THE EFFECT OF PROMOTERS ON THE CATALYTIC ACTIVITY OF GAMMA-AL2O3 FOR DEAMINATION OF ANILINE TO DIPHENYLAMINE (DPA)

Catalytic deamination of aniline to diphenylamine has been studied on gamma-Al2O3 + H3BO3, gamma-Al2O3 + H3BO3 + HCl and gamma-Al2O3 + H3BO3 + AlF3 catalysts in a tubular reactor at fixed set of reaction condit ions. It is observed that the catalyst containing AlF3 as promoter exh ibits the highest activity for the reaction and the activity decreases in the order, gamma-Al2O3 + H3BO3 + AlF3 > gamma-Al2O3 + H3BO3 + HCl > gamma-Al2O3 + H3BO3. The wt.% DPA in product versus time on stream p lots are found to contain three well defined deactivation steps. Times taken by the catalysts for the deactivation down to 20 wt.% DPA in pr oduct level are also found to depend on the initial activities of the catalysts and decrease in the same order as the activities of the cata lysts; the three deactivation steps fully appearing in these periods. The three deactivation steps are attributed to structure sensitivity o f adsorption and deamination of aniline molecules and to coke depositi on on the three Miller index planes of gamma-Al2O3, (440), (400) and ( 311). The action of promoters in enhancing the deamination activity of gamma-Al2O3 is explained by considering the electronegativities of th e promoter elements, B, Cl and F.