| 1. |
- Ahlkvist, Johan, et al.
(författare)
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Heterogeneously catalyzed conversion of nordic pulp to levulinic and formic acids
- 2016
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer. - 1878-5190 .- 1878-5204. ; 119:2, s. 415-427
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Tidskriftsartikel (refereegranskat)abstract
- Herein, one-pot conversion of cellulose to platform chemicals, formic and levulinic acids was demonstrated. The catalyst selected was an affordable, acidic ion-exchange resin, Amberlyst 70, whereas the cellulose used was sulfite cellulose delivered by a Swedish pulp mill. Furthermore, in an attempt to better understand the complex hydrolysis network of the polysaccharide, kinetic experiments were carried out to pinpoint the optimal reaction conditions with an initial substrate concentration of 0.7–6.0 wt% and a temperature range of 180–200 °C. Higher temperatures could not be used due to the limitations in the thermal stability of the catalyst. Overall, maximum theoretical yields of 59 and 68 mol% were obtained for formic and levulinic acid, respectively. The parameters allowing for the best performance were reaction temperature of 180 °C and initial cellulose concentration of 0.7 wt%. After studying the behavior of the system, a simplified reaction network in line with a mechanistic approach was developed and found to follow first order reaction kinetics. A satisfactory fit of the model to the experimental data was achieved (97.8 % degree of explanation). The catalyst chosen exhibited good mechanical strength under the experimental conditions and thus, a route providing green platform chemicals from soft wood pulp from coniferous trees (mixture of Scots Pine and Norway Spruce) was demonstrated.
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| 2. |
- Bonarowska, Magdalena, et al.
(författare)
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Influence of microwave activation on the catalytic behavior of Pd-Au/C catalysts employed in the hydrodechlorination of tetrachloromethane
- 2018
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5190 .- 1878-5204. ; 124:1, s. 375-388
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the influence of activation by microwave irradiation on the catalytic properties of Pd-Au/C-Sibunit catalysts in the hydrodechlorination of CCl4. Pd and Pd-Au samples were thoroughly characterized by CO chemisorption, X-ray diffraction, TPHD and STEM, and used in gas phase hydrodechlorination of tetrachloromethane. The studies showed that homogenous Pd-Au alloys are formed more efficiently if short-time microwave activation is applied instead of conventional activation by H-2 reduction at 380 A degrees C. These catalysts show higher activity, stability and higher selectivity towards the desired products (C1-C5 hydrocarbons) than the catalysts activated by conventional reduction in 10%H-2/Ar flow.
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| 3. |
- Gavrilovic, Lubisa, et al.
(författare)
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The effect of aerosol-deposited ash components on a cobalt-based Fischer–Tropsch catalyst
- 2019
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer. - 1878-5190 .- 1878-5204. ; 127:1, s. 231-240
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ash salts on Co-based Fisher–Tropsch catalysts was studied using an aerosol deposition technique. The major elements in the ash were found to be K, S and Cl. The ash was deposited on a calcined catalyst as dry particles with an average diameter of approx. 350 nm. The loading of ash particles was varied by varying the time of exposure to the particles in a gas stream. Catalyst characterization did not reveal significant differences in cobalt dispersion, reducibility, surface area, pore size, or pore volume between the reference and the catalysts with ash particles deposited. Activity measurements showed that following a short exposure to the mixed ash salts (30 min), there were no significant loss of activity, but a minor change in selectivity of the catalyst . Extended exposure (60 min) led to some activity loss and changes in selectivity. However, extending the exposure time and thus the amount deposited as evidenced by elemental analysis did not lead to a further drop in activity. This behavior is different from that observed with pure potassium salts, and is suggested to be related to the larger size of the aerosol particles deposited. The large aerosol particles used here were probably not penetrating the catalyst bed, and to some extent formed an external layer on the catalyst bed. The ash salts are therefore not able to penetrate to the pore structure and reach the Co active centers, but are mixed with the catalyst and detected in the elemental analysis.
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| 4. |
- Keane, Mark A., et al.
