Selectivity of gold for hydrogenation and dehydrogenation of cyclohexene

Abstract

Rates of reaction of cyclohexene over a gold powder catalyst, in the presence or absence of hydrogen, were measured in a batch recirculation system between 203° and 285°C. After activation of the powder, consisting of a treatment with hydrogen first and then with oxygen, the measured rates are in excellent agreement with those previously reported on gold evaporated films. It has now been shown that, on gold, cyclohexene reacts irreversibly to form either cyclohexane or benzene. The selective production of benzene can be controlled within wide limits at a fixed temperature. It is depressed by high partial pressures of hydrogen, enhanced in the absence of hydrogen, while benzene becomes practically the sole product in the presence of small quantities of oxygen. Thus, at 203°C, the selectivity as measured by the ratio of benzene to cyclohexane is increased by a factor of 3000 when a partial pressure of hydrogen equal to 0.74 atm is replaced by a partial pressure of oxygen equal to 0.041 atm.