Silica phases among oxides

Even for an SMSI oxide, the extent of interaction is dependent on many parameters and a comparison among samples must be done systematically. Under high reduction temperatures encapsulation of the metal particle leads to a decline in CO hydrogenation in niobia-containing support. The niobia-silica surface phase oxide, which shows a similar mechanism of interaction to niobia but is less interacting, should prove useful as a model system in future studies. 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

In this type of composite materials the main load-bearing constituent is the matrix. Small hard particles are distributed evenly in the matrix to block dislocations. The mechanism of the strengthening is described by several authors, among others several years ago by Kelly (1964) and later by Ashby and Jones (2005a). The matrices are made of metals and polymers. The particles are of different origin silica powder or fine sand are used for polymer matrices and, for metallic matrices, second phase precipitates and particles made of oxides, nitrides, carbides and borides. Precipitates are small particles which crystallise from impurities dissolved in metal alloys. The crystallization during the cooling process results in very small and hard particles, closely distributed in the metal matrix. When ceramic particles... 

The most efficient catalysts in liquid-phase oxidation of organic compoimds were crystalline mked oxides [1]. They are ionic mixed oxides or mixed oxides containing oxides supported on oxides. In the latter case, the catalytic activity of the oxide support is increased by adding one or more metal components or is obtained by immobilization of metal oxides on inactive oxide support. Metal ions were isomorphously substituted in framework positions of molecular sieves, for example, zeolites, silicalites, silica, aluminosilicate, aluminophosphates, silico-aluminophosphates, and so on, via hydrothermal synthesis or postsynthesis modification. Among these many mixed oxides with crystalline microporous or mesoporous structure, perovskites were also used as catalysts in liquid-phase oxidation. 

There is not very often accordance among the different models for the acidity prediction of a given oxide structure. Moreover, it is also hard to justify the predicted acid properties with the catalytic activity of the oxide composition this is the case of titania-silica system [67, 104]. Ti02 -Si02 mixed oxide is a very important industrial material and catalyst in both the amorphous and crystalline phases which found several industrial applications (e.g., isomerization of olefins, epoxidation of olefins... 

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