Mathias Laurin

Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

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Publications (56)295.4 Total impact

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    ABSTRACT: Structural control of organic thin films on dielectric substrates is the key to tailor the physical properties of hybrid materials, e.g. for application in solar energy conversion, molecular electronics or catalysis. In this work, we investigate the molecular orientation of phthalic anhydride (PAA) films on atomically well-defined MgO(100) on Ag(100) using temperature-programmed infrared reflection absorption spectroscopy (TP-IRAS) in combination with density-functional theory (DFT). A robust procedure is presented to determine the orientation of the PAA molecules which relies on the intensity ratios of vibrational bands only. We show that even at deposition temperatures of 110 K the PAA multilayer grows with a specific molecular orientation, i.e. the PAA molecular plane is preferentially aligned parallel with the MgO surface. No change of molecular orientation occurs up to a temperature of 145 K. Between 145 and 160 K, the films restructures adopting a nearly flat-lying molecular orientation. Between 170 and 205 K the film undergoes a second structural transition to a crystalline phase. This transition is associated with a pronounced molecular reorientation. The molecules adopt a tilted orientation and, simultaneously, rotate around their C2 axes. The reorientation behavior suggests that the molecular orientation in the crystalline phase is controlled by the interaction with the MgO(100) substrate. At higher temperature, no further restructuring is observed until the PAA multilayer desorbs at temperatures above 230 K.
    Langmuir 06/2015; DOI:10.1021/acs.langmuir.5b01392 · 4.38 Impact Factor
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    ABSTRACT: A catalyst designed for homogeneous catalysis is shown to generate its own liquid phase if deposited onto a support. In this way, a macroscopically heterogeneous catalyst generates a microscopically homogeneous catalytic environment by self-organization. 2,2'-((3,3'-di-tert-butyl-5,5'-dimethoxy-[1,1'-biphenylj-2,2'-diyl)-bis(oxy))bis(4,4,5,5-tetraphenyl-1,3,2-dioxaphospholane) modified rhodium complexes molecularly adsorbed onto porous silica powder show surprisingly high activity and regioselectivity in the gas-phase hydroformylation of propene to but-anal, with no sign of deactivation. Operando IR investigations combined with density functional theory calculations confirm a side reaction: the aldol condensation of the butanal products. These heavier by-products accumulate inside the pores of the catalytic material. IR and gas chromatography show a direct relation between formation of enones, products of the aldol condensation, performance, and stability of the catalytic system. This demonstrates that the aldol condensation products generated in situ act as a solvent providing an ideal environment to the impregnated homogeneous catalyst. (c) 2014 Elsevier Inc. All rights reserved.
    Journal of Catalysis 01/2015; 321. DOI:10.1016/j.jcat.2014.10.019 · 6.07 Impact Factor
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    ABSTRACT: Through the use of temperature-programmed desorption (TPD), the self-metalation and dehydrogenation of deuterated 5,10,15,20-tetraphenyl-21,23D-porphyrin on Cu(111) have been studied, resulting in new insight into the metalation of porphyrins on surfaces. The metalation is found to proceed through the transfer of the central aminic hydrogen atoms to the Cu(111) surface and not, as suggested by gas phase calculations, through the combination of the hydrogen atoms to molecular hydrogen above the partially inserted metal center. This finding suggests that the metalation reaction could be significantly influenced by the stability of hydrogen on the substrate surface. The metalation reaction and the subsequent hydrogenation and dehydrogenation of the periphery of the porphyrin molecule leading to hydrogen–deuterium exchange are modeled with a simple microkinetic reaction model. The model is able to describe the main features of the TPD spectra.
