Center for Molecular Modeling - FWO EOS FWOEOS2018002101

Confined hot-pressurized water in Brønsted-acidic beta zeolite speeds up the O-demethylation of guaiacol

massimo — Thu, 24 Nov 2022 13:15:33 +0000

M. Bocus, E. Van den Broeck, X. Wu, M. Bal, J. Bomon, L. Vanduyfhuys, B. F. Sels, B. U. W. Maes, V. Van Speybroeck

Nature Catalysis

8, 33-45

2025

Abstract

Biorefinery technologies that convert lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In these technologies, a key process is the acid-catalysed O-demethylation of guaiacol derivatives in hot-pressurized water using Brønsted mineral acids or microporous zeolites. The fundamental understanding of how hydronium ions behave in a confined environment versus bulk is still limited. Here we investigate the O-demethylation of guaiacol in hot-pressurized water with HCl or H-BEA zeolite catalysts to elucidate the impact of zeolite microporosity on reaction mechanisms and rates. Operando molecular simulations combined with experimental kinetic studies reveal that, regardless of the catalyst type, O-demethylation follows a concerted O-activated S_N2 mechanism. The reaction rate is higher in the zeolite due to more active, under-coordinated hydronium ions. Additionally, the molecular organization of solvent and reactants around the confined active site plays a crucial role in modulating the association of the reacting species and the reaction kinetics.

DOI

https://doi.org/10.1038/s41929-024-01282-6

Private attachment

Bocus_et_al-2025-Nature_Catalysis.pdf

Insights into the mechanism and reactivity of zeolite catalyzed alkylphenol dealkylation

massimo — Wed, 10 Aug 2022 07:41:32 +0000

M. Bocus, V. Van Speybroeck

ACS Catalysis

12, 22, 14227–14242

2022

Abstract

In the stride toward the production of low-carbon-footprint commodity chemicals, the development of a complete wood biorefinery plays a pivotal role. The lignin fraction of wood can be depolymerized and demethoxylated mainly into 4-alkylphenols. These phenolic compounds can further catalytically be C-dealkylated within the H-ZSM-5 zeolite at relatively high temperatures and in the presence of steam, producing phenol and olefins. Experimentally, the dealkylation reaction was found to have two striking features: first, different reactants possess very different reactivity. 4-Ethylphenol (4-EP) is somehow less reactive than 4-n-propylphenol (4-n-PP), which is in turn much less reactive than 4-isopropylphenol (4-iso-PP). Second, cofeeding of steam in the reaction mixture was necessary to prevent rapid and reversible catalyst deactivation. Herein, a combination of static and dynamic density functional theory (DFT) simulations is used to unravel the molecular and mechanistic origin of these observations. Free-energy profiles obtained from static calculations confirm the experimentally observed reactivity sequence, where our computations show that the secondary nature of the alkyl carbon involved in 4-iso-PP dealkylation strongly stabilizes the respective transition states. To investigate the effect of water on the mobility of the reactive species and their interaction with the active site, we investigated the diffusion of phenol along the H-ZSM-5 straight channel in the presence of water loadings from 0 to 3 molecules per zeolite unit cell. We show that water has a strongly beneficial effect in promoting desorption and diffusion of phenol away from the Brønsted acid site through competitive adsorption and by the formation of hydrogen bond chains with the diffusing phenol. This effect could lead to a shorter residence time inside the zeolite, preventing active site poisoning and condensation to bulkier biphenylether moieties.

DOI

https://doi.org/10.1021/acscatal.2c03844

Private attachment

acscatal.2c03844.pdf

Reductive imino-pinacol coupling reaction of halogenated aromatic imines and iminium ions catalyzed by precious metal catalysts using hydrogen

elias — Mon, 07 Jun 2021 06:55:02 +0000

K.N.R. Dumoleijn, E. Van den Broeck, J. Stavinoha, V. Van Speybroeck, K. Moonen, C.V. Stevens

Journal of Catalysis

400, 103-113

2021

Abstract

The first heterogeneously catalyzed process for the reductive coupling of imines and iminium ions is reported using precious metal catalysts in combination with hydrogen gas as the terminal reductant. The optimized method in terms of catalyst composition and reaction conditions allowed to produce aromatic vicinal diamines without the use of stoichiometric amounts of zero or low valent metals, which is currently the preferred method. The most important mechanistic features of the reaction were unraveled by a combined experimental and computational approach. The developed methodology is very efficient for the coupling of aromatic iminium ions with yields up to 88 % while imines give only low to moderate yields.

