Abstract
Subnanometric clusters (single atoms and ultrasmall clusters) encapsulated inside the pores or cages of zeolite crystals can remarkably enhance their stability and then broaden the catalytic applications. We herein utilized the framework-Sn in Beta zeolite to anchor the guest platinum precursors in the impregnation process, forming Sn-Beta-confined Pt subnanometric clusters (Pt@Sn-Beta) in the following direct reduction. The solid proof for the anchoring effect by forming monodispersed precursor of (Si-O)3(H2O)2Sn(IV)-(O)-[PtCl5]− and final active site of (Si-O)2Sn(II)-(O)-Ptn(n=1~15) was firstly provided in the present study by 119Sn NMR, XAFS and in-situ XPS spectra. The restrictions given by zeolite pores and electronic effect of Sn inhibited the coke formation and sintering of ultrafine Pt clusters, thereby achieving an excellent stability in propane dehydrogenation by maintaining 90% of the maximum propane conversion over 250 h at 99% propene selectivity. This finding has profound significance for understanding the mechanism of heteroatom-containing zeolites as a novel support for highly dispersed metal catalysts.
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