Silica-zirconia

For environmental reasons, reaction (Eqn. 21) (NO -> N2) should be promoted, N20 having a dramatic greenhouse gas effect. The different steps of reaction (Eqn. 23) have been investigated in detail, mainly by FTIR spectroscopy [61-63], One of the possible intermediate is isocyanate. NCO species could be formed on the metal and migrate on the support, which may explain the large differences observed when Rh is supported on different oxides (alumina, silica, zirconia, ceria-alumina, etc.). However, the main step should be the dissociative adsorption of NO ... 

This category includes a large variety of silica, zirconia, and alumina mesoporous films. Although the inorganic scaffold of such layers does not transport electric current, the pore architecture, which can be also used as a host matrix for incorporation of functional molecules, can alter electron transport to and from the conducting surface, thus influencing electronic properties of the complete system. 

Accordingly, work has been done on series of n-paraffins,. isoparaffins, naphthenes, aromatics, and naphthene-aromatics which have been chosen as representative of the major components of petroleum. In addition, olefins, cyclo-olefins, and aromatic olefins have been studied as a means of depicting the important secondary reactions of the copious amounts of unsaturates produced in the majority of catalytic cracking reactions. A silica-zirconia-alumina catalyst was used principally it resembles closely in cracking properties typical commercial synthetic silica-alumina catalysts. 

Mole % 1 atmosphere silica-zirconia-alumina catalyst, Universal Oil Products Co. Type B ... 

Conventionally, a fixed bed catalyst containing palladium, a promoter metal, and an alkali metal acetate is used. The fixed bed catalyst components are supported on a porous carrier such as silica, zirconia or alumina. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

The acid function of the catalyst is supplied by the support. Among the supports mentioned in the literature are silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, silica-titania, acid-treated clays, acidic metal phosphates, alumina, and other such solid acids. The acidic properties of these amorphous catalysts can be further activated by the addition of small proportions of acidic halides such as HF, BF3, SiFit, and the like (3.). Zeolites such as the faujasites and mordenites are also important supports for hydrocracking catalysts (2). 

M. Asaeda, P. Uchytil, T. Tsuru, T. Yoshioka, M. Ootani and N. Nakamura, Pervaporation of Metha-nol/MTBE Mixture by Porous Silica-Zirconia (10%) Membranes , pp 322-25 in Proc. ICIM5 June 22-28, Nagoya, Japan (1998). 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

VOv supported on ai2o3 VO, supported on silica, ceria, alumina, zirconia, niobia, titania-silica, zirconia-silica VOr supported on alumina, silica Dehydration Dehydration at 773 K in 02/He, methanol adsorption 02/He at 773 K, adsorption of isopropanol... 

In a particular experiment, p-cresol (23.54 g, 0.22 mol), methyl-f-butyl ether (19.36 g, 0.22 mol) and a silica/zirconia catalyst (3.5 wt%) were heated at 100°C for 3 hours. After cooling, 13.0 g of the product, 2-t-butyl-p-cresol was obtained, and 10.78 g of p-c resol was left unreacted. The FW of the product = 164 g/mol. Calculate the atom economy, yield, selectivity, carbon efficiency, and environmental factor. 

BASE MATERIAL (SILICA, ZIRCONIA, ALUMINA, POLYMERS)... 

Cements and Ceramics. Refractory cements and ceramics (qv) are prepared from slurries of silica, zirconia, alumina, or magnesia and a prehydrolyzed siHcate (see Cement). Calcining at 1000°C yields cured refractory shapes (48,49). 

Thermal stability. Thermal stability of several common ceramic and metallic membrane materials has been briefly reviewed in Chapter 4. The materials include alumina, glass, silica, zirconia, titania and palladium. As the reactor temperature increases, phase transition of the membrane material may occur. Even if the temperature has not reached but is approaching the phase transition temperature, the membrane may still undergo some structural change which could result in corresponding permeability and permselectivity changes. These issues for the more common ceramic membranes will be further discussed here. 

The submicron-sized and nanosized light-sensitive polyelectrolyte containers have been proposed and laser-stimulated release of corrosion inhibitor from their inner volume was studied. It was shown that the release of corrosion inhibitors from containers embedded into the silica-zirconia based sol-gel matrix under UV or IR laser irradiation ensures effective suppression of corrosion at the damaged sites at the surface of the coating. The possibility of controlling the release properties of polyelectrolyte containers by tuning the illumination wavelength and intensity of the incident laser beam makes the proposed method to be a versatile tool for corrosion protection. 

Several different types and sizes of catalyst have been employed in commercial catalytic cracking processes. The commercial catalysts have been composed predominantly of either silica and alumina, or silica and magnesia. Other compositions have been investigated in the laboratory although some, such as silica-zirconia, alumina-boria, and alumina activated with various fluorides, have high activities, none has yet proved sufficiently attractive to warrant displacing the presently used catalysts. 

The fundamental relationship between cracking activity and acidity is indicated by the fact that a single correlation line is obtained with catalysts of different chemical composition and made in different ways (222). Silica-alumina, silica-magnesia, silica-zirconia, and activated-clay catalysts were included in the comparison. Acidity in this case was meas-... 

Zhang, Q.H. Feng, Y.Q. Da, S.L. Preparation and characterization of silica-zirconia supports for normal-phase liquid chromatograply. J. Liq. Chromatogr. Relat. Technol. 2000, 23, 1461-1470. 

Two excellent reviews that detail procedures for the preparation of bonded phase supports have recently been published by Leonard - and Buchmeiser. One of the most popular methods of surface chemical modification involves the use of organosilanes. These organosilanes react with the surface metal hydroxyl groups and form a surface, which may be represented as M-O-R, where R represents an alkyl chain and M represents the metal (i.e., silica, zirconia, titania, etc.). One important factor that must be stated, however, is that the order of stability of M-O-R bonds increases in the order of M=Si > Zr > Ti > Improvements in the hydrolytic... 

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].)...

Silica Zirconia Zirconia-silica Nal impregnated zirconia - silica... 

Tanabe has reviewed the earlier work with silica-magnesia, silica-zirconia, and other amorphous siliceous materials. In a model for binary siliceous oxide catalysts, only the non-siliceous component was considered in terms of proton affinity and co-ordination number. Tanabe and co-workers " proposed a general model for mixed oxide catalysts in which acidity is caused by an excess of negative or positive charge in a model structure of the binary oxide. The hypothesis is shown to fit 28 of the 31 binary oxides tested. One of these oxides,... 

High quality microporous membranes are almost exclusively reported for silica or for binary silica-titania or silica-zirconia systems [42,46]. This is due to the very fast hydrolysis and condensation rates of the metal organic precursor of the metals relevant for membrane synthesis (Ti, Zr, Sn, Al). This usually results in too large particles in the precursor solution. Though many authors claim to have produced microporous materials by sol-gel methods (see e.g. Section 8.2.3), only a few have shown the synthesis of membranes of these materials and a still smaller number has characterised them with appropriate separation properties to be reasonably defect free. Therefore in the remainder of Section 8.2.1 a focus will be given to silica-based membranes. 

Some hybrid materials have already entered the market. Commercial examples include materials from electronics to automotive coatings with varied mechanical and optical properties, adhesives, and composites, to cite a few. " Recent examples include the indigo dyes embedded in a silica/zirconia matrix (Toshiba TV screens), organically doped sol-gel glassware (Spiegelau), and sol-gel entrapped enzymes (Fluka). 

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