Deposition of Pd, Pt, and PdPt Nanoparticles on TiO$_2$ Powder Using Supercritical Fluid Reactive Deposition: Application in the Direct Synthesis of H$_2$O$_2$

In this study, we investigated the catalytic properties of mono- and bimetallic palladium
(Pd) and platinum (Pt) nanoparticles deposited via supercritical fluid reactive deposition (SFRD)
on titanium dioxide (TiO$_2$) powder. Transmission electron microscopy analyses verified that SFRD
experiments performed at 353 K and 15.6 MPa enabled the deposition of uniform mono- and bimetallic
nanoparticles smaller than 3 nm on TiO$_2$. Electron-dispersive X-ray spectroscopy demonstrated
the formation of alloy-type structures for the bimetallic PdPt nanoparticles. H$_2$O$_2$ is an excellent
oxidizing reagent for the production of fine and bulk chemicals. However, until today, the design
and preparation of catalysts with high H$_2$O$_2$selectivity and productivity remain a great challenge.
The focus of this study was on answering the questions of (a) whether the catalysts produced are
suitable for the direct synthesis of hydrogen peroxide (H$_2$O$_2$) in the liquid phase and (b) how the
metal type affects the catalytic properties. It was found that the metal type (Pd or Pt) influenced
the catalytic performance strongly; the mean productivity of the mono- and bimetallic catalysts
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decreased in the following order: Pd > PdPt > Pt. Furthermore, all catalysts prepared by SFRD
showed a significantly higher mean productivity compared to the catalyst prepared by incipient
wetness impregnation.