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  • 1.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, no 1-2, p. 3-8Article in journal (Refereed)
    Abstract [en]

    The iridium(III) catalyzed hydrogenation of carbon dioxide under basic conditions was studied with density functional theory. It was found that the insertion of CO2 into an Ir-H bond proceeds via a two-step mechanism. The rate-limiting step was calculated to be the regeneration of the iridium(III) trihydride intermediate, and the overall barrier for the reaction was calculated to 26.1 kcal mol(-1). The formation of the iridium trihydride proceeds via formation of a cationic Ir(H)(2)(H-2) complex at which the base abstracts a proton from the dihydrogen ligand. (C) 2010 Elsevier B.V. All rights reserved.

  • 2.
    Bergenudd, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP2011In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 346, no 1-2, p. 20-28Article in journal (Refereed)
    Abstract [en]

    In an attempt to correlate the ATRP kinetics and the redox properties of the mediator, eight iron complexes with nitrogen, phosphorous and carboxylic acid containing ligands were investigated by electrochemical measurements and by using them as mediators in normal and reverse ATRP of MMA in DMF. The redox properties of the iron complexes in DMF, measured by cyclic voltammetry, did not differ significantly, which was reflected in the ATRP kinetics as the apparent rate constants were practically the same with all the complexing ligands. The degree of control over the polymerization was, however, much improved in reverse ATRP as compared to normal ATRP. In this ATRP system, the ligand type is not crucial for the redox or polymerization properties. Several observations indicate that the iron species in the two systems were not the same, the Fe(III) species resulting from oxidation of Fe(II) in normal ATRP is different from the starting Fe(III) species in reverse ATRP.

  • 3.
    Bergenudd, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Nyström, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Heterogeneous iron(II)-chloride mediated radical polymerization of styrene2009In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 306, no 1-2, p. 69-76Article in journal (Refereed)
    Abstract [en]

    In an attempt to perform atom transfer radical polymerization (ATRP) with a more environmentally friendly mediator, polymerization of styrene in the presence of iron(II)-chloride and EDTA was explored from a mechanistic point of view. The presence of EDTA, which normally can form a complex with FeCl2, had no influence on the polymerization results as both the mediator and EDTA were insoluble in the polymerization medium. A mechanism is suggested for the heterogeneous polymerization of styrene mediated by iron (II)-chloride in p-xylene at 50 °C. Varying the mediator amount more than 10-fold revealed that the rate limiting step at low mediator amounts was the adsorption of the initiator or dormant polymer to the mediator surface, whereas at higher mediator amounts, the rate limiting step was instead the activation step in the ATRP equilibrium. The mechanism changed to free radical polymerization in solution at a certain conversion, resulting in lower apparent rate constant and an increased amount of transfer and termination reactions. Chain extension with MMA showed that a significant proportion of the polymer chain ends were active also at high conversions.

  • 4.
    Comini, Elisabetta
    et al.
    CNR IDASC SENSOR Lab.
    Faglia, Guido
    CNR IDASC SENSOR Lab.
    Ferroni, Matteo
    CNR IDASC SENSOR Lab.
    Ponzoni, Andrea
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    INFM-CNR Sensor Lab.
    Sberveglieri, Giorgio
    CNR IDASC SENSOR Lab.
    Metal oxide nanowires: Preparation and application in gas sensing2009In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 305, no 1-2, p. 170-177Article in journal (Refereed)
    Abstract [en]

    Quasi one-dimensional nanowires of metal oxides are promising for the development of nano-devices. Sn, In, and Zn oxides were produced in form of single-crystalline nanowires through condensation from vapor phase. Furthermore longitudinal and radial heterostructures have been prepared. Nanowires growth occurs in controlled condition and allows the exploitation of size reduction effects on the electrical response to gases. Preparation, microstructural, morphological and electrical characterizations of nanowires are presented and the peculiarities of these innovative structures are highlighted. © 2009 Elsevier B.V. All rights reserved.

