Zirconium oxide supports

Materials with inorganic or porous hydrophobic or (less frequently) hydrophilic organic polymer matrices and graphitized carbon are stable over a broad pH range from 0 to 12-14 hence, they are useful for separations of basic compounds. RP phases on aluminium and zirconium oxide supports exhibit hardness and mass transfer properties comparable to silica, and can be prepared by forming a cross-linked polystyrene, polybutadiene, or alkylated polymethylsiloxane layer on the support surface to which alkyls are attached. The inorganic surface, encapsulated by a nonpolar stationary phase, does not come into contact with the mobile phase or with the analyte, so these materials can be used in the pH range 1-14. 

The zirconium oxide supports doped with yttrium oxide were prepared by hydrolyzing with water a mixture of zirconium and yttrium alkoxides (ref. 7),... 

Ti or Zr salts deposited on silicon dioxide the titanium or zirconium oxide supported on Si02 is sulfate-activated and physically blended with an acidic montmorillonite clay... 

Blackwell, J.A. Carr, P.W. Ligand-exchange chromatography of free amino-acids on phosphated zirconium-oxide supports. J. Liq. Chromatogr. 1992, 75, 727-751. 

For the methanol OSR on palladium in fixed-bed reactors, the use of ZnO seems to be necessary [37, 38[ to yield high reforming and WGS activity, whereas decomposition is observed predominantly on zirconium oxide supports [37]. 

Recent research in packed beds [38], ceramic monoliths [20] and microreactors [30] also revealed an excellent performance of a Ce-Zr support mixture, which was explained by an increase in surface area by the addition of zirconium oxide [38]. A zirconium oxide-supported rhodium catalyst also revealed similar ignition performance to a mixed Ce-Zr oxide supported rhodium catalyst on the surface of Fecralloy monoliths with trapezoidal channels [9]. A novel route to a support, which might be useful for CPO and OSR, is the synthesis of silicon carbide foam, recently used for steam reforming [44] (Figure 25.2). This support would also be less acidic and is suitable for building a compact foam catalyst... 

Figure Bl.25.9(a) shows the positive SIMS spectrum of a silica-supported zirconium oxide catalyst precursor, freshly prepared by a condensation reaction between zirconium ethoxide and the hydroxyl groups of the support [17]. Note the simultaneous occurrence of single ions (Ff, Si, Zr and molecular ions (SiO, SiOFf, ZrO, ZrOFf, ZrtK. Also, the isotope pattern of zirconium is clearly visible. Isotopes are important in the identification of peaks, because all peak intensity ratios must agree with the natural abundance. In addition to the peaks expected from zirconia on silica mounted on an indium foil, the spectrum in figure Bl. 25.9(a)...

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

Another type of membrane is the dynamic membrane, formed by dynamically coating a selective membrane layer on a finely porous support. Advantages for these membranes are high water flux, generation and regeneration in situ abiUty to withstand elevated temperatures and corrosive feeds, and relatively low capital and operating costs. Several membrane materials are available, but most of the work has been done with composites of hydrous zirconium oxide and poly(acryhc acid) on porous stainless steel or ceramic tubes. 

The raw materials needed to supply about ten million new automobiles a year do not impose a difficult problem except in the case of the noble metals. Present technology indicates that each car may need up to ten pounds of pellets, two pounds of monoliths, or two pounds of metal alloys. The refractory oxide support materials are usually a mixture of silica, alumina, magnesia, lithium oxide, and zirconium oxide. Fifty thousand tons of such materials a year do not raise serious problems (47). The base metal oxides requirement per car may be 0.1 to 1 lb per car, or up to five thousand tons a year. The current U.S. annual consumption of copper, manganese, and chromium is above a million tons per year, and the consumption of nickel and tungsten above a hundred thousand tons per year. The only important metals used at the low rate of five thousand tons per year are cobalt, vanadium, and the rare earths. 

