Metal chloride precursors

H O, a mixture which incidentally can combust or explode. Ozone (O3) is also used to accelerate oxidization, usually for cases of less-reactive precursors such tetraethoxysilane (TEOS). N O and CO are also used as oxidizers, as in SiH Cl -I- 2Np SiO (s) -I- 2 HCl -I- 2 N, or ZrCl + 2 CO -I- 2 H ZrO (s) -i-2 CO -1- 4 HCl. Hydrolysis reactions are often used with metal chloride precursors 2 AICI3 -1- 3 H O Al303(s) + 6 HCl, or TiCl -1- 2 Hp TiO (s) + 4 HCl. Solid substrates can also be directly oxidized, as in the steam oxidation of silicon Si(s) + 2 Hp SiO Cs) -I- 2 H. This gives a high-quality oxide, but at a relatively slow growth rate. 

Gas-Phase Reactions Gas-phase reactions are typically used for the preparation of thin films or nano-sized transition metal carbides and nitrides. High volatility of metal chloride precursors is useful and nitrides can be obtained by reaction with ammonia (M is the corresponding transition metal) ... 

Moreover, Rothenberg and coworkers [80] have developed copper and copper-based nanocolloids that constitute an inexpensive and eco-friendly alternative to noble metal catalysts. The cluster combinations were prepared by reduction with tetraoctylammonium formate (TOAF) in DMF of the metal chloride precursors, leading to the formation of particles of 1.6 run to 2.1 nm, and tested in the coupling reaction of phenylboronic acid and iodobenzene (Table 11.14). These mono-, hi- or tri-nanocoUoid catalysts have shown interesting catalytic activities in Suzuki cross-coupUng reactions. 

The above synthetic strategy leads to easy generation of [R(Ag°)(Cu )] H and [R(Au°)(Pd°)] Cl nanocomposites with their inverted structures. The order of deposition of the bimetallic shells on the polystyrene beads can be altered by the successive immobilization of their corresponding precursors. Matrixes such as [R (Pd°)(Pt°)] Cl and [R(Ag°)(Au°)]+Cl were also synthesized from their corresponding metal chloride precursors. The layer-by-layer deposition technique has been widely used to fabricate core-shell particles because of its convenience to tailor the thickness and composition of the shells. The thickness can be controlled by varying the number of cycles of operation immobilization and subsequent reduction. In this way, we can deposit more than two metals on any kind of charged polystyrene bead. 

In recent decades, several studies have been made of sol-gel chemistry. This method has been widely used in the ceramics industry and materials science. Typically metal alkoxides and metal chloride precursors are used as the stardng materials. The reacdon is very easy to perform and does not require any special conditions. It is highly suitable for the preparation of metal oxides. The name itself implies... 

The metal chloride precursors are relatively cheap and easy to access. However, they result in halide impurities in the metal oxide nanoparticles. In order to avoid such impurities, halide-free metal oxide precursors such as metal alkox-ides, acetates, or acetylacetonates can be employed. The solvothermal treatment of metal alkoxides with benzyl alcohol offers an alternative route for the synthesis of a htige selection of nanocrystalline binary and ternary metal oxides such as... 

The nonhydrolytic ether route involving the reaction of metal chloride precursors with diisopropyl ether was developed for the synthesis of mesoporous mixed... 

Metathetical precursor reactions are well suited to the synthesis of solid-solution compounds. This approach offers a diverse set of precursors and has the advantage over other methods in that both mixed cation and mixed anion reagents are readily obtained. Mixed metal chloride precursors of molybdenum and tungsten, for example, have been found to be efficacious in the preparation of solid-solution dichalcogenides such as (Mo,W)S2. 

During the reduction of metal chloride precursors, the reaction produces quantitatively gaseous hydrogen chloride, e.g. in the case of platinum ... 

These precursors are generally prepared by alkane elimination (Equation (7a)) or—especially useful with bulkier substituents—the coupling of metal chlorides with lithium pnictides or silyl arsines (Equation (7b)) or salt elimination or silyl halide elimination reactions (Equation (7c)) ... 

There are many documented synthetic routes to metal dichalcogeno-phosph(in)ates although the most common involve reaction of the alkali metal or ammonium salt of the ligand (see Section 5.2.5 for preparation of these species) with a suitable metal precursor (including metal chlorides, oxides,... 

Preparation of amorphous products The preparation of metals (Fe, Co, Ni, Pd, Au), alloys (Au-Pd, Fe-Co, etc.), oxides, chalcogenides, etc. has been reported. The synthesis of sulphides, for instance, has been obtained in solutions (in water, ethanol, etc.) of the metal chloride or acetate using thioacetamide or thiourea as sulphur precursor. 

In general, metal nanoparticles are obtained via reduction of metal complexes, such as metal chlorides, by chemical agents (chemical reduction), or by electrons (electrodeposition). Hybrids of metal oxides are obtained by oxidation, network formation or precipitation of precursors such as metal nitrates and acetates [144]. 

Table 10.3, that widely used precursors to these two-coordinate aniidometal(lll) salts have been the corresponding three-coordinate metal chlorides, methods A and A of Table 10.3, and... 

The purpose of the present work is to study the precursor (metallic chlorides or carbonyl compounds), particle size and support (silica, magnesia and titania) effects in the selective hydrogenation of carvone employing rhodium as active metal. 

Supported metallic Ni, Cr, Fe, Mo, Co, V, Ti, Sn, Ru, and Pd catalysts have been prepared with the help of the CVD method fundamentally using carbonyl and chloride precursors [16]. 

PdAu/Ti02178 and PdAu/Fe203179 (Pd Au = 2) have been prepared by co-impregnation of the chloride precursors. After calcination at 673 K, both samples exhibit metal particles with a bimodal distribution of size (4-10 nm and 30-70 nm). These particles, at least the largest ones, are core-shell type alloy with a Pd-rich shell. 

Methods for preparing bimetallic colloids containing gold have been described in Section 3.2.3. Their composition may be easily tuned since solutions of the mixed chloride precursors are normally used, and are reduced in a variety of ways after addition of a stabiliser. As already mentioned in Section 4.3.6, for gas-phase catalytic reactions, after depositing the colloid on an oxide support the stabilisers must be removed, but for liquid-phase reactions they may be retained providing access to the metal is still possible. 

---