High-Temperature Catalytic Reforming of <i>n</i>‑Hexane over Supported and Core–Shell Pt Nanoparticle Catalysts: Role of Oxide–Metal Interface and Thermal Stability

Designing catalysts with high thermal stability and resistance to deactivation while simultaneously maintaining their catalytic activity and selectivity is of key importance in high-temperature reforming reactions. We prepared Pt nanoparticle catalysts supported on either mesoporous SiO₂ or TiO₂. Sandwich-type Pt core@shell catalysts (SiO₂@Pt@SiO₂ and SiO₂@Pt@TiO₂) were also synthesized from Pt nanoparticles deposited on SiO₂ spheres, which were encapsulated by either mesoporous SiO₂ or TiO₂ shells. <i>n</i>-Hexane reforming was carried out over these four catalysts at 240–500 °C with a hexane/H₂ ratio of 1:5 to investigate thermal stability and the role of the support. For the production of high-octane gasoline, branched C₆ isomers are more highly desired than other cyclic, aromatic, and cracking products. Over Pt/TiO₂ catalyst, production of 2-methylpentane and 3-methylpentane via isomerization was increased selectively up to 420 °C by charge transfer at Pt–TiO₂ interfaces, as compared to Pt/SiO₂. When thermal stability was compared between supported catalysts and sandwich-type core@shell catalysts, the Pt/SiO₂ catalyst suffered sintering above 400 °C, whereas the SiO₂@Pt@SiO₂ catalyst preserved the Pt nanoparticle size and shape up to 500 °C. The SiO₂@Pt@TiO₂ catalyst led to Pt nanoparticle sintering due to incomplete protection of the TiO₂ shells during the reaction at 500 °C. Interestingly, over the Pt/TiO₂ catalyst, the average size of Pt nanoparticles was maintained even after 500 °C without sintering. In situ ambient pressure X-ray photoelectron spectroscopy demonstrated that the Pt/TiO₂ catalyst did not exhibit TiO₂ overgrowth on the Pt surface or deactivation by Pt sintering up to 600 °C. The extraordinarily high stability of the Pt/TiO₂ catalyst promoted high reaction rates (2.0 μmol·g^–1·s^–1), which was 8 times greater than other catalysts and high isomer selectivity (53.0% of C₆ isomers at 440 °C). By the strong metal–support interaction, the Pt/TiO₂ was turned out as the best catalyst with great thermal stability as well as high reaction rate and product selectivity in high-temperature reforming reaction