Dehydrogenation of 3-carene in the vapour phase. II. Performance studies of chromia and chromia-alumina catalysts

Abstract

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.