Influence of the ZrO₂ Crystalline Phases on the Nature of Active Sites in PdCu/ZrO₂ Catalysts for the Methanol Steam Reforming Reaction—An In Situ Spectroscopic Study

Abstract

In this work, the electronic properties of the metal sites in cubic and monoclinic ZrO2 supported Pd and PdCu catalysts have been investigated using CO as probe molecule in in-situ IR studies, and the surface composition of the outermost layers has been studied by APXPS (Ambient Pressure X-ray Photoemission Spectroscopy). The reaction products were followed by mass spectrometry, making it possible to relate the chemical properties of the catalysts under reaction conditions with their selectivity. Combining these techniques, it has been shown that the structure of the support (monoclinic or cubic ZrO2) affects the metal dispersion, mobility, and reorganization of metal sites under methanol steam reforming (MSR) conditions, influencing the oxidation state of surface metal species, with important consequences in the catalytic activity. Correlating the mass spectra of the reaction products with these spectroscopic studies, it was possible to conclude that electropositive metal species play an imperative role for high CO2 and H2 selectivity in the MSR reaction (less CO formation).

Keywords

• APXPS
• Near Ambient Pressure-X-ray Photoelectron Spectroscopy
• X-ray spectroscopy
• in situ characterization
• copper
• palladium