Ta-oxide

Nakamura and Matsui [71] prepared silica nanotubes as a spin-off product of sol-gel synthesis wherein tetraethylorthosilicate (TEOS) was hydrolyzed in the presence of ammonia and D, L-tartaric acid. Ono et al. [72] showed that certain cholesterol derivatives can gelate tetraethyl orthosilicate (TEOS) to obtain tubular silica structures. Using cholesterol based gelators nanotubes of transition metal (Ti, V and Ta) oxides can also be prepared. The organogelators used in these processes are chiral diamino... 

Figure 3.35 Ethylene produced by oxidative dehydrogenation of ethane over Mo-V-Nb and Ni-Ce-Ta oxide catalyst libraries. The detection of ethylene was performed in a scanning mass spectrometer using a photothermal deflection method. Inactive Mo-V-Nb oxide catalyst (a) active Ni-Ce-Ta oxide library (b) [7] (by courtesy of Kluwer Academic Publishers).

Primary screening can be done on wafer-based ternary mixed metal oxide libraries. For the oxidative dehydrogenation of ethane, two interesting libraries consist of Ni-Ce-Nb and Ni-Ce-Ta oxides. The maximum amount of ethylene produced is 1800 ppm at 400 °C in nickel-rich regions of the catalyst mixture (Figure 3.35b) compared with inactive Mo-V-Nb oxide catalysts (Figure 3.35a) [7]. 

In the case of 2,3-disubstituted dihydrobenzo-TAs, oxidation by potassium permanganate results in a mixture of sulfoxides and sulfones (69USP3455915). Only sulfones were obtained by potassium permanganate oxidation (63JOC2160 70JHC1007). 

Oxidative addition reactions for group VA compounds within the context of the discussion found in 5.8.2.9.1 are presented in 10.3.3.1 and 10.3.3.2, including some cases of reactions that may not be true oxidative additions. The discussion on vanadium is separated from its heavier cousins, niobium and tantalum, since the chemistry of V is distinct from that of Nb and Ta. Oxidative additions across metal-metal multiple bonds and involving clusters are not covered. 

Figurel.55 (a) Top view oftheTa205 dielectric (b) bottom view showing that the crystallization nuclei originate at the Ta/oxide interface. The inset in the left corner shows a high resolution TEM shot of the Ta/oxide interface without nuclei. The Ta shows a crystalline lattice whereas the Ta205 is completely amorphous [248].

Surfactant S Inorganic 1 SI covalent (complex) silica, Nb, Ta oxides Ta (hex)... 

R.S. Roth, The American Ceramic Society (eds.), Phase Diagrams for Electronic Ceramics I Dielectric Ti, Nb, and Ta Oxide Systems, The American Ceramic Society, OH, 2003. 

Using submicroporous Ta oxide coatings deposited by a simple hydrolysis-condensation process to increase the biological responses to Ti surface. Surf. Coat. Technol. doi 10.1016/j.surfcoat.2014.03.033... 

Silica-supported Ta oxide catalyst prepared by the reaction between Ta alk-oxide and surface hydroxy groups of Si02 had higher catalytic efficiency than catalysts prepared by impregnation with TaClj or hydrated tantalum oxide [13]. Pt/ sulfated Zr02 is reported in a patent to be active and durable [14],... 

M. Kogure, T. Sato, T. Tanaka, S. Yasujima, T. Suzuki and H. Ohya, Preparation of antimony acid cation exchange membranes by using metal alkoxide-gel method, Bull. Chem. Soc. Jpn., 1991, 1991, 1618 H. Ohya, R. Paterson, T. Nomura, S. McFadzean, T. Suzuki and M. Kogure, Properties of new inorganic membranes prepared by metal alkoxide methods. Part I A new permselective cation exchange membrane based on Si/Ta oxides, J. Membr. Sci., 1995, 105, 103-112. 

