Preparation supported metals

Magnetron Sputtering to Prepare Supported Metal Catalysts... 

The magnetron sputtering technique can prepare supported metal nanoparticles on a wide variety of support materials including WO3 and carbon. 

A SCIENTIFIC METHOD TO PREPARE SUPPORTED METAL CATALYSTS... 

The first example of the use of metal carbonyls to prepare supported metal particles was reported by Parkyns, who prepared an alumina-supported nickel catalyst from Ni(CO)4 [3]. Since then, many studies of the groups of Professors Yermakov, Ugo, Basset, Ichikawa, Guczi and Gates, among others, have constituted the bases for knowledge in this field [4-10]. 

Niobium Products Co., 50 m /g). Many different synthesis methods have been used to prepare supported metal oxide catalysts. In the case of supported vanadium oxide catalysts, the catalysts were prepared by vapor phase grafting with VOCI3, nonaqueous impregnation (vanadium alkoxides), aqueous impregnation (vanadium oxalate), as well as spontaneous dispersion with crystalline V2O5 [4]. No drastic reduction of surface area of the catalysts was observed. 

Although reactions (1)—(4) are the only reactions that appear to have been used in preparing supported metal catalysts, there are several other ways that could be used, for example,... 

A simple but effective means of preparing supported metal ion catalysts is to employ ion exchange resins. For example, a cobalt-exchanged H-type resin (Dowex 50) was shown43 to be an effective solid catalyst for the autoxidation of acetaldehyde to acetic acid at 20°C. No leaching of cobalt ions from the resin was observed and the catalyst was used repeatedly (5x) without any significant loss of activity. More recently the use of weak acid resins exchanged with cobalt ions as catalysts for the autoxidation of cyclohexane... 

An obvious question is whether patterned arrays of metal complexes can be formed on supports, and an approach to the preparation of such materials has been made by use of precursors containing more than one metal atom. Thus, attempts have been made to prepare supported metals with pair (and triplet) sites from dimeric (and trimeric) complexes of oxophilic metals, including Mo, W, and Re, which bond strongly to oxide surfaces. 

It is also possible to prepare supported metal catalysts from casy-to-rcduce elements. For example, [ Supp -0]Rh( /3-C3H5)2 (with supp - Al, Si, or Ti) reacts with H2 at room temperature to give rhodium metal particles (1.5 nm) [54, 58]. Diallyl compounds of Group 10 elements (Ni, Pd, Pt), forming species singly anchored onto silica or alumina, arc transformed into small metal particles ([Pg.175]

To prepare supported metal catalysts for low-temperature CO oxidation, coprecipitation, deposition-precipitation, and grafting methods are effective, because they can give strongly interacting metal particles with the support. 

Metallic glasses have been used in catalysis in two ways, namely, in investigations carried out on as-quenched glassy metals and in those where the glassy metals were subjected to different pretreatments and served merely as precursors to catalytically active materials. The use of glassy metals as catalyst precursors has been shown to open up new possibilities for the preparation of supported metal catalysts with unusual chemical and structural properties. This potential resides mainly on the high reactivity and isotropic nature of these materials compared to their crystalline counterparts. Several efficient supported metal catalysts are compared to conventionally prepared supported metal catalysts in Chap. 3. 

Catalytic liquid phase semihydrogenation of acetylenes is an important industrial and laboratory reaction, especially in fine chemical synthesis [1]. The use of supported metal catalysts for this selective hydrogenation readily facilitates the separation of organic products from the catalyst. However, liquid phase reactions with supported catalysts tend towards mass transport limitation [2] and, therefore, the support particles should be between 1 and 10 pm in size this avoids transport limitations and separation problems. With support particles of this size high temperature reduction in a flow of H2 gas is very difficult and to avoid this step it is possible to prepare supported metal particles by decomposing organometallic compounds under mild conditions [3-5]. 

The ability to prepare supported metal catalysts in which the metal particles are both small (i.e. highly dispersed) and homogeneously distributed on the support surface remains a challenge. The catalytic activity of many hydrogenation or polymerization reactions correlates with the number of available surface metal sites, and the imiformity of nanoscale metal distribution (i.e., maximizing metal particle separation) can be an important factor in minimizing metal coalescence. 

Each of the prepared supported metal catalysts (40 mg) was pressed into self-supporting pellet of 20 mm in diameter, and was placed in an infrared cell, which was connected to an iso-volumetric system equipped with a vacuum line. The pressure of this system can be measured to the order of 1 x 10 Torr by a capacitance manometer. The catalysts were pretreated with O2 at 723 K for ten hours and then reduced under H2 at 723 K for ten hours, followed by evacuation at the same temperature for one hour before use. Adsorption of CO was carried out at 298 K. 

To conclude, it appears well established that different effective synthetic routes are at the disposal of chemists to prepare supported metal catalysts with high dispersions on CNTs or CNFs (Figure 9.11). As in the case of graphite [231,232], it seems that some metals, such as ruthenium, interact more strongly than others with the graphene layers of CNTs or with the surface of CNFs. From the literature reports on group VIII metal dispersions, it seems that the work of metal adhesion... 

There are several key areas that need to be developed in order to be able to prepare supported metal complexes more reliably and better understand their activity. Polymer supports are still expensive to purchase and in order for them to have more widespread use it will be necessary to develop more cost effective routes for their preparation. It is important to understand the role of the polymeric backbone in the catalytic activity of immobilized metal complexes and to realize that very different reactivities and selectivities can be found if, for example, the linker or the degree of cross-linking is altered. When using dendrimer-derived materials, particular attention needs to be focused on dendritic effects. 

MgO-supported Rh6 and Irg clusters were also investigated as catalysts for ethene hydrogenation. Decarbonylation of hexanuclear metal carbonyl cluster precursors on MgO was used to prepare the catalysts. EXAFS data support octahedral clusters as the catalytically active species. Rh5/MgO is 1-2 orders of magnitude more active than Ir /MgO, as is the activity ratio for the conventionally prepared supported metals on silica. 

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