| 1. |
- Acharya, B. S., et al.
(författare)
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Introducing the CTA concept
- 2013
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 43, s. 3-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Actis, M., et al.
(författare)
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Design concepts for the Cherenkov Telescope Array CTA : an advanced facility for ground-based high-energy gamma-ray astronomy
- 2011
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 32:3, s. 193-316
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
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| 3. |
- Andreazza, A, et al.
(författare)
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The DELPHI very forward tracker for LEP200
- 1995
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Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. ; 367:1-3
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Glicenstein, J-F, et al.
(författare)
-
Status of the NectarCAM camera project
- 2014
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Ingår i: High Energy, Optical, and Infrared Detectors for Astronomy VI. - : SPIE - International Society for Optical Engineering. - 9780819496225
-
Konferensbidrag (refereegranskat)abstract
- NectarCAM is a camera designed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range 100 GeV to 30 TeV. It has a modular design based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 7 to 8 degrees. Each module includes the photomultiplier bases, High Voltage supply, pre-amplifier, trigger, readout and Thernet transceiver. Events recorded last between a few nanoseconds and tens of nanoseconds. A flexible trigger scheme allows to read out very long events. NectarCAM can sustain a data rate of 10 kHz. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, the cooling of electronics, read-out, clock distribution, slow control, data-acquisition, trigger, monitoring and services. A 133-pixel prototype with full scale mechanics, cooling, data acquisition and slow control will be built at the end of 2014.
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| 5. |
- Menéndez, M., et al.
(författare)
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Grace : Development of Pd-zeolite composite membranes for hydrogen production by membrane reactor
- 2005
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Ingår i: Carbon Dioxide Capture for Storage in Deep Geologic Formations. - : Elsevier. - 9780080445700 ; , s. 341-364
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Pd–zeolite composite membranes have been prepared over the external surface of macroporous a-alumna tubular supports by secondary growth of zeolite layers followed by Pd modification. Pd nanoparticles (few nanometers in size) filtration and/or impregnation þ in situ reduction of an organic Pd precursor have been explored as deposition techniques devoted to enhance the H2 separation performance of the non-defect free A-type zeolite membranes. The Pd deposition aims toward the partial blockage of the non-selective intercrystalline pathways, which may account for a significant fraction of the total permeation flux. The Pd–zeolite composite substrates have been characterized by XRD, SEM and EDX. The study of the permeation properties of these substrates for single (N2) and binary mixtures (H2–CO2) before and after Pd modification, reveals some improvements in terms of H2 separation performance. The impregnation þ in situ reduction of palladium acetylacetonate solution (Pd(acac)2) carried out over KA zeolite membranes previously seeded with Pd nanoparticles appears as the most adequate among the tested methods. Separation factors for H2-CO2 binary mixtures up to 145 have been achieved, although further optimization is required to improve the H2 permeation fluxes (around 1028 mol H2/m2 s Pa).
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| 6. |
- Montes, V., et al.
(författare)
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Preparation and characterization of Pt-modified Co-based catalysts through the microemulsion technique : Preliminary results on the Fischer-Tropsch synthesis
- 2014
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 223, s. 66-75
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the addition of small amounts of platinum (0.1-0.25% wt) to cobalt-based systems on Fischer-Tropsch synthesis was investigated. The solids were synthesized through microemulsion technique using TiO2 as the support. The best catalytic performance was achieved using Synperonic 13/6.5 as the surfactant. In all cases, the presence of platinum led to an increase in CO conversion which could be ascribed to the promotion of cobalt reducibility as evidenced by XPS. Moreover, the simultaneous reduction of cobalt and platinum precursors during synthetic procedure (ME1) was preferable to the consecutive one (ME2) probably as a result of a better Co-Pt interaction in the former case, as evidenced by TPR. TPR, Raman and XPS data also suggested that not only the presence of Co-0 but also the appearance of Co-TiO2 interactions favor the catalytic performance and that in general those interactions are stronger for ME1 solids.
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| 7. |
- Montes, V., et al.
