Alumina Titania

Physisorption and chemisorption of water on alumina, titania and ferric oxide selection of results (Morimoto ef a/. )... 

Method 1 siHca—alumina, siHca, alumina, titania, tungstic oxides, phosphates, 2eoHtes, and clays. 

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-... 

The thermograms of Cu reduction in silica-, alumina-, titania- and zirconia-supported catalysts show only one pe the maximum of which is reported in Table 3. The amount of hydrogen consumed by the r uction corresponds, within experimental error, to the theoretical amount required for the reaction ... 

As catalysis proceeds at the surface, a catalyst should preferably consist of small particles with a high fraction of surface atoms. This is often achieved by dispersing particles on porous supports such as silica, alumina, titania or carbon (see Fig. 1.2). Unsupported catalysts are also in use. The iron catalysts for ammonia synthesis and CO hydrogenation (the Fischer-Tropsch synthesis) or the mixed metal oxide catalysts for production of acrylonitrile from propylene and ammonia form examples. 

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

Common catalyst compositions include oxides of chromium or molybdenum, or cobalt and nickel metals, supported on silica, alumina, titania, zirconia, or activated carbon. 

The pore size of porous titania can be up to 2000 A. Titania is used for the purification of proteins and as a support for bound enzymes. The purification of /1-lactoglobulin from cheese whey, of protease from pineapple, /5-lactamase, and amylase can be achieved with titania. The latter two purifications are impossible on alumina. Titania is also used as a support in peptide synthesis. The separation of plasmid DNA is shown in Figure 3.24. 

ALUMINA, TITANIA, ZIRCONIA, LANTHANA GEL METAL RESISTENCE... 

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. 

In contrast to silica, alumina, titania, and zirconia surfaces are basic. 

It also became evident that a great variety of catalysts, potentially exhibiting a large flexibility, could be prepared via solid solutions. Three different degrees of freedom can be varied in a controlled fashion the chemical nature of the host matrix AO, the chemical nature of the guest cation M, and the dopant concentration x. Furthermore, solid solutions can be formed not only by cubic oxides but also by alumina, titania, zirconia, and others. Thus, another degree of freedom is added, namely, the different crystal structures. 

The samples prepared have a good surface area after calcination at 500°C, as can be seen in table 1. Alumina-titania mixed oxide supported samples have surface areas larger than those of the alumina and titania single oxides. As expected x-ray diffraction results show that the mixed oxide catalysts are amorphous, but alumina shows a y phase structure, and Ti02 is a well crystallized anatase phase. No nickel metal or nickel oxide was detected in any of the samples, including Ti02 sample, suggesting the metal was well dispersed, and present as small crystallites (< 50A). 

The deactivation constant, obtained by fitting the data to a first order law equation (8), decreases with the reduction temperature for all cases, and is especially low for the impregnated alumina-titania catalyst. These results suggest the formation of carbon deposits and deactivation of catalysts occurs due to the metal activity, The contribution of the acid sites to deactivation seems to be negligible, despite the fact that alumina-titania supports present higher acidity than alumina or titania single oxides (9). 

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