A study of chromia-alumina interaction by temperature-programmed reductionin dehydrogenation catalysts

The interaction of chromium with an alumina submitted to different pretreat ments by temperature-programmed reduction (TPR) was; studied. The Cr-alumin a interaction is analyzed in relation to texture, structure, and surface ac idity 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 taki ng place on the catalyst surface, both after preparation and after the reor dering caused by the catalytic test. Speculations from TPR data were confir med by Raman spectroscopy. The mean oxidation state of the chromium species can be accounted for by two factors: the concentration of Cr3+ as a functi on of the anchoring center concentration and the influence of the Na+ conce ntration. Na+ elimination by washing support, which substantially modifies its acidity, does not modify the Cr-support interaction. The phase transfor mation of the support (from gamma -Al2O3 to delta -Al2O3) caused by its the rmal treatment at 1123 K results in a support with fewer chromium anchoring centers. At low values of specific surface area and low acidity, surface c onditions similar to those of high loading may be attained.