Hydrothermally Stable Zeolite-Encapsulated Metal Catalyst Promoted by Framework Sn Species

Abstract

Hydrothermal stability is a vital performance criterion considered in the design of heterogeneous metal catalysts for practical applications because of the widespread presence of moisture in the reaction feeds or the products. In this work, we substantially promote the hydrothermal stability of the Pt-zeolite catalyst by incorporating Sn into the zeolite framework. Pt species are stabilized as small nanoparticles, and the MFI zeolite structure is well preserved even after hydrothermal treatment at 850 °C in a mixed atmosphere (CO + O₂ + H₂O). Adding Sn into Pt-MFI not only heals the defect sites in pure-silica MFI zeolite to promote its structural stability during hydrothermal treatment but also stabilizes the mobile PtO_x species via the Sn–O–Pt interaction. The remarkably high stability of the Pt particles encapsulated in the Sn-promoted MFI zeolite is reflected in the CO oxidation reaction in which Pt particles stabilized in the Sn-promoted MFI zeolite exhibit much higher stability than the nonpromoted Pt-MFI catalyst. The stabilization effect of Sn is further extended to a Pd-MFI zeolite catalyst in which the average size of the Pd particles remains below 2 nm after the harsh hydrothermal treatments at 850 °C.