RhrC catalysts in ethene hydroformylation: the effect of different supports and pretreatments

The activity, selectivity and stability of RhrC catalysts prepared from nitrate precursor on three different active carbon supports was determined in ethene hydroformylation. The different active carbon supports yielded catalysts, which had Ž . Ž . different extents of reduction 62–94% and dispersion 4–27% after hydrogen reduction. The best activity and selectivity Ž . in the formation of propanal was obtained with the coconut shell based RhrC C catalyst, presumably due to the better Ž . metal dispersion and the presence of unreduced Rh sites. Furthermore, without any pretreatment, the RhrC C catalyst exhibited even higher activity and better propanal yields than its hydrogen treated counterpart. Most likely, the active sites remained better dispersed in the absence of pretreatment than after hydrogen reduction, and it was the well-dispersed sites that were active in the formation of propanal. High temperature CO pretreatment partially blocked the catalyst surface with carbonaceous residues, which improved propanal selectivity, but suppressed the overall activity. Thus, the right choice of pretreatment appears to be a key factor in providing an active and selective catalyst for heterogeneous hydroformylation. It should also be noted that the catalysts lost 10–30% of the metal deposited on the support during 24 h on stream. q 1999 Elsevier Science B.V. All rights reserved.