Titania physical properties

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Despite the many desirable properties of silica, its limited pH stability (between 2 and 7.5) is also a major issue in NPC when strong acidic or basic mobile-phase additives are used to minimize interactions. Hence, other inorganic materials such as alumina, titania, and zirconia, which not only have the desired physical properties of silica but also are stable over a wide pH range, have been studied. Recently, Unger and co-workers [22] have chosen a completely new approach where they use mesoporous particles based not only on silica but also on titania, alumina, zirconia, and alumosilicates. These materials have been used by the authors to analyze and separate different classes of aromatic amines, phenols, and PAHs (polyaromatic hydrocarbons). 

Table 40 shows the physical properties of Zr/silica as a function of the calcination temperature. Also shown for comparison are values characterizing plain silica, titanated silica, and silica treated with two other metal ions. These samples were made by first drying the silica base, then treating it with a metal alkoxide or chloride, followed by calcination in dry air at the specified temperature. It is evident from both the surface areas and the pore volumes of these samples that silica-zirconia made in this way is quite stable, and more stable than silica-titania. 

Table 1.S Physical properties of various polymorphs of titania single crystals.

Some physical properties of the three polymorphs of Ti02 are hsted in Table 1.5. Systematic data on titania single crystals are relatively scarce, and this applies especially to brookite, most likely due to difficulties with its preparation. The presence of impurities also results in a significant scatter of the property values. 

To increase the membrane s operational temperature to 130°C, Matos et al. (2011) prepared Nafion/titania-based filler composites by casting. Three types of titania-based fillers were investiated (1) nanoparticles with nearly spherical shape, (2) mesoporous particles with a high surface area, and (3) hydrogen titanate nanotubes. The addition of titanate nanotubes changed the physical properties of the composites more markedly than did its addition to the other versions. Polarization measurements showed that composite electrolytes boost PEMFC performance significantly at 130°C. 

Vimonses, V., Chong, M., and Jin, B. (2010) Evaluation of the physical properties and photodegradation ability of titania nanocrystalline impregnated onto modified kaolin. Microporous Mesoporous Mater., 132, 201-209. 

Table 1 presents the physical properties of Mo-based catalysts with various titania loadings. When increasing the Ti content on the composites, a decrease in the surface area, porous volume and pore diameter is observed. The physical properties evolution is coherent with the deposition of titania nanoclusters inside the pores of SBA15. Note that the small-angle X-ray diffraction patterns (not showed) always exhibit the (100) reflection suggesting the conservation of the hexagonal pore stracture, even after Mo... 

Cheng, P., Li, W., Zhou, T., Jin, Y., and Gu, M. (2004) Physical and photocatalytic properties of zinc ferrite doped titania under visible light irradiation. Journal of Photochemistry and Photobiology A Chemistry, 168 (1-2), 97-101. 

Cheng P, Li W, Zhou T, Jin Y, Gu M (2004) Physical and photocatalytic properties of zinc ferrite doped titania under... 

Hydrolytically stable inorganic carriers are alumina, titania, and zirconia. Their physical and chemical properties are quite different from that of silica. Their application as a base for bonded phases has been described in literature. 

Wilke, K. and H.D. Breuer (1999). The influence of transition metal doping on the physical and photocatalytic properties of titania. Journal of Photochemistry and Photobiology A-Chemistry, 121(1), 49-53. 

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