Synthesis of tailored nanoparticles for supported oxidation catalysts

Licentiate thesis, 2022

The transition from microscale to nanoscale materials design leads to immense changes of physical and chemical properties of the materials. For decades, the design and making of functional nanomaterials have been at the frontier of what can be achieved, even with the more sophisticated synthesis methods. Thanks to the recent rapid development of synthesis and characterization techniques, multicomponent nanoparticle catalysts are gaining more and more interest because they can be tailored to exhibit higher catalytic efficiency than their monocomponent counterparts. Among them, Au and Pd based catalysts with core@shell structure have attracted great attention due to the possibilities of tuning the catalytic activity by the utilization of unique surface properties such as strain.

 

In this study, Au@Pd core@shell nanoparticles were synthesized by a two-step seeded growth method. The effects of different synthesis parameters, including temperature and Au/Pd molar ratio, on the size of Au@Pd core@shell nanoparticles were investigated. The morphology of the as-prepared Au@Pd and Au@Pd/ -Al2O3 core@shell nanoparticles was imaged by high resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF - STEM). It is shown that Au@Pd core@shell nanoparticles with thin Pd shell can be successfully synthesized and loaded onto alumina using precise synthesis conditions. Moreover, neither agglomeration nor destruction of the core@shell motif under CO oxidation reaction conditions could be observed, indicating good structural stability. Further, in situ infrared spectroscopy reveals that palladium surface properties differ compared to palladium only particles suggesting electronic and structural modification of the Pd shell surface by the Au core.