In situ atomic-scale studies of thermal stability and surface reconstruction of ZnO nanowires based Pd nanocatalysts

Abstract

As innovative nanostructured catalysts, palladium nanoparticles supported on carbon-coated zinc oxide nanowires (PdNPs/C&ZnO-NWs) are widely applied in industrial thermal catalysis, and therefore the real-time insights into their thermal stability and microstructural reconstruction at thermal reaction conditions will greatly extend our knowledge of their physicochemical properties and provide valuable guidance for the applications and designs of future nanocatalysts. The in-situ transmission electron microscopy (TEM) studies revealed the high-temperature resistance to PdNPs aggregations with aids of carbon-coated low-dimensional nanostructures C&ZnO-NWs and elucidated ripening dynamics of PdNPs and the surface reconstruction of C&ZnO-NWs. The operando analysis of PdNPs/C&ZnO-NWs was executed in real-time under working-temperature situations. The aggregations of PdNPs were not observed until reaching a high working temperature of 300 °C and carbon-coated layers could functionally prevent PdNPs from sintering even when ZnO-NWs experienced melting at 500 °C. The time-lapsed TEM investigation proved that the ripening dynamics and time-dependent revolution of PdNPs size are in accordance with the Ostwald ripening process. The subsequent atomic-scale observation revealed the surface reconstruction of ZnO-NWs in the form of ZnO encapsulation over PdNPs and carbon-coated layers during the thermal process, which showed the microscopic evidence of potential deactivation of ZnO-NW-based nanocatalysts in thermal reactions.