Esben Taarning

Haldor Topsøe, Lyngby, Capital Region, Denmark

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Publications (35)216.5 Total impact

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    ABSTRACT: This review is aimed to be a brief tutorial covering the deactivation of solid catalysts in liquid phase, with specific focus on the leaching case, which can be especially helpful to researchers not familiarized with catalytic processes in liquid phase. Leaching refers to the loss of active species from the solid that are transferred into the liquid medium, causing eventually a deactivation of the catalyst. Intriguingly, not many published studies deal with leaching, since this is a specific phenomenon in liquid phase and heterogeneous catalysis occurs traditionally in gaseous phase. However, as a consequence of the development of new processes for biorefieneries, an increasing number of reactions deal with liquid media, and thus, the stability and reusability of solid catalyst in this situation represents a huge challenge that requires specific attention. Leaching of active phases is particularly problematic because of its irreversibility and it can be one of the main causes of catalyst deactivation in liquid media, threatening the sustainability of the process. This tutorial review presents a survey of the main aspects concerning the deactivation due to leaching of active species from the solid catalyst: mechanisms, detection methods, impact of these factors on the global activity and finally, some procedures to try to minimize the leaching or to cope with it. A decision flowchart is presented to help in the study of the catalyst stability and reusability. Interesting biomass conversion reactions have been chosen as examples to illustrate the importance of these aspects.
    No preview · Article · Jun 2015 · Green Chemistry
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    Vitaly L. Sushkevich · Irina I. Ivanova · Esben Taarning
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    ABSTRACT: Synthesis of butadiene-1,3 from ethanol has been studied over silver doped (1 wt%) Zr-containing molecular sieves ZrBEA, ZrMCM-41 and ZrO2 supported on silica. The catalysts were characterized by X-ray diffraction, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, 29Si MAS NMR, SEM/EDX, TEM and FTIR of adsorbed CD3CN. The activity of the catalysts was found to increase in the following range: Ag/ZrO2/SiO2 < Ag/ZrMCM-41 < Ag/ZrBEA. This activity range correlated with the content of Lewis acid sites in the catalysts determined by FTIR of adsorbed CD3CN. The best catalyst performance in terms of butadiene yield was observed over ZrBEA (Si/Zr = 100) promoted with silver, which showed butadiene selectivity of 56% at ethanol conversion of 48%.
    Preview · Article · Feb 2015 · Green Chemistry
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    ABSTRACT: This study focuses on increasing the selectivity to methyl lactate from sugars using stannosilicates as heterogeneous catalyst. All group I ions are found to have a promoting effect on the resulting methyl lactate yield. Besides, the alkali ions can be added both during the preparation of the catalyst or directly to the solvent mixture to achieve the highest reported yield of methyl lactate (ca. 75 %) from sucrose at 170 °C in methanol. The beneficial effect of adding alkali to the reaction media applies not only to highly defect-free Sn-Beta prepared through the fluoride route, but also to materials prepared by post-treatment of dealuminated commercial Beta zeolites, as well as ordered mesoporous stannosilicates, in this case Sn-MCM-41 and Sn-SBA-15. These findings open the door to the possibility of using other preparation methods or different Sn-containing silicates with equally high methyl lactate yields as Sn-Beta. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jan 2015 · ChemSusChem
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    ABSTRACT: The crystallization of Sn-Beta in fluoride medium is greatly influenced by the amount and type of tin source present in the synthesis gel. By varying the amount of tin in the form of tin(IV) chloride pentahydrate, the time required for crystallization was studied. It was found that tin not only drastically affects the time required for crystallization, but also that the presence of tin changes the morphology of the formed Sn-Beta crystals. For low amounts of tin (Si/Sn = 400) crystallization occurs within four days and the Sn-Beta crystals are capped bipyramidal in shape, whereas for high amounts of tin (Si/Sn = 100) it takes about sixty days to reach full crystallinity and the resulting crystals are highly truncated, almost plate-like in shape. Using SEM-WDS to investigate the tin distribution along transverse sections of the Sn-Beta crystals, a gradient distribution of tin was found in all cases. It was observed that the tin density in the outer parts of the Sn-Beta crystals is roughly twice as high as in the tin depleted core of the crystals. Sn-Beta was found to obtain its maximum catalytic activity for the conversion of dihydroxyacetone to methyl lactate close to the minimum time required for obtaining full crystallinity. At excessive crystallization times, the catalytic activity decreased, presumably due to Ostwald ripening.
    Full-text · Article · Oct 2014
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    ABSTRACT: The synthesis of buta-1,3-diene from ethanol has been studied over metal-containing (M=Ag, Cu, Ni) oxide catalysts (MOx=MgO, ZrO2, Nb2O5, TiO2, Al2O3) supported on silica. Kinetic study of a wide range of ethanol conversions (2–90 %) allowed the main reaction pathways leading to butadiene and byproducts to be determined. The key reaction steps of butadiene synthesis were found to involve ethanol dehydrogenation, acetaldehyde condensation, and the reduction of crotonaldehyde with ethanol into crotyl alcohol. Catalyst design included the selection of active components for each key reaction step and merging of these components into multifunctional catalysts and adjusting the catalyst functions to achieve the highest selectivity. The best catalytic performance was achieved over the Ag/ZrO2/SiO2 catalyst, which showed the highest selectivity towards butadiene (74 mol %).
    No preview · Article · Sep 2014 · ChemSusChem
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    ABSTRACT: A Series of Zr-containing catalysts including bulk ZrO2, ZrO2 supported on silica, titania and ceria, Zr-BEA zeolite and Zr-MCM-41 mesoporous material was prepared and characterized by X-ray diffraction, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, Si-29 MAS NMR, TPD NH3, and FTIR of adsorbed CO. The catalytic materials were tested in the MPVO reaction of crotonaldehyde and ethanol in the temperature range of 473-573 K. The results showed that the activity of Zr-based catalysts in the MPVO reduction of crotonaldehyde correlates with the amount of Zr4+ Lewis acid sites in the catalysts. Tetrahedral Zr atom sites isolated within the crystalline structure of zeolite BEA were found to be the most efficient. The best catalyst performance in terms of selectivity was observed over ZrBEA: 72% selectivity to crotyl alcohol was achieved at crotonaldehyde conversion of 15%.
    No preview · Article · Jul 2014 · Journal of Catalysis

