The nature of the Mo(CO)6/alumina catalyst for the metathesis of olefins

Activation of Mo(CO)6/γ-Al2O3 at 100°C in flowing helium yields Mo(CO)3(ads.) which is modestly active in the metathesis of propylene at 53°C. Activation at higher temperatures results in a large increase in activity, the evolution of further CO and, by 280°C, of one molecule of hydrogen from surface OH groups. Activation beyond 280°C decreases the activity. Mo(CO)3(ads.) adsorbs one molecule from a pulse of O2 at 25°C to eject one molecule of CO and form Mo(CO)2O2(ads.), a species 15 times more active than Mo(CO)3(ads.). Interrelations are presented between these surface species and ones known molecularly.