Abstract

Biomass-based amines have received a lot of attention due to their sustainability and carbon economy. Herein, the roles of the metal sites (Rh0 or Pd0) and operating conditions on the kinetics and reaction pathways of the heterogeneous catalytic amination of cyclohexanone with aniline have been discussed. Rh/C provides secondary amines with remarkable selectivity toward the hydrogenation product (ΣSi=72 %). The hydrogenation rate over Rh0 is 1.5-fold higher than that observed over Pd0, while its dehydrogenation capacity diminished (rD_Rh ¡=0.74 h−1 and rD_Pd=1.32 h−1). This difference in the hydrogenation/dehydrogenation performance allows control over the selectivity via disproportionation of an imine intermediate. The kinetic observations can be represented using the Langmuir-Hinshelwood model, indicating that the formation of the aminal intermediate is the rate-limiting step. The apparent activation energy for this step on Rh/C (55 kJ/mol) was higher than that previously reported for Pd/C (48 kJ/mol).