    The Journal of Physical Chemistry C 10/2014; 118(46):26729–26736. DOI:10.1021/jp507303h · 4.84 Impact Factor
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    ABSTRACT: We herein describe a straight forward procedure to increase the performance of platinum-on-alumina catalysts in methanol steam reforming by applying an alkali hydroxide coating according to the "solid catalyst with ionic liquid layer" (SCILL) approach. We demonstrate by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed desorption (TPD) studies that potassium doping plays an important role in the catalyst activation. Moreover, the hygroscopic nature and the basicity of the salt modification contribute to the considerable enhancement in catalytic performance. During reaction, a partly liquid film of alkali hydroxides/carbonates forms on the catalyst/alumina surface, thus significantly enhancing the availability of water at the catalytically active sites. Too high catalyst pore fillings with salt introduce a considerable mass transfer barrier into the system as indicated by kinetic studies. Thus, the optimum interplay between beneficial catalyst modification and detrimental mass transfer effects had to be identified and was found on the applied platinum-on-alumina catalyst at KOH loadings around 7.5 mass %.
    ChemSusChem 08/2014; 7(9). DOI:10.1002/cssc.201402357 · 7.12 Impact Factor
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    ABSTRACT: Five to thirty monolayer thick films of the ionic liquid [C2C1Im][OTf] were vaporized in vacuo onto an atomically clean Pd(111) single crystal surface at 220 K. Time- and temperature-resolved infrared reflection-absorption spectroscopy reveals growth, interactions with the metallic support, and the macroscopic phase behavior of the layer. At 220 K, the IL layer first grows in form of a glassy phase. Crystallization of the IL was witnessed above a critical thickness of about ten monolayers. Based on the known bulk crystal structure of the IL, we suggest the formation of well-oriented checkerboard-like crystalline film structures on the surface. The preferential orientation manifested by the crystal phase with regard to the macroscopic metallic surface is attributed to strong interactions between anionic headgroups and the metal.
    Langmuir 05/2014; 30(23). DOI:10.1021/la500842c · 4.38 Impact Factor
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    ABSTRACT: Liquid organic hydrogen carriers (LOHC) are compounds that enable chemical energy storage through reversible hydrogenation. They are considered a promising technology to decouple energy production and consumption by combining high-energy densities with easy handling. A prominent LOHC is N-ethylcarbazole (NEC), which is reversibly hydrogenated to dodecahydro-N-ethylcarbazole (H12-NEC). We studied the reaction of H12-NEC on Pt(111) under ultrahigh vacuum (UHV) conditions by applying infrared reflection-absorption spectroscopy, synchrotron radiation-based high resolution X-ray photoelectron spectroscopy, and temperature-programmed molecular beam methods. We show that molecular adsorption of H12-NEC on Pt(111) occurs at temperatures between 173 and 223 K, followed by initial C-H bond activation in direct proximity to the N atom. As the first stable dehydrogenation product, we identify octahydro-N-ethylcarbazole (H8-NEC). Dehydrogenation to H8-NEC occurs slowly between 223 and 273 K and much faster above 273 K. Stepwise dehydrogenation to NEC proceeds while heating to 380 K. An undesired side reaction, C-N bond scission, was observed above 390 K. H8-NEC and H8-carbazole are the dominant products desorbing from the surface. Desorption occurs at higher temperatures than H8-NEC formation. We show that desorption and dehydrogenation activity are directly linked to the number of adsorption sites being blocked by reaction intermediates.
    ACS Catalysis 02/2014; 4(2):657-665. DOI:10.1021/cs400946x · 7.57 Impact Factor
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    ABSTRACT: The interactions between ionic liquids and their supports determine many of their applications. The adsorption of the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C2C1Im][OTf] on Pd(111), ordered Al2O3/NiAl(110), and Pd nanoparticles supported on Al2O3/NiAl(110) was investigated under ultrahigh vacuum (UHV) conditions using time-resolved infrared reflection absorption spectroscopy (TR-IRAS). On Pd, the [OTf]− anion stands up with its CF3 group directed toward the vacuum, whereas the anion is less clearly oriented on the oxide. We also find that strong interactions of the IL with the Pd result in migration of the IL from the oxide to the metal nanoparticles.
    The Journal of Physical Chemistry C 02/2014; 118(6):3188–3193. DOI:10.1021/jp5006692 · 4.84 Impact Factor
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    ABSTRACT: From a different angle: Thin films of functionalized ionic liquids are deposited on cerium oxides following a surface science approach. The functionalization of the alkyl chain changes its orientation with respect to the surface plane from normal to parallel. This then leads to a different surface chemistry at higher temperatures.
