Surface Hexagonal Pt1Sn1 Intermetallic on Pt Nanoparticles for Selective Propane Dehydrogenation.

A series of 2-3 nm Pt-Sn bimetallic nanoparticles with different Pt-Sn coordination numbers were synthesized by a stepwise approach including electrostatic adsorption and temperature-programmed reduction of metal precursors on the SiO2 support. In situ synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) demonstrated a highly ordered hexagonal Pt1Sn1 intermetallic shell on Pt nanoparticles. The turnover rates (TORs), propylene selectivity, and stability of these bimetallic catalysts significantly surpass those of the monometallic Pt catalyst for propane dehydrogenation. At the same time, TORs increase with increasing the Pt-Sn coordination number, whereas propylene selectivity is not significantly influenced by the Pt-Sn coordination number. Combined with experiments and theoretical calculations, the high propylene selectivity of Pt-Sn bimetallic nanoparticles is attributed to the geometric effects of Sn that reduce the Pt ensembles, and the high TORs are due to the electronic effects that weaken Pt-hydrocarbon chemisorption energies.