Functionalization of Platinum Nanoparticles with l-Proline: Simultaneous Enhancements of Catalytic Activity and Selectivity

Abstract

In this work we present the successful application of functionalizing Pt nanoparticles (NPs) with hydrophilic organic ligands as a strategy for enhancing their catalytic activity and selectivity. In the first step, Pt NPs were prepared by a colloidal approach and subsequently functionalized in a separate synthesis step with L-proline (PRO). The functionalized NPs were supported onto Al2O3 and investigated as heterogeneous catalysts for the selective hydrogenation of acetophenone. Whereas significant amounts of side products are formed by supported, "unprotected" (ligand-free) NPs, the PRO-functionalized Pt NPs are highly chemoselective even at 100% conversion. Experiments under kinetically controlled conditions reveal that this high chemoselectivity is not accompanied by a loss of catalytic activity. In contrast, an enhanced rate toward the desired product was found for PRO-Pt in comparison to the "unprotected" Pt NPs. This finding demonstrates that the use of ligands in heterogeneous catalysis allows for simultaneous enhancements of activity and selectivity.

Functionalization of small platinum nanoparticles with amines and phosphines: Ligand binding modes and particle stability

“…All samples show good selectivities (defined as the concentration of hexene with respect to the concentration of all reaction products), which ranges from 75 to over [11,[17][18][19][20]44]. However, an acceleration of the reaction by amine ligands, as it has been previously reported for supported platinum nanoparticles protected by L-proline in the hydrogenation of acetophenone [45], is not observed. While particles stabilized by amines or the phosphine react equally fast, protection by thiols lead to a strong decrease in the reaction rate.…”

“…For such cases and for the nanoparticle protection by amines others than quaternary ones, it seems that a binding mode is generally accepted, in which the amine binds via the lone-pair of the nitrogen atom to the particles [23,45,49]. This is in analogy to complex chemistry and other metal nanoparticles, such as gold [51,52].…”

Controllable Catalysis with Nanoparticles: Bimetallic Alloy Systems and Surface Adsorbates

“…Very recently, Kunz and coworkers demonstrated that both the catalytic activity and selectivity were improved simultaneously using the hydrophilic chiral ligand L-proline. 102 The resulting platinum catalyst was highly chemoselective toward the desirable aromatic alcohol with modest stereoselectivity (14% ee) in the hydrogenation reaction of acetophenone ( Figure 13). Heterogeneous asymmetric catalysts with bimetallic NPs have also been successfully developed in recent years.…”

Order and Melting in Self-Assembled Alkanol Monolayers on Amorphous SiO2

“…[9][10][11] However, even for the much simpler spontaneous self-assembly, which has been intensively studied, the underlying basic science is still not fully understood. 12,13 The SAM studied here, is the earliest 1 , and simplest example of an organic SAM.…”