(509bs) Investigation of Synergistic Interfaces in Metal-Metal Oxide Inverted Systems for Catalytic Upgrading

The production process of fuels and value-added chemicals through clean, energy-efficient routes has been in the spotlight of the scientific community due to its potential positive impact on the future energy landscape. Inverted systems, where precious metals are encapsulated in porous metal oxides, have emerged as promising materials that can lead to improvements in catalytic activity, selectivity, and stability for industrially relevant reactions. Their unique structure allows for modification of the 3-dimensional environment of the active sites along with bifunctionality benefits arising from increased presence of interfacial metal-metal oxide (MO) interactions.¹ Thermal stability is also significantly improved through controlled synthesis of inverted catalytic systems, as compared to conventional supported materials.²

Here, we present a thorough investigation aimed at characterizing and understanding the synergistic interactions in inverted structures between Pd and three MO: TiO₂, ZrO₂, and CeO₂. Inverted catalysts were prepared by initial colloidal synthesis of Pd nanoparticles (NPs) capped with a hydrophilic ligand, followed by sol-gel synthesis for encapsulation of the Pd NPs in the MO. We conducted systematic variations of synthesis parameters relevant to the reactivity of the catalysts, employed characterization techniques to gain insight into surface structure and Pd-MO interactions, and tested performance of the catalysts using a probe reaction. We show Pd redispersion on the surface of the MO, at low Pd weight loadings, via CO DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) studies. Redispersion of Pd on the MO was controlled by tuning temperature conditions and gaseous environment used to treat the catalyst. We determined that inverted systems exhibited significant improvements in the overall catalytic performance over conventional supported catalysts. Our work sheds light on metal-MO interactions and provides a platform for optimizing catalytic reactivity via systematic modification of synthesis parameters.

Ind. Eng. Chem. Res. 2019, 58, 4032–4041.

Angew. Chemie - Int. Ed. 2017, 56, 6594–6598.