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Unveiling Catalytic Species in Suspension/Solution-Based Reactions by In Situ X-Ray Absorption Spectroscopy: Evolution of Palladium and Ruthenium Species
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University. (Prof. Xiaodong Zou's group)ORCID iD: 0000-0003-2758-4811
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 [en]
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: urn:nbn:se:su:diva-167340ISBN: 978-91-7797-578-6 (print)ISBN: 978-91-7797-579-3 (electronic)OAI: oai:DiVA.org:su-167340DiVA, id: diva2:1299134
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
List of papers
1. Probing the Evolution of Palladium Species in Pd@MOF Catalysts during the Heck Coupling Reaction: An Operando X-ray Absorption Spectroscopy Study
Open this publication in new window or tab >>Probing the Evolution of Palladium Species in Pd@MOF Catalysts during the Heck Coupling Reaction: An Operando X-ray Absorption Spectroscopy Study
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2018 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 26, p. 8206-8217Article in journal (Refereed) Published
Abstract [en]

The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (H-1 NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl- ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-159117 (URN)10.1021/jacs.8b03505 (DOI)000438309400026 ()29890070 (PubMedID)
Funder
Swedish Research CouncilBerzelii Centre EXSELENT
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2019-07-12Bibliographically approved
2. In Situ XAS Study of the Local Structure and Oxidation State Evolutions of Palladium in a Reduced Graphene Oxide Supported Pd(II) Carbene Complex during an Undirected C−H Acetoxylation Reaction
Open this publication in new window or tab >>In Situ XAS Study of the Local Structure and Oxidation State Evolutions of Palladium in a Reduced Graphene Oxide Supported Pd(II) Carbene Complex during an Undirected C−H Acetoxylation Reaction
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2019 (English)In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 9, no 8, p. 2025-2031Article in journal (Refereed) Published
Abstract [en]

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 p-stacked onto reduced graphene oxide (rGO) was used as 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 bond distance to Pd corresponding to carbon, nitrogen and/or oxygen (L). 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.

National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-167338 (URN)10.1039/C8CY02430H (DOI)000465404200027 ()
Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-27Bibliographically approved
3. In Situ XAS Investigation of the Deactivation and Reactivation Mechanisms of a Heterogeneous Palladium(II) catalyst during the Cycloisomerization of Acetylenic Acids
Open this publication in new window or tab >>In Situ XAS Investigation of the Deactivation and Reactivation Mechanisms of a Heterogeneous Palladium(II) catalyst during the Cycloisomerization of Acetylenic Acids
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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. 

National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-167289 (URN)
Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-09Bibliographically approved
4. Synthesis of Benzofurans and Indoles from Terminal Alkynes and Iodoaromatics Catalyzed by Recyclable Palladium Nanoparticles Immobilized on Siliceous Mesocellular Foam
Open this publication in new window or tab >>Synthesis of Benzofurans and Indoles from Terminal Alkynes and Iodoaromatics Catalyzed by Recyclable Palladium Nanoparticles Immobilized on Siliceous Mesocellular Foam
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2017 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 52, p. 12886-12891Article in journal (Refereed) Published
Abstract [en]

Herein, we report on the utilization of a heterogeneous catalyst, consisting of Pd nanoparticles supported on a siliceous mesocellular foam (Pd-0-AmP-MCF), for the synthesis of heterocycles. Reaction of o-iodophenols and protected o-iodoanilines with acetylenes in the presence of a Pd nanocatalyst produced 2-substituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands. Moreover, the structure of the reported Pd nanocatalyst was further elucidated with extended X-ray absorption fine-structure spectroscopy, and it was proven that the catalyst could be recycled multiple times without significant loss of activity.

Keywords
benzofurans, extended x-ray absorption fine structure, heterogeneous catalysis, indoles, palladium
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-148090 (URN)10.1002/chem.201702614 (DOI)000411033800029 ()28736879 (PubMedID)
Funder
Swedish Research CouncilBerzelii Centre EXSELENTEU, European Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2017-10-20 Created: 2017-10-20 Last updated: 2019-03-29Bibliographically approved
5. Application and further structure elucidation of Pd(0)-CalB CLEA biohybrid catalyst- Chemoenzymatic dynamic kinetic resolution of primary benzylic amines
Open this publication in new window or tab >>Application and further structure elucidation of Pd(0)-CalB CLEA biohybrid catalyst- Chemoenzymatic dynamic kinetic resolution of primary benzylic amines
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(English)Manuscript (preprint) (Other academic)
National Category
Organic Chemistry
Research subject
Organic Chemistry; Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-153897 (URN)
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2019-03-29Bibliographically approved
6. In-Situ Structure Determination of a Ruthenium Racemization Catalyst and its Activated Intermediates using X-ray Absorption Spectroscopy
Open this publication in new window or tab >>In-Situ Structure Determination of a Ruthenium Racemization Catalyst and its Activated Intermediates using X-ray Absorption Spectroscopy
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(English)Manuscript (preprint) (Other academic)
National Category
Organic Chemistry
Research subject
Organic Chemistry; Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-153950 (URN)
Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2019-03-29Bibliographically approved

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