Supported metals impregnation

The combustion temperature of soot particulates can be lowered by the addition of an oxidation catalyst in the form of fuel additives[2], by spraying metal salt solution on an accumulated soot or by the impregnation of filter walls with an oxidation catalyst. For the last option, oxides of supported metals are considered to be... 

As can be seen in table 1, with different preparation methods and active metals, the average size of the copper particle for the catalysts A and D were 20.3 nm and 50.0 nm. While those of the catalysts B and C were 51.3 nm and 45.4 run, respectively. CuO, non-supported metal oxide, made by impregnation is sintered and cluster whose particle size was 30 pm. The water-alcohol method provided more dispersed catalysts than the impregnation method. 

A 5 wt.% CoOx/Ti02 catalyst was prepared via an incipient wetness technique in which an aqueous solution of Co(N03)2 6H20 (Aldrich, 99.999%) was impregnated onto a shaped Ti02 (Milleimium Chemicals, commercially designated as DT51D, 30/40 mesh), as described in detail elsewhere [6]. Other supported metal oxide catalysts, such as FeOx, CuO, and NiOx, were obtained in a fashion similar to that used for preparing the CoO, catalyst. 

A wide variety of solid materials are used in catalytic processes. Generally, the (surface) structure of metal and supported metal catalysts is relatively simple. For that reason, we will first focus on metal catalysts. Supported metal catalysts are produced in many forms. Often, their preparation involves impregnation or ion exchange, followed by calcination and reduction. Depending on the conditions quite different catalyst systems are produced. When crystalline sizes are not very small, typically > 5 nm, the metal crystals behave like bulk crystals with similar crystal faces. However, in catalysis smaller particles are often used. They are referred to as crystallites , aggregates , or clusters . When the dimensions are not known we will refer to them as particles . In principle, the structure of oxidic catalysts is more complex than that of metal catalysts. The surface often contains different types of active sites a combination of acid and basic sites on one catalyst is quite common. 

It is also possible to examine carbon-supported metals an example is given in Fig. 7. The spectra are those of a 50 wt.% make Ni-on-carbon (Ni-C), prepared by the controlled charring of Ni(N03 impregnated cellulose followed by reduction with H2, before and after exposure to CO at room temperature. A... 

While there are extensive reviews of organosols and the catalysts therefrom in the literature, hy-drosols are relatively unknown in spite of the promising electrocatalysts that can emerge from them. Hydrosols of mono-, bi- and multimetallic nanoparticles as isolable precursors for producing supported metal catalyst are an economically beneficial alternative to the traditional wet impregnation of active metal components on carrier surfaces [25],... 

Fig. 6.5 Syntheses of metal loaded nanoparticles (Au) on metal oxide supports using impregnation, coprecipitation, deposition-precipitation, and photo-deposition methods. For Pt loaded nanoparticles H2PtCl6 (aq) is used.

Niobium Products Co., 50 m /g). Many different synthesis methods have been used to prepare supported metal oxide catalysts. In the case of supported vanadium oxide catalysts, the catalysts were prepared by vapor phase grafting with VOCI3, nonaqueous impregnation (vanadium alkoxides), aqueous impregnation (vanadium oxalate), as well as spontaneous dispersion with crystalline V2O5 [4]. No drastic reduction of surface area of the catalysts was observed. 

The basic design of instrument is schematically illustrated in Fig. 2.143 and consists of a metal or glass column approximately 2-3 m in length and 2-4 mm internal diameter, which is in the form of a circular spiral of three or four turns, and packed with supporting medium impregnated with a stationary phase the column is located in a temperature controlled oven. The mobile gas phase... 

Supported catalysts can be prepared in several ways [12], but the simplest is that of impregnation. A support has a characteristic pore volume (e.g., 0.5 mL g-1) hence, adding this volume of a solution containing the appropriate amount of a convenient catalyst precursor (e.g., nickel nitrate in water to prepare a supported nickel catalyst) to the support will simply fill all the pores. However, by allowing the system to dry, and then heating it in air to decompose any undesired salts, the supported material will be converted to the oxidic form. Reduction in hydrogen then converts the oxidic precursor - at least partially - into a supported metal catalyst. 

Despite the convenience of handling and separation in heterogeneous catalysis, many other parameters have a strong influence on the stereochemical outcome pressure temperature modifier purity of substrates high substrate specificity catalyst preparation, which includes type, texture, and porosity of the support dispersion impregnation reduction and pretreatment of the metal.22 Reproducibility of catalyst activities and enantioselectivities can often be a problem attributed to variations in catalyst preparations and purity of the substrate.5-22... 

Chapter 2 aims at understanding which processes take place during the pretreatment of Pt(NH3)4(N03)2 impregnated on SiC>2. The ultimate goal was (i) to understand how a certain metal particle size and particle size distribution is obtained and (ii) based upon these insights to prepare a supported metal catalyst with a narrow particle size distribution. 

This method of preparation of supported metal catalyst requires a closed reactor to perform the preparation in the absence of water, so both the organic solvent and the oxide support must be carefully dehydrated. The method is based on the following principle the metal is evaporated and co-condensed with the organic to 77 K on the walls of the reactor. Under dynamic vacuum, the co-condensate is then warmed up to 195 K, and melted. The oxide support is impregnated with the solvated metal atom (cluster) at the same temperature, After a given time of contact, the slurry is warmed up to ambient temperature, and the solvent is eliminated, after which the sample can be dried. 

The various stages of the preparation and thermal treatments of supported metal catalysts arc very schematically illustrated in Fig. 3. A very similar presentation was earlier given by van Delft et al. [16]. Typically, the support is impregnated with a metal salt (sec Section A.2.2.1.1) which serves as the metal precursor and should be well dispersed. Small metal particles may be formed by either direct reduction under mild conditions or by reduction after an intermediate oxidation step. Mild oxidation will lead to thin oxide films spread out on the support or to small oxide particles, where particles and film may also coexist. More severe treatments in oxidative atmospheres can lead to the... 

---