Formation of ZnO Patches on ZnPd/ZnO during Methanol Steam Reforming: A Strong Metal-Support Interaction Effect?

The high CO2 selectivity of ZnPd/ZnO, an outstanding catalyst in methanol steam reforming, was recently attributed to the interaction between small ZnO patches and ZnPd particles. Yet, the detailed microstructure of this catalytic system and the formation mechanism of the ZnO patches inducing the high catalytic selectivity are unknown. In this work, we uncover the formation mechanism of ZnO patches using aberration-corrected electron microscopy, electron energy loss spectroscopy, X-ray spectroscopy, and in situ heating experiments. We show that Zn-rich regions in chemically inhomogeneous ZnPd particles, penetrating the particle surface, are capped by ZnO. It is demonstrated that the ZnO patches form by direct oxidation of the particles rather than by transport from the ZnO substrate, thus ruling out a classical strong metal-support interaction (SMSI).