different strategies were tested and illustrated to regain or maintain the active state of the catalyst. This information was further used to develop a new protocol, which can effectively prevent the deactivation of the catalyst and prolong its usage. 

Place, publisher, year, edition, pages
2019.
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-167289OAI: oai:DiVA.org:su-167289DiVA, id: diva2:1299081
Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-09Bibliographically approved
In thesis
1. Unveiling Catalytic Species in Suspension/Solution-Based Reactions by In Situ X-Ray Absorption Spectroscopy: Evolution of Palladium and Ruthenium Species
Open this publication in new window or tab >>Unveiling Catalytic Species in Suspension/Solution-Based Reactions by In Situ X-Ray Absorption Spectroscopy: Evolution of Palladium and Ruthenium Species
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The palladium (Pd) and ruthenium (Ru) species in several attractive catalysts have been probed using X-ray absorption spectroscopy (XAS). The study of catalyst evolution in suspension- and solution-based reactions was the primary aim. It was achieved by performing in situ XAS experiments on Pd and Ru over the course of the reactions. A custom-made reactor was employed which allowed the catalysts to be mixed with other reaction components under desired conditions.

The first system investigated was the Heck coupling reaction catalyzed by Pd(II) complexes embedded on metal-organic frameworks. It was realized that the as-synthesized catalysts go through an instant ligand substitution process when added to the reaction mixture. Mononuclear Pd complexes are the active species at the first stage of the measurement which then gradually transform into Pd nanoclusters. At a later stage of the measurement, chloride ligands start to bind to surface atoms of the Pd nanoclusters, leading to a deactivation of the catalyst. Following the first successful in situ XAS experiment, Pd(II) carbene complexes catalyzing undirected C–H acetoxylation of benzene in the presence of an oxidant were explored. A gradual ligand substitution occurs, and the mean oxidation state of Pd increases at the same time. At a later stage, Pd nanoclusters form, while the mean oxidation state of Pd returns to the start value. Deactivation of a heterogeneous Pd(II) catalyst during cycloisomerization of acetylenic acids was then investigated using in situ XAS. The choice of substrates showed to significantly influence the nature of Pd species, and the reduction of Pd(II) forming Pd(0) aggregates causes the deactivation. Moreover, strategies of reactivating the catalyst and prevention of the deactivation were developed and examined. In the end, the activation process of a Ru catalyst was studied and the structure of the intermediate was determined by in situ XAS. It was demonstrated that an electron-donating substituent on the cyclopentadiene ligand exhibits a promoting effect on the activation, while an electron-withdrawing substituent inhibits the activation.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2019. p. 112
Keywords
Palladium and ruthenium species, Catalysts, Suspension and solution, In situ X-ray absorption spectroscopy, Activation, Deactivation
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-167340 (URN)978-91-7797-578-6 (ISBN)978-91-7797-579-3 (ISBN)
Public defence
2019-05-21, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

Available from: 2019-04-25 Created: 2019-03-26 Last updated: 2019-04-12Bibliographically approved

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