Molecular Precursor Routes

These routes rely on the direct transformation of soluble molecular species into supported metal (or mixed metal) particles. One method that has recently become popular is the polyol method. This takes a solution of metal salts, the carbon support, and a polyalcohol such as ethylene glycol. On heating, the polyol acts as both stabilizer and reductant, forming reduced metal particles on the carbon. It has been used successfully to prepare Ft and PtRu catalysts.  

Another route that has been used recently to prepare Ft bimetal-lies (FtRu, i PtNi, and PtCr ) is via metal carbonyl chemistry. In this method, metal carbonyl complexes (either preformed or formed in situ) 

True bimetallic molecular precursors have been used to prepare PtRu catalysts. Steigerwalt, Deluga, and Lukehart impregnated the complex (77-C2H4) (Cl)Pt(77-Cl)2Ru(Cl)(773 r/2-2,7-dimethyloctadienediyl) on graphitic nanofibers via solvent evaporation. The deposited complex was subsequently decomposed by reductive annealing up to 650°C. 

---

Tailoring Properties of Silicon-Containing Oxide Catalysts via the Thermolytic Molecular Precursor Route... 

Thermolytic Molecular Precursor Route to Oxide Materials... 

The recent synthesis of a single-source molecular precursor containing aluminum with 0Si(0 Bu)3 and 02P(0 Bu)2 ligands provided an important step toward general use of molecular precursor routes to materials with more complicated stoichiometries. Indeed, it was shown that this new complex, [( Bu0)3Si0]2Al[p-02P(0 Bu)2]2Al(Me)0Si(0 Bu)3, was readily converted to homogeneous SiyAl/P/0 materials under mild thermolytic conditions via loss of isobutene, H2O, and CH4(Eq. 2) [58]. 

In the development of a molecular precursor route to ODH catalysts, an important discovery was that the composition of materials derived tlierefrom may be manipulated by co-thermolyses in solution [46, 52]. Also, it is often observed that such thermolyses give weU-dispersed materials. This method is inherently versatile, allows control over elemental composition, and should be applicable to many catalyst formulations. Initially, this approach was investigated in the synthesis of catalysts for the ODH of propane. 

Molecular Precursor Routes to Single-Site Catalysts... 

AIN-BN solid solutions or composites via molecular precursor routes has not been reported. 

Livage J., Sanchez C., Babonneau F. Molecular precursor routes to inorganic solids. In Chemistry of Advanced Materials. Interrante L.V., Hampden-Smith M.J., eds. New York Wiley-VCH, 1998 Chapter 9, pp. 389 8... 

R. Rulkens, T.D. Tilley - A Molecular Precursor Route to Active and Selective Vanadia-Silica-Zirconia Heterogeneous Catalysts for the Oxidative Dehydrogenation of Propane, J. Am. Chem. Soc. 120, 9959,1998. 

Poly(arylene vinylenes). The use of the soluble precursor route has been successful in the case of poly(arylene vinylenes), both those containing ben2enoid and heteroaromatic species as the aryl groups. The simplest member of this family is poly(p-phenylene vinylene) [26009-24-5] (PPV). High molecular weight PPV is prepared via a soluble precursor route (99—105). The method involves the synthesis of the bis-sulfonium salt from /)-dichloromethylbenzene, followed by a sodium hydroxide elimination polymerization reaction at 0°C to produce an aqueous solution of a polyelectrolyte precursor polymer (11). This polyelectrolyte is then processed into films, foams, and fibers, and converted to PPV thermally (eq. 8). 

In 1992/1994, Grubbs et al. [29] and MacDiarmid et al. [30] described an improved precursor route to high molecular weight, structurally regular PPP 1, by transition metal-catalyzed polymerization, of the cyclohexa-1,3-diene derivative 14 to a stereoregular precursor polymer 16. The final step of the reaction sequence is the thermal, acid-catalyzed elimination of acetic acid, to convert 16 into PPP 1. They obtained unsupported PPP films of a definite structure, which were, however, badly contaminated with large amounts of polyphosphoric acid. 

By analogy with B-trialkylaminoborazi ne and polyborazine derived therefrom, the first route envisioned to poly(borylaminoborazine) was the thermal condensation of molecular precursors under a convenient atmosphere. As detailed earlier the innovative idea behind this procedure is to tailor the polymeric precursor structure by increasing the distance between the two borazinic rings. For that purpose, we explored... 

These routes rely on vapor phase preparation of catalysts by deposition of metal precursors onto carbon or by direct formation of the catalyst in the vapor phase. Direct vapor deposition of volatile molecular precursors such as acetylacetonate complexes onto carbon has been demonstrated by Sivakumar and Tricoli for PtRu and PtRuIr. ... 

---