Sn surface-enriched Pt-Sn bimetallic nanoparticles as a selective and stable catalyst for propane dehydrogenation

Abstract

A new one pot, surfactant-free, synthetic route based on the surface organometallic chemistry (SOMC) concept has been developed for the synthesis of Sn surface-enriched Pt–Sn nanoparticles. Bu3SnH selectively reacts with [Pt]–H formed in situ at the surface of Pt nanoparticles, Pt NPs, obtained by reduction of K2PtCl4 by LiB(C2H5)3H. Chemical analysis, 1H MAS and 13C CP/MAS solid-state NMR as well as two-dimensional double-quantum (DQ) and triple-quantum (TQ) experiments show that organo-tin moieties Sn(n-C4H9) are chemically linked to the surface of Pt NPs to produce, in fine, after removal of most of the n-butyl fragment, bimetallic Pt–Sn nanoparticles. The triple bondSn(n-CH2CH2CH2CH3) groups remaining at the surface are believed to stabilize the as-synthesized Pt–Sn NPs, enabling the bimetallic NPs to be well dispersed in THF. Additionally, the Pt–Sn nanoparticles can be supported on MgAl2O4 during the synthesis of the nanoparticles. Some of the Pt–Sn/MgAl2O4 catalyst thus prepared exhibits high activity in PROX of CO and an extremely high selectivity and stability in propane dehydrogenation to propylene. The enhanced activity in propane dehydrogenation is associated with the high concentration of inactive Sn at the surface of Pt nanoparticles which “isolates” the active Pt atoms. This conclusion is confirmed by XRD, NMR, TEM, and XPS analysis.