Use of isotopic transient methods for mechanistic analysis of ethylene hydroformylation over 4 wt% Rh/SiO2 catalyst

Abstract The transient responses of deuterated ethylene, ethane, and propionaldehyde to a deuterium pulse during ethylene hydroformylation have been studied on 4 wt% Rh/SiO 2 at 0.1 MPa and 483 to 573 K. This study shows the complexity of the deuterated product formation from the deuterium pulse. The deuterated ethylene/ethane responses overlapped at all temperatures, indicating that rapid H/D exchange and alkyl hydrogenation take place on the catalyst surface consistent with the Horiuti-Polanyi mechanism. The d 1 - and d 2 -propionaldehyde responses exhibited a two-hump response to the D 2 pulse, indicating two distinguishable deuteration pathways contributing to their formation. Activation energy for the production of deuterated propionaldehyde was found to be directly proportional to the number of deuterium atoms in the final product. This isotope effect supports a previous study which suggests acyl hydrogenation to be the rate-limiting step.