Porous alumina protective coatings on palladium nanoparticles by self-poisoned atomic layer deposition

Junling Lu, Bin Liu, Jeffrey P. Greeley, Zhenxing Feng, Joseph A. Libera, Yu Lei, Michael J. Bedzyk, Peter C. Stair, Jeffrey W. Elam

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83 Citations (Scopus)

Abstract

Atomic layer deposition (ALD) of Al 2O 3 using trimethylaluminum (TMA) and water on Pd nanoparticles (NPs) was studied by combining in situ quartz crystal microbalance (QCM) measurements, in situ quadrupole mass spectrometry (QMS), and transmission electron microscopy (TEM) with density functional theory (DFT) calculations. TEM images of the ALD Al 2O 3 overcoated Pd showed conformal Al 2O 3 films on the Pd NPs as expected for ALD. However, hydrogen detected by in situ QMS during the water pulses suggested that the ALD Al 2O 3 films on the Pd NPs were porous rather than being continuous coatings. Additional in situ QCM and QMS measurements indicated that Al 2O 3 ALD on Pd NPs proceeds by a self-poisoning, self-cleaning process. To evaluate this possibility, DFT calculations were performed on Pd(111) and Pd(211) as idealized Pd NP surfaces. These calculations determined that the TMA and water reactions are thermodynamically favored on the stepped Pd(211) surface, consistent with previous observations. Furthermore, the DFT studies identified methylaluminum (AlCH 3*, where the asterisk designates a surface species) as the most stable intermediate on Pd surfaces following the TMA exposures, and that AlCH 3* transforms into Al(OH) 3* species during the subsequent water pulse. The gas phase products observed using in situ QMS support this TMA dissociation/hydration mechanism. Taken together, the DFT and experimental results suggest a process in which the Pd surface becomes poisoned by adsorbed CH 3* species during the TMA exposures that prevent the formation of a complete monolayer of adsorbed Al species. During the subsequent H 2O exposures, the Pd surface is cleaned of CH 3* species, and the net result is a porous Al 2O 3 film. This porous structure can retain the catalytic activity of the Pd NPs by providing reagent gases with access to the Pd surface sites, suggesting a promising route to stabilize active Pd catalysts.

Original languageEnglish
Pages (from-to)2047-2055
Number of pages9
JournalChemistry of Materials
Volume24
Issue number11
DOIs
Publication statusPublished - Jun 12 2012

Keywords

  • alumina
  • atomic layer deposition
  • density functional theory
  • growth mechanism
  • palladium nanoparticle
  • stabilization
  • supported metal catalyst

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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  • Cite this

    Lu, J., Liu, B., Greeley, J. P., Feng, Z., Libera, J. A., Lei, Y., Bedzyk, M. J., Stair, P. C., & Elam, J. W. (2012). Porous alumina protective coatings on palladium nanoparticles by self-poisoned atomic layer deposition. Chemistry of Materials, 24(11), 2047-2055. https://doi.org/10.1021/cm300203s