V. Van Speybroeck

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

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
A1

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

Hydrogen Clathrates: Next Generation Hydrogen Storage Materials

A. Gupta, G.V. Baron, P. Perreault, S. Lenaerts, R.-G. Ciocarlan, P. Cool, P. M. Mileo, S.M.J. Rogge, V. Van Speybroeck, G. Watson, P. Van der Voort, M. Houlleberghs, E. Breynaert, J.A. Martens, J.F.M. Denayer
Energy Storage Materials
41, 69-107
2021
A1

Abstract 

Extensive research has been carried on the molecular adsorption in high surface area materials such as carbonaceous materials and MOFs as well as atomic bonded hydrogen in metals and alloys. Clathrates stand among the ones to be recently suggested for hydrogen storage. Although, the simulations predict lower capacity than the expected by the DOE norms, the additional benefits of clathrates such as low production and operational cost, fully reversible reaction, environmentally benign nature, low risk of flammability make them one of the most promising materials to be explored in the next decade. The inherent ability to tailor the properties of clathrates using techniques such as addition of promoter molecules, use of porous supports and formation of novel reverse micelles morphology provide immense scope customisation and growth. As rapidly evolving materials, clathrates promise to get as close as possible in the search of “holy grail” of hydrogen storage. This review aims to provide the audience with the background of the current developments in the solid-state hydrogen storage materials, with a special focus on the hydrogen clathrates. The in-depth analysis of the hydrogen clathrates will be provided beginning from their discovery, various additives utilised to enhance their thermodynamic and kinetic properties, challenges in the characterisation of hydrogen in clathrates, theoretical developments to justify the experimental findings and the upscaling opportunities presented by this system. The review will present state of the art in the field and also provide a global picture for the path forward.

Gold Open Access

Crystals springing into action: metal-organic framework CUK-1 as a pressure-driven molecular spring dagger

P. Iacomi, J.S. Lee, L. Vanduyfhuys, K. H. Cho, P. Fertey, J. Wieme, D. Granier, G. Maurin, V. Van Speybroeck, J.-S. Chang, P.G. Yot
Chemical Science
12, 5682-5687
2021
A1

Abstract 

Mercury porosimetry and in situ high pressure single crystal X-ray diffraction revealed the wine-rack CUK-1 MOF as a unique crystalline material capable of a fully reversible mechanical pressure-triggered structural contraction. The near-absence of hysteresis upon cycling exhibited by this robust MOF, akin to an ideal molecular spring, is associated with a constant work energy storage capacity of 40 J/gr. Molecular simulations were further deployed to uncover the free-energy landscape behind this unprecedented pressure-responsive phenomenon in the area of compliant hybrid porous materials. This discovery is of utmost importance from the perspective of instant energy storage and delivery.

Open Access version available at UGent repository
Green Open Access

Towards modeling spatiotemporal processes in metal–organic frameworks

V. Van Speybroeck, S. Vandenhaute, A.E.J. Hoffman, S.M.J. Rogge
Trends in Chemistry
3 (8): 605-619
2021
A1

Abstract 

Metal–organic frameworks (MOFs) are hybrid materials constructed from metal clusters linked by organic linkers, which can be engineered for target functional applications in, for example, catalysis, sensing, and storage. The dynamic response of MOFs on external stimuli can be tuned by spatial heterogeneities such as defects and crystal size as well as by operating conditions such as temperature, pressure, moisture, and external fields. Modeling the spatiotemporal evolution of MOFs under operating conditions and at length and time scales comparable with experimental observations is extremely challenging. Herein, we give a status on the modeling of spatiotemporal processes in MOFs under working conditions and reflect on how modeling can be reconciled with in situ spectroscopy measurements.

Gold Open Access

Overview of N-rich antennae investigated in lanthanide-based temperature sensing

F. Vanden Bussche, A.M. Kaczmarek, V. Van Speybroeck, P. Van der Voort, C.V. Stevens
Chemistry - A European Journal
27 (25), 7214-7230
2021
A1

Abstract 

The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide‐based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light‐harvesting antenna is required. This Review provides an overview of the nitrogen‐rich antennae in lanthanide‐based temperature sensors, emitting in the visible light spectrum, and discusses their temperature sensor ability. The N‐rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. Molecular probes, consisting of small molecules, are first discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di‐ and polynuclear complexes, metal–organic frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal–organic frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range, and porous organic polymers are operative in the cryogenic‐to‐medium temperature range.

