The Hydrogenation of Aniline over Supported Rhodium-Palladium Alloy Catalysts

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Abstract
The hydrogenation of aniline was investigated in the temperature range from 30° to 50°C over Rh-Pd alloy catalysts supported on activated carbon. The reactions were mainly carried out in acetic acid at an atmospheric pressure of hydrogen. The activity per unit weight of the catalysts was measured and plotted for the alloy composition. It showed a maximum at 75–85 wt% Rh. However, the activity per unit of surface area showed a maximum at about 25 wt% Rh, and the minimum activation energy of this reaction was observed at the same composition. The relationship between the selectivity and the alloy composition was also studied. The maximum selectivity to dicyclohexylamine was observed at 20–30% Rh, while the maximum formation of N-phenylcyclohexylamine appeared at 50–60% Rh. However, the selectivity to cyclohexylamine showed a minimum at about 25% Rh. The initial rates of the formation of cyclohexylamine and N-phenylcyclohexylamine were measured and plotted for the catalyst composition. The maximum activity was observed at about 85 wt% Rh for the formation of cyclohexylamine and at 50–60% Rh for the formation of N-phenylcyclohexylamine. Then the ratios of the two simple reaction rates were calculated. At a higher Rh content, (above about 25% Rh), the selectivity increased as the ratio increased. The reaction over the catalysts prepared by different methods and the hydrogenation of aniline in cyclohexane were also investigated.