Metal oxide-based phases

Nawrocki, J. et al. Part II. Chromatography using ultrastable metal oxide-based stationary phases for HPLC. J. Chromatogr. A. 2004,1028, 31-62. 

J. Nawrocki, C. Dunlap, A. McCormick, and E W. Carr, Part I. Chromatography using ultra-stable metal oxide-based stationary phases for HPLC, /. Chromatogr. 

Although the above-described examples have all been based on relatively simple nanocrystalline metal oxides, additional phases might have been introduced. The use of more complex metal oxides has also been investigated, with nanocrystalline thick films of both barium titanate [96] and cobalt titanate [97] having been considered as possible sensor materials. When the response of such barium titanate films doped with 10% CuO and 10% CdO was studied with respect to CO, LPG, H2S, and H2 [96], sensor selectivity was improved for LPG over the other gases at 250 °C. However, the addition of 0.3 wt% Pd resulted in an even greater selectivity to LPG at a lower temperature, of 225 °C. 

Development work has also been undertaken to manufacture acetic scid from propylene. operating in the gas phase, in the presence of metallic oxide base catalysts (U. W, Mo. Ti etc.) and steam between 250 and 400 C, at atmospheric pressure, with molar yields not exceeding 50 to TO per cent. 

There are some excellent review articles on different aspects of mesostructured materials, such as synthesis, properties, and applications. " Extensive research effort has been devoted to the exploitation of new phases (lamellar, cubic, hexagonal structures), expansion of the pore sizes (about 2-50 nm are accessible), and variable framework compositions (from pure silica, through mixed metal oxides to purely metal oxide-based frameworks, and inorganic-organic hybrid mesostructures). Another research focus is on the formation of mesostructured materials in other morphologies than powders, e.g. monolithic materials and films, which are required for a variety of applications including, but not limited to, sensors (based on piezoelectric mass balances or surface acoustic wave devices), catalyst supports, (size- and shape-selective) filtration membranes or (opto)electronic devices. The current article is focused... 

In addition, we have to take into account that metal oxide-based nanocomposites have specific structure. Research on such a two-phase system, in which the concentration of the second oxide phase is much less than the concentration of the base oxide, has shown that the second phase, as a rule, is finely dispersed on the surface of the base oxide grains (Szezuko et al. 2001 Pagnier et al. 2000 Carreno et al. 2002). Possible versions of segregation layers of foreign cations on the surface of SnOj grains are shown in Fig. 14.4 (Varela et al. 1999 Carreno et al. 2002). It has been established... 

Bertinchamps F, Gregoire C, Gaigneaux EM. Systematic Investigation of Supported Transition Metal Oxide Based Formulations for the Catalytic Oxidative Elimination of (Chloro)-Aromatics. Part II Influence of the Nature and Addition Protocol of Secondary Phases to VOx/Ti02. Appl Catal B Environ 2006 66 10-22. 

Kweon, H. K. Hakansson, K. Metal oxide-based enrichment combined with gas-phase ion-electron... 

The field of surface-mediated synthesis of metal carbonyl clusters has developed briskly in recent years [4-6], although many organometallic chemists still seem to be unfamiliar with the methods or consider themselves ill-equipped to carry them out. In a typical synthesis, a metal salt or an organometallic precursor is brought from solution or the gas phase onto a high-area porous metal oxide, and then gas-phase reactants are brought in contact with the sample to cause conversion of the surface species into the desired products. In these syntheses, characteristics such as the acid-base properties of the support influence fhe chemisfry, much as a solvenf or coreactant influences fhe chemisfry in a convenfional synfhesis. An advanfage of... 

Oxysalt bonded cements are formed by acid-base reactions between a metal oxide in powdered solid form and aqueous solutions of metal chloride or sulphate. These reactions typically give rise to non-homo-geneous materials containing a number of phases, some of which are crystalline and have been well-characterized by the technique of X-ray diffraction. The structures of the components of these cements and the phase relationships which exist between them are complex. However, as will be described in the succeeding parts of this chapter, in many cases there is enough knowledge about these cements to enable their properties and limitations to be generally understood. 

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