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N. Köpfle, K. Ploner, P. Lackner, T. Götsch, C. Thurner, E. Carbonio, M. Hävecker, A. Knop-Gericke, L. Schlicker, A. Doran, D. Kober, A. Gurlo, M. Willinger, S. Penner, M. Schmid, B. Klötzer:
"Carbide-modified Pd on ZrO₂ as active phase for CO₂-reforming of methane - A model phase boundary approach";
Catalysts, 10 (2020), 100001 - 100029.

Starting from subsurface Zr0-doped "inverse" Pd and bulk-intermetallic Pd0Zr0modelcatalyst precursors, we investigated the dry reforming reaction of methane (DRM) usingsynchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS),in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batchreactor cell. Both intermetallic precursors develop a Pd0-ZrO2phase boundary under realistic DRMconditions, whereby the oxidative segregation of ZrO2from bulk intermetallic PdxZryleads to a highlyactive composite layer of carbide-modified Pd0metal nanoparticles in contact with tetragonal ZrO2.This active state exhibits reaction rates exceeding those of a conventional supported Pd-ZrO2referencecatalyst and its high activity is unambiguously linked to the fast conversion of the highly reactivecarbidic/dissolved C-species inside Pd0toward CO at the Pd/ZrO2phase boundary, which serves therole of providing efficient CO2activation sites. In contrast, the near-surface intermetallic precursordecomposes toward ZrO2islands at the surface of a quasi-infinite Pd0metal bulk. Strongly delayedPd carbide accumulation and thus carbon resegregation under reaction conditions leads to a muchless active interfacial ZrO2-Pd0state.

palladium carbide; graphite; metal-support interaction; coking; palladium-zirconiumintermetallic phase; in-situ X-ray photoelectron spectroscopy; in-situ X-ray diffraction; high resolutionelectron microscopy; dry reforming of methane; carbon dioxide activ

http://dx.doi.org/10.3390/catal10091000