Carbide-Modified Pd on ZrO2 as Active Phase for CO2-Reforming of Methane—A Model Phase Boundary Approach

• Published in: Catalysts Vol. 10; no. 9; p. 1000
• Main Authors: Norbert Köpfle, Kevin Ploner, Peter Lackner, Thomas Götsch, Christoph Thurner, Emilia Carbonio, Michael Hävecker, Axel Knop-Gericke, Lukas Schlicker, Andrew Doran, Delf Kober, Aleksander Gurlo, Marc Willinger, Simon Penner, Michael Schmid, Bernhard Klötzer
• Format: Journal Article
• Language: English
• Published: MDPI AG 02-09-2020
• Subjects: coking; graphite; in-situ X-ray photoelectron spectroscopy; metal-support interaction; palladium carbide; palladium-zirconium intermetallic phase
• DOI: 10.3390/catal10091000
• EISSN: 2073-4344

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-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 batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.