    ChemPhysChem 11/2013; 14(16). DOI:10.1002/cphc.201300792 · 3.36 Impact Factor
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    ABSTRACT: Dodecahydro-N-ethylcarbazole (H12 -NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H12 -NEC on Pd(111) by using a surface-science approach under ultrahigh vacuum conditions. By combining infrared reflection-absorption spectroscopy, density functional theory calculations and X-ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H12 -NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of CH bonds is observed within the five-membered ring. Rapid dehydrogenation occurs to octahydro-N-ethylcarbazole (H8 -NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H8 -NEC proceeds within the six-membered rings. Starting from clean Pd(111), CN bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature-programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H8 -NEC as the main product desorbing from Pd(111). The onset temperature for H8 -NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H8 -NEC is observed even above the temperature threshold for H8 -NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.
    Chemistry - A European Journal 08/2013; 19(33). DOI:10.1002/chem.201301323 · 5.70 Impact Factor
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    Mathias Laurin
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    ABSTRACT: QVibeplot is a software program that automatically generates two-dimensional visualizations of molecular vibrations. The representations show the changes of bond lengths, angles, and torsions occurring upon a vibration. This is consistent with the experimentalist’s understanding of molecular vibrations that makes a distinction between stretching and deformation modes. Two-dimensionality is achieved by basing the representation on a skeletal formula of the molecule. The program also displays the spectrum and the list of frequencies. The phase and amplitude are indicated as well, providing a comprehensive visualization of molecular vibrations. The software is available online as a free and open-source software.
    Journal of chemical education 07/2013; 90(7):944-946. DOI:10.1021/ed300554z · 1.00 Impact Factor
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    ABSTRACT: Tri-salts added: Pt on alumina catalysts can be used for converting methanol and water into hydrogen and carbon dioxide, for applications such as hydrogen storage. Both the activity and selectivity could be enhanced by coating these materials with a thin layer of a molten salt mixture of Li/K/Cs acetate. Potassium doping was identified by DRIFTS measurements to be an important factor for the boost in catalyst performance.
    Angewandte Chemie International Edition 05/2013; 52(19). DOI:10.1002/anie.201209758 · 11.34 Impact Factor
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    ABSTRACT: Practical applications of ionic liquids (ILs) often involve IL/oxide interfaces, but little is known regarding their interfacial chemistry. The unusual physicochemical properties of ILs, including their exceptionally low vapor pressure, provide access to such interfaces using a surface science approach in ultrahigh vacuum (UHV). We have applied synchrotron radiation photoelectron spectroscopy (SR-PES) to the study of a thin film of the ionic liquid [C6C1Im][Tf2N] prepared in situ in UHV on ordered stoichiometric CeO2(111) and partially reduced CeO2–x. On the partially reduced surface, we mostly observe decomposition of the anion. On the stoichiometric CeO2(111) surface, however, a layer of surface-anchored organic products with high thermal stability is formed upon reaction of the cation. The suggested acid–base reaction pathway may provide well-defined functionalized IL/solid interfaces on basic oxides.
    Journal of Physical Chemistry Letters 12/2012; 4(1):30–35. DOI:10.1021/jz301856a · 6.69 Impact Factor
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    ABSTRACT: Towards a better understanding of the interface chemistry of ionic liquid (IL) thin film catalytic systems we have applied a rigorous surface science model approach. For the first time, a model homogeneous catalyst has been prepared under ultrahigh vacuum conditions. The catalyst, di-μ-chlorobis(chlorotricarbonylruthenium) [Ru(CO)(3)Cl(2)](2), and the solvent, the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf(2)N], have been deposited by physical vapor deposition onto an alumina model support [Al(2)O(3)/NiAl(110)]. First, the interaction between thin films of [Ru(CO)(3)Cl(2)](2) and the support is investigated. Then, the ruthenium complex is co-deposited with the IL and the influence of the solvent on the catalyst is discussed. D(2)O, which is a model reactant, is further added. Growth, surface interactions, and mutual interactions in the thin films are studied with IRAS in combination with density functional (DFT) calculations. At 105 K, molecular adsorption of [Ru(CO)(3)Cl(2)](2) is observed on Al(2)O(3)/NiAl(110). The IRAS spectra of the binary [Ru(CO)(3)Cl(2)](2) + [BMIM][Tf(2)N] and ternary [Ru(CO)(3)Cl(2)](2) + [BMIM][Tf(2)N] + D(2)O show every characteristic band of the individual components. Above 223 K, partial decomposition of the ruthenium complex leads to species of molecular nature attributed to Ru(CO) and Ru(CO)(2) surface species. Formation of metallic ruthenium clusters occurs above 300 K and the model catalyst decomposes further at higher temperatures. Neither the presence of the IL nor of D(2)O prevents this partial decomposition of [Ru(CO)(3)Cl(2)](2) on alumina.