  • 5. Hagelin, H.
    et al.
    Hedman, B.
    Orabona, I.
    Åkermark, Torbjörn
    KTH, Superseded Departments, Chemistry.
    Åkermark, B.
    Klug, C. A.
    Investigation of the palladium catalyzed aromatic coupling of pyridine derivatives2000In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 164, no 1-2, p. 137-146Article in journal (Refereed)
    Abstract [en]

    The coupling reaction of 4-methylpyridine to form 4,4 ' -dimethyl-2,2 ' -bipyridine using a carbon-supported palladium catalyst was studied. Whereas previous research indicated that the reaction is catalyzed by palladium(0), we have found evidence that the reaction is catalyzed by palladium(II). Although oxygen can be used as the oxidative agent, the reaction is ultimately Limited by catalyst deactivation. The major source of deactivation is most likely depletion of the palladium(II) oxide. The catalyst is reduced during the reaction and in the case of the oxygen-treated catalyst a small amount of palladium appears to be dissolved. In an investigation of the catalyst using X-ray photoelectron spectroscopy (XPS) and solid state nuclear magnetic resonance (NMR) it was found that deactivation is also caused by poisoning, the poison being either the product and/or the by-product.

  • 6. Henschel, Henning
    et al.
    Prosenc, Marc H.
    Nicholls, Ian A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    A density functional study on the factors governing metal catalysis of the direct aldol reaction2011In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 351, p. 76-80Article in journal (Refereed)
    Abstract [en]

    Density functional calculations are employed in the study of the C-C bond formation step of an aldol reaction in presence of a series of metals. Focus was placed on first row d-block metals that have been used in catalysis of direct aldol reactions. The obtained energy profiles are analysed in order to differentiate between factors governing catalysis. Results demonstrate a major influence of d-orbital occupation, and suggest some of the so far less commonly used metals as promising candidates for development of new catalytic systems.

  • 7.
    Henschel, Henning
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Prosenc, Marc H.
    University of Hamburg, Germany.
    Nicholls, Ian A.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. Uppsala University.
    A Density Functional Study on the Factors Governing Metal Catalysis of the Direct Aldol Reaction2011In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 351, p. 76-80Article in journal (Refereed)
    Abstract [en]

    Density functional calculations are employed in the study of the C-C bond formation step of an aldol reaction in presence of a series of metals. Focus was placed on first row d-block metals that have been used in catalysis of direct aldol reactions. The obtained energy profiles are analysed in order to differentiate between factors governing catalysis. Results demonstrate a major influence of d-orbital occupation, and suggest some of the so far less commonly used metals as promising candidates for development of new catalytic systems.

  • 8.
    Jeenpadiphat, Sirima
    et al.
    Chulalongkorn University, Thailand.
    Björk, Emma
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Nuntasri Tungasmita, Duangamol
    Chulalongkorn University, Thailand.
    Propylsulfonic acid functionalized mesoporous silica catalysts for esterification of fatty acids2015In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 410, p. 253-259Article in journal (Refereed)
    Abstract [en]

    The catalytic properties of 3 types of mesoporous silica SBA-15 (rope, rod and fiber), with 9.2 nm or 12.1 nm large mesopores, were examined with respect to their morphology and pore size. Commercially available Amberlyst-15 and the small pore sized MCM-41 were used for comparison. The catalysts were prepared by functionalization of the silica supports with propylsulfonic acid (Pr-SO3H) using postsynthesis grafting with 3 -mercaptopropyltrimethoxysilane as a propyl-thiol precursor. All materials remained in a well-ordered hexagonal mesoporous structure after Pr-SO3H functionalization. The performance of the Pr-SO3H-functionalized mesoporous silicas was evaluated in terms of their catalytic activity in the esterification of oleic acid with short (methanol) and long (glycerol) chain alcohols, i.e., to test the effect of the pore size on the substrate conversion and product yield. The synthesized catalysts were highly active and the product composition could be tuned by selective choice of the mesopore size. The Pr-SO3H-functionalized rope-shaped SBA-15 gave the highest catalytic activity (in terms of the highest methyl oleate and triglyceride yields and oleic acid conversion level), which was higher than that obtained with the commercial Amberlyst-15 catalyst. A high acid amount, large specific surface area and a suitable pore size are the likely reasons for the high yield gained by Pr-SO3H-functionalized rope-shaped SBA-15 silica. (C) 2015 Elsevier B.V. All rights reserved.

