Unusual Effects of the Reaction Temperature on the Catalytic Activity of Rh/Active-Carbon for Ethylene Hydroformylation

Article abstract of DOI:10.1246/bcsj.66.1273

The apparent activation energies for propionaldehyde and ethane formation from C2H4, CO, and H2 on a Rh/active-carbon catalyst, once used for a reaction at 453 K, were found to be 40 and 76 kJ mol^-1, respectively.These values were much lower than those on a fresh Rh/active-carbon catalyst (120 and 125 kJ mol^-1).Changes in the apparent activation energies were also induced by exposure of a fresh catalyst to CO at temperatures > 433 K.Such catalytic behaviors, however, were not observed on a Rh/silica-gel catalyst.On the fresh Rh/active-carbon catalyst, the amount of adorbed CO was found to be much more than that of adsorbed H2.The temperature-programmed desorption spectrum (TPD) of CO on the catalyst exposed to CO at 353 K after an H2 treatment at 573 K showed a single desorption peak at ca. 470 K; the value for the CO/Rh molar ratio was found to be 2.6.The amount of CO desorbed from the catalyst exposed to CO at 473 K, however, was found to be much less than that on the catalyst exposed to CO at 353 K.Namely, unusual effects of the reaction temperature on the catalytic activities, which were observed on the fresh Rh/active-carbon catalyst, were very closely related to changes in the amount of CO desorbed from the catalyst during TPD runs.