  • No preview · Chapter · Dec 2013
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    ABSTRACT: Furylglycolic acid (FA), a pseudoaromatic hydroxy-acid suitable for copolymerization with lactic acid, can be produced from glucose via enzymatically derived cortalcerone using a combination of Brønsted and Lewis acid catalysts. Cortalcerone is first converted to furylglyoxal hydrate (FH) over a Brønsted acid site (HCl or Al-containing beta-zeolite), and FH is subsequently converted to FA over a Lewis acid site (Sn-beta zeolite). Selectivity for conversion of FH to FA is as high as 80% at 12% conversion using tetrahydrofuran (THF) as a solvent at 358 K. Higher conversion of FH leads to FA-catalyzed degradation of FH and subsequent deactivation of the catalyst by the deposition of carbonaceous residues. The deactivated catalyst can be regenerated by calcination. Cortalcerone can be produced from 10% glucose solution using recombinant Escherichia coli strains expressing pyranose 2-oxidase and aldos-2-ulose dehydratase from the wood-decay fungus Phanerochaete chrysosporium BKM-F-1767. This enzymatically derived cortalcerone is converted in one pot to FA in a methanol/water solvent over an Al-containing Sn-beta zeolite possessing both Brønsted and Lewis acid sites, achieving 42% selectivity to FA at 53% cortalcerone conversion.
    Preview · Article · Oct 2013 · ACS Catalysis

