Dehydrogenation of Δ3-carene over chromia and chromia–alumina catalysts

Abstract

3-Carene is dehydrogenated over oxidized and reduced chromia and chromia–alumina catalysts at 340 to 500 °C, without and with pyridine. Dehydrogenation is found to be more effective over reduced than oxidized catalysts; in either state, however, chromia–alumina is more active than chromia. Pyridine brings down the dehydrogenation ability of chromia and chromia–alumina in both reduced and oxidized states, more markedly in the reduced state. The ratio of p-cymene to m-cymene at 360 to 425 °C is higher over chromia than over chromia–alumina. Increase of temperature from 360 °C to higher values decreases the ratio of cymenes over chromia but does not affect the ratio over chromia–alumina. Pyridine has no effect on the ratio of cymenes over chromia; over chromia–alumina, neither, pyridine nor the pretreatment of the catalyst with oxygen or hydrogen has any effect on the ratio.