Sulfur promoted Pt/SiO ₂ catalyzed cross-coupling of anilines and amines

Pt/SiO ₂ (Pt = 5 wt%) catalysts with average Pt particle size of 3.3 and 6.8 nm and sulfur-loaded Pt/SiO ₂ (S/Pt ratio = 0.1 and 0.13; Pt size = 5.2 and 5.5 nm), prepared by adding ammonium sulfate on Pt/SiO ₂ followed by H ₂-reduction at 500 °C, are tested for mono-N-alkylation of aniline with di-iso-propylamine. The turnover frequency (TOF), defined as the reaction rate per number of surface Pt species, increases with sulfur loading. The catalyst with S/Pt ratio of 0.13 shows more than 5 times higher TOF than unmodified catalysts, and it acts as effective and recyclable catalyst for cross-coupling of various anilines and amines. Combined with kinetic results and characterizations, XAFS (X-ray absorption fine structure), TEM, and CO adsorption IR, a possible reason for the promotion effect of sulfur species (probably sulfidic species) is discussed.