Catalytic CO Oxidation and H₂O₂ Direct Synthesis over Pd and Pt-Impregnated Titania Nanotubes

• Main Authors: Lucas Warmuth, Gülperi Nails, Maria Casapu, Sheng Wang, Silke Behrens, Jan-Dierk Grunwaldt, Claus Feldmann
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Catalysts
• Subjects: titania; nanotubes; catalysis; CO oxidation; H₂O₂ direct synthesis
• Online Access: https://www.mdpi.com/2073-4344/11/8/949

Titania nanotubes (TNTs) impregnated with Pd and Pt nanoparticles are evaluated as heterogeneous catalysts in different conditions in two reactions: catalytic CO oxidation (gas phase, up to 500 °C) and H₂O₂ direct synthesis (liquid phase, 30 °C). The TNTs are obtained via oxidation of titanium metal and the intermediate layer-type sodium titanate Na₂Ti₃O₇. Thereafter, the titanate layers are exfoliated and show self-rolling to TNTs, which, finally, are impregnated with Pd or Pt nanoparticles at room temperature by using Pd(ac)₂ and Pt(ac)₂. The resulting crystalline Pd/TNTs and Pt/TNTs are realized with different lengths (long TNTs: 2.0–2.5 µm, short TNTs: 0.23–0.27 µm) and a specific surface area up to 390 m²/g. The deposited Pd and Pt particles are 2–5 nm in diameter. The TNT-derived catalysts show good thermal (up to 500 °C) and chemical stability (in liquid-phase and gas-phase reactions). The catalytic evaluation results in a low CO oxidation light-out temperature of 150 °C for Pt/TNTs (1 wt-%) and promising H₂O₂ generation with a productivity of 3240 mol_H2O2 kg_Pd⁻¹ h⁻¹ (Pd/TNTs, 5 wt-%, 30 °C). Despite their smaller surface area, long TNTs outperform short TNTs with regard to both CO oxidation and H₂O₂ formation.