Pretreatment of supports

As the support of catalyst, the pretreatment of activated carbon is necessary. The main purpose of pretreatment is to improve the physical structure and chemical properties of the surface in order to meet the requirements of the catalytic supports. The method of pretreatment includes high temperature (graphitization), acid-alkali, gases and microwave treatment and so on. 

Under ammonia synthesis conditions. Ruthenium is an active catalyst for the activated carbons methanation, which leads to the losing of supports and the 

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J.W. Geus, Production and Thermal Pretreatment of Supported Catalysts, Preparation of Catalysts III, Elsevier, Amsterdam, 1983, pp. 1-32. 

Figure 9. Conversion-time curves of the hydrogenation of nitrobenzene after pretreatment of support in...

The results of this study suggest that the dynamics of the nucleatlon process are of the utmost Importance In determining the structure and the surface composition of supported bimetallic clusters. Because the surface mobility of the metal phase during pretreatment is strongly influenced by the nature of the precursor-support Interaction, it is useful to consider this Interaction in some detail. 

Table 1. Changes of nanostructure and catalytic properties during acrolein hydrogenation in the gas phase after pretreatment of a Zr02 supported gold catalysF with H2 (taken from [85]).

It was shown (8,9) that the pretreatment of PET yarns with certain strongly interacting solvents can lead not only to swelling but also to irreversible modifications of polymers structure. The basis of structural modification during the DMF treatment of PET is solvent-induced crystallization which occurs while the PET structure is swollen by DMF. At low treatment temperatures (i.e., 50-100°C, Table I), only small crystallites are formed and after removal of the solvent the swollen structure cannot be supported by the small crystallites and consequently collapses. 

For farther improvement of hydrogen enzyme electrode the commercial carbon filament materials were used as an electrode matrix. Such type of materials are accessible and well characterized, that provides the reproducibility of the results. A procedure for hydrogen enzyme electrode preparation included the pretreatment of electrode support with sulfuric acid followed by enzyme immobilization. This procedure is a critical step, since initially carbon filament material is completely hydrophobic [9]. 

In many cases, during the impregnahon a surface reaction between the organometallic compound and the surface takes place. The pretreatment of the support can be used to define the distribution of anchorage centers on the surface, and a homogeneous distribution of metal carbonyl surface species can be achieved. 

The pretreatment of the support and the treatment carried out for the CO ligand elimination define the characteristics of the metallic entities on the support. 

The surface reaction of Ru3(CO)i2 with alumina is complex and depends on the temperature of support pretreatment. With partially hydroxylated alumina, an interaction between the CO ligands and the hydroxyl groups, via an oxidative addition, occurs with release of CO [91, 95, 99, 104] ... 

Scheme 12.4 pfQ criterion (measure of surface reactivity) and the thermal pretreatment of the support (here silica) govern the surface reactivity L= monovalent alkoxo, (silyl)amido or alkyl ligand. 

A detailed study on the immobilization of Ln[N(SiMe3)2]3 on fumed silica showed that the nature of the grafted species is considerably affected by the thermal pretreatment of the support [117]. Whereas at low (AS-380.2so) and intermediate dehydroxylation temperatures (AS-380.5oo) mixtures of bipodal [(=SiO)2Ln N(SiMe3)2 ] and monopodal [(=SiO)Ln N(SiMe3)2 2] species prevailed... 

Scheme 12.7 Effect of thermal pretreatment of the support on the nature of the immobilized silylamide surface complex and determination of the bonding strength of siloxane bridges by displacement with triphenylphosphine oxide on an AS-3 0 m hybrid material.

A similar study with materials [Ln N(SiMe3)2 3] AS-380. (T = 250, 500, 700°C) revealed the implications of thermal pretreatment of the support for ethylene polymerization [117]. Materials featuring predominantly monopodal neodymium silylamido surface species produced the most achve catalysts [12b (100% monopodal) > 13b (40%)> 14b (25%), Table 12.6 cf, Nd[N(SiMe3)2]3 0.03 kg-PE molm h bar ]. Apparently, extensive replacement of silylamido by (surface) siloxo ligands, that is, an increase of podality of the supported species at... 

Fourier-transform infrared (FT-IR) spectra (resolution 2 cm" ) were recorded with a Perkin-Elmer 1750 instrument in a cell connected to grease-free evacuation and gas manipulation lines. The self-supporting disk technique was used. The usual pretreatment of the samples was evacuation at 500 C. 

One might expect that the more developed porous layer produced by the PAA process would tend to provide a greater number of successful mechanical interlocking sites 54-86-135-136> and initiate a larger degree of plastic deformation in the resin upon failure than the FPL oxide. Test data i29) comparing PAA and FPL pretreated systems have supported this conclusion. Also, the oxides formed by the PAA pretreatment have exhibited better stability in wet environments 54). Hence, the PAA process has replaced the FPL etch as the method of choice for the pretreatment of aluminum for adhesion systems i32-133>. 

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