(författare)
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Isokinetic behavior in the gas phase hydrogenation of nitroarenes over Au/TiO2: application of the selective energy transfer model
- 2012
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 106:2, s. 267-288
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Tidskriftsartikel (refereegranskat)abstract
- The gas phase selective hydrogenation of a series of nitroarenes (nitrobenzene, p-chloronitrobenzene, p-bromonitrobenzene, p-nitroaniline, p-nitrotoluene, p-nitrophenol and p-nitroanisole) has been examined over Au/TiO2 (0.3 % w/w Au, mean Au particle size = 3.9 nm). Compensation behavior is demonstrated with an associated isokinetic temperature (T-iso) of 558 +/- 32 K. We account for this response in terms of the selective energy transfer (SET) model where the occurrence of resonance between catalyst and reactant vibrations generates the activated complex. An analysis of the stepwise variation of the activation energies has identified a critical vibrational frequency of 853 cm(-1), which is close (+/- 2 cm(-1)) to the reference value for nitro-group (in-plane symmetric O-N-O bending and stretching) vibrations. Application of SET suggests activation of weakly adsorbed nitroarene (at the support or metal/support interface) by excitation of the nitro-group via IR radiation from a strongly adsorbed surface nitroarene component. The excited nitroarene is then attacked by reactive hydrogen supplied by the Au sites to generate the respective aromatic amine with 100 % selectivity. Agreement of the SET predicted T-iso with the experimental value requires the incorporation of a term due to C-N torsional entropy resulting from distortion of the O-N-O plane.
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| 5. |
- Konwar, Lakhya Jyoti, et al.
(författare)
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Selective esterification of fatty acids with glycerol to monoglycerides over –SO3H functionalized carbon catalysts
- 2016
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer. - 1878-5190 .- 1878-5204. ; 119:1, s. 121-139
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Tidskriftsartikel (refereegranskat)abstract
- –SO3H containing carbon materials (sulfonated carbons) were successfully employed as heterogeneous catalysts upon the selective esterification of glycerol with lauric and oleic acids. The functionalized carbon catalysts outperformed zeolites H–Y, H-ZSM-5 and liquid H2SO4 with respect to activity and selectivity, thus producing commercially important monoglycerides with excellent selectivity (70–80 %), at fatty acid conversion levels of 80–95 %. Most importantly, upon use of these catalysts, significant improvements were obtained with respect to process parameters in comparison to the solid acids reported before: our reaction (1) required shorter reaction time (7–24 h), (2) operated at equimolar fatty acid-to-glycerol ratio, (3) could be employed at moderate reaction temperatures (100–125 °C) and (4) catalyst reused was feasible thus confirming the catalytic potential of sulfonated carbons for production of high concentration monoglycerides. Moreover, the experimental results also demonstrate the existence of strong effects of catalyst pore structure (shape selectivity) and surface hydrophilicity imposed to the reaction products similar to the reactivity selectivity trends observed for –SO3H functionalized silica catalysts reported in previous studies.
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| 6. |
- Pasti, Igor A., et al.
(författare)
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Theoretical studies in catalysis and electrocatalysis : from fundamental knowledge to catalyst design
- 2015
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5190 .- 1878-5204. ; 115:1, s. 5-32
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic processes are an indispensable part of a large number of contemporary technologies that stimulate a constant research and development effort in the field. Computational methods represent a valuable tool to investigate crucial steps of catalytic cycles able to reveal the main characteristics of a catalyst and provide a basis for the design of materials with superior catalytic activity. This review is focused on the recent advances in density functional theory studies of the interactions of reactive species and intermediates with solid surfaces. As examples, we discuss the catalysts for the CO oxidation and electrocatalysis of H-2 and O-2 electrode reactions. We demonstrate how the theoretical modelling can contribute to the understanding of catalytic processes and help to design new catalysts and electrocatalysts.
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| 7. |
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| 8. |
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| 9. |
- Varga, Gabor, et al.
(författare)
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Bioinspired covalently grafted Cu(II)-C protected amino acid complexes: selective catalysts in the epoxidation of cyclohexene
- 2015
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 115:1, s. 33-43
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the syntheses of covalently grafted C-protected Cu(II)-amino acid (methylesters of l-histidine and l-cystine) uniform and mixed ligand complexes with two different amino acid esters are described using chloropropylated silica gel as the support. The conditions of the syntheses were systematically altered. The structural features of the substances obtained were studied by the Kjeldahl method, ICP-MS, X-ray absorption and mid/far infrared spectroscopies. The superoxide dismutase-like activities of the materials were determined in a biochemical test reaction and these substances were also tested as catalysts in the oxidation of cyclohexene. It was possible to prepare metal ion-amino acid complexes grafted with covalent bonds onto the supports. All the covalently anchored materials displayed superoxide dismutase-like activity and most of them were active in the oxidation of cyclohexene, providing the epoxide with high selectivity.
