Catalytic properties lattice constants

Indeed, lattice parameters of both the copper and the zinc oxide were found to depend on the catalyst composition. The lattice extension of copper was attributed to alpha brass formation upon partial reduction of zine oxide, and an attempt was made to correlate the lattice constant of copper with the decomposition rate of methanol to methyl formate. Furthermore, the decomposition rate of methanol to carbon monoxide was found to correlate with the changes of lattice constant of zinc oxide. Although such correlations did not establish the cause of the promotion in the absence of surface-area measurements and of correlations of specific activities, the changes of lattice parameters determined by Frolich et al. are real and indicate for the first time that the interaction of catalyst components can result in observable changes of bulk properties of the individual phases. Frolich et al. did not offer an interpretation of the observed changes in lattice parameters of zinc oxide. Yet these changes accompany the formation of an active catalyst, and much of this review will be devoted to the origin, physicochemical nature, and catalytic activity of the active phase in the zinc oxide-copper catalysts. 

Not only the permeability, permselectivity and mechanical properties, but also the catalytic properties are affected by the two hydride forms that can exist in palladium. The a phase corresponds to solid solutions with a H/Pd ratio of about 0.1 and the P phase with a H/Pd ratio of about 0.6. The phase change is associated with a large change in lattice constant that often leads to microcracks and distortion in the palladium membrane. As a result, the mechanical properties are reduced. The transformation depends on the operating conditions such as temperature and hydrogen partial pressure. Repeated thermal cycles, for example, between 100 and 250 C under 1 atm of hydrogen pressure can make a 0.1 mm thick Pd foil expand to become 30 times thicker [Armor, 1992]. 

Lattice constants and variations of these constants have oec.asionallj been discussed as being related to the specific activities of certain catalysts. The poor x-ray diagrams usually obtained with high surface materials do not lend themselves to such determinations, particularly if it is considered that the lattice constants in the uppermost surface layers of the catalyst woidd have to be measured in order to give information on the catalytic properties. The dimensions of a lattice of a given crystal are usually a function of the temperature at which the crystal is held. However, if other elements or compounds can go into solid solution in this crystal, changes in the lattice may occur. 

Because the concentration of tetrahedrally coordinated metal cations of a kind is frequently not constant throughout the crystal, it might be difficult to rationalize the catalytic activity or the acid - base properties as function of the overall lattice charge or the overall composition of the material (3). This complicated situation is also reflected in widely varying values for the n-butane cracking rate constants for even a material of one given kind, e.g. 

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