Atomic-Level Understanding on the Evolution Behavior of Subnanometric Pt and Sn Species during High-Temperature Treatments for Generation of Dense PtSn Clusters in Zeolites

Abstract To achieve high-loading of stable subnanometric metal clusters on solid carriers is a challenge since those small metal clusters have strong tendency to sinter into larger nanoparticles. Development of facile synthesis methodologies to obtain subnanometric metal catalysts with high metal loading and high stability against sintering at high temperature (>500 oC) in reductive atmosphere (such as H2) is critical for the practical applications. In this work, we will present and discuss the generation of high-loading (∼1.4 wt%) subnanometric Pt clusters confined in the sinusoidal channels of MFI zeolite, on the basis of the atomic-level understanding on the evolution of Pt and Sn species during high-temperature oxidation-reduction treatments. It will be shown that the structural evolution of Pt and Sn species is dependent on the post-synthesis treatments. The Pt particles on the external surface can disintegrate into subnanometric Pt species and get stabilized in the zeolite channels during high-temperature calcination in air while Sn species migrate from surface region to internal region during high-temperature reduction treatment at 650 oC. The resultant material containing bimetallic PtSn clusters confined in the 10MR sinusoidal channels of the purely siliceous MFI zeolite show excellent catalytic activity and stability, as demonstrated for dehydrogenation of light alkanes at high reaction temperature.