Open Access version available at UGent repository

DOI 

10.1002/chem.202100007

Coordination and activation of nitrous oxide by iron zeolites

M.L. Bols, B.E.R. Snyder, H.M. Rhoda, P. Cnudde, G. Fayad, R.A. Schoonheydt, V. Van Speybroeck, E.I. Solomon, B. F. Sels
Nature Catalysis
4, 332-340
2021
A1

Abstract 

Iron-containing zeolites are heterogeneous catalysts that exhibit remarkable activity in the selective oxidation of inert hydrocarbons and catalytic decomposition of nitrous oxide (N2O). The reduction of N2O is critical to both these functions, but experimental data tracking the iron active sites during N2O binding and activation are limited. Here, the N2O-ligated Fe(ii) active site in iron-exchanged zeolite beta is isolated and characterized by variable-temperature Mössbauer, diffuse reflectance UV-vis-NIR and Fourier transform infrared spectroscopy. N2O binds through the terminal nitrogen atom with substantial backbonding from the Fe(ii) centre at low temperature. At higher temperatures, the Fe–N2O interaction is weakened, facilitating isomerization to the O-bound form, which is competent in O-atom transfer. Density functional theory calculations show the geometric and electronic structure requirements for N2O binding and activation. A geometric distortion imposed by the zeolite lattice plays an important role in activating N2O. This highlights a mechanism for structural control over function in Fe-zeolite catalysts.

High-rate nanofluidic energy absorption in porous zeolitic frameworks

Y. Sun, S.M.J. Rogge, A. Lamaire, S. Vandenbrande, J. Wieme, C.R. Siviour, V. Van Speybroeck, J.-C. Tan
Nature Materials
20 (7), 1015–1023
2021
A1

Abstract 

Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and extrusion mechanisms under realistic, high-rate deformation conditions. Here, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate dependence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable and reusable impact energy absorbers for challenging new applications.

Correlating MOF-808 parameters with mixed-matrix membrane (MMM) CO2 permeation for a more rational MMM development

R. Thür, D. Van Havere, N. Van Velthoven, S. Smolders, A. Lamaire, J. Wieme, V. Van Speybroeck, D. De Vos, I. Vankelecom
Journal of Materials Chemistry A
9 (21), 12782-12796
2021
A1

Abstract 

Consistent structure-performance relationships for the design of MOF (metal-organic framework)-based mixed-matrix membranes (MMMs) for gas separation are currently scarce in MMM literature. An important step in establishing such relationships could be to correlate intrinsic MOF parameters, such as CO2 uptake and the CO2 adsorption enthalpy (Qst), with the separation performance indicators of the MMM (i.e. separation factor and permeability). Such a study presumes the availability of a platform MOF, which allows systematic comparison of the relevant MOF parameters. MOF-808 can take up the role of such platform MOF, owing to its unique cluster coordination and subsequent ease of introducing additional functional molecules. For this purpose, formic acid (FA) modulated MOF-808 (MOF-FA) was post-synthetically functionalized with five different ligands (histidine (His), benzoic acid (BA), glycolic acid (GA), lithium sulfate (Li2SO4) and trifluoroacetic acid (TFA)) to create a series of isostructural MOFs with varying affinity/diffusivity properties but as constant as possible remaining properties (e.g. particles size distribution). CO2 uptake and CO2 adsorption enthalpy of the MOFs were determined with CO2 sorption experiments and Clausius-Clapeyron analysis. These MOF properties were subsequently linked to the CO2/N2 separation factor and CO2 permeability of the corresponding MMM. Unlike what is often assumed in literature, MOF-808 CO2 uptake proved to be a poor indicator for MMM performance. In contrast, a strong correlation was observed between Qst at high CO2 loadings on one hand and CO2 permeability under varying feed conditions on the other hand. Furthermore, correlation coefficients of Qst,15 and Qst,30 (Qst at 15 and 30 cm3 (STP)/g) with the separation factor were significantly better than those calculated for CO2 uptake. The surprising lack of correlation between membrane performance and CO2 uptake and the strong correlation with Qst opens possibilities to rationally design MMMs and stresses the need for more fundamental research focused on finding consistent relationships between filler properties and the final membrane performance.