  • 9. Konwar, Lakhya Jyoti
    et al.
    Dasa, Rupali
    Thakurb, Ashim Jyoti
    Salminen, Eero
    Mäki-Arvelac, Päivi
    Kumar, Narendra
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Center, Åbo Akademi University, FI-20500 Åbo-Turku, Finland.
    Deka, Dhanapati
    Biodiesel production from acid oils using sulfonated carbon catalyst derived from oil-cake waste2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 388, p. 167-176Article in journal (Refereed)
    Abstract [en]

    The utilization of oil-cake waste (OCW) derived catalysts in biodiesel production was demonstrated. The sulfonated carbon materials were utilized as catalysts for pretreatment of acid oils (oils containing 8.17-43.73 wt% of free fatty acids). The catalysts could be used to convert free fatty acids (FFA) present in acid oils into corresponding methyl esters within 6-8 h at 80 °C, thus reducing the FFA content to desirable levels below 2 wt%. The esterification activity was found to be dependent on the initial FFA concentration found in the acid oil as well as methanol-to-oil molar ratio. High methanol-to-oil molar ratios and the presence of higher initial FFA concentrations resulted in enhanced esterification rates. Acid oil containing 43.7 wt% FFA was easily converted into mixtures containing up to 71% methyl esters (FAME). The reported catalyst was successfully recycled in five consecutive experiments and exhibited high thermal stability. Most importantly, the catalytic activity of the solid acid was found to outperform homogeneous case when equivalent amount of H2SO4 under similar conditions was applied. Therefore, the OCW derived sulfonated carbon catalyst reported herein could be used as a potential substitute for corrosive, concentrated H2SO4 currently employed for acid oil pretreatment.

  • 10.
    Lousada, Claudio Miguel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Yang, Miao
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Nilsson, Kristina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides2013In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 379, p. 178-184Article in journal (Refereed)
    Abstract [en]

    We have investigated the reactions of H2O2 with Fe2O3, CuO, HfO2, CeO2 and Gd 2O3 in aqueous solution. The reactions rate constants at room temperature were determined. From the temperature dependence of the rate constants we extracted the Arrhenius parameters and the standard enthalpies of activation for the reactions. In addition, we studied the dynamics of formation of the intermediate species formed during decomposition of H2O 2, the HO radical. The kinetic data for H2O2 reactivity and the yields of hydroxyl radical formation differ considerably between many of the materials studied. We compared the energetic and mechanistic data obtained in this work with literature data for a set of nine oxides in total. The Arrhenius pre-exponential factors normalized to surface area for the decomposition of H2O2 vary by nine orders of magnitude for some of the oxides investigated. This indicates that the surfaces of the oxides have very different catalytic capacity towards the decomposition of H 2O2. The standard enthalpies of activation for H 2O2 decomposition vary between 30 and 73 kJ mol -1, revealing also differences in the catalytic efficiency for the different materials. The mechanistic study consists of quantifying the HO radical scavenged by tris(hydroxymethyl)aminomethane (Tris) during the course of the decomposition of H2O2 for the whole set of oxides. The yields and dynamics of scavenging of HO• differ considerably between the oxides analyzed. Surprisingly, the time-independent plots of the amount of HO scavenged as a function of the conversion of H2O 2 reveals that during the decomposition of H2O2 there are turnover points where the amount of HO scavenged by Tris suffers a sudden increase. The location of these points and the curvatures of the plots at the near-neighbours is considerably different for the different materials.

