C–H Bond Activation by Pd-substituted CeO2: Substituted Ions versus Reduced Species

• Published in: Chemistry of materials Vol. 23; no. 24; pp. 5432 - 5439
• Main Authors: Misch, Lauren M, Kurzman, Joshua A, Derk, Alan R, Kim, Young-Il, Seshadri, Ram, Metiu, Horia, McFarland, Eric W, Stucky, Galen D
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27.12.2011; American Chemical Society (ACS)
• Subjects: CATALYSIS; CATALYSTS; DIFFRACTION; ETHYLENE; HYDROGENATION; MATERIALS SCIENCE; MORPHOLOGY; OXIDATION; OXIDES; PYROLYSIS; SURFACE AREA; SYNCHROTRONS; ULTRASONIC WAVES; WATER GAS; X-RAY DIFFRACTION; catalyst; nanoparticle; hydrocarbon
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm202709y

Substituted metal oxides containing ionic species have been attracting a great deal of attention because of their potential ability to reduce the usage of precious metals in heterogeneous catalysts. We investigate Pd-substituted CeO2 for C–H bond activation reactions including the partial oxidation and dry reforming of CH4. This catalyst has been previously studied for CO oxidation, NO x reduction, and the water-gas shift reaction. Pd-substituted CeO2, Ce1–x Pd x O2−δ, was prepared as a powder with high surface area and a hollow sphere morphology using ultrasonic spray pyrolysis. The catalysts were extensively characterized using synchrotron X-ray diffraction and other techniques, confirming phase pure samples up to 10 mol % Pd substitution. Ce0.95Pd0.05O2−δ was found to be active for partial oxidation of CH4 around 500 °C and higher. Our studies, including postcatalytic synchrotron diffraction, suggest that the single-phase Ce1–x Pd x O2−δ material is not the active species and that catalysis occurs instead over the reduced two-phase Pd0/CeO2. This observation has been further confirmed by verifying the activity of the reduced Pd0/CeO2 catalysts for ethylene hydrogenation, a reaction that is known to require Pd0.