Improved Stability and Catalytic Activity of Palladium Nanoparticle Catalysts using Phosphine-Functionalized Imidazolium Ionic Liquids

Palladium nanoparticles (Pd NPs) stabilized by 6 different phosphine-functionalized ionic liquids (PFILs) were synthesized in imidazolium-based ionic liquids (ILs) using H-2(g) (4 bar) as a reductant. Characterization showed well-dispersed particles of similar to 3 nm (TEM) and confirmed the PFIL stabilization of the NPs (XPS). The PFILs were composed of an imidazolium functionality separated from the phosphine group by a propyl or undecyl chain. The counter anions for both FILs and IL solvents were chosen from N-bis(trifluoromethanesulfonyl) imide (Tf2N-), trifluoromethanesulfonate (TfO-) or hexafluorophosphate (PF6-). Colloidal suspensions of the Pd NPs were employed as biphasic hydrogenation catalysts for the reduction of the olefinic bond in styrene under mild conditions (50 degrees C, 4 bar H-2(g), 1.5 h). The PFIL-stabilized Pd NPs were effective hydrogenation catalysts and showed superior activity and recyclability over NPs synthesized in the absence of PFILs. Poisoning tests of the Pd NP catalysts and characterization of the electronic properties of the phosphine were also performed.