  • 11. Lu, H
    et al.
    Pradier, C M
    Karlsson, Ulf O
    KTH, School of Information and Communication Technology (ICT).
    Catalytic reduction of nitric oxide over copper Part III: Influence of water vapour1999In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 138, no 2-3, p. 227-236Article in journal (Refereed)
    Abstract [en]

    This paper reports on the effect of water vapour on the reduction of NO over copper in the presence of oxygen and isobutene. Reactions were studied at 700 K and at 770 K. Mass spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) were used to monitor the gas phase composition during reaction and to analyse the catalyst surface, respectively. XPS spectra show that the presence of water vapour influences the Cu oxidation state. At 700 K adsorption of aldehyde is partly blocked by copper oxide resulting in a decrease in the activity of the reaction, although the main mechanism is not changed. At 770 K, water vapour generates an even more oxidised surface, which promotes a complete oxidation of hydrocarbon, the main mechanism of NO reduction is changed, and the activity of the reaction is slightly increased. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 12.
    Mohamed, Alaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Akhbar El Yom Academy, Egypt.
    Osman, T. A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Yilmaz, E.
    Uheida, Abdusalam
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Visible light photocatalytic reduction of Cr(VI) by surface modified CNT/titanium dioxide composites nanofibers2016In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 424, p. 45-53Article in journal (Refereed)
    Abstract [en]

    In this work we report a highly efficient photocatalytic reduction of Cr(VI) based on PAN-CNT/TiO2-NH2 composite nanofibers fabricated by using electrospinning technique followed by chemical crosslinking of surface modified TiO2 NPs functionalized with amino group. The structure and morphology of the fabricated composite nanofibers were characterized by FTIR, SEM, TEM, TGA, and XPS. The results indicate that the composite nanofibers possess excellent photoreduction performance for Cr(VI) under visible light (125 W) after 30 min, which is much faster than previous reports. The effects of various experimental parameters such as catalyst dose, irradiation time, initial concentration of Cr(VI), and pH on the photoreduction efficiency of Cr(VI) were investigated. The highest photoreduction efficiency of Cr (VI) was obtained at low acidity and low amount of TiO2/CNT photocatalyst. The kinetic experimental data was attained and fitted well with a pseudo-first-order model. The UV–vis spectrophotometer and XPS analyses proved that chromate Cr(VI) was reduced to Cr(III). In addition, it can be concluded that the addition of the phenol enhances the photocatalytic reduction of Cr(VI). Furthermore, the photoreduction mechanism has also been discussed. Finally, the fabricated composite nanofibers were found to be stable after at least five regeneration cycles.

  • 13.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogenation of carbon-heteroatom unsaturated bonds: An assessment of consistency of density functional methods2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, no 1-2, p. 97-103Article in journal (Refereed)
    Abstract [en]

    Hydrogenation of unsaturated carbon-heteroatom bonds, C = X, is the general process for which we assess consistency of quantum chemical calculations in the context of B(C6F5)3-catalyzed reduction of imines with H2. According to the mechanism of the reaction, computational uncertainty of energies of hydrogenation of imines, i.e. the difference between results obtained with different methods, contributes to method related uncertainties of the computed relative energies of key H2-activating species. For this reason, it is desirable to know the magnitude of methodological dependence/uncertainty of energies of hydrogenation. Calculations were performed with a number of different density functionals, such as M05-2X, M06-2X, B3LYP, B3PW91, BH&HLYP, MPW1K, MPW1PW91, HCTH407 and PBE, on a number of relevant imines and ketones/aldehydes. Additionally, second order Møller-Plesset perturbation theory was also evaluated. The results quantitatively reveal the manner in which the form of a method affects the calculated energy change and that there is substantial difference between results obtained with different methods even for structurally simple species.

  • 14.
    Paul, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sayan, S.
    Bilkent University, Ankara.
    Hydrogenation of naphthalene and methylnaphthalene: modeling and spectroscopy2002In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 185, no 1-2, p. 211-222Article in journal (Refereed)
    Abstract [en]

