Lr. Mentasty et al., A study of chromia-alumina interaction by temperature-programmed reductionin dehydrogenation catalysts, IND ENG RES, 40(1), 2001, pp. 136-143
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.