Karen Hemelsoet

Ghent University | UGhent · Department of Textiles

The absorption properties of UiO-type metal–organic frameworks are computed using TD-DFT simulations on the organic linkers. A set of nine isoreticular structures, including the UiO-66 and UiO-67 materials and functionalized variants, are examined. The excitation energies from a static geometry optimization are compared with dynamic averages obtain...

Zinc gallate doped with chromium is a recently developed near-infrared emitting persistent phosphor, which is now extensively studied for in vivo bioimaging and security applications. The precise mechanism of this persistent luminescence relies on defects, in particular, on antisite defects and antisite pairs. A theoretical model combining the soli...

The role of water in the methanol-to-olefins (MTO) process over H-SAPO-34 has been elucidated by a combined theoretical and experimental approach, encompassing advanced molecular dynamics simulations and in-situ micro-spectroscopy. First principle calculations at the molecular level point out that water competes with methanol and propene for direct...

The application of pH-sensitive dye molecules onto textile materials is a promising method for the development of sensor materials. Ten commonly used pH-indicators, namely sulfonphthaleine dyes, are applied onto polyamide 6 using two distinct methods: conventional dyeing of fabrics and dye-doping of nanofibres. The influence of the substituents of...

A combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-X materials. This study, in which both mono- and difunctionalized linkers (with X = OH, NH2, or SH) are investigated, aims to obtain a more complete picture of the choice of functionali...

Ammonia-Selective Catalytic Reduction (NH3-SCR) using Cu-zeolites is a well-established strategy for the abatement of NOx gases. Recent studies have demonstrated that Cu is particularly active when exchanged into the SSZ-13 zeolite, and its location in either the 6r or 8r renders it an excellent model system for fundamental studies. In this work, w...

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functio...

A new concept has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M2(BTC)(NO3)(DMF) (M = Ba or Sr, H3BTC = 1,3,5-benzenetricarboxylic acid, DMF = N,N-dimethylformamide) was studied as a function of their activation procedure. The catalytic a...

To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous c...

A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitat...

Sulfonphthaleine dyes are an important class of pH indicators, finding applications in novel (textile) sensors. In this paper, we present a combined experimental and theoretical study to elucidate the halochromic behaviour of a large set of sulfonphthaleine compounds. Starting from an experimental analysis consisting of UV–Vis spectroscopy, the pH...

Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Brønsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 ad...

The optical absorption properties of (poly)aromatic hydrocarbons occluded in a nanoporous environment were investigated by theoretical and experimental methods. The carbonaceous species are an essential part of a working catalyst for the methanol-to-olefins (MTO) process. In situ UV/Vis microscopy measurements on methanol conversion over the acidic...

A gallium 2,2’-bipyridine-5,5’-dicarboxylate metal–organic framework (MOF), denoted as COMOC-4, has been synthesized by solvothermal synthesis. This MOF exhibits the same topology as MOF-253. CuCl2 was incorporated into COMOC-4 by a post-synthetic modification (PSM). The spectroscopic absorption properties of the MOF framework before and after PSM...

Diphosphonylated diazaheterocyclic compounds were synthesized in a one-step reaction by using dimethyl trimethylsilyl phosphite (DMPTMS) under acidic conditions. The reaction of DMPTMS with 1,5-naphthyridine yielded the corresponding diphosphonylated product through a tandem 1,4–1,2 addition under microwave conditions. This tandem 1,4–1,2 addition...

The methanol to olefins process is an alternative for oil-based production of ethene and propene. However, detailed information on the reaction mechanisms of olefin formation in different zeolite is lacking. Herein a first principle kinetic study allows elucidating the importance of a side-chain mechanism during methanol conversion in H-SAPO-34. St...

The methylation of ethene, propene, and trans-2-butene on zeolites H-ZSM-58 (DDR), H-ZSM-22 (TON), and H-ZSM-5 (MFI) is studied to elucidate the particular influence of topology on the kinetics of zeolite-catalyzed reactions. H-ZSM-58 and H-ZSM-22 are found to display overall lower methylation rates compared to H-ZSM-5 and also different trends in...

The conversion of methanol to olefins (MTO) over a heterogeneous nanoporous catalyst material is a highly complex process involving a cascade of elementary reactions. The elucidation of the reaction mechanisms leading to either the desired production of ethene and/or propene or undesired deactivation has challenged researchers for many decades. Cle...

A gallium 2,2′-bipyridine-5,5′-dicarboxylate metal−organic framework, Ga(OH)(bpydc), denoted as COMOC-4 (COMOC = Center for Ordered Materials, Organometallics and Catalysis, Ghent University) has been synthesized via solvothermal synthesis procedure. The structure has the topology of an aluminum 2,2′-bipyridine-5,5′-dicarboxylate − the so-called MO...

