Catalyst synthesis metal depositions

The numerous applications of phosphines include (1) synthetic reagents, (2) ligands in metallo-phosphorus compounds, (3) catalysts, (4) metal deposition agents, (5) electron-rich compounds. Metallophosphines (metal phosphides) types MPR2 and M2PR (M=Li, Na, K) are especially useful in synthesis (Chapter 8.8) (Table 6.8). 

T5 pically, supported metal catalysts are used in order to hydrogenate or oxidize the educt to the desired compound. Such catalysts often contain a metal (for example, 0.5-5 wt.%), which was deposited on the surface of a support (e.g., Si02, AI2O3, Ti02, zeolites, activated carbon) by means of an appropriate catalyst synthesis procedure (Figure 1). 

A detailed discussion of the deposition of metals on monolithic supports was presented by Vergimst et al. (75). The most popular methods are the same as those applied in typical catalyst synthesis, namely, impregnation, ion exchange, and deposition precipitation. 

Similar to normal catalyst synthesis whereby ion exchange methods can result in egg-shell structures, in the preparation of monolith catalysts the majority of the metal can be deposited at the entrance of the monolith. Egg-shell structures can be attractive for catalyst particles, but for monoliths, analogous uneven distributions of the active phase are a disaster. Fortunately, extensive literature is available describing ion-exchange procedures for conventional catalysts that yield homogeneous metal distributions. This literature can be used as a guide for preparing satisfactory monolithic catalysts. 

Catalyst. The catalyst studied in this work was a platinum (0.205% wt) supported on an amorphous mesoporous silica-alumina, MSA (Si02/Al203=100) extrud with 50% wt alumina. The synthesis of the catalyst and the metal deposition procedure were described in detail [9]. A used catalyst, prepared as the former and containing 0.186% wt of Pt, was studied after the hydroisomerization of an n-paraffin feed containing 10 ppm S. 

That the adsorption of the cyclopentane ring seems to proceed mainly flatly in deuterium exchange on films has been stated above (see Section I,D). Of considerable interest are the investigations on asymmetric catalysis initiated by Schwab et al. (273). In their work, one of the optical isomers reacted a little faster than the other in a racemic mixture. Terent yev and Klabunovskii (274, 273) carried out the catalytic asymmetric synthesis from optically inactive substances. The reactions were accomplished on metals deposited on dextro- and levorotatory quartz. Organic optically active carriers and admixtures give a still greater effect. On this problem see Klabunovskii (276). At the present time still more active catalysts for the reaction of asymmetric hydrogenation and polymerization have been revealed (277-279). 

The next step in the synthesis of supported metal catalysts via dendrimers is the immobilization of dendrimer-metal nanocomposites onto a solid support. An array of techniques exists for achieving this task. Wet impregnation and sol-gel incorporation of dendrimer-metal nanocomposites may lead to strongly adhered metal particles. Other techniques, such as functionalization of the support to facilitate dendrimer growth or adhesion, provide a route for deposition of empty dendrimers that can subsequently undergo complexation with metal precursors to form dendrimer-metal complexes and eventually zerovalent nanoparticles. Whereas the complexation and reduction phases of catalyst synthesis via dendrimers can be fairly complicated, most methods of dendrimer deposition are rather straightforward. 

The synthesis and characterization of the PEDOT/PSS supported catalyst followed a previously reported procedure (13, 15), with formaldehyde as the reductant for metal deposition. A 4 1 RuCl3 H2PtCl6 mole ratio was required to provide a Ru Pt mole ratio close to the target of 1 1. 

The future prospect of the catalyst monolayer synthesis using metal deposition via SLRR... 

Recently, interesting results have been obtained in this field by combining the plasma polymerization and sputtering methods. For instance, the synthesis of composite thin films made of platinum nanoclusters (3-7 nm) embedded in a porous hydrocarbon matrix was carried out by simultaneous PECVD of pp-ethylene and sputtering of a platinum target. The metal content in the films could be controlled over a wide range of atomic percentages (5-80%) (Dilonardo et al., 2011). Aniline mixed with functionalized platinum nanoparticles as a precursor of PECVD was, in turn, used to prepare a typical 3D-catalyst. The plasma deposition was performed under atmospheric pressure conditions. Plasma polymerized aniline (pp-aniline), which is characterized by both electronic and ionic conductivity, associated with the Pt catalyst in a 3D porous network, without doubt lead to the development of the three-phase boundary (Michel et al., 2010). 

---