Reconciling Gas- and Liquid-Phase Ethylene Hydroformylation Kinetics on a Heterogeneous Alumina-Supported Rhodium Catalyst

Gas- and liquid-phase kinetic data for heterogeneously catalyzed ethylene hydroformylation to propanal have been assessed using analytical Langmuir–Hinshelwood/Hougen–Watson type of expressions. The more extensive gas-phase dataset was employed to discriminate between three models assuming a different surface reaction as rate-determining step (RDS). The model where CO insertion was considered as RDS exhibited the best agreement with the experimental observations. Composite activation energies amounting to −24 and 14 kJ/mol were obtained. Adsorption enthalpies amounted to −33 kJ/mol for ethylene and −47 kJ/mol for CO. Adequately accounting for the thermodynamics of the presence of a liquid phase in the best-performing model sufficed to reproduce the liquid-phase experimental data, indicating that the developed kinetic model performs well at both gas- and liquid-phase conditions.