Coking and deactivation of HZSM-5 zeolite catalyst for benzene oxidation to phenol

Coking and deactivation experiments of HZSM-5 zeolite catalyst during benzene oxidation to phenol were carried out in a fixed-bed reactor, and the zeolite was pretreated with steam at high temperature. The reaction conditions were catalyst loading of 1 g, 9.7% N2O-90.3 % N-2 (flow rate 115 ml/min), benzene flow rate of 6 g/h, reaction temperature of 400 degreesC and reaction time of 0similar to6 h. The catalyst was characterized by TG, IR after pyridine adsorption, C-13 NMR and N-2 adsorption techniques. The adsorption amount of hexane and cyclohexane was measured by continuous flow method. The results showed that the deactivation of HZSM-5 was due to the coke formed on the catalyst surface which blocked the pore mouth of zeolite channels. Similar to most coking processes of other organic compounds on ZSM-5 zeolite, Bronsted acid sites were the active sites which promoted coke formation. The coke consisted mainly of aromatic compounds with alkyl and polycyclic aromatic hydrocarbons, and it also comprised some aromatic compounds with hydroxy group produced by further oxidation, dehydrogenation and polymerization of phenol on Lewis acid sites.