Atomic-Scale Observation of Bimetallic Au-CuO _x Nanoparticles and Their Interfaces for Activation of CO Molecules

Supported gold nanoparticles with sizes below 5 nm display attractive catalytic activities for heterogeneous reactions, particularly those promoted by secondary metal (e.g., Cu) because of the well-defined synergy between metal compositions. However, the specific atomic structure at interfaces is less interpreted systematically. In this work, various bimetallic Au-CuO_x catalysts with specific surface structures were synthesized and explored by aberration-corrected scanning transmission electron microscopy (AC-STEM), temperature-programmed experiments and in situ DRIFT experiments. Results suggest that the atomic structure and interfaces between gold and CuO_x are determined by the nucleation behaviors of the nanoparticles and result in subsequently the distinctive ability for CO activation. Bimetallic CuO*/Au sample formatted by gold particles surrounded with CuO_x nanoclusters have rough surface with prominently exposed low-coordinated Au step defects. Whereas the bimetallic Au@CuO sample formatted by copper precursor in the presence of gold nanoparticles have core-shell structure with relatively smooth surface. The former structure of CuO*/Au displays much accelerated properties for CO adsorption and activation with 90% CO converted to CO₂ at 90 °C and nice stability with time on stream. The results clearly determine from atomic scale the significance of exposed gold step sites and intrinsic formation of defected surface by different nucleation. The above properties are directly responsible for the induced variation in chemical composition and the catalytic activity.