In Situ Dispersion of Palladium on TiO2 During Reverse Water-Gas Shift Reaction: Formation of Atomically Dispersed Palladium

Nicholas C Nelson; Linxiao Chen; Debora Meira; Libor Kovarik; János Szanyi

doi:10.1002/anie.202007576

In Situ Dispersion of Palladium on TiO₂ During Reverse Water-Gas Shift Reaction: Formation of Atomically Dispersed Palladium

Angew Chem Int Ed Engl. 2020 Sep 28;59(40):17657-17663. doi: 10.1002/anie.202007576. Epub 2020 Aug 11.

Authors

Nicholas C Nelson¹, Linxiao Chen¹, Debora Meira^{2

3}, Libor Kovarik¹, János Szanyi¹

Affiliations

¹ Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
² CLS@APS sector 20, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL, 60439, USA.
³ Canadian Light Source Inc., 44 Innovation Boulevard, Saskatoon, Saskatchewan, S7N 2V3, Canada.

PMID: 32589820
DOI: 10.1002/anie.202007576

Abstract

The application of single-atom catalysts (SACs) to high-temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd can be predominantly dispersed as isolated atoms onto TiO₂ during the reverse water-gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO₂ surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO₂ ) with neat TiO₂ prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X-ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high-temperature rWGS conditions is associated with Pd-Ti coordination, which manifests upon O-vacancy formation, and the artificial increase in TiO₂ surface area.

Keywords: Pd1-TiO2; in situ metal dispersion; reverse water-gas shift; thermodynamic stability.