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

• Published in: Nano letters Vol. 14; no. 8; pp. 4907 - 4912
• Main Authors: An, Kwangjin, Zhang, Qiao, Alayoglu, Selim, Musselwhite, Nathan, Shin, Jae-Youn, Somorjai, Gabor A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13.08.2014
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Optoelectronic devices; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Thermal properties of condensed matter; Thermal properties of small particles, nanocrystals, nanotubes; selectivity; thermal stability; Pt; reforming; n-hexane; core@shell; Encapsulation; Strong interactions; Core shell structure; Porous materials; Reaction product; Cracking; Mechanical properties; Light emitting diodes; Selectivity; Isomers; Sandwich structures; Supported catalyst; Mesoporosity; Thermal stability; Interfaces; Nanoparticles; Thermal properties; Thermal resistance; Sintering; Catalyst supports; Charge transfer; Catalyst activity; Nanostructured materials; X-ray photoelectron spectra
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl502434m

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. n-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.