The influence of contact
time on the dehydrogenation of 3-carene over reduced chromia and
chromia-alumina catalysts has been investigated at 450 and 400°C respectively.
For the dehydrogenation, reduced chromia- alumina catalyst is more active than
reduced chromia alone. It has been found that the dehydrogenating ability of
reduced chromia is superior to that of oxidized chromia. The effect of water
vapour on reduced chromia showed an initial suppression of its reactivity, but
at intermediate values increased its activity. Progressive increase of water
vapour was seen to modify the active sites of reduced chromia, an effect
similar to that of the oxidized sample. ��� The dehydrogenation of 3-carene, over
chromia, follows second-order kinetics. The energy of activation is found to be
greater for oxidized than for reduced chromia. Impregnation of chromia with
potassium decreases the activation energy of reduced chromia and enhances its
dehydrogenation ability by suppressing the side reactions. ��� The observed experimental data are
explained in terms of the acidity of the catalysts, oxidation states of
chromium ions and the promoting influence of potassium ions.