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ReaxFF Simulations of Lignin Fragmentation on a Palladium-Based Heterogeneous Catalyst in Methanol-Water Solution
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.ORCID iD: 0000-0001-8735-5397
Number of Authors: 42018 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 18, p. 5233-5239Article in journal (Refereed) Published
Abstract [en]

The interaction of fragments derived from lignin depolymerization with a heterogeneous palladium catalyst in methanol-water solution is studied by means of experimental and theoretical methodologies. Quantum chemistry calculations and molecular dynamics simulations based on the ReaxFF approach are combined effectively to obtain an atomic level characterization of the crucial steps of the adsorption of the molecules on the catalyst, their fragmentation, reactions, and desorption. The main products are identified, and the most important routes to obtain them are explained through extensive computational procedures. The simulation results are in excellent agreement with the experiments and suggest that the mechanisms comprise a fast chemisorption of identified fragments from lignin on the metal interface accompanied by bond breaking, release of some of their hydrogens and oxygens to the support, and eventual desorption depending on the local environment. The strongest connections are those involving the aromatic rings, as confirmed by the binding energies of selected representative structures, estimated at the quantum chemistry level. The satisfactory agreement with the literature, quantum chemistry data, and experiments confirms the reliability of the multilevel computational procedure to study complex reaction mixtures and its potential application in the design of high-performance catalytic devices.

Place, publisher, year, edition, pages
2018. Vol. 9, no 18, p. 5233-5239
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-161204DOI: 10.1021/acs.jpclett.8b02275ISI: 000445713200006PubMedID: 30130109OAI: oai:DiVA.org:su-161204DiVA, id: diva2:1258941
Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-04-01Bibliographically approved
In thesis
1. Theoretical Investigations of C–O Activation in Biomass
Open this publication in new window or tab >>Theoretical Investigations of C–O Activation in Biomass
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on using computational chemistry approaches to study how biobased molecules interact with both homo- and heterogeneous catalysts. The reaction mechanisms of such transformations have also been studied.

The first section comprises studies of interactions between organic molecules and a heterogeneous catalyst in the palladium-catalyzed depolymerization of models of lignin derivatives. From experiments, it was proposed that a keto intermediate and its enol tautomer play a significant role in the β-O-4′ bond cleavage. The study in the first section of this thesis has been divided into three parts. First, simplified models of the keto intermediate and its enol tautomer were used to investigate the adsorption to a Pd(111) surface. By using a combination of periodic density functional theory (DFT) calculations and a constrained minima hopping method, the most stable adsorption which is the so-called global minimum, was found to be an enol adsorbed to the surface.

In the second part, the study was expanded to cope with models of lignin which were used in experiments. In addition, we studied the effect of adsorbate coverage, where two different Pd(111) super cells were compared. The optimizations were performed via dispersion-corrected density functional theory (DFT-D3). The molecules were found to bind more strongly to the surface at low coverages. These results support the experimental data and show that the tautomerization has an important role during lignin depolymerization. 

The third part relates to using a multilevel procedure to study the interaction of fragments derived from lignin depolymerisation with a palladium catalyst in a solvent mixture. Specifically, QM calculations and MD simulations based on the ReaxFF approach were combined to explore the reaction mechanisms occurring on Pd surfaces with lignin derivatives obtained from a solvolysis reaction. The strongest adsorptions were found to be between the aromatic rings and the Pd surfaces.

The second section focuses on a Brønsted acid-catalyzed nucleophilic substitution of the hydroxyl group in alcohols. Experimentally, phosphinic acid (H3PO2) was found to be an excellent catalyst for the direct intramolecular substitution of non-derivatized alcohols proceeding with good to excellent chirality transfer. In this section, benzylic alcohols with internal O-, N-, and S-centered nucleophiles were used in the calculations. By using a hybrid functional method, we found a bicyclic transition state where the proton of the H3PO2 protonates the leaving hydroxyl group, and the oxo-group of the same catalyst partially deprotonates the nucleophile. The transition state energies for the reactions were determined computationally. The calculations support an SN2 mechanism, which corresponds to the experimental data where inversion of the stereogenic carbon was observed.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2019. p. 77
Keywords
DFT calculations, global minima hopping, reactive force field, lignin, palladium, nucleophilic substitution
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-167592 (URN)978-91-7797-709-4 (ISBN)978-91-7797-710-0 (ISBN)
Public defence
2019-05-22, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2019-04-25 Created: 2019-04-01 Last updated: 2020-05-18Bibliographically approved

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