A gallium 2,2′-bipyridine-5,5′-dicarboxylate metal−organic framework, Ga(OH)(bpydc), denoted as COMOC-4 (COMOC = Center for Ordered Materials, Organometallics and Catalysis, Ghent University) has been synthesized via solvothermal synthesis procedure. The structure has the topology of an aluminum 2,2′-bipyridine-5,5′-dicarboxylate − the so-called MO...

Nanofibres functionalised with pH-sensitive dyes could greatly contribute to the development of stimuli-responsive materials. However, the application of biocompatible polymers is vital to allow for their use in (bio)medical applications. Therefore, this paper focuses on the development and characterisation of pH-sensitive polycaprolactone (PCL) na...

The formation and nature of active sites for methanol conversion over solid acid catalyst materials are studied by using a unique combined spectroscopic and theoretical approach. A working catalyst for the methanol‐to‐olefin conversion has a hybrid organic–inorganic nature in which a cocatalytic organic species is trapped in zeolite pores. As a cas...

Shiny disco catalysts! The cover picture shows a cationic hydrocarbon pool species of increasing size and methylation degree confined in a zeolitic cage. In their Full Paper on p. 173 ff., V. Van Speybroek, B. M. Weckhuysen et al. explain that these aromatic hydrocarbon species are reaction intermediates, coke precursors, or both, for the methanol-...

It is of great interest to introduce pH-sensitive dyes into fibrous materials since this may result in flexible sensor systems. However, to date, the effect of a textile matrix on the halochromic properties of dyes is still unknown which severely limits their further development. Therefore, this paper focuses on an in-depth study of the halochromis...

The halochromism in solution of a prototypical example of an azo dye, ethyl orange, was investigated by using a combined theoretical and experimental approach. Experimental UV/Vis and Raman spectroscopy pointed towards a structural change of the azo dye with changing pH value (in the range pH 5-3). The pH-sensitive behavior was modeled through a se...

Since many industrially important processes start with the adsorption of guest molecules inside the pores of an acidic zeolite catalyst, a proper estimate of the adsorption enthalpy is of paramount importance. In this contribution, we report ab initio calculations on the adsorption of water, alcohols, and nitriles at the bridging Bronsted sites of...

Theoretical and experimental IR data are combined to gain insight into the methanol and ethanol conversion over an acidic H-SAPO-34 catalyst. The theoretical simulations use a large finite cluster and the initial physisorption energy of both alcohols is calculated. Dispersive contributions turn out to be vital and ethanol adsorbs stronger than meth...

Organophosphorus additives are used as coke-inhibiting agents to reduce coking, an undesirable process that occurs in cracking units. DFT calculations show that organophosphorus radicals compete with coke-inducing carbonaceous radicals for the peripheral sites of the growing coke layer. The figure illustrates the organophosphorus radical that adds...

The efficacy of organophosphorus radicals as anticoking agents was subjected to a computational study in which a representative set of radicals derived from industrially relevant organophosphorus additives was used to explore competitive reaction pathways on the graphene-like coke surface formed during thermal cracking. The aim was to investigate t...

The role of naphthalenic species during the methanol-to-olefins (MTO) process in a silicoaluminophosphate zeolitic material exhibiting the chabazite topology (H-SAPO-34) has been studied from first principles. These species could either act as active olefin-eliminating compounds or as precursors for deactivating species. Results incorporating van d...

We present a validation of computationally efficient density functional-based methods for the reproduction of relative bond dissociation energies of large polyaromatic hydrocarbons. Through the calculation of intrinsic radical stabilities and the computation of spin densities, the extent of delocalization of the unpaired electron in the benzylic ra...

Methylations of ethene, propene, and butene by methanol over the acidic microporous H-ZSM-5 catalyst are studied by means of state of the art computational techniques, to derive Arrhenius plots and rate constants from first principles that can directly be compared with the experimental data. For these key elementary reactions in the methanol to hyd...

TAMkin is a program for the calculation and analysis of normal modes, thermochemical properties and chemical reaction rates. At present, the output from the frequently applied software programs ADF, CHARMM, CPMD, CP2K, Gaussian, Q-Chem, and VASP can be analyzed. The normal-mode analysis can be performed using a broad variety of advanced models, inc...

Ring opening of 1-arylmethyl-2-(cyanomethyl)aziridines with HBr afforded 3-(arylmethyl)amino-4-bromobutyronitriles via regiospecific ring opening at the unsubstituted aziridine carbon. Previous experimental and theoretical reports show treatment of the same compounds with benzyl bromide to furnish 4-amino-3-bromobutanenitriles through ring opening...

The control of stereochemistry in the free radical polymerization of methyl methacrylate (MMA) is important because the physical properties of PMMA are often significantly affected by the main-chain tacticity. In this study, the role of the solvent on the tacticity of MMA polymerization has been investigated by considering the propagation rate cons...

Thermodynamic properties of phosphorus-containing compounds were investigated using high-level ab initio computations. An extended set of contemporary density functional theory (DFT) procedures was assessed for their ability to accurately predict bond dissociation energies of a set of phosphoranyl radicals. The results of meta- and double-hybrids a...