    Physical Chemistry Chemical Physics 07/2012; 14(30):10603-12. DOI:10.1039/c2cp40697g · 4.20 Impact Factor
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    ABSTRACT: Nickel(II) complexes with double alkyl chain functionalized N-heterocyclic carbene (NHC) ligands, [NiCl2(C12MIM)2] and [NiCl2(C12C12IM)2], where C12MIM = 1-dodecyl-3-methylimidazolin-2-ylidene (1) and C12C12IM = 1,3-didodecylimidazolin-2-ylidene (2), have been prepared and fully characterized by 1H NMR, 13C NMR, and CHN elemental analyses. Furthermore, we have developed a system, in which double long alkyl chain derivatized Ni–NHC complexes are dissolved in the related ionic liquid crystalline 1,3-didodecylimidazolium tetrafluoroborate, [C12C12IM][BF4], to form pre-organized structures for enhanced reactivity. Remarkably, differential scanning calorimetry, polarized optical microscopy, and temperature-programmed IR reflection absorption spectroscopy performed on a mixture of 10 wt% Ni complexes in [C12C12IM][BF4] demonstrate that this system retains an ionic liquid crystalline phase; even after immobilization onto a silica-100 support with pore filling α = 1.
    Journal of Materials Chemistry 01/2012; 22(5):1893-1898. DOI:10.1039/C1JM13416G · 7.44 Impact Factor
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    ABSTRACT: The influence of confinement on the ionic liquid crystal (ILC) [C(18)C(1)Im][OTf] is studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The ILC studied is supported on Si-based powders and glasses with pore sizes ranging from 11 to 50 nm. The temperature of the solid-to-liquid-crystalline phase transition seems mostly unaffected by the confinement, whereas the temperature of the liquid-crystalline-to-liquid phase transition is depressed for smaller pore sizes. A contact layer with a thickness in the order of 2 nm is identified. The contact layer exhibits a phase transition at a temperature 30 K lower than the solid-to-liquid-crystalline phase transition observed for the neat ILC. For applications within the "supported ionic liquid phase (SILP)" concept, the experiments show that in pores of diameter 50 nm a pore filling of α>0.4 is sufficient to reproduce the phase transitions of the neat ILC.
    ChemPhysChem 12/2011; 12(18):3539-46. DOI:10.1002/cphc.201100379 · 3.36 Impact Factor
  • ChemPhysChem 12/2011; 12(18). DOI:10.1002/cphc.201190091 · 3.36 Impact Factor
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    ABSTRACT: To elucidate the dehydrogenation mechanism of dodecahydro-N-ethylcarbazole (H(12)-NEC) on supported Pd catalysts, we have performed a model study under ultra high vacuum (UHV) conditions. H(12)-NEC and its final dehydrogenation product, N-ethylcarbazole (NEC), were deposited by physical vapor deposition (PVD) at temperatures between 120 K and 520 K onto a supported model catalyst, which consisted of Pd nanoparticles grown on a well-ordered alumina film on NiAl(110). Adsorption and thermally induced surface reactions were followed by infrared reflection absorption spectroscopy (IRAS) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) in combination with density functional theory (DFT) calculations. It was shown that, at 120 K, H(12)-NEC adsorbs molecularly both on the Al(2)O(3)/NiAl(110) support and on the Pd particles. Initial activation of the molecule occurs through C-H bond scission at the 8a- and 9a-positions of the carbazole skeleton at temperatures above 170 K. Dehydrogenation successively proceeds with increasing temperature. Around 350 K, breakage of one C-N bond occurs accompanied by further dehydrogenation of the carbon skeleton. The decomposition intermediates reside on the surface up to 500 K. At higher temperatures, further decay to small fragments and atomic species is observed. These species block most of the absorption sites on the Pd particles, but can be oxidatively removed by heating in oxygen at 600 K, fully restoring the original adsorption properties of the model catalyst.
