Impregnation and Drying

As their name indicates, supported catalysts consist of a catalytically active phase dispersed over a support. Requirements for their preparation are threefold as far as the introduction of the active phase is concerned  

The first requirement can be reached by dissolving the precursor in a liquid. The solution is then introduced into the voids of the support, after which the solvent is eliminated. The former step of the procedure is called impregnation and the latter step, usually thermally activated, is called drying. Altogether, they allow fulfilling the second and the third requirements, because the number of unit operations is only two and the whole of the solute remains on the support after solvent elimination. 

Impregnation is often described on a container/contents basis and does not need chemistry to be comprehended. H owever, simplicity from a practical point of view does not necessarily mean simpler physical and chemical phenomena. The present chapter provides guidelines to help the reader understand what lies behind this method of preparation, which is still deemed the favorite by the industry and the most convenient at the laboratory scale for the reasons stated above. 

The term impregnation belongs to the traditional vocabulary of industrial chemistry. It refers to the contacting of a solid and a liquid phase, and absorption of the latter by the former, be it wood or textile. It is difficult to ascertain who introduced this term in the field of catalysts preparation, but a plausible candidate is the English industrialist Henry Deacon, a former 

Student of Michael Faraday who invented a process of oxidation of HCl to CI2 over copper compounds. Only 33 years after Berzelius had coined the term catalysis , procedure and rationale for the use and choice of a support were exposed hy Deacon with striking clarity [1]  

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Figure 4.17 illustrates how Mossbauer spectroscopy reveals the identity of the major iron phases in a supported iron catalyst after different treatments. The top spectrum belongs to a fresh Fe/Ti02 catalyst, i.e. after impregnation and drying. 

Figure 4.6 Positive SIMS spectrum of a 9 wt% Zr02/Si02 catalyst prepared from zirconium ethoxide, after impregnation and drying, and after calcination in air at 400°C (from Meijers et al. [151).

Figure 5. Unfavorable distribution of active precursor after impregnation and drying.

Application of one or more precursors) uniformly over the internal surface of preshaped support bodies is attractive for the development of industrial catalysts within a short period of time. Since impregnation and drying often leads to deposition more or less exclusively at the external edge of the support bodies, an improved procedure is highly desirable. 

Effects of the impregnating and drying process factors on the mechanieal properties of a PC0M0/AI2O3 hydrotreating catalyst... 

Reference samples Pd(0Ac)2/Si02 and Pd(OAc)2/Na7PWn039/Si02 were prepared by means of standard impregnation procedure. Acetone solution of palladium acetate and aqueous solution of heteropolytungstate salt were used. After evaporation of the solvent at room temperature, the samples were dried at 100°C. The second sample was prepared by means of consequent impregnating and drying procedures. 

Application of ordered mesoporous materials as model supports to study catalyst preparation by impregnation and drying... 

The preparation according to the recipes involved both automated and manual operations. Impregnation and drying steps were carried out on a Sophas synthesis robot described elsewhere [8], Samples were then transferred manually to ceramic crucibles and calcined in air in programmable ovens. 

Using three different preparation methods copper oxide modified MCM-41 silica and Al-MCM-41 materials were obtained and characterized by various techniques (nitrogen physisorption, XRD and TPR-TGA) and methanol decomposition as a catalytic test reaction. At certain conditions of impregnation and drying at room temperature and under vacuum it was possible to form highly dispersed CuO nanoparticles incorporated almost exclusively within the mesoporous host structure. These particles could be reduced with H2 at considerably lower temperatures than the bulk CuO. 

All samples of paper products maintained their initial shape and size after impregnation and drying and no curling up occurred. However, an increase in the rigidity of samples was observed. The use of the impregnant had no influence whatsoever on the possibility of writing with a ball pen. 

Commercial a-cellulose sheets (14.5 mm x 5.5 mm x 0.17 mm) were used as sample with 89.62 g/m of lignin, hexamine hardener (5% on lignan grammage) and with 1.53% paper moisture content. The lignins were dissolved at 42% solids content at pH 12. The paper samples were then impregnated, and dried in an oven at 36°C. 

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