Methylation reactions of naphthalenic species over the acidic microporous zeolite with chabazite topology have been investigated by means of two-layered ab initio computations. Large cluster results combined with van der Waals contributions provide thermodynamic and kinetic results of successive methylation steps. The growth of fused bicyclic speci...

Ozonation of the quinolone antibiotic levofloxacin was investigated with focus on both the levofloxacin degradation rate and degradation product formation. Degradation was about 2 times faster at pH 10 compared to pH 3 and 7 explained by direct ozonation at the unprotonated N4('), one of the tertiary amines of the piperazinyl substituent. H2O2 conc...

Carbon-hydrogen bond dissociation enthalpy (BDE) values are computed for the class of benzylic radicals. An extended and representative set of large methylated polyaromatics has been submitted to an accurate computational Study using various levels of theory. The hybrid B3P86 as well as two contemporary functionals (BMK and M05-2X) are applied. For...

The growth of polycyclic aromatic hydrocarbons (PAHs) is in many areas of combustion and pyrolysis of hydrocarbons an inconvenient side effect that warrants an extensive investigation of the underlying reaction mechanism, which is known to be a cascade of radical reactions. Herein, the focus lies on one of the key reaction classes within the coke f...

Density functional theory results are presented for elementary steps leading to coke growth within a steam cracking unit. The discussed pathway starts from toluene and ultimately, 1-methylnaphthalene is formed. In order to find the rate determining step for coke formation, the pseudo first-order rate coefficients of the various steps are compared t...

Theoretical calculations are presented on elementary reactions which are important during coke formation in a thermal cracking unit. This process is known to proceed through a free radical chain mechanism. The elementary reaction steps that lead to the growth of the coke surface can be divided into five classes of reversible reactions: hydrogen abs...

Hydrogen abstraction reactions at polyaromatic hydrocarbons by a methyl radical are investigated from the viewpoint of DFT-based reactivity descriptors. The BMK functional succeeds in accurately reproducing experimental data for the global indicators. All species are found to be soft. The local HSAB principle shows an overall good qualitative agree...

The regioselectivity of ring-forming radical reactions is investigated within the framework of the so-called spin-polarized conceptual density functional theory. Two different types of cyclizations were studied. First, a series of model reactions of alkyl- and acyl-substituted radicals were investigated. Next, attention was focused on the radical c...

The dependence of global reactivity descriptors on electronic structure method as well as basis set is investigated for typical reactions in zeolite catalysis. This research is especially focused on hard−hard interactions between small probe molecules (such as chloromethane, methanol, ethylene, and propene) and different zeolite clusters containing...

Thermodynamic and kinetic properties relating to hydrogen abstraction by methyl radical from various sites in polycyclic aromatic hydrocarbons (PAHs) have been investigated. The reaction enthalpies (298 K), barriers (0 K), and activation energies and pre-exponential factors (700-1100 K), have been calculated by means of density functional theory, s...

The reaction enthalpy (298 K), barrier (0 K), and activation energy and preexponential factor (600-800 K) have been examined computationally for the abstraction of hydrogen from benzene by the methyl radical, to assess their sensitivity to the applied level of theory. The computational methods considered include high-level composite procedures, inc...

The cyclization of functionalized aminophosphonates is studied on both experimental and theoretical grounds. In a recently described route to phosphono-beta-lactams [Stevens C. V.; Vekemans, W.; Moonen, K.; Rammeloo, T. Tetrahedron Lett. 2003, 44, 1619], it was found that starting from an ambident allylic anion only four-membered rings were formed...

The applicability of the hard and soft acids and bases principle is investigated for the interaction of 5T zeolite clusters with probe molecules such as chloromethane, methanol and olefins. The reactions are intermediately hard–hard and, therefore, mainly charge-controlled. This is confirmed by the success of the atomic charges and the electrostati...

Density functional theory calculations are used to determine the kinetics and reactivity indices of the first propagation steps of the polyethylene and poly(vinyl chloride) polymerization. Transition state theory is applied to evaluate the rate coefficient from the microscopically determined energies and partition functions. A comparison with the e...

The reactivity of polyaromatics involved in various radical reactions is studied. The reactions under study are hydrogen abstractions by a methyl radical and additions to double bonds both intra- and intermolecular. The chemical reactivity of the involved molecules is described through different properties, which are calculated within the density f...

Theoretical ab initio calculations are presented on cyclization reactions of polyaromatics that occur by a radical mechanism. Such processes are one of the elementary steps for polyaromatic hydrocarbon formation in thermal cracking units and during soot formation. Ring closure can take place at various sites of the polyaromatic surface. It is the a...

Ab initio Density Functional Theory calculations are presented on cyclization and hydrogen abstraction reactions of various polycyclic aromatic hydrocarbons (PAH) which are important for numerous applications. Attention is focussed on the influence of the local structure of the cluster on the reactivity of these elementary radical processes. This i...