| 1. |
- Kirilin, Alexey V., et al.
(författare)
-
Aqueous-phase reforming of xylitol over Pt/C and Pt/TiC-CDC catalysts : catalyst characterization and catalytic performance
- 2014
-
Ingår i: Catalysis Science & Technology. - : RSC Publishing. - 2044-4753. ; 4:2, s. 387-401
-
Tidskriftsartikel (refereegranskat)abstract
- The aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM. The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF.
|
|
| 2. |
- Arve, Kalle, et al.
(författare)
-
Did Chemisorption Become an Obsolete Method With Advent of Tem? Comparison of Mean Particle Size and Distribution of Silver on Alumina
- 2011
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 665-669
-
Tidskriftsartikel (refereegranskat)abstract
- Silver particle size and dispersion on a Ag/Al2O3 for HC-SCR were examined by means of chemisorption and TEM. Experimental results showed that determination of the accurate mean particle size (mps) is challenging and that the both applied methods have specific characteristics increasing the inaccuracy in the results which has to be taken into account in evaluation of catalytic activity. The results from TEM imaging were found to depend highly on the mode in which the surface was scanned (bright field versus dark field). Generally the point resolution was higher in dark field but the obtained mps did not increased along with the increasing silver loading. The main limitation with the O-2-chemisorption was related to the choice of the stoichiometric factor between the adsorbent and silver atoms. However, together these techniques support each other and help to give a more realistic picture of the mean silver particle size, distribution and indications of the oxidation states on the alumina support.
|
|
| 3. |
- Behravesh, Erfan, et al.
(författare)
-
Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol : Influence of solution pH, Au nanoparticle size, support structure and acidity
- 2017
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 353, s. 223-238
-
Tidskriftsartikel (refereegranskat)abstract
- Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm.
|
|
| 4. |
- Bernas, Andreas, et al.
(författare)
-
Catalytic transformation of abietic acid to hydrocarbons
- 2012
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 55:7-10, s. 673-679
-
Tidskriftsartikel (refereegranskat)abstract
- Catalytic and thermal conversion of abietic acid was investigated in a laboratory scale high-pressure autoclave. Fractionation of crude tall oil produces rosin acids of which abietic acid is the main compound. Tall oil rosin acid, a forest product industry residue, is an abundant, inexpensive and chemically desirable feedstock for production of lighter hydrocarbons that can be used as diesel fuel additives. The carboxylic acid functionality of the main reactant, abietic acid, must first be removed, followed by double bond hydrogenation of the remaining aromatic rings. In this study, a number of catalytic and non-catalytic reaction steps in the conversion of abietic acid were investigated. The aim was to study hydrogenation and decarboxylation reactions of abietic acid in order to produce lighter hydrocarbons. The experiments were performed by using toluene as a solvent as well as with neat abietic acid, in the absence of any solvent. Hydrogenation of abietic acid to tetrahydroabietic acid in toluene was successfully performed over palladium on carbon catalyst at the temperature range of 100-200 A degrees C and at 30 bar hydrogen pressure. Thermal non-catalytic decarboxylation of abietic acid in toluene takes place at 200-300 A degrees C resulting in one main product. The hydrocarbon products were further hydrogenated under hydrogen pressure. Catalytic decarboxylation of abietic acid in toluene was achieved over 5 wt% Ru/C, giving a wider product distribution than thermal decarboxylation.
|
|
| 5. |
- Eta, Valerie, et al.
(författare)
-
Synthesis of dimethyl carbonate from methanol and carbon dioxide : Circumventing thermodynamic limitations
- 2010
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 49:20, s. 9609-17
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis of dimethyl carbonate from methanol and CO2 catalyzed by ZrO2 doped with KCl was investigated using chemical traps for water to circumvent thermodynamic limitations. The reaction, promoted by magnesium, occurred via the formation of carbonated magnesium methoxide (CMM) which adsorbed on the surface of ZrO2. The surface migration of the oxygen atom of ZrO2 to the surface methoxy groups of CMM resulted in the formation of dimethyl carbonate. The resulting MgO then reacted with methanol forming water and regenerating magnesium methoxide. The water formed reacted with the dehydrating agent, thus shifting the equilibrium toward a higher yield of DMC. The yield of 7.2 mol % DMC and 13.6 mol % conversion of methanol was obtained when methanol reacted with CO2 at 150 °C and 9.5 MPa for 8 h. The plausible reaction pathway is described.
|
|
| 6. |
|
|
| 7. |
- Eta, Valerie, et al.