Gold Open Access

DOI

https://doi.org/10.1016/j.jcat.2021.05.023

Private attachment

1-s2.0-S0021951721002153-main (1).pdf

Shape-selective C–H activation of aromatics to biarylic compounds using molecular palladium in zeolites

massimo — Mon, 16 Nov 2020 16:24:26 +0000

J. Vercammen, M. Bocus, S. E. Neale, A. Bugaev, P. Tomkins, J. Hajek, S. Van Minnebruggen, A. Soldatov, A. Krajnc, G. Mali, V. Van Speybroeck, D. De Vos

Nature Catalysis

3, 1002-1009

2020

Abstract

The selective activation of inert C–H bonds has emerged as a promising tool for avoiding the use of wasteful traditional coupling reactions. Oxidative coupling of simple aromatics allows for a cost-effective synthesis of biaryls. However, utilization of this technology is severely hampered by poor regioselectivity and by the limited stability of state-of-the-art homogeneous Pd catalysts. Here, we show that confinement of cationic Pd in the pores of a zeolite allows for the shape-selective C–H activation of simple aromatics without a functional handle or electronic bias. For instance, out of six possible isomers, 4,4′-bitolyl is produced with high shape selectivity (80%) in oxidative toluene coupling on Pd-Beta. Not only is a robust, heterogeneous catalytic system obtained, but this concept is also set to control the selectivity in transition-metal-catalysed arene C–H activation through spatial confinement in zeolite pores.

DOI

http://dx.doi.org/10.1038/s41929-020-00533-6

Private attachment

Paper_final.pdf

Access to bio-renewable and CO2-based polycarbonates from exovinylene cyclic carbonates

elias — Tue, 10 Nov 2020 08:30:01 +0000

F. Siragusa, E. Van den Broeck, C. Ocando, A. Müller, G. De Smet, B. U. W. Maes, J. De Winter, V. Van Speybroeck, B. Grignard, C. Detrembleur

ACS Sustainable Chemistry & Engineering

9 (4), 1714–1728

2021

Abstract

We investigate the scope of the organocatalyzed step-growth copolymerization of CO2-sourced exovinylene bicyclic carbonates with bio-based diols into polycarbonates. A series of regioregular poly(oxo-carbonate)s were prepared from sugar- (1,4-butanediol and isosorbide) or lignin-derived (1,4-benzenedimethanol and 1,4-cyclohexanediol) diols at 25 °C with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst, and their defect-free structure was confirmed by nuclear magnetic resonance spectroscopy studies. Their characterization by differential scanning calorimetry and wide-angle X-ray scattering showed that most of them were able to crystallize. When the polymerizations were carried out at 80 °C, some structural defects were introduced within the polycarbonate chains, which limited the polymer molar mass. Model reactions were carried out to understand the influence of the structure of alcohols, the temperature (25 or 80 °C), and the use of DBU on the rate of alcoholysis of the carbonate and on the product/linkage selectivity. A full mechanistic understanding was given by means of static- and dynamic-based density functional theory (DFT) calculations showing the determining role of DBU in the stability of intermediates, and its important role in the rate-determining steps is revealed. Furthermore, the origin of side reactions observed at 80 °C was discussed and rationalized by DFT modeling. As impressive diversified bio-based diols are accessible on a large scale and at low cost, this process of valorization of carbon dioxide gives new perspectives on the sustainable production of bioplastics under mild conditions.