    In situ infrared spectra of 1-methylnaphthalene (1-MeNapht) hydrogenation, over sulfided NiMo/Al2O3-TiO2 catalysts, were compared with theoretically derived properties of methylnaphthalene and its bicyclic products: MeDilin, MeTetralin, MeOctalin and MeDecalin, and with conversion data from literature. Comparisons were also made between the un-substituted and methyl-substituted two-rings, and between the 1- and 5-methyl isomers of 1,4-dihydronaphthalene (dilin) and 1,2,3,4-tetrahydronaphthalene (tetralin). IR spectra of MeNapht adsorption, on the sulfided catalyst, were matched with data for adsorption on the catalyst without sulfidation and the empty support. Surface bound MeNapht is observed below 250 °C on all catalysts. MeNapht adsorption suppresses OH groups non-discriminatory on the empty support and the metal loaded catalyst. We relate the results to previous data on the interaction between the supported metal sulfides and titanium modified aluminas. Calculated total energies, and experimentally derived heats of formation, pointed at decahydronaphthalene (decalin) as the dominant product of naphthalene hydrogenation, with tetralin as an abundant intermediate, and dilin and 1,2,3,4,5,6,7,8-octahydronaphthalene (octalin) as short lived transient stages. The spectroscopic modeling showed that the orbital fingerprints of the five bicyclic compounds were not distinctly different, nor more than marginally modified by methyl substitution or isomerization. The only significant difference came at the highest occupied orbital, where a high naphthalene density of states (DoS) overlapped with the valence bands of metal or metal sulfide catalysts. The vibrational bands for naphthalene, dilin, tetralin and octalin were well separated. Octalin and decalin, alone, have similar vibrational spectra. Upheaval of ring degeneracy for methyl-substituted two-ring structures broadened all infrared bands in a characteristic way.

  • 15. Sellappan, Raja
    et al.
    Zhu, Jiefang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
    Fredriksson, Hans
    Martins, Rafael S.
    Zach, Michael
    Chakarov, Dinko
    Preparation and characterization of TiO2/carbon composite thin films with enhanced photocatalytic activity2011In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 335, no 1-2, p. 136-144Article in journal (Refereed)
    Abstract [en]

    Composite TiO2/carbon thin films prepared by physical vapor deposition techniques on fused silica substrates show enhanced photocatalytic activity towards decomposition of methanol to CO2 and water, as compared to pure TiO2 films of similar thickness. Raman and XRD measurements confirm that annealed TiO2 films exhibit anatase structure while the carbon layer becomes graphitic. Characteristic for the composite films is an enhanced optical absorption in the visible range. The presence of the carbon film causes a shift of the TiO2 absorption edge and modifies its grain size to be smaller. We hypothesize that the observed enhancement of photocatalytic activity is due to synergy effects at the carbon/TiO2 interface, resulting in smaller titania crystallite size and anisotropic charge carrier transport, which in turn reduces their recombination probability.

  • 16.
    Stefanov, B. I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde Adsorption and Condensation on Anatase TiO2: Influence of Acetaldehyde Dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
  • 17.
    Stefanov, Bozhidar I
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
    Abstract [en]

    Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ FTIR showed that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, which is shown to be due to acetaldehyde dimers. The results were supported by DFT calculations. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with experimental results. A kinetic model was constructed based on the combined FTIR and DFT results, and was shown to explain the essential features of the acetaldehyde condensation reaction.

  • 18.
    Szabó, Kálmán J
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mechanism of the oxidative addition of hypervalent iodonium salts to palladium(II) pincer-complexes2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, no 1-2, p. 56-63Article in journal (Refereed)
    Abstract [en]

    Oxidative addition of hypervalent iodonium salts to palladium pincer-complexes was studied to rationalize the mechanism of the key-step in related Pd(II)/Pd(IV) based catalytic processes. It was found that this oxidative addition is an exothermic process with a relatively low activation barrier. The activation energy is highly dependent on the organic substituents of the iodoniun salts. For example, an ethynyl group is transferred with a considerably lower activation barrier from iodine to palladium, than a phenyl functionality. We have compared the reaction profiles of the oxidative addition of hypervalent iodonium salts and phenyl iodide. The most important difference between the two processes is that the oxidative addition of phenyl iodide is highly endothermic, as the reductive elimination of phenyl iodide from the Pd(IV) species requires a very low barrier. In contrast, the formation of the Pd(IV) species using hypervalent iodonium salts is an irreversible process, which allows ligand exchange and trasmetallation reactions generating a productive catalytic cycle. The studies indicate that the most important MO's involved in the oxidation is the antibonding σ* orbital of the iodonium salt and a non-bonding Pd(4d) orbital, which is perpendicular to the coordination plane of the palladium atom.

