Impregnation solutions

it is crucial that the active phase shows reasonable solubility in the solvent and sufficient interaction with the support. If the interaction with the support is too strong, there is a risk that most of the active phase will be deposited on the outer part of the support particle. If the interaction is too weak, there is a risk of redistribution of 

The wetting behavior of a solid by a liquid can be described using the Young equation 

Another important factor is capillary forces. The pressure increase Ap across the liquid-vapor meniscus in a cylindrical pore of radius r is described by the Young-Laplace equation. 

In catalysis expensive noble metals are usually used as the active phase. Thus, solution impregnation methods are optimized on maximum utilization, that is, small 

It depends on the nature of the active phase, whether the hydrogenated form (i.e., metal hydride) or the dehydrogenated form (i.e., metal) is more suitable for the synthesis. In the first case, it has to be considered that hydrides can decompose before or during the melting process (e.g., NaAlHJ, so it might be necessary to conduct the infiltration process under hydrogen pressure. For a successful melt infiltration, the following key requirements should be met  

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Colbow, Zhang, and Wilkinson [128] showed that the performance of liquid feed fuel cells could be increased by oxidizing the carbon diffusion layer. The DL was electrochemically oxidized in acidic aqueous solution (impregnated in some cases with proton-conducting ionomer) prior to application of the electrocatalyst. 

Moyano, P. and Berna, A. (2002). Modeling water loss during frying of potato strips Effect of solute impregnation. Drying Technol. 20(7), 1303-1318. 

Because protein and cellulosic fibers are buried in contact with copper metal objects, a chemical microsystem is established whereby the degradation of the fiber and the corrosion of the metal interact physically and chemically. As the corrosion solution impregnates and swells the fibers, polymer molecules in amorphous areas are spread apart but are prevented from complete dissolution by the resistant crystalline segments. Copper ion from the corrosion solution is bound to the polymers (Figure 5). As the fiber degrades and more end groups are formed, more copper is bound. Polymers expand further apart as interchain forces are reduced. 

In solution impregnation, a porous support is infiltrated with a solution of the active phase or its precursor. After careful removal of the solvent, a high dispersion of the active phase over the whole support is obtained (if a precursor of the active phase is used, a conversion step after drying is necessary). The basic principle of the process is shown in Figure 10.21. 

Figure 10.21 Schematic illustration of solution impregnation used to synthesize highly dispersed nanoparticles on a porous support.

Figure 10.22 Interactions during solution impregnation between support, solvent and active phase.

Increased activity was found by Anwander et al. who grafted aluminum alkoxide moieties on siliceous mesoporous MCM-41 [25]. These materials were first prepared by a one-step solution impregnation by treating Al(Oi-Pr)3 with partially dehydroxylated MCM-41 in hexane. In a second approach, MCM-41 was reacted... 

The role of adsorption kinetics and the diffusion of surfactants is especially important in controlling capillary impregnation. According to studies by N.N. Churaev, the solution impregnating the capillary quickly loses its dissolved surfactant due to adsorption of the latter on capillary walls, so the rate of impregnation may be limited by the diffusional transport of surfactant from the bulk of the solution to the menisci in the pores. 

In general, the results from the left branch of the regression tree indicate the importance of the amount of impregnating solution, impregnation time and drying speed (preparation parameters). 

Catalyst preparation by impregnation is carried out by contacting the support with a solution containing the precursors of the active phases. Two different approaches can be followed incipient-wemess impregnation and excess-solution impregnation. In the former, the carbon support is wetted with a solution of the precursor, drop by drop, in the proper amount to just fill its pores. A slurry is formed with the pore volume filled wifh fhe solution, which is finally dried to remove the solvent, leaving the precursor of the active phase deposited on the... 

In summary, highly cubic ordered cobalt oxides with crystalline walls have been synthesized by an accurately controlled incipient wetness approach using mesoporous silica as hard template and cobalt nitrate as the precursors. Compared with the previously reported solution impregnation processes, this technique is facile, time-saving and economical. This technique can be used to synthesize ordered mesoporous metal oxides, and we expect that rvith this approach various kinds of mesoporous oxides or other materials can be synthesized, which may benefits their applications in many areas such as in catalysis, sensors, clean energy and electronics. 

For industrial application usually such metals as palladium, platinum, iron, ruthenium, cobalt, molybdemun, nickel, either alone or as bimetallic catalyst are used. They are introduced using ion exchange, excess solution impregnation, incipient-wetness impregnation or physical vapor deposition methods. 

Two types of environmentally friendly jute fibre reinforced green composites have been studied. These are based on Mesua ferrea L. seed oil-based poly(urethane ester) and poly(urethane amide) resin blends with commercially available partially butylated melamine-formaldehyde and epoxy resins by solution impregnation and hot-curing methods. The composites were cured at a temperature of about 130-140°C under a pressure of 35.5 kg cm for around 2 h.The physical, mechanical and chemical properties of the epoxy-modified polyurethane composites were better than those of the MF-modified composites. They also possessed excellent chemical resistance and hydrolytic stability in water, acid and salt solutions, making them useful for low load-bearing applications. 

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