Incipient wetness impregnation with dispersant

Figure 3.10 XPS spectra in the range from 150 to 200 eV, showing the Zr 3d and Si 2s peaks of the 7.r02/Si02 catalysts after calcination at 700 °C. All XPS spectra have been corrected for electrical charging by positioning the Si 2s peak at 154 eV. The spectra labeled nitrate correspond to the catalysts prepared by incipient wetness impregnation with an aqueous solution of zirconium nitrate, and the spectrum labeled ethoxide to that prepared by contacting the support with a solution of zirconium ethoxide and acetic acid in ethanol. The latter preparation leads to a better Zr02 dispersion over the Si02 than the standard incipient wetness preparation does, as is evidenced by the high Zr 3d intensity of the bottom spectrum (adapted from Meijers et at, [33]).

Preparation of Pt-TiOx/Pd membranes. It was also desirable to prepare metalloceramic membranes in which the catalytic activity of the ceramic phase was enhanced through the addition of a noble metal. The very low surface area of the titania films prepared as described above made them difficult to impregnate with adequate dispersion by traditional incipient wetness techniques. Instead, finely ground titania (>200 mesh) was impregnated with platinum via the incipient wetness method with a chloroplatinic acid solution. This powder was then sprinkled onto the surface of a freshly dipped membrane, which was dried and heat treated as described. These materials were activated before use at 350°C in hydrogen for three hours. 

Incipient wetness impregnation is by far the most widely used method for the preparation of heterogeneous catalysts. This method is attractive because of its technical simplicity, low costs and limited amount of waste. Generally, a support is impregnated with a precursor-containing solution and dried. The dry product is then further treated through activation treatments (e.g. calcination and/or reduction) to obtain the desired catalyst. It is important that optimal synthesis parameters are found, since the efficiency of a catalyst is defined by the size of the active metal(oxide) particles, and their accessibility and distribution over the support. It is well-known that the use of metal nitrates as precursor salts for cobalt, iron and nickel catalysts ultimately yields poorly dispersed catalysts [1-3]. This is regrettable, as the use of nitrates as precursor is... 

In this work, nanocomposite supports formed by nanometric domains of alumina dispersed on a-Al203 beads were synthesized by a modified incipient wetness impregnation method in order to improve specific surface area and surface reactivily of a-Al203 large porosity precursor. The obtained composites were characterized by conventional physical methods like N2 adsorption-desorption, mercury porosimetry, TEM and SEM, in order to describe the evolution of the composite textural properties with the impregnated phase morphology. 

The hgure also shows that loading the carbon with hnely dispersed palladium has a further accelerating effect on surface oxidation, which is most pronounced with the carbon black. This can be explained by dissociative adsorption of O2 molecules on the metal surface and oxygen spillover. Platinum had a similar effect. Palladium (200 p.mol/g) was deposited on the carbons by incipient wetness impregnation followed by H2 reduction at 523 K the dispersion was about 25% with Norit and 15% with Corax 3. 

Similar Pt catalysts with three different dispersions as in Section 17.3, supported on silica and alumina and the homolog containing ceria, were prepared by incipient wetness impregnation of tetraammine-platinum nitrate of the support. In the case of the ceria-containing catalysts, a solution of Ce(N03)3-6H20 in 15.5 ml HjO was added to the silica or alumina supports, followed by drying in air overnight and calcinations at 300°C in air. Specific conditions used in the preparation of these materials are reported elsewhere. Table 17.4 summarizes the various catalysts studied in this case as well as their dispersion. 

Fig. 9. Energy Dispersive X-ray Analysis and SEM of the rhodium containing alumina catalyst layer on top of the steel microstructure a) catalyst prepared by segregation of alumina during annealing on FeCrAlloy with subsequent incipaent wetness impregnation with rhodium precursor, b) sol-gel alumina layer with rhodium by incipient wetness impregnation on alloy 800.

Carbon fibrils can be produced rather easily, e.g., by exposing supported, finely dispersed iron or nickel particles to reducing carbon containing gas flows. To this end, one has to produce first finely dispersed iron or nickel particles on a support material, such as alumina or silica. The desired catalyst can be prepared, e.g., by incipient wetness impregnation of the support material with a suitable metal salt solution or by means of homogeneous deposition-precipitation of the metal ions onto the carrier. 

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