| 1. |
- Björkegren, Sanna, 1984, et al.
(författare)
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Surface activity and flocculation behavior of polyethylene glycol-functionalized silica nanoparticles
- 2015
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 452, s. 215-223
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal silica nanoparticles have been functionalized with methyl polyethylene glycol silane (mPEG silane) and the PEGylated particles have been characterized with focus on exploring their surface chemical properties. The degree of surface functionalization was quantified using NMR diffusometry, and the measurements showed that the silane binds covalently to the silica surface. Samples with surface coverages ranging from 0.068 to 0.315 gmol silane/m(2) have been analyzed. The functionalized particles proved to be surface active and showed a significant reduction in surface charge and zeta potential with increasing degree of PEG functionalization. All samples showed colloidal stability at neutral pH and above within the range studied. At lower pH, the samples with low surface coverage displayed a reversible flocculation behavior, while samples with a high surface coverage and samples without functionalization remained stable. This suggests that steric stabilization is effective at low pH when the surface coverage is high enough; electrostatic stabilization is effective for samples without functionalization; and that inter-particle PEG-silica interactions cause flocculation of particles with too low degrees of PEG functionalization.
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| 2. |
- Fridell, Erik, 1963, et al.
(författare)
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Investigation of NOx storage catalysts
- 1997
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Ingår i: 4th International Congress on Catalysis and Automotive Pollution Control (CAPoC4) in Brussels, Belgium, April 9-11, 1997.
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Konferensbidrag (refereegranskat)
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| 3. |
- Fridell, Erik, 1963, et al.
(författare)
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Investigations of NOx storage catalysts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 537-547
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Tidskriftsartikel (refereegranskat)abstract
- NOx storage catalysts are used to reduce nitrogen oxides from lean-burn vehicles. The nitrogen oxides are stored in the catalyst during lean conditions and subsequently released and reduced during short periods of rich conditions. In the present study, we systematically investigate the sequence of elementary steps in the NOx reduction cycle, and the extent to which these steps influence the maximum NOx, reduction potential of the catalyst. As a model system, we use barium oxide as the NOx, storing compound in a Pt/Rh/Al2O3 system. Kinetics of NO oxidation, NO and NO2 adsorption, NO and NO2 release and reduction are studied under controlled conditions with systematic variations of temperature, gas composition, and storing/release times. The transient experiments comprise a storing phase using a lean NO/C3H6/O2/N2 gas mixture, and a regenerating phase where the O2 now is turned off. Experimentally, a significant amount of NOx is found to be stored in the Ba-containing material. A maximum in NOx storage is observed around 380 degrees C. For most of the experiments, there are clear NO and NO2 desorption peaks upon switching from the storing to the regeneration phase. TPD studies of NO and NO2 reveal a significant difference between prereduced and pre-oxidised samples where the former produce predominantly N2 and N2O at around 200 degrees C while NO and O2 desorb from the latter around 500 degrees C. In situ FTIR spectra show nitrate peaks in the region 1300-1400 cm(-1) when NOx is stored under lean conditions.
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| 6. |
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| 7. |
- Gevert, Börje Sten, 1956, et al.
(författare)
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Preparation of discrete colloidal ZSM-5 crystals with high Al-content
- 2011
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Ingår i: Journal of Porous Materials. - : Springer Science and Business Media LLC. - 1573-4854 .- 1380-2224. ; 18:6, s. 723-728
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Tidskriftsartikel (refereegranskat)abstract
- A new method for synthesis of discrete colloidal ZSM-5 particles with SiO(2)/Al(2)O(3) M ratios as low as 30 and sizes .4-1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO(2)/Al(2)O(3) ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO(2)/Al(2)O(3) ratio. The SiO(2)/Al(2)O(3) ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO(2)/Al(2)O(3) ratio. Synthesis mixture, aimed to yield a high SiO(2)/Al(2)O(3) ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO(2)/Al(2)O(3) ratios.
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| 8. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Light-off performance over cobalt oxide- and ceria-promoted platinum and palladium catalysts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 113-122
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Tidskriftsartikel (refereegranskat)abstract
- Monolith catalysts containing Co, Ce, Pt and Pd supported on alumina were prepared and tested with respect to low-temperature activity for oxidation of CO and propene. The catalysts were either pre-oxidised or pre-reduced prior to evaluation with respect to light-off performance, using net oxidising and net reducing CO/C3H6/O2/N2 gas mixtures. Promotion of Pt and Pd with cobalt or cerium oxide, favoured the low temperature activity significantly. Pre-reduction of Co- and Ce-promoted noble metals shifted the conversion starts of CO and propene toward lower temperatures compared with pre-oxidised samples. Pre-reduction of cobalt oxide, without Pt or Pd, yielded a dramatic improvement of the low-temperature catalytic performance compared with pre-oxidation of the said oxide. The catalysts were characterised by temperature programmed desorption of CO and specific surface area measurements. The high activity over the pre-reduced cobalt containing catalysts is suggested to be due to the presence of reduced cobalt oxide sites on those samples.
