Titania-Zirconia Mixed Oxides

Negligible uptake of Na and Cl is reported in [3201] (at point of equal uptake, no independent estimation of PZC). 

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Vanadium oxide and cerium oxide have also been used to dope titania-zirconia mixed oxides. Their results will be discussed in the next section. 

Titania-zirconia mixed oxides doped with vanadium and cerium oxides were also explored. The Ti02-Zr02 mixed oxide support, synthesized by a co-precipitation... 

Likewise, Park et al. [123,124] have studied the effect of ceria on the structure and catalytic activity of V205/Ti02-Zr02 catalyst for the CO2-ODE reaction. In their previous research, the authors had found that titania-zirconia mixed oxides exhibited excellent catalytic activity and selectivity for the CO2-ODE to styrene because of the high specific surface area, good acid-base and redox properties. 

In polymerization-induced colloidal aggregation (PICA) processes, a reactive monomer, generally urea formaldehyde, is mixed with a stable, submicrometer diameter metal oxide sol and undergoes an acid-catalyzed polymerization that results in porous, uniformly sized polymer-oxide composite microspheres [24,25], PICA has been applied to a variety of metal oxide systems, primarily silica, but also alumina, titania, zirconia, ferric oxide, and antimony pentoxide [24,25]. The process is affected strongly by solution acidity [26]. At lower pH, polymerization is more rapid and a more porous but mechanically weaker particle is formed. 

Reddy et al synthesized ceria-based mixed oxides with various dopants, namely SiOg, TiOs, ZrOg and AlgOj, by the microwave-induced solution combustion method and analysed them for CO oxidation activity. Of the samples tested, ceria-zirconia exhibited the highest conversion and lowest light-off temperature (100%, 351 °C), followed by ceria-titania (85%, 404 °C), ceria-alumina (70%, 454 °C) and ceria-silica (40%), respectively. The incorporation of zirconia into the ceria lattice facilitates the formation of more defect sites, which are responsible for the better activity of the ceria-zirconia mixed oxide. 

Also for this reaction, namely esterification plus transesterification, mixed oxides, this time acidic in nature, appear to be the most promising alternative. Tungstated zirconia-alumina (WZA), sulfated zirconia-alumina and sulfated tin oxide were shown to be active in the transesterification of soybean oil with methanol at 200-300 °C and in the esterification of n-octanoic acid with methanol at 175-200 °C. Although the order of activities is different for the two reactions, WZA gives high conversions in both readions and it is stable under the reaction conditions [31]. Titania on zirconia, alumina on zirconia and zirconia on alumina also showed good performances [32, 6]. 

Some dense inorganic membranes made of metals and metal oxides are oxygen specific. Notable ones include silver, zirconia stabilized by yttria or calcia, lead oxide, perovskite-type oxides and some mixed oxides such as yttria stabilized titania-zirconia. Their usage as a membrane reactor is profiled in Table 8.4 for a number of reactions decomposition of carbon dioxide to form carbon monoxide and oxygen, oxidation of ammonia to nitrogen and nitrous oxide, oxidation of methane to syngas and oxidative coupling of methane to form C2 hydrocarbons, and oxidation of other hydrocarbons such as ethylene, methanol, ethanol, propylene and butene. 

Fig. 5 Chromatograms obtained on four mixed oxide packing materials. Solute 1 = benzene 2 = dimethyl phthalate 3 = pyridine. Column packing material (a) silica-zirconia (b) silica-alumina (c) silica-titania (d) silica-magnesia (e) silica gel. Mobile phase, -hexane containing 1% methanol flow rate, 1 mL/min column temperature, ambient detection, UV 254 nm. (From Ref. [1].)...

Since then, other colloidal oxide systems have been investigated in order to prepare ceramic mesoporous membranes designed for ultrafiltration. The preparation of an electronically conductive membrane from a Ru02 Ti02 mixed oxides sol and the application to an electro-ultrafiltration process [25,26], as well as the preparation of titania and zirconia ultrafiltration membranes [27], have been described following a colloidal process in which a partial destabilization of a metal oxide colloidal suspension is used to produce top layers with different pore size and pore volume in the mesoporous range. In agreement... 

In the search for novel, more stable and efficient supports for gold catalysts for the WGS, mixed oxide supports (Fe203-Zn0 and Fe203-Zr02), as well as supports of a different crystalline state—amorphous zirconia and titania—have been used also by Andreeva and co-workers (Fig. 6.6) [228]. Gold deposited on well-crystallised metal oxides was found to have higher... 

Holland et al. extended the possible oxide structures to include not only silica, mesoporous silica, titania, zirconia, a yttria stabilized zirconia, and alumina but also oxides of W, Fe, V, and Sb [21]. These latter transition metals formed less ordered structures, containing areas of non-porous material. Different dilutions of alkoxide in alcohol resulted in various inorganic loadings, and moderate control in the wall thickness and window sizes between spherical voids [21 ]. SEM images of a series of macroporous titania structures obtained with different alkoxide dilutions in ethanol are shown in Fig. 3. Gundiah and Rao have also prepared macroporous materials of ternary mixed oxides, PdTiOj and Pb(ZrTi)03 [22]. 

The acidic solids investigated in this study belong to one the following families 1) bulk oxides [95], 2) doped oxides (chlorinated alumina, doped silica,. ..) [101], 3) supported oxides [109], 4) mixed oxides such as silica-alumina, silica-titania or silica-zirconia, zeolites and clays [11,14], 5) heteropolyanions such as H3PW12O40, H4SiWi204o and H5BW12O40, 6) phosphates (Zr, Al, V, Ti, B, Sn), 7) superacids such as sulfated oxides or Nafion H (perfluororesin sulfonic polymeric acid). 

Wen, J. Mark, J. E., Synthesis, Structure, and Properties of Poly (dimethylsiloxane) Networks Reinforced by In Situ-Precipitated Silica-Titania, Silica-Zirconia, and Silica-Alumina Mixed Oxides. J.Appl. Polym. Sci. 1995,58, 1135-1145. 

Alumina-zirconia and alumina-titania mixed oxides were prepared by coprec itation of thdr corresponding chlorides. Samples were synthezised at several concentrations, dried and calcined at ten eratures between 400°C and 800T. All dried samples showed the bayeiite structure, which upon calcination became first amorphous and later AljOj. Anatase was observed only on the high content, high calcination temperature sample, but no mystalline phase of zirconia was detected. Surface areas of mixed oxides were higher than for alumina single oxide, and decreased with ten ierature. Carbon tetrachloride adsorption increased with TiO content, but the opposite effect was observed on alumina-zirconia samples. 

In this work we report the preparation of alumina modified by zirconia or titania using a precipitation technique. The objective was to obtain mixed oxide supports for wdiich we could asses the resulting structural and textural properties, and their thermal stability. Al303-Ti02 and AljOj -ZrOj at several compositions were characterized by TGA, DTA, XRD, Nj adsorption and CCI4 adsorption. 

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