| AVS 65th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Thursday Sessions |
| Session HC+SS-ThA |
| Session: | Bridging Gaps in Heterogeneously Catalyzed Reactions |
| Presenter: | Johan Gustafson, Lund University, Sweden |
| Authors: | J. Gustafson, Lund University, Sweden O. Balmes, MAX IV Laboratory, Sweden C. Zhang, Lund University, Sweden M. Shipilin, Stockholm University, Sweden A. Schaefer, Chalmers University of Technology, Gothenburg, Sweden B. Hagman, Lund University, Sweden L. Merte, Chalmers University of Technology, Gothenburg, Sweden N.M. Martin, Chalmers University of Technology, Gothenburg, Sweden P-A. Carlsson, Chalmers University of Technology, Gothenburg, Sweden M. Jankowski, ESRF, France E.J. Crumlin, Advanced Light Source, Lawrence Berkeley National Laboratory E. Lundgren, Lund University, Sweden |
| Correspondent: | Click to Email |
Catalytic CO oxidation is a seemingly simple reaction between CO and O2 molecules, one of the reactions in automotive catalytic converters, and the fruit-fly reaction in model catalysis. Surprisingly, the phase responsible for the catalytic activity is still under debate, despite decades of investigations. We have performed a simple but yet conclusive study of single crystal Rh and Pd model catalysts, resolving this controversy. For Rh, the oxygen covered metallic surface is more active than the oxide, while for Pd, thin oxide films are at least as active as the metallic surface, but a thicker oxide is less active [1]. The difference between these oxide structures is that the thin PdO films expose coordinatively unsaturated (CUS) metal atoms that act as active sites, while Rh oxides and thicker PdO films do not expose such sites and are hence less active. Similar results have also been found for methane oxidation over Pd [2].
Under highly oxidizing conditions, which are, for instance, desirable for optimal efficiency of combustion engines, there is a general problem of deactivation of catalysts due to too high oxygen exposure, so-called oxygen poisoning. With the above results in mind, this problem is likely related to the formation of oxides that do not expose CUS sites. We therefore believe that the problem of oxygen poisoning over Pd catalysts can be solved by growing a PdO film on top of a more inert metal such as Ag or Au, as this will limit the thickness of the oxide film and hence stabilize the active oxide surface.
In this presentation, we will discuss the active phase of Pd and Rh for CO oxidation, and hopefully show the first results of lower degree of oxygen poisoning for CO and methane oxidation over Pd/Au and Pd/Ag systems.
References
1. J. Gustafson et al., The Role of Oxides in Catalytic CO Oxidation over Rhodium and Palladium, ACS Catal., 2018, 8, 4438–4445.
2. A. Hellman et al., The active phase of palladiumduring methane oxidation, J. Phys. Chem. Lett. 2012, 3, 678–682.