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  • 1.
    Ahlquist, Mårten S. G.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory2010Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, nr 1-2, s. 3-8Artikel i tidskrift (Refereegranskat)
    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, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP2011Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 346, nr 1-2, s. 20-28Artikel i tidskrift (Refereegranskat)
    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, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Nyström, Daniel
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Heterogeneous iron(II)-chloride mediated radical polymerization of styrene2009Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 306, nr 1-2, s. 69-76Artikel i tidskrift (Refereegranskat)
    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. Hagelin, H.
    et al.
    Hedman, B.
    Orabona, I.
    Åkermark, Torbjörn
    KTH, Tidigare Institutioner                               , Kemi.
    Åkermark, B.
    Klug, C. A.
    Investigation of the palladium catalyzed aromatic coupling of pyridine derivatives2000Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 164, nr 1-2, s. 137-146Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Lousada, Claudio Miguel
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Yang, Miao
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Nilsson, Kristina
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides2013Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 379, s. 178-184Artikel i tidskrift (Refereegranskat)
    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.

  • 6. Lu, H
    et al.
    Pradier, C M
    Karlsson, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Catalytic reduction of nitric oxide over copper Part III: Influence of water vapour1999Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 138, nr 2-3, s. 227-236Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Mohamed, Alaa
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. Akhbar El Yom Academy, Egypt.
    Osman, T. A.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Yilmaz, E.
    Uheida, Abdusalam
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Visible light photocatalytic reduction of Cr(VI) by surface modified CNT/titanium dioxide composites nanofibers2016Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 424, s. 45-53Artikel i tidskrift (Refereegranskat)
    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.

  • 8. Wang, Dongping
    et al.
    Wang, Mei
    Wang, Xiuna
    Zhang, Rong
    Ma, Jia
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Influence of the built-in pyridinium salt on asymmetric epoxidation of substituted chromenes catalysed by chiral (pyrrolidine salen)Mn(III) complexes2007Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 270, nr 02-jan, s. 278-283Artikel i tidskrift (Refereegranskat)
    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.

  • 9. 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 ethene2004Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 216, nr 1, s. 13-17Artikel i tidskrift (Refereegranskat)
    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.

  • 10.
    Yang, Miao
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO22015Ingår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 400, s. 49-55Artikel i tidskrift (Refereegranskat)
    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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