Titania/alumina particles

At the end of the seventies, scientists at Exxon discovered that metal particles supported on titania, alumina, ceria and a range of other oxides, lose their ability to chemisorb gases such as H2 or CO after reduction at temperatures of about 500 °C. Electron microscopy revealed that the decreased adsorption capacity was not caused by particle sintering. Oxidation, followed by reduction at moderate temperatures restored the adsorption properties of the metal in full. The suppression of adsorption after high temperature reduction was attributed to a strong metal-support interaction, abbreviated as SMSI [2]. 

SiC, titania, alumina and polymer particles Cu, Ni Submicrometer ceramic powders were coated by electroless deposition 77... 

In a more extensive study,37,52 it was found that small gold particles could be obtained on titania, alumina and ceria (Table 4.4) providing that the DP time at 353 K was long enough (at least 4 h). Moreover, it was found... 

In addition to titania, alumina and ceria supports (Table 4.4), the DPU method has been applied to other supports. Gold particles supported on ferric oxide were quite small (3-7 nm) after thermal treatment is static air at 623 K.80 Another study reported the use of the DPU method to deposit gold onto other supports (MgO, CaO, SrC>2 and BaO).81 After calcination at 673 K, gold particles of moderate size were obtained on magnesia (8 nm) and on calcia (6nm). In all cases, all the gold in solution was deposited on the support. 

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). 

Another major reason for studying mixed metal oxide membranes from double metal alkoxides is the potential for preparing zeolite>like membranes which can exhibit not only separation but also catalytic properties. It has been suggested that combinations of silica and alumina in a membrane could impart properties similar to those of natural and synthetic zeolites [Anderson and Chu, 1993]. Membranes with a pore diameter of 10 to 20 nm and consisting of combinations of titania, alumina and silica have been demonstrated by using a mixture of a meta>titanic acid sol, an alumina sol and silicic acid fine particles followed by calcining at a temperature of 500 to 900 C [Mitsubishi Heavy Ind., 1984d]. 

Rezwan, K., Meier, L.P, and Gauckler, L.J., A prediction method for the isoelectric point of binary protein mixtures of bovine serum albumin and lysozyme adsorbed on colloidal titania and alumina particles, Langmuir, 21, 3493, 2005. 

In this chapter processes for coating a-alumina particles with MSA and for characterizing the coated particles to show the MSA is deposited as monomeric units to form a dense silica coating are described. The same procedures can be applied to coating titania and p-zeolite particles (4). 

The observation of individual AST particles with the hydrodynamic diameter of 10-20 nm (Figure 2.56), i.e., smaller than the average geometrical diameter of primary particles, is untypical for the aqueous suspensions of fumed silica, alumina, titania, or binary oxides (Gun ko et al. 2001e). This result can be caused by a very broad size distribution of primary particles of AST (broad primary particle size distribution is characteristic for nanooxides with a low specific surface area [vide supra Degussa 1997]). Therefore, one can assume that primary AST particles of strongly different sizes are characterized by different contributions of titania, alumina, and silica, since they can be formed in different zones of the flame during the synthesis. 

The SPSDs of mixed oxides (initial and carbonized) depend strongly on pH (Figures 2.53, 2.55, and 2.56) since the electrostatic interactions between silica, titania, alumina, andpyrocarbon phases characterized by different points of zero charge, PZC are differently affected by pH (Figures 2.52 and 2.54). The studied characteristics of nanooxides can correlate with the adsorption of metal ions because of the common basis (structure of oxide particle surfaces and their behavior in the aqueous medium) of these phenomena. 

XRD data reveal that alumina particles in the sol are of boehmite crystalline structure and the particles in zircornia and titania sols are of amorphous structure [34], The alumina, titania and zirconia samples obtained from the sols after gelation and calcination at 450°C are respectively in the phases of y-alumina, tetragonal zirconia and anatase. These are thermodynamically metastable phases, and may transform to the thermodynamically stable phases, which are a-alumina, monoclinic zirconia and rutile. The crystallite structure and lattice parameters of these phases are listed in Table 1. 

Kaiser A., Gorsmann C., Schubert U. Influence of the metal complexation on size and composition of Cu/Ni nano-particles prepared by sol-gel processing. J. Sol-Gel Sci. Technol. 1997 8 795-799 Kaneko E.Y., Pulcinelli S.H., da Silva V.T., Santilli C.V. Sol-gel synthesis of titania-alumina catalyst supports. Appl. Catal. A Gen. 2002 235 71-78... 

The particles were between 10 and 15 nm in diameter. It has also been shown that the addition of 13 run diameter alumina particles increased the fracture toughness of epoxy, cured using a cycloaliphatic amine, from 0.5 to 1.2 MPam using 11 vol% of alumina (Wetzel et al. 2006). Similarly, the addition of 11 vol% of 300 nm diameter titania particles increased Kq to 0.85... 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

Electron micrographs (scanning and transmission) showed that tungsten carbide is well dispersed on the surface of each support as nanosized particles (20 - 50 nm) as typified by the images in Figs. 3 (a b). However, BET surface area decreased in the order alumina > silica > titania > zirconia. With highest surface area obtained for each support being 240,133,18 and 9 m g respectively. 

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