| 1. |
- Lu, H, et al.
(author)
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Catalytic reduction of nitric oxide over copper Part III : Influence of water vapour
- 1999
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In: Journal of Molecular Catalysis A. - 1381-1169 .- 1873-314X. ; 138:2-3, s. 227-236
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Sayan, Ş., et al.
(author)
-
Hydrogenation of naphthalene and methylnaphthalene: modeling and spectroscopy
- 2002
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In: Journal of Molecular Catalysis A. - 1381-1169 .- 1873-314X. ; 185:1-2, s. 211-222
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Ahlquist, Mårten S. G.
(author)
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Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory
- 2010
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In: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 324:1-2, s. 3-8
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Bergenudd, Helena, et al.
(author)
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Heterogeneous iron(II)-chloride mediated radical polymerization of styrene
- 2009
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In: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 306:1-2, s. 69-76
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Bergenudd, Helena, 1978-, et al.
(author)
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Investigation of iron complexes in ATRP : Indications of different iron species in normal and reverse ATRP
- 2011
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In: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 346:1-2, s. 20-28
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Comini, Elisabetta, et al.
(author)
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Metal oxide nanowires : Preparation and application in gas sensing
- 2009
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In: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 305:1-2, s. 170-177
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Hagelin, H., et al.
(author)
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Investigation of the palladium catalyzed aromatic coupling of pyridine derivatives
- 2000
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In: Journal of Molecular Catalysis A. - 1381-1169 .- 1873-314X. ; 164:1-2, s. 137-146
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Henschel, Henning, et al.
(author)
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A Density Functional Study on the Factors Governing Metal Catalysis of the Direct Aldol Reaction
- 2011
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In: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 351, s. 76-80
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Jeenpadiphat, Sirima, et al.
(author)
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Propylsulfonic acid functionalized mesoporous silica catalysts for esterification of fatty acids
- 2015
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In: Journal of Molecular Catalysis A. - : ELSEVIER SCIENCE BV. - 1381-1169 .- 1873-314X. ; 410, s. 253-259
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Journal article (peer-reviewed)abstract
- 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.
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| 10. |
- Konwar, Lakhya Jyoti, et al.
(author)
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Biodiesel production from acid oils using sulfonated carbon catalyst derived from oil-cake waste
- 2014
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In: Journal of Molecular Catalysis A. - : Elsevier. - 1381-1169 .- 1873-314X. ; 388, s. 167-176
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Journal article (peer-reviewed)abstract
- 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.
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