Influence of extra-framework alumina in H-[Al]ZSM-5 zeolite on the direct hydroxylation of benzene to phenol

The catalytic properties of dealuminated H-[Al]ZSM-5 zeolites in the reaction of benzene and N2O to phenol are studied. The catalytic behaviour is shown to be determined by the presence of Lewis acidic extra-framework aluminium created by hydrothermal treatment of the zeolite. The maximum activity is achieved for the maximum amount of extra-framework aluminium species created. The maximum amount of these species is controlled by the dislodgement of aluminium from the framework and by the tendency of extra-framework aluminium to agglomerate. A correlation between Lewis acidity, amount of extra-framework aluminium species and yield of phenol depending, on the period of steaming is found. With a dealuminated H-[Al]ZSM-5 zeolite a yield of up to 35% and a selectivity of 99% was achieved using no inert gas.