Catalyst impregnated

To ensure a thorough impregnation, the air in the pores of the support is removed by evacuation or is replaced by steam or a soluble gas (COz, NH,). 

The great virtue the of the impregnation process is the separation of the production of the active phase and of the support phase, which is clearly not possible in the case of the manufacture of precipitated catalysts. 

The disadvantage of impregnation lies in the limited amount of material that can be incorporated in a support by impregnation. 

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Among continuous reactors, the dominant system used to produce parasubstituted alkylphenols is a fixed-bed reactor holding a soHd acid catalyst. Figure 3 shows an example of this type of reactor. The phenol and alkene are premixed and heated or cooled to the desired feed temperature. This mix is fed to the reactor where it contacts the porous soHd, acid-impregnated catalyst. A key design consideration for this type of reactor is the removal of the heat of reaction. 

Distribution of Catalyst in Pores Because of the prac tical reqmrements of manufacturing, commercial impregnated catalysts usually have a higher concentration of ac tive ingredient near the outside than near the tip of the pores. This may not be harmful, because it seems that effectiveness sometimes is better with some kind of nonuni-form distribution of a given mass of catalyst. Such effects may be present in cases where the rate exhibits a maximum as a function of... 

G. A. White We have done some experimental work on impregnating catalyst with potash, and, in fact, potash has been used in related fields to inhibit carbon formation primarily from hydrocarbons. We find that the mechanism of carbon formation from hydrocarbons is quite different from that from syngas. So an agent that is effective in reducing the formation of carbon from one source can be quite different with that from another source. You have to be a little bit specific in terms of the feed material from which you are trying to prevent carbon formation. 

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

GL 18] [R 6a] ]P 17] About 100% selectivity was achieved for the hydrogenation of p-nitrotoluene [17], with conversions of 58-98%. The conversion for the electro-deposited catalyst was 58%, whereas the impregnated catalyst gave a 58-98% conversion, depending on the process conditions (see Table 5.1). 

Depending on the process conditions, different profiles of the active phase over the particle will be obtained. A completely uniform distribution of the active material over the particle is not always the optimum profile for impregnated catalysts. It is possible to purposely generate profiles in order to improve the catalyst performance. Fig. 3.28 shows four major types of active phase distribution in catalyst spheres. 

In the case of methyloxirane, however, on Pt and Pd catalysts the extent of the rupture of the sterically hindered bond is indicative of the electrophilic character of the catalyst. Unsupported or silica-supported ion-exchanged catalysts cleave the sterically less hindered bond, whereas on the impregnated catalysts, the rupture of the more hindered C-O bond is dominant.290 It is likely that Pt or Pd surface metal ions are responsible for the rupture of the sterically more hindered bond and residual chlorine from the catalyst preparation can stabilize these ions in the hydrogen atmosphere. 

The temperature of hydrogen reduction of impregnated catalysts may influence the amount of halogen retained by the catalyst. This residual chlorine may have catalytic consequences. For instance, Dorling, Eastlake,... 

On the whole, with impregnated catalysts, nickel/alumina is more difficult to reduce than nickel/silica, (with nickel/silica-alumina occupying an intermediate position). 

Gallium was incorporated by incipient wetness impregnation of gallium nitrate, in three different amounts, namely ca. 2, 3 and 4 wt. %. The impregnated catalysts were calcined at 773K for four hours under dry air flow. 

Figure 3.11 shows the Zr/Si intensity ratio as a function of calcination temperature. The three conventionally impregnated catalysts show a clear decrease of the /Zr//Si ratio at relatively low temperatures, indicating loss of dispersion, whereas the bJIs, ratio of the catalyst from zirconium ethoxide decreases only slightly over a temperature range up to 700 °C. 

The factors 4 and 4 accormt for the heterogeneity of the interface. The interfacial flux conditions. Equations (6.56) and (6.57), can be straightforwardly applied at plain interfaces of the PEM with adjacent homogeneous phases of water (either vapor or liquid). However, in PEFCs with ionomer-impregnated catalyst layers, the ionomer interfaces with vapor and liquid water are randomly dispersed inside the porous composite media. This leads to a highly distributed heterogeneous interface. An attempt to incorporate vaporization exchange into models of catalyst layer operation has been made and will be described in Section 6.9.4. 

The catalyst/substrate ratio is 1.5 mol% for the supported ionic liquid phase (SILP) catalyst, 3 mol% for the impregnated catalyst and 2 mol% for the homogeneous reaction aRuns 1 -4 are consecutive experiments with the same catalyst in a stirred batch reactor. bDimeric Cr (salen) catalyst impregnated on silica cHomogeneous reaction at 0-2 OC optimized for product selectivity dHomogeneous reaction at room temperature optimized for product selectivity... 

Impregnated Catalysts the Role of Metal, Support and Promoters... 

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