(författare)
-
Chemoselective hydrogenation of furfural to furfuryl alcohol on ZrO2 systems synthesized through the microemulsion method
- 2018
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Ingår i: Catalysis Today. - : ELSEVIER SCIENCE BV. - 0920-5861 .- 1873-4308. ; 306, s. 89-95
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Tidskriftsartikel (refereegranskat)abstract
- Different solids consisting in hydrous zirconia were synthesized by the water in oil microemulsion technique (ME series). For comparative purposes, diverse solids were also obtained by the conventional sol-gel method (Pseries). The solids were tested for liquid-phase selective hydrogenation of furfural to furfuryl alcohol, using propan-2-ol as the hydrogen donor (Meerwein-Ponndorf-Verley process). The best results corresponded to catalysts calcined at 200 degrees C which consisted in amorphous solids with surface areas of ca 200 m(2)/g. The presence of some surfactant remaining from the synthetic process in solids obtained through the microemulsion technique favored selectivity to furfuryl alcohol with values >= 98%. Results were explained by the steric hindrance of furfural by the surfactant molecules in micelles thus favoring the interaction of the substrate with hydroxyl groups in hydrous zirconia through the C=O group. Application of microwave irradiation accelerated the reaction (15-30 times) as compared to conventional heating.
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| 8. |
- Montes, V., et al.
(författare)
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Synthesis of different ZnO-supported metal systems through microemulsion technique and application to catalytic transformation of glycerol to acetol and 1,2-propanediol
- 2014
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 223, s. 129-137
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Tidskriftsartikel (refereegranskat)abstract
- Different systems consisting of diverse metals (Au, Pt, Pd, Rh) supported on ZnO (5% by weight) were synthesized through the microemulsion technique (ME) and tested for glycerol hydrogenolysis, the main products being hydroxyacetone (acetol) and 1,2-propanediol (1,2-PDO). The solids synthesized using sodium borohydride as the reducing agent (B series) had smaller particle sizes as compared to the use of hydrazine (H series) which, in turn, resulted in a better catalytic performance. This synthetic method allowed us to obtain similar metal particle sizes (2-4 nm) for Pt, Pd and Rh solids in B series, whereas average gold metal particle was higher (> 8 nm) which probably accounts for Au-containing systems being inactive under our experimental conditions. Reactivity order followed the sequence Rh > Pt > Pd. A comparison of the systems synthesized in the present paper through ME technique with those obtained in a previous work through the deposition-precipitation process revealed a higher activity and selectivity to acetol for the former solids which could be related to the presence of surfactant. Moreover, results suggested that metal sites could participate not only in hydrogenation of acetol to 1,2-propanediol but also in the previous dehydration step of glycerol to acetol.
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| 9. |
- Agrell, J., et al.
(författare)
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Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O3
- 2003
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 219:2, s. 389-403
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Tidskriftsartikel (refereegranskat)abstract
- Production of H-2 from methanol by steam reforming, partial oxidation, or a combination thereof was studied over Cu/ZnO-based catalysts. The catalysts were characterized by a variety of techniques, including N2O chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction/oxidation. The influence of feed composition, reaction temperature, and catalyst formulation on H-2 production rate, product distribution, and catalyst lifetime was investigated. Distinct differences between the processes were observed with respect to catalyst behavior. ZrO2-containing catalysts, especially Cu/ZnO/ZrO2/Al2O3, exhibit the best performance in the steam reforming reaction. During partial oxidation, however, a binary Cu/ZnO catalyst exhibits the lowest light-off temperature and the lowest level of CO by-product. The redox properties of the catalyst appear to play a key role in determining the pathway for H-2 production. In particular. the extent of methanol and/or H-2 combustion at differential O-2 conversion is strongly dependent on the ease of copper oxidation in the catalyst.
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| 10. |
- Boutonnet-Kizling, M, et al.
(författare)
-
Surface oxidation of silicon carbide: quantitative measurement and Rh effect
- 1992
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Ingår i: Materials Chemistry and Physics. - 0254-0584 .- 1879-3312. ; 30, s. 273-277
-
Tidskriftsartikel (refereegranskat)abstract
- The oxidation degree of a commercial silicon carbide (SiC) powder was studied by means of Fourier transform infrared spectroscopy, using the intensity of the (SiO2) band at 450 cm-1 for measurements. Results are related to data obtained by LECO and gravimetric measurements. The influence of water in oxygen on the rate of the oxidation process was particularly examined. It was found that water alone had an oxidizing efficiency and that its mixture with oxygen increased the effect of the latter. The presence of Rh particles on SiC promoted the formation of SiO2. However, as shown by the IR study of CO adsorption, this formation embedded the metal particles. This effect can be avoided by loading Rh on a precalcined SiC sample.
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| 11. |
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| 12. |
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| 13. |
- Di Carlo, Gabriella, et al.
