Abstract
The interaction of cupric ions with γ-alumina supports was studied by physical characterization of a wide range of catalyst preparations. The results from the different techniques, extended X-ray absorption fine structure (EXAFS), X-ray absorption edge shifts, X-ray diffraction, ESR, ESCA, and optical spectroscopy, were combined with prior work to develop a coherent description of the phases present and cation site distribution in the virgin and aged catalysts. Apparent inconsistencies between earlier workers are rationalized in terms of the present model and the details of the experimental probe used. A number of transition γ-aluminas appear to have a similar threshold loading for the appearance of crystalline cupric oxide, ~4 wt% Cu/100 m 2/g support surface area. In the dispersed phase, the cupric ions are predominantly, but not exclusively, in a tetragonally distorted octahedral environment; there are some tetrahedrally coordinated ions present. The relative proportion of tetrahedral to octahedral cupric ions increases with time at calcination temperatures above 600 °C until the cation distribution of bulk copper aluminate is reached; i.e., 60% tetrahedral and 40% octahedral sites.
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