Fowler 1991). Insoluble species of tantalum, administered orally to rats, are poorly absorbed from the gastrointestinal tract, with total excretion accounted for in the feces. Ta administered orally to rats as soluble potassium tantalate was rapidly excreted almost exclusively via the fecal route less than 2% of the dose was retained after 1 day (Fleshman etal. 1971). More than 96% of the administered dose was excreted after 3 days, and less than 0.5% was recovered in urine after 7 days, although more than 97% of the total dose had been excreted. After absorption, Ta was primarily localized in the bone compartment, which retained over 40% of the total body burden after 14 days, and in the kidneys (Fleshman et al. 1971). The biological half life of the soluble, short-lived radionuclide (tj2 = 9.3 min) Ta given as Ta-chloride or Ta-oxide to dogs via intravenous administration was 190 min, with 78% of the Ta being found in the plasma ( 33% with the plasma protein fraction) and the remainder in red blood cells (Wilson etal. 1987). The distribution of soluble Ta administered intravenously to mice demonstrated Ta accumulation primarily in kidney (17% of the dose), followed by liver (9%) and blood (8.5%) (Wilson et al. 1987). 

Figure 3. AFM image of surface structured layers of anodic Al-Ta oxides formed in electrolytes based on phosphoric (a) and sulfuric (b) acid and coated with a Ni layer.

That there are such differences between the structural chemistry of reduced Nb and Ta oxides is slightly surprising and two basic questions arise. Firstly, is there also a chemistry of condensed TaeO clusters as found for reduced oxoniobates and, secondly, how do the physical properties of such tantalum compounds compare with those of the niobates Future studies are required to answer this question. 

Nonvolatile by-products range from mono- to polycarboxylated monoaromatics, and diaromatic compounds are found in the reaction mixture. Among the monoaromatic varieties are benzoic acid and trimellitic acid (TMLA or 1,2,4-benzenetricarboxylic acid). Orthophthalic and isophthalic acids can also be formed, particularly from o-xylene and w-xylene impurities in pX feed. Polycarboxylated diaromatic by-products are further classified as biphenyl- or diphenylmethane-based compounds. Biphenyl-based by-products are 2,4, 5-tricarboxybiphenyl (TCBi) and 2,6-dicarboxyfluorenone (DCF). Diphenylmethane-based by-products include 2,4, 5-tricarboxybenzophenone (TCBen) and 2,6-dicarboxyanthraquinone (DCAq). Detailed discussion of by-products formed in pX to TA oxidation process can be found in the review by Tomas etal. and references therein [9]. 

An overview of alternative TA oxidation strategies is given in Loydd, L. (2011) Handbook of Industrial Catalysis, Springer-Verlag294 v.v,... 

Mondo. J.N. Takahara, Y. Lu, D. Domen. K. Mesoporous ta oxide. 2. Improvement of the synthetic method and observation of mesostracture formation. Cliem. Mater. 

Graphite will form carbides with B, Si, V, Fe, Mo, W and Ta. Oxidizing gases such as oxygen (>150°C), air (>250°C) and steam (>300°Q will attack graphite and such media can be used to manufacture activated carbon. A more graphitic carbon with fewer active sites will be less active. 

Imai et al. analyzed the local structure of the surface Ta-oxide phase of TaC cNj,/Ta205 core-shell particles that have a high oxygen reduction activity by... 

Seo J, Cha D, Takanabe K, Kubota J, Domen K (2012) Highly-dispersed Ta-oxide catalysts prepared by electrode position in a non-aqueous plating bath for polymer electrolyte fuel cell cathodes. Chem Commun 48 9074-9076... 

Shoyama M, Tomimura T, Okubo Y, Nambu H, Lin M-L, Hara K, Fukuoka A, Ishihara A, K-I O (2009) Synthesis of Ta-oxide based nano-sized cathode catalyst on highly ordered meso-porous carbon for PEM fuel cells. ECS Trans 25 1903-1908... 

Co and Fe, which are well-known catalysts for the Fischer-Tropsch reaction (in principle the reverse reaction of Eqs. 8.3 and 8.4) have also been tested as CPO catalysts. However, Co, and especially Fe, are more difficult to reduce than Ni, and in general show lower activity for the CPO reaction than Ni. CoO and Fe304 have further been reported to have signihcant activity for the complete oxidation of methane. Enger et al recently tested C0/AI2O3 catalysts for the CPO reaction and reported that the addition of promoters such as Ee, Cr, Re, Mn, W, Mo, V and Ta oxides dramatically reduced the conversion capacity of Co, while Ni promotion enhanced it. ... 

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