Synthesis, microscopy and catalysis: Probing structure-performance relationships of Au-Pd core-shell nanoparticles

Abstract

This thesis covers a range of studies that aim to establish structure-property relationships for Au-Pd nanocatalysts. The three pillars of this work are 1) colloidal synthesis to make uniform Au-Pd core-shell nanoparticles with controlled size, shape, composition and metal distribution, 2) transmission electron microscopy to characterize the nanoparticles, sometimes in situ under a gas atmosphere to learn how the particles change under operating conditions, and 3) catalytic testing in selective hydrogenation reactions to see how the well-defined and well-characterized nanoparticle structure affects the catalytic properties.In general, this thesis showcases how the control of the metal distribution, the composition and the nanoparticle shape of Au-Pd bimetallic nanocatalysts is useful to tune the catalytic performance. We demonstrate how enhanced activity in liquid- and gas-phase hydrogenation reactions can be achieved combining Au and Pd in a core-shell structure, and attribute this to a stronger interaction between the strained Pd-shell atoms and hydrogen. We find that the interaction with hydrogen is crucial to understand the performance in selective hydrogenation reactions, as a larger activity in HD exchange also translates to a higher activity in the selective hydrogenation of butadiene. Lastly, by studying structural changes with in situ TEM we show how core-shell nanoparticles alloy under different gas atmospheres, and how Pd incorporates and releases hydrogen at relevant temperatures of our catalytic tests. In summary, thanks to careful (in situ) TEM characterization we probed different structure-property relationships of colloidally synthesized Au-Pd bimetallic nanoparticles in hydrogenation catalysis.