Catalyst normal impregnation

Promoters have been used to reduce the temperature at which the catalyst normally decomposes and to effect polymerization at ambient temperature. The use of a combination of monomer, catalyst, and promoter may have some advantage for field impregnation of cast-in-place concrete. 

Catalysts were normally prepared by double impregnation of the alumina support, first with ammonium paramolybdate solution to give 12 wt% MoO (8% Mo) after 500°C calcination, then with cobalt... 

Normally, the best activities observed during the development process are found for catalysts prepared in the laboratory where special attention is paid to each preparation step and where better control of e.g. impregnation and calcination temperature history can be achieved. This should be kept in mind when comparing activities of new lab-prepared catalysts with standard products from a production facility. As a consequence, it is seldom worth the effort to continue with a test production if the activity of the lab-prepared catalyst fails to meet the requirements. Important results for the test-produced catalysts are activity measurements covering the full range of operating conditions in the industrial converter and the mechanical strength. 

For practical (real) catalyst systems, precipitation, ion exchange, impregnation and sol-gel processing procedures are used. In precipitation methods, a hydroxide or a carbonate of a metal may be precipitated from a solution of a metal salt onto the support material held in the solution. Thus, a copper-silica catalyst may be prepared using a Cu-nitrate solution in which silica is suspended. Additives of any alkali cause the precipitation of copper hydroxide onto the silica support. This is then dried and normally reduced in hydrogen at moderate temperatures ( 400-500 °C) to form the catalyst. In co-precipitation techniques , the support is precipitated simultaneously with the active catalyst. In the ion-exchange method, for example, highly dispersed Pt on... 

In the preceding sections the use of catalysts in which vanadium oxides are supported on a more or less inert carrier has been mentioned quite often. Because of the importance of this type of catalyst they are discussed more extensively in this section. Often a distinction is made between the normal supported catalysts and so called monolayer catalysts. In the latter the vanadium oxide is supposed to be dispersed in a monomolecular layer on the support, which may be covered completely or only partly. The normal supported catalysts are usually made by impregnation, either wet or dry, of the porous carrier with an aqueous solution, often of NH4V03, sometimes with oxalate added.12 14,75,95,139,140... 

The type of polymer obtained depends on factors such as the pH and temperature of reaction, the ratio of melamine to formaldehyde, and the type of catalyst employed. For decorative laminates, melamine-formaldehyde is prepared by reacting melamine in stainless steel kettles under reflux, alkaline conditions with 37% to 46% formaldehyde in aqueous solution. The reaction temperatures used vary from 80 to 100°C and are maintained until the condensation has reached the desired end point—that is, reacted sufficiently but still water-soluble. The end point is checked by measurements of viscosity, cure time, and water tolerance. Depending on the type of laminate to be produced, other constituents (surfactants, plasticizers, release and anti-foam agents) normally are added to the base resin before impregnation of the surface papers. It is common practice also at this stage to adjust the pH by adding acid catalysts. 

The preparation of egg shell catalysts from more weakly adsorbed speeies that would normally give a uniform distribution has been accomplished by using volumes of the impregnating solution which are smaller than the pore volume of the support. A half pore volume, for instance, can give an egg shell distribution when a full pore volume gives a uniform profile. 

In the case where there is no interaction between the catalyst precursor and the support surface to fix the former to the latter, the dynamics of dr)dng become of prime importance. Briefly, upon drying impregnated porous particles (extru-dates, pellets, spheres), evaporation of the solvent (almost always water), starts at the external surface, resulting in menisci at the pore mouths and setting up a suction pressure. At normal drying rates, and employing simple aqueous solu-... 

Pt-Sn-K/y-Al203 (0.3wt%Pt, 0.3wt%Sn, 0.6wt%K) were used in the research. The catalysts were prepared by a conventional dry impregnation method using H2PtCl6, SnCh and alkali metal nitrates as salt precursors. All chemicals used are normally analytical grade. 

In excess solution adsorption, the support material is submerged in excess amount of impregnation solution (the volume of impregnation solution is much higher than the pore volume of the support). The excess solution is filtered after adsorption equilibrium is reached. In many cases, competitive adsorption between solvent and solutes and/or between different solutes leads to a nonuniform distribution of active components throughout the support particles. This phenomenon can be utilized to enhance performance (normally selectivity) of certain types of catalysts. The distribution of the active components can also be tailored by the manipulation of the pore structure of the support, pH and viscosity of the solution. ... 

FIGURE 156 The presence of sulfate on Cr/alumina changes the polymer MW distribution. Cr/alumina was impregnated with 3.0 (NH4)2S04 nm-2, activated at 600 °C, and tested at 95 °C with 8 ppm BEt3, 0.34 MPa H2, and 3.8 MPa ethylene. The difference curve (sulfate minus no sulfate) was obtained after normalizing the parent curves to catalyst activity. 

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