(författare)
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Design of Cobalt Nanoparticles with Tailored Structural and Morphological Properties via O/W and W/O Microemulsions and Their Deposition onto Silica
- 2015
-
Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 5:1, s. 442-459
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Tidskriftsartikel (refereegranskat)abstract
- Cobalt nanostructures with different size and morphology, i.e., spherical nanoparticles, nanorods, and particles arranged into elongated structures, were prepared using micelles and microemulsions as confined reaction media. The syntheses were carried out using three types of systems: aqueous surfactant solutions, oil-in water (O/W), and water-in-oil (W/O) microemulsions. The influence of the surfactant and the precipitating agent used for synthesis was also investigated. For this purpose, cobalt nanostructures were prepared using different non-ionic surfactants, namely Synperonic((R)) 10/6, Pluronic((R)) P123 and a mixture of SPAN 20-TWEEN 80. Three different precipitating agents were used: sodium borohydride, sodium hydroxide, and oxalic acid. Our findings revealed that by changing the type of reaction media as well as the precipitating agent it is possible to modify the shape and size of the cobalt nanostructures. Moreover, the use of O/W microemulsion generates better results in terms of colloidal stability and uniformity of particle size with respect to W/O microemulsion. The different cobalt nanostructures were supported on commercial and mesoporous silica; transmission electron microscopy (TEM) images showed that after deposition the Co nanocrystals remain well dispersed on the silica supports. This behavior suggests their great potential in catalytic applications.
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| 14. |
- Eriksson, Sara, et al.
(författare)
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Fuel-rich catalytic combustion of methane in zero emissions power generation processes
- 2006
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 117:4, s. 447-453
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Tidskriftsartikel (refereegranskat)abstract
- A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO2, Ce-ZrO2 or alpha-Al2O3 were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO2 < Rh/ZrO2 < Rh/alpha-Al2O3. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO2 is probably related to the high dispersion of Rh on Ce-ZrO2 and the high oxygen mobility of this support compared to pure ZrO2. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.
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| 15. |
- Escudero, M. J., et al.
(författare)
-
Development and performance characterisation of new electrocatalysts for PEMFC
- 2002
-
Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 106:1-2, s. 206-214
-
Konferensbidrag (refereegranskat)abstract
- New electrocatalysts based on Pt, Pt-Ru and Pt-Pd have been prepared by the microemulsion method. This method allows the production of a very narrow size distribution of metal particles, with an average size smaller than that of conventional electrocatalysts prepared by impregnation. Eight membrane electrode assemblies (MEAs) with an active surface area of 50 cm(2) were characterised in a single fuel cell. The MEAs consist of Nation 117 as membrane and a commercial electrocatalyst (40% Pt/C from E-TEK) on the cathode side, Four MEAs have electrocatalysts prepared by the microemulsion technique and the other four have commercial electrocatalysts on the anode side. The performance of the eight MEAs was evaluated by measuring the fuel cell polarisation curves and the internal resistance with H-2/O-2 and H-2/air, at 60 T and pressure in the range from I to 3 bar. The MEAs with the electrocatalysts prepared by microemulsion showed a performance comparable to that of the MEAs with commercial electrocatalysts. The satisfactory results obtained show that microemulsion is a promising method for the preparation of electrocatalysts for fuel cells. Further effort will be devoted to the optimisation of the method, mainly, the deposition of the metal particles on the carbon support, which it is expected to enhance the fuel cell performance.
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| 16. |
- Garcilaso, V., et al.
(författare)
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Promoting effect of CeO2, ZrO2 and Ce/Zr mixed oxides on Co/Γ-Al2O3 catalyst for Fischer-Tropsch synthesis
- 2019
-
Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 132, s. 1141-1150
-
Tidskriftsartikel (refereegranskat)abstract
- A series of cobalt-based catalysts have been synthesized using as support γ-Al2O3 promoted by ceria/zirconia mixed oxides with a variable Ce/Zr molar ratio. The obtained catalysts demonstrated oxide promotion results in the protection of the major textural properties, especially for Zr-rich solids. Reducibility of cobalt species was enhanced by the presence of mixed oxides. The chemical composition of the oxide promoter influenced not only physicochemical properties of final catalysts but also determined their performance during the reaction. In this sense, Zr-rich systems presented a superior catalytic performance both in total conversion and in selectivity towards long chain hydrocarbons. The observed Zr-promotion effect could be explained by two significant contributions: firstly, the partial inhibition of Co–Al spinel compound formation by the presence of Zr-rich phases which enhances the availability of Co actives site and secondly, Zr-associate acidic sites promote higher hydrocarbons selectivity.
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| 17. |
- Ilieva, L., et al.