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| 9. |
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| 10. |
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| 11. |
- Törncrona, Anders, 1967, et al.
(författare)
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Low temperature catalytic activity of cobalt oxide and ceria promoted Pt and Pd: -Influence of pretreatment and gas composition
- 1997
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 14:1-2, s. 131-146
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pretreatment, gas composition and metal (Ce or Co) oxide promotion on the low-temperature CO and C3H6 oxidation activity over alumina-supported Pt and Pd has been studied. The monolith catalysts have either been preoxidised in O2/N2 Or prereduced in H2/N2 prior to evaluation with respect to light-off performance, using either net oxidising or net reducing CO/C3H6/O2/N2 gas mixtures. Compared with unpromoted Pt, promotion with preoxidised ceria or cobalt oxide enhances the low-temperature activity significantly and lowers the light-off temperatures by about 60-70 degrees C for both CO and C3H6. Prereduction of a cobalt-oxide catalyst (without precious metals) gives a dramatically improved performance compared with a preoxidised catalyst in terms of light-off and overall conversion. Prereduction of metal oxide promoted Pt and Pd can shift the light-off temperatures for CO and C3H6 by up to 100 degrees C toward lower temperatures compared with preoxidised samples. When using gas mixtures containing both CO and C3H6, the conversion of CO always starts at lower temperatures than the conversion of C3H6 The catalysts have been characterised by temperature-programmed desorption (TPD) of carbon monoxide, X-ray photoelectron spectroscopy (XPS), and specific surface area measurements (BET). The reduced cobalt containing samples adsorb large amounts of CO. The high activity over the catalysts containing prereduced cobalt oxide is suggested to be due to the presence of reduced cobalt-oxide sites on the surface of those samples.
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| 12. |
- Törncrona, Anders, 1967
(författare)
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Preparation of New Catalytic Materials by Small Particle Technology
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New techniques for preparation of catalytic materials with novel properties are presented in this thesis. Three new catalytic materials; washcoated fibres, highly dispersed metal oxides on titania coated silica particles and discrete colloidal ZSM-5 crystals with a low SiO2/Al2O3 ratio have been prepared and characterised. The catalytic properties of cobalt oxide and ceria promoted noble metals, and Cu-ZSM-5 catalysts made of commercial and discrete colloidal ZSM-5 crystals have been evaluated. Porous coatings were applied to alumina and silica fibre substrates by a stepwise procedure comprising charge reversal of the fibres, electrostatic adsorption of sol particles and fixing of the sol particles onto the fibre surface. Charged polymers proved to be excellent for charge reversal of fibre substrates owing to low sensitivity to dilution, whereas charge reversal was more difficult to accomplish with low molecular weight agents. The role of the charge reversing agent in the coating of the fibre substrates is discussed. Oxides of cerium(IV), iron(III), chromium(III), manganese(II), tin(II), nickel(II) and cobalt(II) and sulfides of nickel(II) and cobalt(II) were highly dispersed on the surface of TiO2/SiO2 particles with a particle size in the range 80-500 nm by a stepwise procedure. The mechanisms of controlled deposition of metal hydrous oxides on substrate particles are discussed. Discrete colloidal ZSM-5 crystals with a SiO2/Al2O3 ratio in the range 40-80 were prepared in a joint project by autoclaving an aluminosilicate gel at 120-160 °C formed upon mixing of TPAOH containing silicate and aluminate solutions. A high synthesis temperature was found to favour the incorporation of aluminium in the zeolite structure. The size of the crystals increased with decreasing SiO2/Al2O3 ratio. Catalysts made of discrete Cu-ZSM-5 crystals exhibited a higher NO-reducing ability in oxygen excess atmosphere compared with catalysts made of commercial Cu-ZSM-5 crystals of the same SiO2/Al2O3 ratio and copper exchange level. The low temperature oxidation of CO and propene over alumina supported Pt and Pd was significantly affected by the reactant gas stoichiometry, promoting oxide and pretreatment atmosphere. Prereduced cobalt oxide exhibited a light-off performance that resembles those normally observed over noble metal catalysts, whereas preoxidised cobalt oxide performed as regular catalytically active metal oxides. The support particles (Al2O3,TiO2/SiO2) were found not to affect the light-off performance of prereduced Pt/Co3O4 catalysts under the experimental conditions used. A mechanism to explain the remarkable low temperature activity over prereduced cobalt oxide is suggested.
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| 13. |
- Törncrona, Anders, 1967, et al.
(författare)
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Sol-gel coating of alumina bundle fibres
- 1997
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Ingår i: Journal of the European Ceramic Society. - 1873-619X .- 0955-2219. ; 17, s. 1459-1465
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Tidskriftsartikel (refereegranskat)
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