Roles of noble metals (M = Ag, Au, Pd, Pt and Rh) on CeO2 in enhancing activity toward soot oxidation: Active oxygen species and DFT calculations

• Published in: Journal of hazardous materials 2021-02, Vol.403, p.124085-124085, Article 124085
• Main Authors: Lee, Jae Hwan, Jo, Deok Yeon, Choung, Jin Woo, Kim, Chang Hwan, Ham, Hyung Chul, Lee, Kwan-Young
• Format: Article
• Language: English
• Subjects: Active oxygen species; Density Functional Theory (DFT); Noble metal; Soot oxidation; Vacancy formation energy
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2020.124085

The effects of noble metal (M = Ag, Au, Pd, Pt, and Rh) on CeO2 in enhancing the activity toward soot oxidation were studied through experimental methods and density functional theory (DFT) calculations. Each noble metal (3 mol.%) was supported on CeO2 (M/CeO2) and the properties of the catalysts were verified by XRD, HRTEM, N2 physisorption, CO chemisorption, XPS, and H2-TPR results. The noble metal was highly dispersed over CeO2, except for Au due to the sintering of Au, and the reducibility of the catalysts was greatly improved according to degree of the interaction between each noble metal and CeO2. The activities of M/CeO2 catalysts for soot oxidation were better than that of CeO2, and followed the order Rh/CeO2 > Ag/CeO2 > Pt/CeO2 > Au/CeO2 > Pd/CeO2 > CeO2. Moreover, our DFT calculations showed that vacancy formation energy was gradually lowered in the following order: CeO2 > Pd4/CeO2 > Pt4/CeO2 > Au4/CeO2 = Ag4/CeO2 > Rh4/CeO2, which was similar order with experimental activity. In addition, the electronic states of the p and f orbitals of CeO2 were studied to compare with the occupied Ce 4f electrons, which affect the redox property. Rh/CeO2 and Ag/CeO2 showed the improved soot oxidation activity, with an enhanced ability to generate oxygen vacancy formation and oxygen adsorption and increased electron transfer. Consequently, the experimental and DFT calculation results revealed the roles of noble metals on ceria with respect to catalytic activity. [Display omitted] •The M/CeO2 catalysts showed improved soot oxidation activity than that of CeO2.•The experimental and DFT calculation results revealed the roles of noble metals on ceria.•The activity of M/CeO2 highly depended on the vacancy formation energy.•The assisted metals supply electrons to the f orbitals in CeO2 surfaces.•The more electrons enriched in the f orbital, the vacancy formation of CeO2 was promoted.