(509bz) Understanding Pd-MO Interfaces in Inverted Catalytic Structures

The functionality of heterogeneous catalysts is influenced by a delicate interplay between multiple parameters, including morphology and structure.¹ Catalytic structures that take advantage of metal–metal oxide interfaces have attracted considerable attention because of providing unique active sites that exploit the distinct properties of the two types of materials.² Among these, “inverted” catalytic structures where size/shape-controlled metal nanoparticles (NPs) are encapsulated by porous oxide film have shown significant potential for generation of highly active catalytic interfaces and providing directed pathways for reactive species leading to selective catalytic pathways.¹

In this presentation, we combine controlled synthesis and advanced characterization to shed light on how the interfaces of “inverted” Pd-MO (MO = TiO₂, CeO_2, and ZrO₂) structures are impacted by the synthesis parameters and oxide composition. Hydrophilic Pd NPs were consistently synthesized using an appropriate surface stabilizing and reducing agent. A modified sol-gel approach was used for encapsulation, as previously reported³. To gain insight into the structure of the porous oxide shell, N₂ physisorption and x-ray diffraction (XRD) studies were used. The active surface area of Pd NPs and their dispersion in the various metal oxide porous shells was determined by CO chemisorption. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and x-ray photoelectron spectroscopy (XPS) studies were performed to describe the surface reactivity and electronic structure of Pd as a function of variations in the interfaces. We show that compared with the traditional supported catalysts, the “inverted” catalytic structures exhibited higher activity, stability, and selectivity for probe catalytic reactions. These findings provide critical insights into the interactions at metal-support interfaces of “inverted” Pd-MO catalysts, which can be used to tune their catalytic performance.

References

(1) Surface Science Reports 2018, 73 (4), 117–152.

(2) Angewandte Chemie Int. Ed. 2017, 56, 6594-6598.

(3) Industrial and Engineering Chemistry Research 2019, 58, 4032–4041.