Activity and selectivity of supported Rh catalysts for oxidative carbonylation of aniline

Abstract

Oxidative carbonylation of aniline to ethyl phenyl carbamate (EPC) over supported Rh catalysts has been studied. The effect of catalyst preparation methods, supports, metal content, reusability, solvents, promoters, co-catalysts, and pretreatment on the activity and selectivity of the Rh/C catalyst has been investigated. Selectivity of EPC based on both aniline and CO has been discussed. Above 373 K, CO₂ formation was found to be significant, leading to lower selectivity based on CO. Below 393 K, the major product formed was N,N'-diphenylurea (DPU), but with increased temperature the selectivity of EPC based on aniline increased. The intrinsic kinetics of the reaction has been investigated at 443 K. The rate was found to be first order with respect to aniline, CO, and catalyst. With respect to oxygen, the rate showed linear dependence below 0.75 MPa, but was zero order at higher pressures. A rate equation has been proposed. Characterization of the Rh/C catalyst, before and after the reaction, was done by ESCA, XRD, and TEM. It was observed that the oxidation state of rhodium metal was 0 in both the fresh and the used catalysts. Redispersion of rhodium metal on the support was indicated in the used catalyst by XRD and TEM analysis.