(författare)
-
The Effect of Alkoxide Ionic Liquids on the Synthesis of Dimethyl Carbonate from CO2 and Methanol over ZrO2-MgO
- 2011
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1011-372X .- 1572-879X. ; 141:9, s. 1254-1261
-
Tidskriftsartikel (refereegranskat)abstract
- The use of carbon dioxide in the synthesis of chemicals, such as dimethyl carbonate (DMC), constitutes an environmentally attractive alternative to hazardous and toxic reagents. However, the direct synthesis of DMC from methanol and CO2 is characterized by low yields due to the reaction equilibrium and the thermodynamic limitations (Delta G(298K)(0) = + 26.3 kj/mol). Alkoxide ionic liquids possessing alkylimidazolium and benzalkonium cations were prepared, characterised and tested together with ZrO2-MgO catalyst for the synthesis of DMC from methanol and CO2. By using the novel ionic liquid as additives, ca. 12% conversion of methanol, and 90% selectivity to DMC was obtained at 120 A degrees C and 7.5 MPa. The water abstracting potential of the ionic liquids influenced the conversion of methanol and the selectivity to DMC. The alkoxide ionic liquids were recovered and reused in DMC synthesis without loss in activity and selectivity.
|
|
| 8. |
- Grénman, Henrik, et al.
(författare)
-
Modeling the influence of wood anisotropy and internal diffusion on delignification kinetics
- 2010
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 49:20, s. 9703-11
-
Tidskriftsartikel (refereegranskat)abstract
- A general mathematical model for the chemical pulping of wood including coupled chemical reactions and diffusion limitations in anisotropic wood chips was developed. The model, which consists of coupled parabolic partial differential equations (PDEs) and ordinary differential equations (ODEs), describes the time-dependent behavior of wood chips as they are exposed to chemicals in the liquid phase. In addition to the reaction−diffusion phenomena, the model describes the change of the wood chip porosity during the process. A numerical algorithm that combines spatial discretization by finite differences with a stiff ODE solver based on the backward difference method was used as an efficient strategy to solve the mass balances of wood chips in batch reactors. Numerical simulations with the software can be used to predict the progress of industrial delignification, that is, production of primarily cellulose through chemical pulping. The effect of the reaction parameters, such as the temperature and the concentrations of the alkaline delignification chemicals, as well as the sizes of the wood chips, can be evaluated with the model, the final goal being the intensification of the chemical pulping process. The model can be used to describe both the current kraft pulping (sulfate pulping) technique, as well as other processes, such as sulfite pulping and pulping in nonaqueous solvents.
|
|
| 9. |
- Hajek, Jan, et al.
(författare)
-
Interconversion of Lactose to Lactulose in Alkaline Environment : Comparison of Different Catalysis Concepts
- 2013
-
Ingår i: Topics in catalysis. - : Springer/Plenum Publishers. - 1022-5528 .- 1572-9028. ; 56:9-10, s. 839-845
-
Tidskriftsartikel (refereegranskat)abstract
- Interconversion of lactulose to lactulose with the aim to determine and optimize the yield of ketose was carried out. Various homogenous and heterogeneous alkaline catalysts were applied (NaOH, MgO, hydrotalcite etc.). The selectivity and activity of the catalysts were compared. The results gave insight to the performance differences among the screened catalysts under the various reaction conditions. From the activity performance point of view, the conversion was limited by the formation of acidic end-products. In general, the selectivity decreased with conversion and the conversion-selectivity pattern was independent of the catalyst.
|
|
| 10. |
- Hara, Piia, et al.
(författare)
-
Supported ionic liquids in Burkholderia cepacia lipase-catalyzed asymmetric acylation
- 2010
-
Ingår i: Journal of Molecular Catalysis B. - : Elsevier. - 1381-1177 .- 1873-3158. ; 67:1-2, s. 129-134
-
Tidskriftsartikel (refereegranskat)abstract
- Lipase PS from Burkholderia cepacia was successfully immobilized on Kynol™ ACC 507-15 active carbon cloth with and without ionic liquids as SILE catalysts. Activity, enantioselectivity and reuse of the catalysts were evaluated in the acylation of 1-phenylethanol with vinyl acetate in toluene and in hexane over the temperature range 25 - 60 °C. The presence of [EMIM][NTf2] clearly stabilized the enzyme against inactivation and preserved enantioselectivity in reuse in a process which is affected by the nature of the IL, solvent and substrate structure.
|
|