  • 19. Wang, Dongping
    et al.
    Wang, Mei
    Wang, Xiuna
    Zhang, Rong
    Ma, Jia
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Influence of the built-in pyridinium salt on asymmetric epoxidation of substituted chromenes catalysed by chiral (pyrrolidine salen)Mn(III) complexes2007In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 270, no 02-jan, p. 278-283Article in journal (Refereed)
    Abstract [en]

    Chiral (pyrrolidine salen)Mn(III) complexes 1 with an N-benzoyl group and 2 with an N-isonicotinoyl group as well as the corresponding N-methyl (3) and N-benzyl (4) pyridinium salts of 2 were synthesized. The catalytic properties of 1-4 and 2 with excess CH3I were explored to figure out the influence of the internal pyridinium salt in the catalyst on asymmetric epoxidation of substituted chromenes with NaClO/PPNO as an oxidant system in the aqueous/organic biphasic medium. The (pyrrolidine salen)Mn(III) complexes with an internal pyridinium salt, either formed in situ or isolated, displayed higher activities than analogous complexes 1, 2 and Jacobsen's catalyst in the aforementioned reaction, with comparable high yields and ee values. The acceleration of the reaction rate is attributed to the phase transfer capability of the built-in pyridinium salt of the (salen)Mn(III) catalyst. The effect of the internal pyridinium salt on the epoxidation of substituted chromenes is similar to that of the external pyridinium salts and ammonium halides.

  • 20. Wang, M.
    et al.
    Dai, D.
    Zhu, H. J.
    Zhang, X.
    Sun, Licheng C.
    Effects of the precatalyst structure and the Mg-containing third-component on cyclo-oligomerization of ethene2004In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 216, no 1, p. 13-17Article in journal (Refereed)
    Abstract [en]

    The catalytic cyclo-oligomerization of ethene by metallocene complexes Cp2ZrCl2 with Et3Al as cocatalyst in the presence of Mg-containing third-components is described. Under optimal conditions (Cp2ZrCl2/Et3Al/Et2Mg = 1:100:10, 150degreesC, P(C2H4) = 1.4 MPa) the reaction afforded 51% of cyclic oligomers, including exo-methylenecyclopentane (41%) and a small amount of methylcyclopentane (3%), 1-methyl-1-ethylcyclopentane (4%) and vinylcyclohexane (3%), along with usual open-chain alkenes. When the pi-ligand was changed to eta(5)-pentamethylcyclopentadienyl and indenyl (Ind) or Cp2TiCl2 was used in place of Cp2ZrCl2, the selectivity of exo-methylenecyclopentane dropped dramatically to 1-8%. In contrast, the catalytic reactions by post-metallocene complexes (LZrCl2)-Zr-2 (L-2 = salen, salphen) under identical conditions generated open-chain alkenes exclusively. A zirconacyclopentane mechanism is proposed to explain the products formed in cyclo-oligomerization of ethene.

  • 21.
    Yang, Miao
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO22015In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 400, p. 49-55Article in journal (Refereed)
    Abstract [en]

    In this work, the surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO2 in the presence of Tris(hydroxymethyl) aminomethane was studied experimentally. Two sets of competition experiments were performed: the competition between H2O2 and Tris for the surface bound hydroxyl radical (HO) and between O2 and H2O2 for the hydroxymethyl radical (CH2OH) (precursor for formaldehyde). A 5-fold increase in initial concentration of Tris or H2O2 does not lead to a 5-fold increase in CH2O formation (only by a factor of 2-3 in the studied concentration range). The O2-dependent enhancement of the final production of CH2O becomes weaker upon increasing the initial concentration of H2O2 from 0.5 mM to 5 mM. The final production of CH2O becomes independent of the concentration of Tris when [Tris]0 is above 100 mM, i.e., the surface is saturated with Tris at this concentration. Based on the experimental results, a site-specific mechanism of H2O2 decomposition on the surface of ZrO2 was proposed. This model was used for numerical simulations of the dynamics of the reaction system. The kinetics was simulated using the kinetic simulation software Gepasi 3.0 and the results are in good agreement with the experimental observations.

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