(författare)
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Nanosized gold catalysts on Pr-modified ceria for pure hydrogen production via WGS reaction
- 2015
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 157, s. 138-146
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Tidskriftsartikel (refereegranskat)abstract
- The WGS activity of gold catalysts on ceria doped with Pr (5 and 10 at% Pr) was studied. The supports were synthesized by impregnation (IM) and microemulsion (ME) method. Gold (3 wt%) was introduced by deposition-precipitation method. The samples were characterized by means of XRD, TEM, XPS and TPR measurements. The catalytic activity in WGSR of fresh catalysts did not differ significantly. After re-oxidation following the first catalytic run, the activity of gold catalyst on IM support with 5 at% Pr increased, while a significant drop in activity of the gold catalyst on ME support containing 10 at% Pr was registered. In the latter case the presence of very small gold particles were responsible for the initial WGS activity, while their agglomeration after the catalytic reaction caused the observed activity decrease. In the former case the higher activity during the second catalytic run could be explained by: (i) the redox behavior, showing that only in this case the most mobile oxygen could be fully recovered; (ii) the morphology of the support, revealing better crystallization of the support after WGS catalytic test as compared to the presence of partially amorphous ceria in the fresh gold catalyst.
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| 18. |
- Ilieva, L., et al.
(författare)
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Pure hydrogen production via PROX over gold catalysts supported on Pr-modified ceria
- 2014
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 134, s. 628-635
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Tidskriftsartikel (refereegranskat)abstract
- Two series of Pr-doped (5 and 10 at.% Pr) cerium oxides were synthesized by impregnation (IM) and microemulsion method (ME). The Au catalysts (3 wt.%) supported on these oxides were tested in PROX. The samples were characterized by XRD, XPS and TPR measurements. At the operating temperature of the fuel cells (80-120 degrees C) gold catalysts on Pr-doped ceria supports synthesized by IM method exhibited much higher PROX activity as compared to the case of ME method. The observed different catalytic behavior was attributed to the different support preparation affecting the gold particle sizes and the mixed support features. In the case of mixed supports synthesized by IM the size of gold particles established by XRD is smaller and the supply of oxygen evidenced by the obtained TPR results is higher as compared to the gold catalysts on the ME prepared mixed supports. The higher gold dispersion as well as the more defective structure assumed by higher microstrain parameter of ceria lattice (XRD data) due to Pr-doping by IM method, improved both the reducibility and the PROX activity up to 120 degrees C.
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| 19. |
- Kizling, J, et al.
(författare)
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Preparation of colloidal metals by reduction or precipitation in microheterogeneous fluids
- 1992
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Ingår i: Electrochemistry in Colloids and Dispersions. - New York : VCH Publishers Inc.. ; , s. 333-344
-
Bokkapitel (refereegranskat)abstract
- Several methods of preparing colloidal particles of metals or metal oxides by reduction of salts dissolved in the water pools of microemulsions have been reported. These are briefly reviewed. In many cases the reduction is followed by aggregation of the precipitated material to colloidal particles that contain much larger numbers of metal atoms than those contained in each water pool. However, by judicious choice of systems and reaction conditions it appears possible to limit the initial reaction to each water pool. In such cases, the method offers the possibility to carry out the reduction under conditions corresponding to relatively concentrated electrolyte solutions in spite of the system as a whole being very dilute. Using this method it is also possible to prepare alloys of metals directly by reduction. This has been demonstrated for H2PtCl6 and PdCl2 in C12E5-hydrocarbon-water micro-emulsions. The state of the metal ions in the water pools was investigated by EXAFS. The results show that Pt and Pd do indeed form an alloy and that the coordination number for Pt and Pd in particles is lower than it is in bulk metal.
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| 20. |
- Laguna, O. H., et al.
(författare)
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Au-supported on Fe-doped ceria solids prepared in water-in-oil microemulsions : Catalysts for CO oxidation
- 2016
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Ingår i: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 278, s. 140-149
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Tidskriftsartikel (refereegranskat)abstract
- Gold catalysts were synthesized by deposition-precipitation employing Fe-doped ceria systems, previously obtained by means of the water-in-oil microemulsions methodology with different iron contents (10, 25 and 50 Fe at.%). The final catalysts were tested in the CO oxidation reaction in presence of H-2. After gold deposition the crystalline structure of the supports was not altered. Moreover no XRD lines associated to gold were detected, indicating its high dispersion. Solid solution was generated in all samples, although the segregation of iron oxide was detected for the material with the highest iron loading. This phenomenon was then enhanced for the corresponding gold catalyst that also presented sintering of the gold nanoparticles. Strong interaction between gold and the oxygen vacancies of the supports was demonstrated, as well as the promotion of the reducibility of surface Ce4+ and Fe3+ species at low temperatures. A remarkable promotion of the CO conversion at lower temperatures respect to that of the supports was observed for the gold catalysts. Below 120 degrees C, lower the amount of iron incorporated, higher the catalytic performance of the catalyst. This behaviour is closely related not only to a high gold dispersion but also to the ability for creating additional oxygen vacancies in the support, required for the CO oxidation reaction.
