| 1. |
|
|
| 2. |
|
|
| 3. |
- Kizling, J, et al.
(författare)
-
Preparation of colloidal metals by reduction or precipitation in microheterogeneous fluids
- 1992
-
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.
|
|
| 4. |
|
|
| 5. |
- Nordli, KG, et al.
(författare)
-
Water-in-crude oil emulsions from the Norwegian continental shelf. 4. Monolayer properties of the interfacially active crude oil fraction
- 1991
-
Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 57, s. 83-98
-
Tidskriftsartikel (refereegranskat)abstract
- Monolayer properties of interfacially active fractions in six different North Sea crude oils have been studied. The fractions were separated by a consecutive adsorption procedure utilizing functionalized silica as adsorbent. The molecular weight of the fractions are between 950 and 1450 g mol - 1. They are built up of carbon and hydrogen to 99 mol% and of nitrogen, oxygen and sulfur to 1 mol%. The fractions form monomolecular films in the air/water interface. The films enter the highly compressible liquid expanded state at specific areas in the rage of 0.20-0.28m2mg-1 lytes, pH, temerature and chemical additives is reported. It is shown that aromatic solvents strongly interact with the film hence modifying its monolayer properties. Relaxation studies of strongly interact with partly water-soluble groups. Correlation between the monolayer properties of these fractions and their ability to stabilize water-in crude oil emulsions is undertaken.
|
|
| 6. |
- Touroude, R, et al.
(författare)
-
Preparation of colloidal platinum/palladium alloy particles from nonionic microemulsions: Characterization and catalytic behaviour
- 1992
-
Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 67, s. 9-19
-
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%.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Gutfelt, S, et al.
(författare)
-
Microemulsions as reaction medium for surfactant synthesis
- 1997
-
Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 128, s. 265-271
-
Tidskriftsartikel (refereegranskat)abstract
- Various microemulsion formulations were evaluated as reaction medium for synthesis of a surface active compound, decyl sulfonate, from decyl bromide and sodium sulfite. The reaction rate was fast both in water-in-oil and in bicontinuous microemulsions based on nonionic surfactant. Two-phase systems with added phase transfer agent (quaternary ammonium salt or crown ether) was much less efficient. It is postulated that the low efficiency of the phase transfer agents in catalyzing the reaction is caused by strong ion pair formation between the product formed, decyl sulfonate, and the phase transfer agent. To prove this point decyl bromide was reacted with two other nucleophiles, sodium cyanide and sodium azide. Neither of these give a reaction product that can form ion pair with the phase transfer agent. With these reagents phase transfer catalysis was almost as efficient as synthesis in microemulsion. It was also demonstrated that the rate of decyl sulfonate formation in microemulsion can be increased further by addition of a small amount of cationic surfactant. The choice of surfactant counterion is decisive of the effect on reaction rate, however. Whereas a small non-polarizable ion, such as acetate, gives a considerable reaction rate increase, a large polarizable ion, such as bromide, slows down the reaction. Bromide is believed to interact so strongly with the interface that it prevents the reacting ion, sodium sulfite to reach into the interfacial zone.
|
|
| 10. |
|
|