  • No preview · Patent · Aug 2013
  • Vitaly L. Sushkevich · Irina I. Ivanova · Esben Taarning
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    ABSTRACT: AbstractA silica‐supported Ag catalyst has been shown to be an efficient heterogeneous catalyst for the oxidant‐free dehydrogenation of ethanol into acetaldehyde. The reaction mechanism has been investigated by in situ FTIR spectroscopy. The kinetic isotope effects for proton and hydride abstraction have been studied by using CH3CD2OH and CH3CH2OD as labeled reactants. The results indicate that OH bond activation and the formation of a hydrogen‐bonded complex take place on the silica support and that the Ag particles are necessary for the activation of the CH bond. The kinetic isotope effect (k H/k D) is 1.9 for CH3CD2OH and 1.8 for CH3CH2OD. The concerted mechanism of CH cleavage on the Ag sites and proton abstraction on the silica sites is proposed to account for the results of the spectroscopic and kinetic experiments.
    No preview · Article · Aug 2013 · ChemCatChem
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    ABSTRACT: Solid acid catalysts were studied at temperatures near 523 K for the production of benzene, toluene, and p-xylene by the reaction of ethylene with furan, 2-methylfuran, and 2,5-dimethylfuran, respectively, through the combination of cycloaddition and dehydrative aromatization reactions. Catalysts containing Brønsted acid and Lewis acid sites (i.e., WOx–ZrO2, niobic acid, zeolite Y, silica–alumina) were more active than catalysts containing predominantly Lewis acid sites (γ-Al2O3, TiO2), which indicates the importance of Brønsted acidity in the production of aromatics. Microporosity is not required for this reaction, because amorphous solid acids and homogeneous Brønsted acids demonstrate significant activity for p-xylene production. The production of p-xylene from 2,5-dimethylfuran proceeded at higher rates compared with the production of toluene and benzene from 2-methylfuran and furan, respectively. Both WOx–ZrO2 and niobic acid demonstrate superior activity for aromatics production than does zeolite Y. WOx–ZrO2 demonstrates a turnover frequency for p-xylene production that is 35 times higher than that demonstrated by zeolite Y. In addition, mesoporous materials such as WOx–ZrO2 offer higher resistance to deactivation by carbon deposition than do microporous materials. Results from Raman spectroscopy and the trend of turnover frequency with varying tungsten surface densities for a series of WOx–ZrO2 catalysts are consistent with previous investigations of other acid-catalyzed reactions; this suggests that the high reactivity of WOx–ZrO2 is mainly associated with the presence of subnanometer WOx clusters mixed with zirconium, which reach a maximum surface concentration at intermediate tungsten coverage.
    No preview · Article · Jul 2013 · ChemCatChem
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    ABSTRACT: The selective conversion of biomass-derived substrates is one of the major challenges facing the chemical industry. Recently stannosilicates have been employed as highly active and selective Lewis acid catalysts for a number of industrially relevan reactions. In the present work, four different stannosilicates have been investigated: Sn-BEA, Sn-MFI, Sn-MCM-41 and Sn-SBA-15. When comparing the properties of tin sites in the structures, substantial differences are observed. Sn-beta displays the highes Lewis acid strength, as measured by probe molecule studies using infrared spectroscopy, which gives it a significantly highe activity at low temperatures than the other structures investigated. Furthermore, the increased acid strength translates int large differences in selectivity between the catalysts, thus demonstrating the influence of the structure on the active site and pointing the way forward for tailoring the active site to the desired reaction.
    Preview · Article · Jul 2012 · Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences
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    ABSTRACT: The formation of hydroxymethylfurfural (HMF) from glucose was studied. It was found that the CrCl2-catalyzed conversion in the ionic liquid, butylmethylimidazolium chloride ([Bmim]Cl) leads to negligible quantities of 3-deoxyglucosone confirming that fructose is the main intermediate. It was found that the environmentally unfriendly chromium salt could be replaced with zeolite (H-ZSM-5) leading to a 45% yield of HMF. It was also found that the solvent [Bmim]Cl could be replaced with non-toxic tetrabutylammonium chloride (TBAC) giving a 56% yield of HMF.
    No preview · Article · Feb 2012 · Tetrahedron Letters

