Precipitation at constant

In this chapter, the most common techniques for preparation of supported metal catalysts will be discussed, including impregnation, coprecipitation, homogeneous deposition precipitation, and precipitation at constant pH. In principle, these techniques can all be used to attach the active phase to supports, some preferably in the form of a powder, others in the form of a pre-shaped body. First, a general description of the techniques will be presented. Then, the techniques are illustrated by specific examples of the preparation of metallic catalysts. In view of the expertise of the authors of this chapter, Pt, Au, and Ag as the active metal phases will be emphasized. The last two examples are focused on the production of propene oxide and, as a consequence, they refer to an unresolved research issue. The results on the Ag catalysis have not been published elsewhere, and are therefore treated extensively. 

Precipitation at constant pH is also a prerequisite in order to coprecipitate two catalyst components at the same time. This is illustrated for example by the preparation of Pd/La catalysts for methanol decomposition.13 The preparation procedure and the La203/Pd weight ratio of these Pd/La203/Si02 catalysts (5wt% Pd) was found to be important for high catalytic activities in methanol decomposition. If the... 

Fig. 1.9 Set-up for precipitation at constant pH. The pump-speed of the basic solution is adjusted to maintain the pH at the desired value. This set-up was employed for precipitation of Pd(OH)2 onto a La203/SiC>2 support and the conditions are indicated.13...

Figure 7.4 Effect of order of addition on alumina composition XRD patterns of alumina obtained by (a) 2-jet precipitation at constant pH, (b) acid to base addition, and (c) base to acid addition [18].

Effect of pressure on CPT for gases UnliKc liquids where a pressure increase often enhances the wax precipitation at constant temperature, for gases pressure has often the opposite effect pre.s.> ure increase may inhibit the precipitation at constant temperature. The solubility of nC- s in CO2 at 308 K. and the solubility of nC2o in Cj are provided in Tables 5.11 and 5.12 below. First derive the expression... 

Catalyst prepared by oxalate gel co-preeipitation, "conventional co-preeipitation, co-precipitation at constant pH (ca. 7) and constant temperature (70 °C). NC = Nano catalyst... 

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