Zirconium oxide is of interest as a catalyst, as a support for other catalysts and as a diffusion barrier. In the latter application a thin layer of Zr02 prevents the dissolution of rhodium in alumina supports under severe oxidative conditions [32], Here it is essential to apply Zr02 on the support at the highest possible... 

Catalysts employed in this study are zirconium(lV)-hydrides on oxide support (silica, silica-alumina and alumina). Their synthesis is described above. We present here some transformations or modifications of polystyrene, linear alkanes and polyethylene with Zr-H catalyst... 

Thus, the SIMS intensity ratios sensitively reflect the transition from zirconium ethoxide to zirconium oxide, and indicate that this reaction takes place at temperatures between 300 and 400 °C. Infrared spectroscopy measured in transmission confirms the disappearance of ethoxide groups at the same temperatures at which the SIMS ZrO+/Zr+ and ZrC>2+/Zr+ intensity ratios change to those characteristic of Zr02. Whilst the infrared spectra might also be due to free ethoxide ligands on the support, the inherent advantage of SIMS is that it confirms -albeit indirectly - that the ethoxide ligands are connected to zirconium [17]. 

The dynamic membranes originally developed by Union Carbide are protected by three core patents U.S, 3977967, 4078112, and 4412921 (Trulson and Litz, 1976 Bibeau, 1978 and Leung and Cacciola, 1983) and their foreign equivalents. Those patents cover a broad range of metal oxides such as zirconia, gamma alumina, magnesia>alumina spinel, tantalum oxide and silica as the membrane materials and carbon, alumina, aluminosilicates, sintered metals, fiberglass or paper as the potential porous support materials. However, their marketed product, trade named Ucarscp membranes, focused on dynamic membranes of hydrous zirconium oxide on porous carbon support. 

While the formed-in-place or dynamic hydrous zirconium oxide membranes on porous stainless steel supports have been studied mostly for biotechnology applications, they have also demonstrated promises for processing the effluents of the textile industry [Neytzell-de-Wilde et al, 1989]. One such application is the treatment of wool scouring effluent. With a TMP of 47 bars and a crossflow velocity of 2 m/s at 60-70°C, the permeate quality was considered acceptable for re-use in the scouring operation. The resulting permeate flux was 30-40 L/hr-m. Another potential application is the removal of dyes. At 45 C, the dynamic membranes achieved a color removal rate of 95% or better and an average permeate flux of 33 L/hr-m under a TMP of 50 bars and a crossflow velocity of 1.5 m/s. 

Additional measurements on a full series of ceria and cerium-zirconium mixed oxides supported noble metals showed that Ru was at least 10000 times more active than Pd and about 20 times more active than Rh for the activation of oxygen [70]. Up to now, most results were obtained with Rh catalysts but Ru could be a good candidate for surface diffusion measurements. 

Two useful membranes developed by the group at the Oak Ridge National Laboratory have dominated the application of dynamic membranes the hydrous zirconium oxide ultrafilter and the hydrous zirconium oxide-poly(acrylic acid) hyperfilter. The technology of formation and utilization of zirconium oxide-poly(acrylic acid) dynamic membranes has been described in detail by Thomas ( ). The effects of molecular weight of the poly(acrylic acid), pore diameter of the porous support, formation cross-flow velocity, formation pressure, and pH of poly(acrylic acid) solution during initial deposition of the polyacid on the hyperfiltration performance are described and discussed. 

Two different cerium oxide promoted zirconias were prepared and tested as supports for Pd catalysts for the catalytic oxidation of methane, alone and in presence of a strong catalyst poison (SO2). The introduction of cerium oxide was carried out by incipient wetness of zirconium hydroxide or zirconium oxide, followed by calcination. Both catalysts present very different properties, the first method producing a catalyst with better performance, and thermal stability markedly higher than the unmodified zirconia support. However, the addition of cerium does not lead to any enhancement of the catalyst performance in presence ofSC>2,... 

---