Size- and support-dependent selective amine cross-coupling with platinum nanocluster catalysts

gamma-Alumina-supported Pt nanoclusters with an average particle size of 0.8 nm, Pt/Al2O3-0.8, act as an effective heterogeneous catalyst for mono-N-alkylation of amines with different amines. To establish a catalyst design concept, systematic studies on the structure-activity relationship are carried out, combined with characterization by Pt L-3-edge XAFS (X-ray absorption fine structure), X-ray photoelectron spectroscopy (XPS), and infrared (IR) study of CO adsorption. By changing the particle size of Pt over the size range of 0.8-24 nm, it is demonstrated that the present reaction is a structure-sensitive reaction, demanding coordinatively unsaturated Pt atoms on metallic nanoclusters. The support also affects the activity and electronic state of Pt. The electron density of Pt increases with basicity of the support oxide, and the support with moderate basicity (Al2O3) gives the highest activity probably due to a moderate electron density of Pt. Kinetic studies suggest that the present reaction proceeds through a hydrogen-borrowing mechanism.