Abstract

Biomass-based amines have received a lot of attention due to their sustainability and carbon economy. Herein, the roles of the metal sites (Rh-0 or Pd-0) 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 (sigma S-i=72 %). The hydrogenation rate over Rh-0 is 1.5-fold higher than that observed over Pd-0, while its dehydrogenation capacity diminished (r(D_Rh )=0.74 h(-1) and r(D_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).