Alumina, porous

Ail these data confirm that a well-defined zeolite silicalite-type crystalline phase has been formed in the presence of the alumina porous tube (which seems indispensable for the zeolite synthesis, as no material is formed in its absence). 

Oxides are widely used as supports. The major examples are silica (porous Si02), alumina (porous AI2O3), and zeolites. Oxides are also u.sed as catalysts. In bulk chemistry they are... 

Aluminas. Aluminas, porous AI2O3, are available in many forms. They constitute the most important carrier material in heterogeneous catalysis. Alumina is amphoteric and, as a con.sequence, soluble in both acidic and basic media. Precipitation can be performed from an acid solution by adding a base or from a basic solution by adding an acid, as schematically represented in Fig. 3.18. If, for example, at a pH of less than about 3 a base is added to an aqueous solution of aluminium sulphate, a precipitate is formed. If this material is filtered, dried and calcined, an amorphous porous AI2O3 is obtained. At other pH values different porous aluminas can be synthesized. 

These phases are composed of adsorbing materials molecular sieves, alumina, porous glass and gels (such as Chromosorb 100, Porapak and PoraPLOT1 ), and graphitised carbon black. They are mainly used to separate gases or volatile compounds. Capillary columns made by deposition of these materials in the form of very fine particulates are called PLOT (porous layer open tubular) columns. 

HPLC in the adsorption mode can be carried out with silica or alumina porous-layer-bead columns. Small glass beads are often used for the inert core. Some of the more widely used packings are /a Porasil (Waters Associates), BioSilA (Bio-Rad Laboratories), LiChrosorb Si-100 Partisil, Vydac, ALOX 60D (several suppliers), and Supelcosil (Supelco). 

The choice of the sorbent is dictated by the characteristics of both the analytes and their potential interferences. The sorbents most frequently employed here are silica, alkylsilane-modified silica (bonded phases), alumina, porous polymers (with and without ion-exchange groups) and carbon-based materials. One typical application is a method for the determination of hexavalent chromium in soils [10] using the on-line system depicted in Fig. 4.9. After USAL, the analytes in the leachate were directly determined or preconcentrated depending on their concentration. Concentration was performed by on-line solid-phase extraction using a laboratory-made minicolumn packed with a strong anion-exchange resin. The absolute limits of detection were 4.52 and 1.23 ng without and with preconcentration, respectively. 

Its advantages and ease of use have made SPE an appropriate method for concentration and fractionation of lipid classes [2,3]. Many different solid-phase types have been used in lipid fractionation on silica, alumina, porous carbon, and ion-exchange resins. Various bonded phases have been used, particularly with the silica gel matrix. 

In addition to dense sintered alumina, porous alumina materials, i.e. those fired at lower temperatures, are also manufactured for special or less stringent purposes. They are characterized by lower strength. 

Support - porous alumina - porous carbon - porous metal plate, disc, tube, monolith plate, tube, hollow fibre woven structures, disc, tube... 

Pt(IV) than Pd(n) [49], An interesting system, with asymmetric inorganic membranes, was used for selective metal ion separation. The membrane phase was a self-assembled monolayer of alkyl thiols as a hydrophobic phase for a trialkyl phosphate and phosphine oxide-based metal ion carrier. This organic mixture was attached on alumina porous supports with thin layers of gold. The thin membrane layer gave high fluxes and high selectivity, while metal ions transport was carrier limited [50]. 

The achievements of making controllable self-organized columnar porous alumina, porous Si and porous InP [27-32] raise the question whether we can obtain a similar porous structure in SiC by controlling the etching conditions. This section focuses on the fabrication of columnar porous SiC. The necessary etching conditions and formation mechanisms are also discussed. 

Chou, K. S. Wang, S. M. "Studies on the preparation of Pd/alumina/porous stainless steel membranes for hydrogen separation". J. Chinese Inst. Chem. Eng., 2000, 31, 499. 

Solid-liquid extraction by use of sorbents (silica, alkyIsllane-modified silica, alumina, porous polymers with or without ion-exchange groups or carbon materials) contained in a cartridge or a short stainless-steel or glass column is the pretreatment most commonly used at present for some types of samples... 

Pore etching allows to rich the porosity up to 60 % and the pore entrances up to 20-30 nm (Fig. lc). In this case the LC alignment has vertical orientation as shown in Fig. Id. The top left part in Fig. Id is planar non anodized area of the initial aluminum film with the horizontal LC alignment. It should be noted that LC penetration in the alumina porous structure with 60 % porosity was almost complete. 

Supported NAFION. In order to Increase the activity of the acid sites by achieving better dispersion, NAFION has been supported on silica gel, sillca/alumina, alumina, porous glass and Chromosorb T (fluoropolymer support). These supports can have either low or high surface area and various pore diameters (50-600A). Catalysts prepared in this fashion have been used in the alkylation of benzene, isomerization of normal alkanes and disproportionation of toluene. Table XVIII summarizes the results on the alkylation of benzene with ethene for NAFION and several supported catalysts (66-68). 

In a second example, a filamentous microstructured catalyst was used in a membrane reactor specially developed for the continuous production of propene from propane via nonoxidative dehydrogenation. The catalytic filaments with a diameter of about 7 pm consisted of a siUca core covered by a y-alumina porous layer on which an active phase of Pt/Sn is supported [8]. 

H, asymmetric y-alumina porous tubular membrane (id of 0.0070 m, od of 0.010 m, MembraloxTM) coated by polyetherimide (UltemR-1000) (home prepared) silica membranes on y-alumina (Pervatech BV)... 

Some types of membrane and catalytic membranes for three-phase reactions prepared in the Genoa membrane research group. Porous flat sheet catalytic membrane (a) unsupported (b) supported on a polymeric non-woven substrate, (c) Hollow fibres (d) single-channel Pd membrane supported on alumina porous substrate (e) three-channel catalytic zeolite membrane (f) multi-channel porous alumina substrate. 

USP 4,806,658 speaks to cleavage of glycol ethers by hydrolysis in the presence of aluminum oxide, activated alumina, porous aluminosilicates and porous days at temperatures from 170°C to 350°C (340°F to 660 F)... 

As is demonstrated by the results summarized in Tables I and II, introduction of water vapour into the carrier gas led to a decrease in the retention times of all the sorbates, compared with those obtained in the dry carrier gas. An analogous decrease in the retention times when using water vapour in the carrier gas was also described in e.g. the paper by Guillemin and Millet [18]. The authors employed much higher water vapour contents (above 10%) and classical adsorbents (silica gel, alumina, porous polymers). With cyclodextrins, a perceptible decrease in the retention occurs even for 0.8% water vapour in the carrier gas. This phenomenon can be explained by partial adsorption of water molecules on the stationary phase surface, in a similar manner to common adsorbents. However, the experimental results, especially those obtained with a-CD as the stationary phase (Table I), indicate an effect on the equilibrium in the formation of the sorbate-cyclodextrin inclusion complex, in favour of the free guest. A great excess of water vapour over the sorbate apparently leads to competitive inclusion of water molecules and thus to faster desorption of the guest. 

Aluminum oxides have several crystal forms. Active alumina (porous alumina) used as an adsorbent is mainly y alumina. Specific surface area is in the range of 150 and 500 m g with pore radius of 15 to 60 A (1.5 to 6 nm), depending on how they are prepared. Porosity ranges from 0.4 to 0.76 which gives particle density of 1.8 to 0.8 g/cm ... 

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