Deactivation by coking and regeneration of zeolite catalysts for benzene-to-phenol oxidation

The object of the study was to determine the effect of coke, formed in the nitrous oxide oxidation of benzene-to-phenol (BTOP), on the catalytic and texture properties of ZSM-5. The study was conducted on three series of catalyst samples. The samples of the first series were withdrawn from the benzene oxidation reactor after different amount of time-on-stream. The samples of the second series were obtained by partial regeneration of coked zeolite with O-2. Finally, the samples of the third series were similar to the second series, except in this case they were partially regenerated with N2O. Catalytic activity and concentration of active sites on the samples of the first series linearly decreased with the increase of coke content. Catalytic activity of partially regenerated samples was not directly proportional to the coke amount on a sample. In the case of catalyst regeneration with nitrous oxide, a complete restoration of catalytic activity required the removal of only 30-35% coke. In the case of regeneration in oxygen, catalytic activity was fully restored after removal 60-65% of the total coke amount. Despite these differences, the dependence of catalytic activity on active site concentration appeared to be the same for all samples of the three series; catalytic activity was directly proportional to the concentration of active sites. This indicates that the activity of a single site is constant regardless of coke content and the method of coked sample preparation. The deactivating effect of coke is caused by poisoning of these sites. (C) 2002 Elsevier Science BN. All rights reserved.