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In this study, we present an investigation aimed at characterizing and understanding the synergistic interactions in encapsulated catalytic structures between the metal core ( i.e. , Pd) and oxide shell ( i.e. , TiO 2 , ZrO 2 , and CeO 2 ). Encapsulated catalysts were synthesized using a two-step procedure involving the initial colloidal synthesis of Pd nanoparticles (NPs) capped by various ligands and subsequent sol–gel encapsulation of the NPs with porous MO 2 (M = Ti, Zr, Ce) shells. The encapsulated catalytic systems displayed higher activity than the Pd/MO 2 supported structures due to unique physicochemical properties at the Pd–MO 2 interface. Pd@ZrO 2 exhibited the highest catalytic activity for CO oxidation. Results also suggested that the active sites in Pd encapsulated by an amorphous ZrO 2 shell structure were significantly more active than the crystalline oxide encapsulated structures at low temperatures. Furthermore, CO DRIFTS studies showed that Pd redispersion occurred under CO oxidation reaction conditions and as a function of the oxide shell composition, being observed in Pd@TiO 2 systems only, with potential formation of smaller NPs and oxide-supported Pd clusters after reaction. This investigation demonstrated that metal oxide composition and (in some cases) crystallinity play major roles in catalyst activity for encapsulated catalytic systems.
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Ligand‐Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?
Abstract Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L‐cysteine [HOCOCH(NH2)CH2SH] ligands (Pdn(L‐Cys)m) and supported on the surfaces of CeO2, TiO2, Fe3O4, and ZnO nanoparticles for CO catalytic oxidation. The Pdn(L‐Cys)mnanoclusters supported on the reducible metal oxides CeO2, TiO2and Fe3O4exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand‐protected clusters Pdn(L‐Cys)mis observed on the three reducible oxides where 100 % CO conversion occurs at 93–110 °C. The high activity is attributed to the ligand‐protected Pd nanoclusters where the L‐cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub‐2‐nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L‐cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand‐protected clusters. However, for the TiO2and Fe3O4supports, complete removal of the ligands from the Pdn(L‐Cys)mclusters leads to a slight decrease in activity where the T100%CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO2and Fe3O4supports appears to aid in efficient encapsulation of the bare Pdnnanoclusters within the mesoporous pores of the support.
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- Award ID(s):
- 1900094
- PAR ID:
- 10257649
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 22
- Issue:
- 3
- ISSN:
- 1439-4235
- Format(s):
- Medium: X Size: p. 312-322
- Size(s):
- p. 312-322
- Sponsoring Org:
- National Science Foundation
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