Mobile oxygen

From the previous results, it has been proven that the nature of the support, although it has no significant influence on the Pd electronic properties, modifies the catalytic properties of the solids To permit a better understanding of these supports effects, the surface properties of the supports (in the presence of the metal) have been studied, in particular the acidic properties and the oxygen mobilities. The A1203 and Z1O2 supports have been mainly onsidered. 

It is clear that following NO dissociation, the formation of the (2 x 1)0 structure involves facile oxygen mobility the formation of the well-formed (2 x 3)N structure is more restricted due to the less mobile nitrogen adatoms, however, and with increasing temperature ordering occurs. Associated with the development of both structures is the diffusion of copper atoms from surface steps to form the new structures. 

Catalyst redox properties, oxygen mobility and supported metal characterization... 

The results indicate that Ce02 addition improves the WGS rate. Surface oxygen mobility was also quantified over the various oxides, with and without Rh promoter,... 

This easier redueibility of the in the grain boundaries would also be the result of a higher oxygen mobility in these highly defective zones. 

Royer, S Duprez, D Kaliaguine, S. Role of bulk and grain boundary oxygen mobility in the catalytic oxidation activity of LaCoi. Fe Os, J. Catal, 2005, Volume 234, Issue 2, 364-375. 

In recent years, research on catalysts for the ATR of hydrocarbons has paid considerable attention to perovskite systems of general formula ABO3. In the perovskite stmcture, both A and B ions can be partially substituted, leading to a wide variety of mixed oxides, characterized by structural and electronic defects. The oxidation activity of perovskites has been ascribed to ionic conductivity, oxygen mobility within the lattice [64], reducibility and oxygen sorption properties [65, 66]. 

The oxygen mobility on three types of Ce02-Zr02 mixed oxide (M-CZ,... 

The replenishment of the vacancy can be directly from the gas phase or indirectly from the catalyst. In the latter case, the oxygen mobility within the catalyst is so large that bulk oxygen can diffuse to the vacancy. Then oxygen from the gas phase reoxidizes the lattice on sites which differ from hydrocarbon reaction sites. In a steady state, the rate of catalyst oxidation will be equal to the rate of reduction by the substrate. The steady state degree of reduction, equivalent to the surface coverage with oxygen, is determined by the ratio of these two rates. Kinetic models based on these principles are called redox models, for which the simplest mathematical expression is... 

The only known difference between our preparation of Cu20 and that of Garner and co-workers is that we used ammoniacal hydrazine for the reduction of cuprammonium sulfate to copper, whereas they used a mixture of hydrazine and caustic soda this may have produced a pronounced difference in oxygen mobility in the Cu20 finally formed on the Cu surface. A re-examination of the subject with the simultaneous application of both the isotopic and the calorimetric techniques is very desirable. 

Figure 13. Survey on inherently chiral calix[4]arenes. Capital letters (A-D) characterize phenolic units which are conformationally not mobile (e.g. by larger residues attached to the oxygen). Mobile units (hydroxy or methoxy) are not indicated.

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