Abstract
Structural and morphological characterizations of bimetallic Pd-Pt/Al2O3 model catalysts are performed using X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, and CO chemisorption. Further, the catalysts were studied under oxidizing and reducing conditions using both X-ray absorption spectroscopy and low-energy ion scattering spectroscopy. For the as-prepared catalysts, the existence of alloyed bimetallic Pd-Pt particles and of (tetragonal) PdO was found for the samples calcined at 800 °C. PdO is present in the form of crystals at the surface of the Pd-Pt particles or as isolated PdO crystals on the support oxide. Bimetallic Pd-Pt nanoparticles were only formed on the Pd-Pt catalysts after calcination at 800 °C. The results show that the Pd-Pt nanoparticles undergo reversible changes in surface structure composition and chemical state in response to oxidizing or reducing conditions. Under oxidizing conditions Pd segregates to the shell and oxidizes forming PdO, while under reducing conditions regions with metallic Pd and Pd-Pt alloys were observed at the surface. No bimetallic Pd-Pt nanoparticles were observed for the sample initially calcined at 500 °C, but instead isolated monometallic particles, where small Pt particles are easily oxidized under O2 treatment. In the monometallic catalysts, the Pd is found to be completely oxidized already after calcination and to consist of metallic Pd after reductive treatment.
| Original language | English |
|---|---|
| Pages (from-to) | 28009-28020 |
| Number of pages | 12 |
| Journal | Journal of Physical Chemistry C |
| Volume | 120 |
| Issue number | 49 |
| DOIs | |
| Publication status | Published - 1 Jan 2016 |
Funding
Dr. Stefan Gustafsson is thanked for his assistance with the TEM characterization. The authors thank MAX IV Laboratory (Lund, Sweden) and the European Synchrotron Radiation Facility (ESRF) (Grenoble, France) for providing the beamtimes. This work was financially supported by the Swedish Research Council through the Röntgen-Ångström collaborations “Catalysis on the atomic scale” (No. 349-2011-6491) and “Time-resolved in situ methods for design of catalytic sites within sustainable chemistry” (No. 349-2013-567) and the Swedish Energy Agency through the FFI program “Fundamental studies on the influence of water on oxidation catalyst for biogas applications” (No. 40274-1), and partly the Competence Centre for Catalysis, which is financially supported by Chalmers University of Technology, the Swedish Energy Agency and the member companies: AB Volvo, ECAPS AB, Haldor Topsøe A/S, Volvo Car Corporation, Scania CV AB, and War̈ tsilä Finland Oy.