Amorphous solute-poor

Impregnation has been used to prepare a number of catalysts having different metal support combinations. Highly loaded nickel catalysts supported on alumina, titania, silica, niobia and vanadium pentoxide were prepared by adsorption of nickel nitrate from an ammoniacal solution onto the support material. The supported salts were dried at 120°C and calcined at 370°C before reduction to the supported metallic nickel. It was found that the ease of reduction depended on the crystallinity of the support. Amorphous or poorly crystalline supports made the reduction of the nickel oxide more difficult than on crystalline supports. As examples of its generality, this procedure was also used to prepare... 

Some types of aggregate can react with Na, K and OH ions in the pore solution, giving rise to detrimental expansion. The principal reactions can take place with aggregate containing certain forms of amorphous or poorly crystalline sihca (alkah sihca reaction, ASR) and with dolomitic hmestone aggregate (alkali carbonate reaction). 

Addition of sufficient base to give a > 3 to a ferric solution immediately leads to precipitation of a poorly ordered, amorphous, red-brown ferric hydroxide precipitate. This synthetic precipitate resembles the mineral ferrihydrite, and also shows some similarity to the iron oxyhydroxide core of ferritin (see Chapter 6). Ferrihydrite can be considered as the least stable but most reactive form of iron(III), the group name for amorphous phases with large specific surface areas (>340 m2 /g). We will discuss the transformation of ferrihydrite into other more-crystalline products such as goethite and haematite shortly, but we begin with some remarks concerning the biological distribution and structure of ferrihydrite (Jambor and Dutrizac, 1998). 

In Refs. 10 and 11, aqueous NaiSiOs was added to SbCls in glacial acetic acid (SbCls hydrolyzes in water unless complexed or the solution is moderately acidic or strongly alkaline). A pH of ca. 3 was optimum below 2.5, adhesion was poor above 4, basic antimony salts precipitated. The solution was kept below room temperature to prevent rapid bulk precipitation. No XRD pattern was found for the as-deposited film, which was presumed to be amorphous. Annealing at 170°C crystallized the film, at least partly. The bandgap of the as-deposited film was reported to be 2.48 eV and that of the annealed film 1.76 eV. Photoconductivity was exhibited by the annealed film but not by the as-deposited one. 

The stability of MCM-41 is of great interest because, from the practical point of view, it is important to evaluate its potential application as a catalyst or adsorbent. It is known that purely-siliceous MCM-41 (designated here as PSM) has a high thermal stability in air and in oxygen containing low concentration (2.3 kPa) of water vapor at 700 °C for 2 h [1], However, the uniform mesoporous structure of PSM was found to be collapsed in hot water and aqueous solution due to silicate hydrolysis [2], limiting its applications associated with aqueous solutions. After MCM-41 samples were steamed in 100% water vapor at 750°C for 5 h. their surface areas were found to be lower than amorphous silica-alumina and no mesoporous structure could be identified by XRD measurement [3]. In addition, PSM showed poor stability in basic solution [4]. 

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