    Chemistry - A European Journal 10/2011; 17(41):11542-52. DOI:10.1002/chem.201101311 · 5.70 Impact Factor
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    ABSTRACT: Materials making use of thin ionic liquid (IL) films as support-modifying functional layer open up a variety of new possibilities in heterogeneous catalysis, which range from the tailoring of gas-surface interactions to the immobilization of molecularly defined reactive sites. The present report reviews recent progress towards an understanding of "supported ionic liquid phase (SILP)" and "solid catalysts with ionic liquid layer (SCILL)" materials at the microscopic level, using a surface science and model catalysis type of approach. Thin film IL systems can be prepared not only ex-situ, but also in-situ under ultrahigh vacuum (UHV) conditions using atomically well-defined surfaces as substrates, for example by physical vapor deposition (PVD). Due to their low vapor pressure, these systems can be studied in UHV using the full spectrum of surface science techniques. We discuss general strategies and considerations of this approach and exemplify the information available from complementary methods, specifically photoelectron spectroscopy and surface vibrational spectroscopy.
    Advanced Materials 06/2011; 23(22-23):2571-87. DOI:10.1002/adma.201100211 · 15.41 Impact Factor
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    ABSTRACT: Ionic liquids (ILs), such as [BMIM][Tf2N], on well-defined SCILL model catalysts are able to replace weakly adsorbed CO. On Pt, on-top CO remains adsorbed under the ionic liquid layer, but its IR signal red-shifts by over 30 cm(-1). IL-adsorbate interactions are mediated by the noble metal and similar to ligands.
    Advanced Materials 06/2011; 23(22-23):2617-21. DOI:10.1002/adma.201004064 · 15.41 Impact Factor
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    ABSTRACT: We have performed a combined molecular beam (MB)/infrared reflection absorption spectroscopy (IRAS) and density functional (DF) study on the adsorption of sulfur dioxide (SO2) on clean and oxygen precovered Pt(111). The adsorbate species formed as a function of coverage and their structural and chemical transformations upon subsequent annealing were followed systematically by IRAS. It is shown that, upon adsorption on clean Pt(111) at 100 K, SO2 adsorbs molecularly in two geometries. Calculations reveal that these geometries correspond to molecules oriented parallel or perpendicular to the surface. Upon heating up to 250 K, conversion between the two species occurs with the fraction of upright standing SO2 increasing with increasing temperature. Between 300 and 350 K, all surface species desorb without decomposition. This is in sharp contrast to oxygen precovered Pt(111), on which, in addition to the formation of molecular SO2 in flat and perpendicular geometry, partial formation of SO3 is observed even at low temperature. Upon annealing, part of the surface SOx species are converted to SO3 and, subsequently, to SO4, which remains stable up to 450 K. DF calculations on the stable adsorption structures of SOx species provide characteristic IR frequencies, which can be correlated with the present IRAS data and photoelectron spectroscopy (PES) data previously published.1
    The Journal of Physical Chemistry C 12/2010; 115(2). DOI:10.1021/jp107171t · 4.84 Impact Factor

Publication Stats

879 Citations
295.40 Total Impact Points

Institutions

  • 2007–2015
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Lehrstuhl für Technische Elektronik
      Erlangen, Bavaria, Germany
  • 2008–2014
    • Universitätsklinikum Erlangen
      Erlangen, Bavaria, Germany
  • 2003–2007
    • Max Planck Society
      München, Bavaria, Germany
    • Fritz Haber Institute of the Max Planck Society
      • Department of Physical Chemistry
      Berlín, Berlin, Germany