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| 10. |
- Zhdanov, Vladimir, 1952
(författare)
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A kinetic model of standard selective catalytic reduction of NO by NH3 on single sites
- 2011
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 103:1, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- Reduction of NO by NH3 in the presence of O-2 may occur on single Fe or Cu atoms or dimers incorporated into the inner walls of a zeolite. Although this process is of considerable intrinsic interest as an example of complex reactions running on single sites and is also important from the perspective of environmental chemistry, its mechanism is still open for debate. One of the likely schemes of the process implies the formation of N-2 and H2O via the reaction of gas-phase NO and adsorbed NH3. The author presents a detailed analysis of the steady-state kinetics corresponding to this scheme. The model employed includes eleven elementary steps. The results obtained allow one to interpret the apparent reaction orders observed experimentally.
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| 11. |
- Zhdanov, Vladimir, 1952
(författare)
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A kinetic model of standard selective catalytic reduction of NO by NH3 on two sites
- 2011
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 104:2, s. 267-272
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Tidskriftsartikel (refereegranskat)abstract
- Reduction of NO by NH(3) in the presence of O(2) may occur on single Fe or Cu atoms or dimers incorporated into the inner walls of zeolite. One of the likely schemes of this reaction implies the formation of N(2) and H(2)O through the reaction of gas-phase NO and adsorbed NH(3). The steady-state kinetics corresponding to this scheme was recently analyzed by the author assuming that the reaction runs on single metal atoms. In this work, the author presents a model including two metal atoms. Under the practically important conditions, the kinetics predicted by the one- and two-site models are demonstrated to be similar. In particular, both models allow one to interpret the apparent reaction orders observed experimentally.
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| 12. |
- Zhdanov, Vladimir, 1952
(författare)
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Simulation of reduction of oxidized metal nanoparticles
- 2023
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - 1878-5204 .- 1878-5190. ; 136:3, s. 1185-1195
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Tidskriftsartikel (refereegranskat)abstract
- I analyze theoretically the spatio-temporal kinetics of reduction of oxidized metal nanoparticles by hydrogen (or methane). The focus is on the experimentally observed formation of metal and oxide domains separated partly by pores. The interpretation of such multiphase processes in nanoparticles at the mean-field level is hardly possible primarily due to complex geometry, and accordingly I use the lattice Monte Carlo technique in order to tackle this problem. The main conclusions drawn from the corresponding generic simulations are as follows. (i) The patterns predicted are fairly sensitive to the metal-metal and metal-oxygen interactions. With decreasing the former interaction and increasing the latter interaction, there is transition from the formation of metal aggregates and voids to the formation of a metal film around the oxide core. (ii) During the initial phase of these kinetics, the extent of reduction can roughly be described by using the power law, and the corresponding exponent is about 0.3. (iii) With decreasing the hydrogen (or methane) pressure and/or increasing the oxide nanoparticle size, as expected, the kinetics are predicted to become longer. (iv) The dependence of the patterns on the presence of the support and/or Kirkendall void in an oxide nanoparticle is shown as well.
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| 13. |
- Zhdanov, Vladimir, 1952
(författare)
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Simulation of the catalytic oxidation of soot
- 2013
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 108:1, s. 41-49
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Tidskriftsartikel (refereegranskat)abstract
- Soot oxidation by supported metal nanoparticles is simulated by using the Monte Carlo technique. The coarse-grained lattice model proposed for this process describes the deposition, diffusion, aggregation and reaction of carbon nanoparticles. Each carbon or catalyst nanoparticle is assumed to occupy a single site of a 3D cubic lattice. With increasing deposition rate (or decreasing reaction rate), the model predicts a transition from the steady state with a submonolayer of soot to the growth of mesoscopic 3D carbon agglomerates. In these cases, the reaction rate is, respectively, close to and lower than the deposition rate.
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| 14. |
- Zhdanov, Vladimir, 1952
(författare)
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Simulations of oxidation of metal nanoparticles with a grain boundary inside
- 2020
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 130:2, s. 685-697
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Tidskriftsartikel (refereegranskat)abstract
- The generic 2D lattice Monte Carlo simulations presented herein are focused on the spatio-temporal kinetics of oxidation of metal nanoparticles composed of two grains separated by a single grain boundary. The oxidation is assumed to occur via inward diffusion of interstitial oxygen ions in the oxide. The results of simulations illustrate that the regimes of oxidation can range from one where the presence of grains is negligible and the oxide shell is formed at the periphery of a whole nanoparticle to one where each grain is oxidized almost independently.
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