In situ NAP-XPS spectroscopy during methane dry reforming on ZrO₂/Pt(1 1 1) inverse model catalyst

Due to the need of sustainable energy sources, methane dry reforming is a useful reaction for conversion of the greenhouse gases CH₄ and CO₂ to synthesis gas (CO  +  H₂). Syngas is the basis for a wide range of commodity chemicals and can be utilized for fuel production via Fischer-Tropsch synthesis. The current study focuses on spectroscopic investigations of the surface and reaction properties of a ZrO₂/Pt inverse model catalyst, i.e. ZrO₂ particles (islands) grown on a Pt(1 1 1) single crystal, with emphasis on in situ near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) during MDR reaction. In comparison to technological systems, model catalysts facilitate characterization of the surface (oxidation) state, surface adsorbates, and the role of the metal-support interface. Using XPS and infrared reflection absorption spectroscopy we demonstrated that under reducing conditions (UHV or CH₄) the ZrO₂ particles transformed to an ultrathin ZrO₂ film that started to cover (wet) the Pt surface in an SMSI-like fashion, paralleled by a decrease in surface/interface oxygen. In contrast, (more oxidizing) dry reforming conditions with a 1:1 ratio of CH₄ and CO₂ were stabilizing the ZrO₂ particles on the model catalyst surface (or were even reversing the strong metal support interaction (SMSI) effect), as revealed by in situ XPS. Carbon deposits resulting from CH₄ dissociation were easily removed by CO₂ or by switching to dry reforming conditions (673-873 K). Thus, at these temperatures the active Pt surface remained free of carbon deposits, also preserving the ZrO₂/Pt interface.