Active Phase in the Direct Synthesis of H₂O₂ from H₂ and O₂ over Pd/SiO₂ Catalyst in a H₂SO₄/Ethanol System

• Published in: Catalysis letters Vol. 132; no. 3-4; pp. 342 - 348
• Main Authors: Liu, Qingsheng, Gath, Kerrie K, Bauer, J. Chris, Schaak, Raymond E, Lunsford, Jack H
• Format: Journal Article
• Language: English
• Published: Boston Boston : Springer US 2009; Springer US; Springer; Springer Nature B.V
• Subjects: Catalysis; Catalysts; Chemistry; Chemistry and Materials Science; Chloride ions; Ethanol; Exact sciences and technology; General and physical chemistry; Hydrogen peroxide; Industrial Chemistry/Chemical Engineering; Organometallic Chemistry; Palladium; Physical Chemistry; Silicon dioxide; Slurries; Sulfuric acid; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; X ray photoelectron spectroscopy; PdO/silica; Hydrogen peroxide formation; Palladium/silica; Binary compound; Hydrogen peroxide; Support; Alcohol; X ray; Silica; Particle; Synthesis; Chlorides; Alkanol; Photoelectron spectrometry; Platinoid; Catalytic reaction; Ethanol; Ions; Transition metal; Palladium; X ray diffraction; Heterogeneous catalysis; Transmission electron microscopy; Silicon oxides; Catalyst
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-009-0104-y

In an effort to determine the active state of supported palladium for the direct formation of H₂O₂ from H₂ and O₂, the catalytic behavior of Pd⁰/SiO₂, PdO/SiO₂ and partially reduced PdO/SiO₂ was determined. The results obtained in an ethanol slurry, with chloride ions and H₂SO₄ being present, showed that the PdO/SiO₂ catalyst was almost completely inactive for the formation of H₂O₂ at 10 °C. The Pd⁰/SiO₂ catalyst exhibited the highest activity for H₂O₂ formation, and the PdO/SiO₂ material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd⁰ (the metal phase) and PdO were observed on Pd⁰/SiO₂ and PdO/SiO₂, respectively. As expected, with the partially reduced PdO/SiO₂ catalyst, both Pd⁰ and PdO phases were evident. The TEM results revealed that the Pd⁰ particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H₂O₂.