Noble metal ion substituted CeO2 catalysts: Electronic interaction between noble metal ions and CeO2 lattice

• Published in: Catalysis today 2015-09, Vol.253, p.40-50
• Main Authors: Hegde, M.S., Bera, Parthasarathi
• Format: Article
• Language: English
• Subjects: CeO2; DFT; Interaction; Noble metal ionic catalyst; XPS; XRD
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2015.03.035

•Noble metals are dispersed on CeO2 as ions leading to Ce1−xMxO2−δ (M=Pt, Pd, Rh and Ru) solid solutions.•Valence band positions of noble metals, noble metal ions and Ce stabilize noble metal ions in CeO2 lattice through electron transfer.•Noble metal ions in CeO2 based catalysts act as adsorption sites for catalysis.•Substitution of Ti, Zr, Sn and Fe in CeO2 increase oxygen storage capacities due to structural distortion.•Noble metal ionic catalysts show much higher catalytic activities than supported noble metal catalysts. In last 40 years, CeO2 has been found to play a major role in the area of auto exhaust catalysis due to its unique redox properties. Catalytic activity is enhanced when CeO2 is added to the noble metals supported Al2O3 catalysts. Reason for increase in catalytic activity is due to higher dispersion of noble metals in the form of ions in CeO2. This has led to the idea of substitution of noble metal ions in CeO2 lattice acting as adsorption sites instead of nanocrystalline noble metal particles on CeO2. In this article, a brief review of synthesis, structure and catalytic properties of noble metal ions dispersed on CeO2 resulting in noble metal ionic catalysts (NMIC) like Ce1−xMxO2−δ, Ce1−x−yTixMyO2−δ, Ce1−x−yZrxMyO2−δ, Ce1−x−ySnxMyO2−δ and Ce1−x−yFexMyO2−δ (M=Pt, Pd, Rh and Ru) are presented. Substitution of Ti, Zr, Sn and Fe in CeO2 increases oxygen storage capacities (OSC) due to structural distortion, whereas dispersion of noble metal ions in Ti, Zr, Sn and Fe substituted CeO2 supports increase both OSC and catalytic activities. Electronic interaction between noble metal ions and CeO2 in NMICs responsible for higher OSC and higher catalytic activities is discussed.