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| 21. |
- Laguna, O. H., et al.
(författare)
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Fe-doped ceria solids synthesized by the microemulsion method for CO oxidation reactions
- 2011
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 106:3-4, s. 621-629
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Tidskriftsartikel (refereegranskat)abstract
- A series of Ce-Fe mixed oxides as well as the pure oxides were synthesized by the microemulsions method. The solid solution formation was established for all the Fe-doped systems and only a hardly noticeable segregation of alpha-Fe(2)O(3) was appreciated for the solid with the maximum iron content (50 at.% Fe). The oxygen exchange is improved for all the Fe-doped systems; however the 10 at.% Fe appears as the optimal iron content for achieving the maximum oxygen vacancies concentration and the higher reducibility efficiency. The CO oxidation (TOX. PROX) is especially achieved for the solids with the lower iron contents but with a superior oxygen vacancies proportion. These Ce-Fe systems prepared from microemulsions are very attractive to be considered as supports for depositing active phases capable of enhancing oxygen exchange ability of the whole system, allowing higher CO oxidation abilities.
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| 22. |
- Lualdi, Matteo, et al.
(författare)
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Effect of Ti and Al addition via direct synthesis to SBA-15 as support for cobalt based Fischer-Tropsch catalysts
- 2012
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 443-444, s. 76-86
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Tidskriftsartikel (refereegranskat)abstract
- Different mesoporous SBA-15 supports doped with Ti and Al at 5 and 10 wt% have been synthesized by means of direct synthesis. The supports have been characterized by N 2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH 3-temperature programmed desorption (NH 3-TPD), H 2-chemisorption, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM). Titanium doped materials showed to have much shorter channels than the pristine SBA-15, while aluminum addition did not have a significant effect on channel length. After impregnation with 12 wt% Co, the catalysts were further characterized and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H 2/CO ratio = 2.1, pellet size: 53-90 μm) with and without external water addition. The S C5 + values of the different SBA-supported catalysts were low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitations increased the H 2/CO ratio inside the 1-dimensional (1D) porous network. The selectivity data showed a correlation between the channel length and the extent of CO-diffusion limitations at much shorter diffusion distances than those for conventional 3D porous supports. Water partial pressure showed to increase the syngas diffusion rate (i.e. removal of diffusion limitations on reactants’ arrival), to have a positive kinetic effect on the rate and to favor longer chain hydrocarbons.
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| 23. |
- Lualdi, Matteo, et al.
(författare)
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Evidence for diffusion-controlled hydrocarbon selectivities in the fischer-tropsch synthesis over cobalt supported on ordered mesoporous silica
- 2011
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 54:16-18, s. 1175-1184
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Tidskriftsartikel (refereegranskat)abstract
- A series of four cobalt-based catalysts (two of which promoted with ruthenium) supported on SiO2 or SBA-15 were prepared and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H2/CO ratio = 2.1, pellet size: 53-90 μm). The catalysts were characterized by N2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), H2-chemisorption and transmission electron microscopy (TEM). Ru as promoter enhanced the activity but not the selectivity to long-chain hydrocarbons ({S}-{C}-{ 5+}). The {{S}}-{{C}}-{5+}} values of the SBA-supported catalysts were very low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitation increased the H2/CO ratio inside the 1-dimensional (1-D) porous network. A superimposition of the selectivity results on the correlations found in our recent study, derived for Co-based catalysts supported on γ-Al2O3, α-Al2O3 and TiO2 free from diffusion limitations, was made. While the SiO2-supported catalysts with a 3-D porous structure followed the correlations, the SBA-catalysts deviated significantly at low conversions, giving a further indication that the selectivity results of these catalysts were affected by CO diffusion limitations. Hence, it may be concluded that the kinetically significant diffusion distances (i.e. those long enough to cause an intrapore H 2/CO ratio higher than that of the bulk gas phase) are probably much shorter for 1-D porous networks than for conventional 3-D supports. This is explained by a significantly lower effective diffusivity in 1-D porous networks. The potential of using the correlations between non-ASF distributed hydrocarbons and C5+, to give insight on the occurrence of diffusion limitations, was confirmed by superimposing data from the literature that were anticipated to be influenced by CO diffusion limitations.
