Multiple impregnations

Extremely good distributions of the active precursor over the internal surface of the support bodies were obtained. The difficulty, however, is the loading that can be achieved. The limited pore volume of preshaped support bodies and the solubility of the precursor to be deposited and of the agent(s) for deposition-precipitation necessitate multiple impregnations in order to achieve loadings characteristic of base metal (compounds). With urea and simple nitrates, however, highly... 

These results demonstrated that the selectivity for the samples prepared by multiple impregnation in 1 A/ Ni solution increase with increasing of the Ni-loading... 

Comparing the selectivity for the samples obtained by multiple impregnation with IM Ni solution it can be observed that the maximum selectivity is achieved on the catalyst with 3,04 wt% Ni, i.e for the catalyst with the medium Ni-content. 

The catalyst sample with the Ni-crystallite having the smaller size is obtained by the multiple impregnation in solution of the lowest Ni concentration. 

The bimetallic catalyst was prepared as 5Co-15Ni on 80y-Al2O3 support via multiple impregnation. The support was pre-treated at 1073 K for 6 hours to ensure thermal stability of the alumina phase. It was then mixed with an aqueous solution of Co(N03)2 and stirred at 303 K for 3 hours. The slurry was left to dry overnight in an oven at 393 K. The dried solution was subsequently mixed with calculated amount of Ni(N03)2 solution. Each metal nitrate impregnation was carried out at a constant pH of 2. The final slurry was further dried at 393 K for 12 hours and calcined for 5 hours at a heating rate of 5 K min . The calcined solid was then crushed and sieved to 212-250 pm for further use. 

The data point, indicated by a square at a nickel concentration of 10.5%, is of special interest. For this sample of nickel oxide on alumina, the concentration of 10.5% was built up in a series of nine impregnations. Single impregnations were used for the other samples. The 10.5% multiple impregnation sample has a moment of 3.1. This corresponds to the moments observed for single impregnation samples having a nickel concentration of 2%. 

It was hoped that multiple impregnation would lead in this case to higher, more readily measurable, susceptibilities, but such proved not to... 

If catalysts with high loadings of the active compounds are to be made, limited solubility of the precmsor compoimd may cause problems, and multiple impregnations may have to be applied. With incipient wetness impregnation, even precursor com-poimds which do not interact with the support can be deposited when the solvent is removed during a subsequent drying procedme. This can be illustrated with Figure 6-4. 

Multiple impregnations-final nickel content control... 

In a different approach again, the open porosity of an ordered inverse siUca opal material has been filled by multiple impregnation steps with sulfonated polysulfone (sPSU). In a highly polymer-charged composite, the polymer and silica phases are co-continuous, and the conductivity of a material with mass ratio of polymer to silica of 70 30 was ca. 0.1 Scm at 80 °C and 90% RH,... 

To prepare these capacitors, the surface of an aluminum or tantalum electrode was roughened by etching or metal powder can be sintered to obtain a high-surface-area electrode with high capacitance. A thin film of metal oxide, which would serve as a dielectric, can be applied to the electrode by anodization. A counter electrode was ultimately applied to complete the capacitor. In the preparation of conventional capacitors, this last step was performed by multiple impregnations with manganese nitrate solution and P50 olysis was applied to form electrically conductive manganese dioxide. 

Gibson and Gibson [216] infiltrated a carbon fiber preform with a saturated aqueous solution of tantalum fluoride in sucrose and treated with NH3 under pressure to convert to the hydrated pentoxide liberating NH4F. The tantalum pentoxide, when heated, reacted with carbon from the partially carbonized sucrose to give tantalum carbide, with release of CO. Since the yield was low, multiple impregnations were required to give an eventual porosity of 5 10 vol %. 

Zheng G, Sano H, Uchiyama Y, Kobayashi K, Suzuki K, Cheng H, Preparation and fracture behavior of carbon fibre/SiC composites by multiple impregnation and pyrolysis of poly-carbosilane, J Ceramic Soc Japan, 106(12), 1155-1161, 1998. 

For applications where high surface area is not important, the ceramic foam may be loaded ndi catalytic agents through single or multiple impregnation of suitable salts, followed Iw heat-treatment at moderate temperatures. Alternatively, a washcoat may be added with the same procedures used for monolithic substrates [20]. Surface areas increase from less than 1 mV to above 30 mV depending on the amount of washcoat added. In Ais way, washcoated foams have been loaded with metals and oxides [18,19], zeolites [20] and carbon [21]. Other methods, e.g. chemical vapor deposition, have also been su ested [23,24]. 

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