Synthesis of Birdcage-type zeolite encapsulating ultrafine Pt nanoparticles and its application in dry reforming of methane

Abstract

Dry reforming of methane (DRM) is a useful reaction because it can produce syngas with a low H2/CO molar ratio, which is suitable for the production of hydrocarbons and alcohols. However, deactivation of the catalysts typically occurs because of the severe reaction conditions employed. Hence, the development of effective catalysts having high thermal stability for DRM has been extensively investigated. To achieve high activity and thermal stability of the catalysts, this study focused on the preparation of a noble zeolite-supported metal structure (Birdcage structure) that encapsulates metal nanoparticles (NPs) inside the zeolite. A Birdcage-type zeolite catalyst encapsulating Pt NPs (Pt@Silicalite-1) was successfully synthesized by combining the techniques for the preparation of amorphous-silica-coated metal NPs and nanocrystalline zeolite using a water-in-oil microemulsion was prepared. By X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses, it was confirmed that the prepared Pt@Silicalite-1 possessed MFI-type zeolite structures encapsulating Pt NPs with diameters smaller than 2 nm. This catalyst exhibited higher and more stable activity for DRM at 620 °C over 24 h as compared to the Pt-loaded zeolite catalyst prepared using an impregnation method, mainly because sintering of the Pt NPs were strongly suppressed by the Birdcage structure. Moreover, the Birdcage-type zeolite exhibited high catalytic activity and thermal stability at temperatures lower than 620 °C until the Birdcage structure was maintained, which immobilized the metal NPs inside the zeolite.