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| 24. |
- Montes, V., et al.
(författare)
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Selective transformation of glycerol into 1,2-propanediol on several Pt/ZnO solids : Further insight into the role and origin of catalyst acidity
- 2015
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 257, s. 246-258
-
Tidskriftsartikel (refereegranskat)abstract
- Microemulsion technique allowed us to synthesize different ZnO solids with similar particle sizes and textural properties. Platinum was subsequently incorporated by deposition-precipitation and impregnation methods and solids tested for glycerol selective transformation into 1,2-PDO. Incorporation of platinum led to the creation of new (mainly Lewis) acid sites. A good correlation between conversion and acidity of Pt/ZnO solids was obtained. Interestingly, despite exhibiting some acidity, supports alone were inactive in the process which evidenced the role of the metal in dehydration of glycerol into acetol. Furthermore, as the reaction proceeded some chlorine coming from the precursor (H2PtCl6) was leached which led to the disappearance of the strongest acid sites, associated to side reactions (catalytic cracking) thus resulting in an increase in selectivity to 1,2-PDO. Eventual formation of Pt-Zn alloy upon reduction of the systems at ca. 400 degrees C was beneficial to 1,2-PDO selectivity.
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| 25. |
- Ojeda, M., et al.
(författare)
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Synthesis of Rh nano-particles by the microemulsion technology - Particle size effect on the CO+H-2 reaction
- 2004
-
Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 274:1-2, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- Several alumina-supported rhodium-based catalysts have been prepared using the microemulsion technology. The change of microemulsion properties led to catalysts with different Rh particle size and narrow size distribution while keeping the same metal loading. The metal particle size was determined by XRD and TEM. These catalysts were tested in the CO hydrogenation reaction in order to investigate the influence of the Rh particle size. The catalytic results indicated that turnover frequency (TOF) increased about four times when the Rh particle size increased approximately from
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| 26. |
- Rojas, S., et al.
(författare)
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Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion - Electrocatalysts for fuel cell applications
- 2005
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 285:02-jan, s. 24-35
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Tidskriftsartikel (refereegranskat)abstract
- A series of platinum and platinum ruthenium carbon supported electrocatalyst have been prepared by the microemulsion technique. The influence of parameters such as the preparation route, the metal loading and the PtRu stoichiometry on the morphology of the final nanoparticles has been studied. Irrespective the total metal loading, nanosized particles, displaying a narrow size distribution were obtained. In addition, particle size was found to be independent of the metal loading. Structural characteristics of these systems have been studied by XPS, X-ray diffraction, TEM, and TPR-TPO and their textural parameters by N-2 adsorption. The catalytic performance of the samples was evaluated in the electrochemical oxidation of methanol. The influence of the morphology on the catalytic performance of the catalysts is discussed in terms of their synthesis route. © 2005 Elsevier B.V. All rights reserved.
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| 27. |
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| 28. |
- Sanchez-Dominguez, M., et al.
(författare)
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Preparation of inorganic nanoparticles in oil-in-water microemulsions : A soft and versatile approach
- 2012
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 17:5, s. 297-305
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Forskningsöversikt (refereegranskat)abstract
- In this review, the synthesis of inorganic nanoparticles using oil-in-water (O/W) microemulsions as confined reaction media is discussed. Synthesis using (O/W) microemulsions has been demonstrated for a great variety of inorganic nanoparticles: metallic (Pt, Pd, Rh, Ag), single metal oxides (CeO 2, ZrO 2, TiO 2, Fe 2O 3), mixed and doped metal oxides (Ce 0.5Zr 0.5O 2, Ce 0.99Eu 0.01O 2, Zr 0.99Eu 0.01O 2, and Fe 2Mn 0.5Zn 0.5O 4), semiconductors (PbS, CdS, Ag 2S, ZnS, CdSe, PbSe, Ag 2Se), fluorides (CaF 2, YF 3, NdF 3, PrF 3), phosphates (CePO 4, HoPO 4), and chromates (BaCrO 4 and PbCrO 4). There are two synthetic strategies: 1) the use of oil-in water (O/W) microemulsions, in which the precursor is an ionic salt which is dissolved in the continuous aqueous phase; and 2) use of O/W microemulsions, in which the precursor is an organometallic salt dissolved in the oil droplets of the microemulsion. The latter approach keeps more resemblance to the typical W/O microemulsion reaction method, as it has the greatest level of precursor confinement.
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| 29. |
- Sanchez-Dominguez, Margarita, et al.