DOI

http://dx.doi.org/10.1021/acssuschemeng.0c07683

Private attachment

acssuschemeng.0c07683.pdf

Brønsted Acid Catalyzed Tandem Defunctionalization of Biorenewable Ferulic acid and Derivates into Bio-catechol

samuel — Fri, 10 Jan 2020 13:57:03 +0000

J. Bomon, E. Van den Broeck, M. Bal, Y. H. Liao, S. Sergeyev, V. Van Speybroeck, B. F. Sels, B. U. W. Maes

Angewandte Chemie int. Ed.

59 (8), 3063-3068

2020

Abstract

An efficient conversion of biorenewable ferulic acid into bio‐catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C−O (demethylation) and C−C (de‐2‐carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H2SO4) as catalyst in pressurized hot water (250 °C, 50 bar N2). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di‐ (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work‐up.

DOI

https://doi.org/10.1002/anie.201913023

Private attachment

Bomon_et_al-2019-Angewandte_Chemie.pdf

A switchable domino process for the construction of novel CO2‐sourced sulfur‐containing building blocks and polymers

wim — Mon, 15 Jul 2019 08:17:06 +0000

F. Ouhib, B. Grignard, E. Van den Broeck, A. Luxen, K. Robeyns, V. Van Speybroeck, C. Jerome, C. Detrembleur

Angewandte Chemie int. Ed.

58 (34), 11768-11773

2019

Abstract

α‐Alkylidene cyclic carbonates (αCCs) recently emerged as attractive CO2‐sourced synthons for the construction of complex organic molecules. Herein, we report the transformation of αCCs into novel families of sulfur‐containing compounds by organocatalyzed chemoselective addition of thiols, following a domino process that is switched on/off depending on the desired product. The process is extremely fast and versatile in substrate scope, provides selectively linear thiocarbonates or elusive tetrasubstituted ethylene carbonates with high yields following a 100 % atom economy reaction, and valorizes CO2 as a renewable feedstock. It is also exploited to produce a large diversity of unprecedented functional polymers. It constitutes a robust platform for the design of new sulfur‐containing organic synthons and important families of polymers.

DOI

http://dx.doi.org/10.1002/anie.201905969

Private attachment

ange.201905969.pdf

FWO EOS (Sustainable chemistry from wood)

samuel — Wed, 11 Dec 2019 08:43:44 +0000

SAP ref.

FWOEOS2018

Promotor(s)

V. Van Speybroeck

Description

Fossil oil depletion imposes a societal driven shift to non-edible biomass as a renewable
feedstock for chemicals. Wood is among the most abundant carbon sources on earth, and is
ideal to address this challenge. Wood contains (hemi)cellulose (carbohydrates) and lignin, a
polymeric network of arenes. Biorefineries mostly focus on the former, using lignin only as low
value fuel. This project's ambitious aim is to transform lignin into high-value chemicals and
polymers, starting with the very challenging selective depolymerization of lignin. In
KULeuven's ‘lignin-first' concept, even before carbohydrate valorization, wood is treated in a
selective way to recover just 4 biobased aromatic molecules in high yield. Next, selective
catalytic (de)functionalization of the 4 molecules will lead to catechol and pyrogallol.
Innovative synthetic methods (aminations, reductions, C(sp2)-O cross-coupling and
C(sp2/sp3)-H functionalization) will transform these into important chemicals (substituted
phenols, anilines etc). Finally, biobased chemicals are coupled with CO2 to form valuable
functional polymers. Modelling, e.g. via Advanced Molecular Dynamics will allow to rationalize
and even predict reactivity and selectivity in realistic operating conditions, lending strong
support to the development of new concepts for transformation of aromatics.

Attachments (ZAP restricted field)

Aanvraag

Massimo Bocus

wim — Mon, 01 Oct 2018 12:58:35 +0000

FWO EOS G0H0918N

wim — Thu, 24 May 2018 07:02:06 +0000

Project promotor

V. Van Speybroeck

Financierende instantie

FWO

Project data

01/01/2018 to 31/12/2021

Bedrag

€619 736,83

Project titel

Bio based factory: Sustainable chemistry from wood

Project ref.

FWO EOS FWOEOS2018002101