Boosting the Activity in Supported Ionic Liquid-Phase-Catalyzed Hydroformylation via Surface Functionalization of the Carbon Support

Supported ionic liquid phase (SILP) catalysts are comprised of a thin ionic liquid film containing a homogeneous transition metal complex that is supported on a highly porous substrate. The application of functionalized activated carbon as a support material for SILP catalysts in a continuous gas-phase propene hydroformylation reaction reveals that the surface properties of the carbon support have a significant influence on the catalytic performance. The catalytic activity of the pristine activated carbon-based SILP catalysts was found to be negligibly small (TOF4h = 3.5 h(-1)) in contrast to that of common oxidic supports such as silica (TOF4h = 15 h(-1)) or alumina. By amine functionalization of the carbon support surface, a dramatic increase in catalytic activity could be observed outperforming the tested oxidic supports by an order of magnitude. A distinct relationship between increased nitrogen content and the point of zero charge of the support and the catalytic activity could be observed. The largest activity increase (TOF4h = 105 h(-1)) was found for functionalized activated carbon SILP catalysts featuring a high point of zero charge and a high nitrogen content. Despite the fact that aldol formation is catalyzed by a base, the respective alcohol was the only detectable byproduct in the reactions.