Abstract
The interaction of chromium with an alumina submitted to different pretreatments by temperature-programmed reduction (TPR) was studied. The Cr-alumina interaction is analyzed in relation to texture, structure, and surface acidity of the support, in catalysts with different chromium loads. A careful interpretation of TPR results, considering both the T max values and the H 2 /m 2 consumption, may allow a better understanding of the phenomena taking place on the catalyst surface, both after preparation and after the reordering caused by the catalytic test. Speculations from TPR data were confirmed by Raman spectroscopy. The mean oxidation state of the chromium species can be accounted for by two factors: the concentration of Cr 3+ as a function of the anchoring center concentration and the influence of the Na + concentration. Na + elimination by washing support, which substantially modifies its acidity, does not modify the Cr-support interaction. The phase transformation of the support (from γ-Al 2 O 3 to δ-Al 2 O 3 ) caused by its thermal treatment at 1123 K results in a support with fewer chromium anchoring centers. At low values of specific surface area and low acidity, surface conditions similar to those of high loading may be attained.
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