Regensburg 2007 – scientific programme
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O: Fachverband Oberflächenphysik
O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)
O 44.76: Poster
Wednesday, March 28, 2007, 17:00–19:30, Poster C
Thermal and Redox Stability of PdZn Catalysts in Vacuum and During Methanol Adsorption Studied by In-Situ XPS — •Karifala Dumbuya, Reinhard Denecke, and Hans-Peter Steinrück — Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen
We have investigated the thermal and redox behaviour of the technically important methanol steam reforming PdZn catalysts between 300-700 K in UHV and during MeOH dosage at 300 K for pressures up to 0.1 mbar. We compare samples from a washcoating process1 before and after the reduction to PdZn. In both cases, we observed significant structural changes upon heating in the Zn 2p, Pd 3d and O 1s regions, respectively, in agreement with studies on Pd(111)2. However, annealing both samples to 700 K led to a significant drop in intensity of the Zn 2p signals, indicating alloy destruction in UHV, accompanied by the emergence of large Mg peaks, which are further enhanced by H2 exposure of the surfaces at this temperature.
The resulting surface was exposed to MeOH background pressures (1.2*10−6-0.1 mbar) at 300 K and C 1s, O 1s, Pd 3d and Zn 2p spectra were collected. A comparison with similar results on fully intact catalysts3 show slightly different adsorption behaviour of MeOH. This is relevant, because Mg is known to affect the oxidative methanol steam reforming on Pd/ZnO catalysts.
[1] Pfeifer et al., Appl. Cat. A: 270 (2004) 165. [2] Bayer et al., Surf. Sci. 600 (2006) 78. [3] Pantförder, PhD thesis, Universität Erlangen-Nürnberg, 2004.