Multicomponent oxides

Multicomponent oxide Thermolytic molecular precursor (TMP) method... 

Furthermore, by emphasizing film quality and the chemical prerequisites for multicomponent oxide film deposition, the potential for qualitatively ideal solution-deposited dielectrics has been established. Additionally, new processing conditions and chemical modifications that will facilitate lower dehydration and precursor decomposition temperatures are readily envisioned. 

Lieby-Muller F, Allais C, Constantieux T, Rodriguez J (2008) Metal-free Michael addition initiated multicomponent oxidative cyclodehydration route to polysubstituted pyridines from 1,3-dicarbonyls. Chem Commun 4207-4209... 

Kriesel JW, Sander MS, et al (2001) Block copolymer-assisted synthesis of mesoporous, multicomponent oxides by nonhydrolytic, thermolytic decomposition of molecular precursors in nonpolar media. Chemistry of Materials 13(10), 3554-3563... 

More recent research efforts have focused on the development of other possible catalysts such as promoted Raney copper,371,403 catalysts prepared from intermetal-lic precursors,362,371 386 404-406 and catalysts that tolerate high C02 content.407 Catalyst modifications allowed to shift the selectivity to the formation of higher alcohols.208,408 110 For example, in a process developed by IFP, a multicomponent oxide catalyst is applied with copper and chromium as the main components 410 By this method, 70-75% total alcohol selectivities and 30-50% of C2 and higher alcohol selectivities can be achieved at 12-18% conversion levels (260-320°C, 60-100 atm). 

As mentioned earlier, the multicomponent oxide catalysts currently commercialized contain bismuth, iron, and molybdenum, in addition to several other cations. Although few reports concerning multicomponent catalysts have appeared in the literature, there is agreement that iron affects several aspects of the catalyst system. Measurements on multicomponent catalysts by Wolfs et al. (109-111) showed that Fe3+ was partially reduced to Fe2+ after the catalytic reaction, indicating that Fe3+ ions are involved in the reaction mechanism. The observed Fe3+/Fe2+ redox couple was associated with the increased activity of the catalyst. 

LEIS is most often carried out with a beam of helium ions, but when a catalyst contains heavier elements, it may be advantageous to use neon ions to distinguish better between the elements (see Fig. 4.13). Of course, elements with a mass smaller than neon cannot be detected in that case. Figure 4.20 illustrates this with He- and Ne-LEIS spectra of a multicomponent oxide catalysts containing vanadium, molybdenum, niobium and tellurium. These mixtures are of inter-... 

A. A Malygin, Synthesis of Multicomponent Oxide Low-Dimension Systems on Surface of Porous Silicon Dioxide Using Molecular Layering Method, J. General Chem. (in Russian) 72(4), 617-632 (2002). 

The ability to introduce several components into solution during the sol-gel step makes this approach especially attractive for the preparation of multicomponent oxides and bimetallic catalysts. Of course, the solution chemistry becomes more complex with additional components. But many of the concepts that we have discussed, such as matching relative precursor reactivity and changing the microstructure of the gel network, remain valid in principle. Furthermore, a promoter or an active species can be introduced the same way. There have been recent reports on the onc-step preparation of zirconia-sulfate aerogels [45] and Li/MgO catalysts [46], These samples arc active in the isomerization of n-butane and the oxidative coupling of methane, respectively. 

The study of the heterogeneous oxidation of carbon monoxide has been a fruitful field of research for many investigators in heterogeneous catalysis. Highly active catalysts have been prepared from simple oxides, multicomponent oxides, and salts of acidic metal anhydrides, derived... 

Vanetsev AS, Tretyakov YD. Microwave synthesis of individual and multicomponent oxides. Uspekhi Khimii. 2007 76(5) 435-453. 

In the monograph, the experimental data on soft mechanochemical synthesis of double and multicomponent oxides obtained by the present authors and other researchers have been systematized. The specific features and regularities of the reactions of soft mechanochemical synthesis have been estabhshed. It was demonstrated that at the first stage the interaction proceeds with the participation of surface acid and base centres, while at the second stage, the process goes on with the participation of dissolved state since water is formed in the result of interaction, i.e. according to hydrothermal-like mechanism. 

Hydrolysis and condensation rates depend on the molecular structure of metal alkoxides and alkoxide precursors have to be chosen as a function of the desired material final product. In the case of Ti02, for instance, monomeric precursors such as Ti(OPF)4, in which Ti is fourfold coordinated, react very quickly with water leading to the uncontrolled precipitation of polydispersed Ti02. The reaction is much slower with oligomeric precursors such as [Ti(OEt)4] in which Ti has a higher coordination number. Spherical monodispersed Ti02 powders can be produced via the controlled hydrolysis of diluted solutions of Ti(OEt)4 in EtOH. On the contrary, monomeric precursors are more convenient for the sol-gel synthesis of multicomponent oxides. The perovskite phase BaTiOs is formed upon heating around 800 °C when [Ti(OEt)4] is used as a precursor. This temperature decreases down to 600 °C with the monomeric precursor Ti(OPT)4 which favors the formation of Ti-O-Ba bonds. ... 

This method is closely related to the nonhydrolytic sol-gel method. For example, titania is prepared by etherolysis/condensation of TiCl4 by diisopropyl ether (Equation 2.4) or by direct condensation between TiCl4 and Ti(0- Pr)4 (Equation 2.5). Detailed chemistry of the reaction was examined by means of nuclear magnetic resonance (NMR), and it has been reported that the tme precursors are titanium chloroisopropoxides in equilibrium through fast ligand exchange reactions. A variety of metal oxides, " nomnetal oxides," multicomponent oxides" " were studied, and the nonhydrolytic sol-gel method was surveyed by Vioux and Leclercq. ... 

Hydroxycarboxylic acids, which include citric acid, malic acid, lactic acid, etc., are benign to the environment and very convenient for the solution processing. Moreover, since these reagents can form stable complexes with other cations, they rarely yield a precipitate. For several complexes single crystals of well-defined composition suitable for the X-ray structural analysis were isolated. Thus, these water-soluble titanium complexes of hydroxycarboxylic acids are promising precursors for the synthesis of ceramics from an aqueous solution and their industrial utilization is expected in the future. In this chapter we decribe the method of synthesis, structural analysis, and stability of these complexes. The examples of multicomponent oxide materials preparation using these compounds are presented. 

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