Non-food applications of natural dyes extracted from agro-food residues: A critical review

K.T. Phan, K. Raes, V. Van Speybroeck, M. Roosen, K. De Clerck, S. De Meester
Journal of Cleaner Production
126920
2021
A1

Abstract 

Fruit and vegetables contain molecules that have particular colors, which can potentially be an environmentally attractive substitute for their synthetic counterparts in (non )food applications. The most sustainable source for such natural colorants would be by the valorization of by-products from the fruit and vegetable industries, but qualitative and quantitative characteristics of food by-products for this purpose remain scarce. Natural dyes also show mediocre stability and affinity toward textile fibers, which questions their potential feasibility for application and level of sustainability to overcome these issues. This review describes three dye classes (i.e., anthocyanins, quinones, and carotenoids) along with their occurrence, mass, and concentration in by-products that are generated from agricultural losses as well as the fruit and vegetable processing industries. To tackle the shortcomings of natural dyes on fibers, several application techniques were collected from the literature. A discussion on techno-economic potential and environmental sustainability is included. The latter is done by including a life cycle assessment (LCA) to investigate the environmental impact of extracting anthocyanins, quinones, and carotenoids from fruit and vegetable processing by-products and their subsequent application to the dyeing process. The mapping of by-products for each natural dye class illustrates the vast availability of agro-food residues (>0.1 Mt annually in the EU-28) with a natural dye content of up to 56 kg/t DW for anthocyanins, 18 kg/t DW for quinones, and 593 kg/t DW for carotenoids. Metallic mordants are mostly favored for improving the fixation of natural dyes but entail potential environmental issues. Greener approaches, such as biomordants and enzymes, still show room for improvement, chemical modification methods might also guarantee dye fixation, though questionable in environmental sustainability. The different valorization scenarios of anthocyanins, quinones, and carotenoids from food waste, analyzed with LCA, showed the environmental competitiveness of these natural dyes, applied as a crude extract, compared to synthetic dyes. The valorization routes design shows that agricultural losses and food processing waste streams are adequate sources of natural dyes, especially to be applied in niche scale applications.

Identification of vanadium dopant sites in the metal–organic framework DUT-5(Al)

K. Maes, L.I.D.J. Martin, S. Khelifi, A.E.J. Hoffman, K. Leus, P. Van der Voort, E. Goovaerts, P.F. Smet, V. Van Speybroeck, F. Callens, H. Vrielinck
Physical Chemistry Chemical Physics (PCCP)
23, 7088-7100
2021
A1

Abstract 

Studying the structural environment of the VIV ions doped in the metal–organic framework (MOF) DUT-5(Al) ((AlIIIOH)BPDC) with electron paramagnetic resonance (EPR) reveals four different vanadium-related spectral components. The spin-Hamiltonian parameters are derived by analysis of X-, Q- and W-band powder EPR spectra. Complementary Q-band Electron Nuclear DOuble Resonance (ENDOR) experiments, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), X-Ray Diffraction (XRD) and Fourier Transform InfraRed (FTIR) measurements are performed to investigate the origin of these spectral components. Two spectral components with well resolved 51V hyperfine structure are visible, one corresponding to VIV=O substitution in a large (or open) pore and one to a narrow (or closed) pore variant of this MOF. Furthermore, a broad structureless Lorentzian line assigned to interacting vanadyl centers in each other's close neighborhood grows with increasing V-concentration. The last spectral component is best visible at low V-concentrations. We tentatively attribute it to (VIV=O)2+ linked with DMF or dimethylamine in the pores of the MOF. Simulations using these four spectral components convincingly reproduce the experimental spectra and allow to estimate the contribution of each vanadyl species as a function of V-concentration.

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