Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 85: Heterogeneous Catalysis I

O 85.6: Talk

Thursday, March 21, 2024, 11:45–12:00, TC 006

The relation between substrate, Sm alloy, and surface sensitivity of ceria (111)- and (100)-oriented nano-islands on Ru(0001) and Cu(111). — •Raquel Sanchez-Barquilla, Rudi Tschammer, Lars Buss, Carlos Morales, and Jan Ingo Flege — Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Germany

Inverse oxide/metal catalysis allows achieving better catalytic performance than its traditional counterpart. For example, in cerium-based inverse catalyst systems, the Ce³⁺ states have been shown to be the active sites for methanol synthesis. This suggests that the activity can be enhanced by promoting those through alloying with trivalent, catalytically active rare-earth metals, as, e.g. Sm. We present low-energy and X-ray photoemission electron microscopy (LEEM/XPEEM), investigations that show how epitaxially grown (100)- and (111)-oriented CeO₂ islands may be modified and/or alloyed by post-deposited metallic Sm. For the Ce_1−xSm_xO_2−δ/Ru(0001) system, the CeO₂ (111)-oriented islands undergo a structural change, concomitant with a partial conversion from Ce⁴⁺ to Ce³⁺. Surprisingly, for Ce_1−xSm_xO_2−δ/Cu(111) the result is found to be face-dependent since only (100)-oriented CeO_x islands were reduced whereas the (111)-oriented islands remained unaltered. Both systems have been exposed to reducing (H₂) and oxidizing (CO₂) conditions, resulting in higher reduction and in a complete recovery of the Ce⁴⁺ states, respectively. These unexpected results indicate a complex interaction not only between cerium and the doping element, but also an intricate interplay with the metallic substrate.

Keywords: Ceria; Samaria; LEEM; Structure sensitivity