  • No preview · Article · Feb 2012 · ChemInform
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    ABSTRACT: Conversions of various pentoses and hexoses into methyl lactate has been demonstrated for the Sn-Beta catalyst. It is found that pentoses are converted to methyl lactate in slightly lower yields (40%) than what is obtained for hexoses (50%), but higher yields of glycolaldehyde dimethyl acetal are observed for the pentoses. This finding is in accordance to a reaction pathway that involves the retro aldol condensation of the sugars to form a triose and glycolaldehyde for the pentoses, and two trioses for hexoses. When reacting glycolaldehyde (formally a C2-sugar) in the presence of Sn-Beta, aldol condensation occurs, leading to the formation of methyl lactate, methyl vinylglycolate and methyl 2-hydroxy-4-methoxybutanoate. In contrast, when converting the sugars in water at low temperatures (100 °C), Sn-Beta catalyses the isomerisation of sugars (ketose–aldose epimers), rather than the formation of lactates.
    Full-text · Article · Jan 2012 · Green Chemistry
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    ABSTRACT: From petroleum to bioleum: Since biomass is a limited resource, it is necessary to consider its best use. The production of select chemicals from biomass, rather than its use as fuel, could effectively replace the use of petroleum in the chemical industry, but the inherent functionality of biomass must be exploited (see picture).
    No preview · Article · Nov 2011 · Angewandte Chemie International Edition

  • No preview · Article · Nov 2011 · Angewandte Chemie

  • No preview · Article · Sep 2011 · ChemInform
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    ABSTRACT: Hierarchical (or mesoporous) zeolites have attracted significant attention during the first decade of the 21st century, and so far this interest continues to increase. There have already been several reviews giving detailed accounts of the developments emphasizing different aspects of this research topic. Until now, the main reason for developing hierarchical zeolites has been to achieve heterogeneous catalysts with improved performance but this particular facet has not yet been reviewed in detail. Thus, the present paper summaries and categorizes the catalytic studies utilizing hierarchical zeolites that have been reported hitherto. Prototypical examples from some of the different categories of catalytic reactions that have been studied using hierarchical zeolite catalysts are highlighted. This clearly illustrates the different ways that improved performance can be achieved with this family of zeolite catalysts. Finally, future opportunities for hierarchical zeolite catalysts are discussed, and the virtues of various preparation methods are outlined, including a discussion of possible pitfalls in the evaluation of new, potential hierarchical zeolite catalysts.
    No preview · Article · Jun 2011 · Catalysis Today
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    ABSTRACT: Heterogeneous catalysts have been a central element in the efficient conversion of fossil resources to fuels and chemicals, but their role in biomass utilization is more ambiguous. Zeolites constitute a promising class of heterogeneous catalysts and developments in recent years have demonstrated their potential to find broad use in the conversion of biomass. In this perspective we review and discuss the developments that have taken place in the field of biomass conversion using zeolites. Emphasis is put on the conversion of lignocellulosic material to fuels using conventional zeolites as well as conversion of sugars using Lewis acidic zeolites to produce useful chemicals.
    No preview · Article · Mar 2011 · Energy & Environmental Science

Publication Stats

2k Citations
216.50 Total Impact Points


  • 2010-2015
    • Haldor Topsøe
      Lyngby, Capital Region, Denmark
  • 2014
    • Lomonosov Moscow State University
      • Division of Chemistry
      Moskva, Moscow, Russia
  • 2007-2010
    • Technical University of Denmark
      • Department of Chemistry
      København, Capital Region, Denmark