(författare)
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Synthesis of CeO2, ZrO2, Ce0.5Zr0.5O2, and TiO2 nanoparticles by a novel oil-in-water microemulsion reaction method and their use as catalyst support for CO oxidation
- 2010
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 158:1-2, s. 35-43
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Tidskriftsartikel (refereegranskat)abstract
- A novel and straightforward approach for the synthesis of mesoporous inorganic oxide nanoparticles, with a small particle size and high specific surface area is reported, by using oil-in-water microemulsions, in contrast to the typically used water-in-oil microemulsion method. The new strategy implies the use of organometallic precursors, dissolved in nanometer-scale oil droplets (stabilised by surfactant), and dispersed in a continuous aqueous phase. The potential of this approach is explored for producing nanocrystalline ceria, zirconia, ceria/zirconia mixed oxide and titania. Nanocrystalline cubic CeO2 and Ce0.5Zr0.5O2 were obtained under soft conditions, whilst ZrO2 and TiO2 presented wide X-ray diffraction peaks. The specific surface area (SSA) of the obtained materials was in the order of 200-370 m(2)/g and the particle size was very small (similar to 2-3 nm). The materials were calcined at 400 degrees C after which a high SSA was maintained (100-150 m(2)/g) and the crystallinity was improved, yielding tetragonal phases for both TiO2 (anatase) and ZrO2. The potential of the calcined materials as catalyst support was explored in the CO oxidation reaction by doping the oxides with Au (2 wt%). The obtained results demonstrate the feasibility of this approach for the preparation of various supports with high SSA for catalytic purposes.
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| 30. |
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| 31. |
- Sanchez-Dominguez, M., et al.
(författare)
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Synthesis of Pt Nanoparticles in oil-in-water microemulsions : Phase Behavior and Effect of Formulation Parameters on Nanoparticle Characteristics
- 2011
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 32:12, s. 1765-1770
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Tidskriftsartikel (refereegranskat)abstract
- Pt nanoparticles were synthesized in oil-in-water (o/w) microemulsions, in contrast to the typically used water-in-oil microemulsion method. The new strategy implies the use of a Pt organometallic precursor (1,5-cyclooctadiene dimethyl platinum (II)), dissolved in nanometre-scale oil droplets, stabilized by surfactant, and dispersed in a continuous aqueous phase. Three different nonionic microemulsion systems were used. Characterization studies demonstrate that small, nanocrystalline Pt nanoparticles were obtained. The particle size and agglomeration was dependant on the microemulsion system used and its composition. The obtained results demonstrate the feasibility of this approach for the controlled synthesis of Pt nanoparticles with potential for catalytic purposes.
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| 32. |
- Tiseanu, C., et al.
(författare)
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In situ Raman and time-resolved luminescence investigation of the local structure of ZrO 2 in the amorphous to crystalline phase transition
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:31, s. 16776-16783
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Tidskriftsartikel (refereegranskat)abstract
- The local structure of europium doped and impregnated ZrO 2 in the amorphous state and during crystallization is investigated by in situ X-ray diffraction and in situ Raman, high-resolution transmission electron microscopy (HRTEM) and time-resolved photoluminescence spectroscopy. From Raman spectra excited at three different wavelengths (λ ex= 488, 514, and 633 nm), both phonon modes of ZrO 2 and photoluminescence (PL) corresponding to europium electronic transitions were investigated. In the as-synthetized state, samples were X-ray and Raman amorphous with few tetragonal (also monoclinic) crystallites being observed under HRTEM microscopy. In situ XRD patterns show that all samples crystallize in the tetragonal phase around 450 °C. The time-resolved PL spectra of europium doped and impregnated ZrO 2 show spectral dynamics with time delay after lamp/laser pulse which is assigned to the coexistence of the different amorphous and crystalline components or unreacted europium precursor. From in situ Raman spectra, crystallization was detected at 300-350 °C, monitoring for the characteristic tetragonal-like 5D 0- 7F 2 emission of europium at 606 nm. The ratio of tetragonal to amorphous emission increased abruptly from ca. 2-4% at 300-400 °C to almost 25% at 400-450 °C, whereas at 500 °C the emission is mostly tetragonal. A similar trend was found with the ex situ calcined samples, but relative strong tetragonal emission was observed at lower temperature in the range of 350 to 400 °C.
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| 33. |
- Tiseanu, C., et al.
