(582bx) Aqueous One-Pot Synthesis of Pd-Based Core@Shell Catalysts with Tunable Core and Shell Sizes

Authors: 
Seo, C. Y., University of Michigan
Nahata, M., University of Michigan
Fisher, G. B., University of Michigan
Schwank, J. W., University of Michigan
Encapulating an active metal core such as palladium (Pd) in a porous oxide shell material can lead to improved catalytic activity, selectivity, and thermal stability compared to conventional supported catalysts. However, many reported synthetic methods include some drawbacks which increase the difficulty of synthesis and limits the scalability of the method. For example, many methods require the use of organic solvents and surfactants in large quantities to form microemulsions, which are used as templates for core@shell particle formation. However, such a method is not very versatile in terms of tuning the catalyst composition, since microemulsions require very specific chemical conditions to form. Such a requirement also limits the scalability. Therefore, prior to a larger-scale implementation of core@shell catalysts, which has been hindered, a new synthesis method needs to be developed.

Here, we are reporting a versatile, water-based and therefore environmentally benign synthesis method to facilitate the use of core@shell catalysts. The described method can be used to prepare core@shell nanoparticles with Pd cores and oxide shells (e.g., SiO2, CeO2) with independently tunable core and shell sizes. By using water as the synthesis medium, the new method effectively overcomes the limitations of previously reported synthetic approaches that require the use of toxic organic solvents. In addition, not only the sizes of the cores and the shell, but also the compositions of the resultant core@shell nanoparticles could be adjusted by making simple modifications to the synthesis procedure. The prepared catalysts were characterized by transmission electron microscopy, X-ray diffraction, and nitrogen-physisorption to confirm the morphology with different compositions. Following the characterization, the accessibility and the catalytic activity of the core was tested using simple probe reactions such as the oxidation of CO. Some of these novel core@shelll structures exhibited remarkable thermal stability, maintaining the particle size and pore structure at very high temperatures (800-900 °C), close to those one may encounter in automotive exhaust applications.