(författare)
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Order and disorder effects in nano-ZrO 2 investigated by micro-Raman and spectrally and temporarily resolved photoluminescence
- 2012
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:37, s. 12970-12981
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Tidskriftsartikel (refereegranskat)abstract
- Pure and europium (Eu 3+) doped ZrO 2 synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm -1 the correlation between the phonon spectra of ZrO 2 and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu 3+ f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500°C, the overall Eu 3+ emission is dominated by Eu 3+ located in tetragonal symmetry lattice sites with a crystal-field splitting of the 5D 0- 7F 1 emission of 20 cm -1. Annealing of ZrO 2 at 1000°C leads to a superposition of Eu 3+ emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm -1 for the 5D 0- 7F 1 transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu 3+ doped ZrO 2 samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases.
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| 34. |
- Tiseanu, Carmen, et al.
(författare)
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Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:38, s. 17135-17145
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Tidskriftsartikel (refereegranskat)abstract
- Pure and europium (Eu(3+)) doped cerium dioxide (CeO(2)) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce(4+) sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce(4+) relative to Ce(3+) ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.
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| 35. |
- Tiseanu, C., et al.
(författare)
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Temperature induced conversion from surface to bulk sites in Eu 3-impregnated CeO 2 nanocrystals
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:1, s. 013521-
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Tidskriftsartikel (refereegranskat)abstract
- Evolution with calcination temperature of Eu 3 sites in CeO 2 nanocrystals is investigated by time-resolved photoluminescence spectroscopy. In the as-synthesized Eu 3 impregnated CeO 2, most of Eu 3 ions reside on surface (S) sites. The Eu 3emission in S sites is broad and short-lived (τ 240 Όs) being dominated by the electric dipole (ED) 5D 0- 7F 2 emission with little evidence for clustering. After calcination (between 500 and 1300 °C), Eu 3 is distributed on surface, cubic and up to three additional crystalline sites. Surface type emission could be detected until 1100 °C. In cubic sites, Eu 3 substitute for the lattice Ce 4 with O h symmetry (O sites). The emission of Eu 3 in O sites is characterized by relative long-lived (τ 1.8-2 ms) and ultra-narrow (FWHM 7 cm -1) magnetic dipole (MD) 5D 0- 7F 1 emission centered at ∌591 nm. Three more crystalline sites are attributed to the oxygen vacancy charge-compensated defects: trigonal with C 3v symmetry (C1 sites) and C2 and C3 sites with C 2v or lower symmetry. Eu 3 in C1 sites exhibits predominant ED 5D 0- 7F 2 emission centered at ∌610 and 632 nm with lifetime of 0.85-1 ms. The C1 sites are assigned to Eu 3-(oxygen vacancy)-associated cubic sites. The O 2- to Ce 4 electronic charge-transfer band sensitizes preferentially the Eu 3 emission in O and, to a less extent, C1 sites but not the S sites. Overall, the results show that the oxygen vacancies are distributed around both Eu 3 and Ce 4 and the Eu 3-oxygen vacancy interaction mode as nearest-neighbour or next-nearest-neighbour depends on the calcination temperature.
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| 36. |
- Touroude, R, et al.
(författare)
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Preparation of colloidal platinum/palladium alloy particles from nonionic microemulsions: Characterization and catalytic behaviour
- 1992
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 67, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- Bimetallic particles of platinum and palladium have been prepared by reduction with hydrazine at ambient temperature of H2PtCl6 and PdCl2 dissolved in microemulsions consisting of water, hexadecane and pentaetyleneglycol dodecyl ether. The particles were deposited onto Al2O3.. Examination by STEM and EXAFS of particles with atomic ratio Pt:Pd = 35:65 showed that the particles are true Pt/Pd alloys. Indirect evidence was also obtained that particles containing only 4% Pd are alloys. The diameter of the particles ranges from 10-100 nm; there is evidence that they are formed by aggregation of particles in the diameter range 2-5 nm. The catalytic properties of the Pt/Pd/Al2O3 catalysts prepared from microemulsions were similar to those of catalysts prepared by conventional impregnation. Catalysts with low Pd content had the same selectivity in the isomerization of 2-methylpentane and hydrogenolysis of methylcyclopentane as a highly dispersed Pt catalyst (or a pure Pd catalyst). The catalytic cracking of 2-methylpentane indicates that the particle surfaces behave as Pt surfaces up to a Pd concentration of 60% in the particles. Isomerization of hexanes is dominated by the cyclic mechanism already at Pd concentrations as low as 4%; for these very low Pd concentrations hydrogenolysis of methylcyclopentane is the same as observed for very small Pt particles. It is concluded that Pd is enriched in the particle surfaces in such way that they consist of Pd and some highly dispersed Pt, even at bulk Pd concentrations as low as 4%.
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