The CO oxidation mechanism on small Pd clusters. A theoretical study

• Published in: Journal of molecular modeling 2015-11, Vol.21 (11), p.279-279, Article 279
• Main Authors: González-Torres, Julio César, Bertin, Virineya, Poulain, Enrique, Olvera-Neria, Oscar
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Molecular Medicine; Original Paper; Theoretical and Computational Chemistry
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-015-2828-5

CO is a pollutant that is removed by oxidation using Pd, Pt or Rh as catalysts in the exhaust pipes of vehicles. Here, a quantum chemistry study on the CO + O 2 reaction catalyzed by small Pd n clusters (n ≤ 5) using the PBE/TZ2P/ZORA method is performed. The limiting step in this reaction at low temperature and coverage is the O 2 dissociation. Pd n clusters catalyze the O=O bond breaking, reducing the energy barrier from 119 kcal mol -1 without catalyst to ∼35 kcal mol -1 . The charge transfer from Pd to the O 2,ad antibonding orbital weakens, and finally breaks the O─O bond. The CO oxidation takes place by the Eley-Rideal (ER) mechanism or the Langmuir-Hinshelwood (LH) mechanism. The ER mechanism presents an energy barrier of 4.10-7.05 kcal mol -1 and the formed CO 2 is released after the reaction. The LH mechanism also shows barrier energies to produce CO 2 (7-15 kcal mol -1 ) but it remains adsorbed on Pd clusters. An additional energy (7-25 kcal mol -1 ) is necessary to desorb CO 2 and release the metal site. The triplet multiplicity is the ground states of studied Pd n clusters, with the following order of stability: triplet > singlet > quintet state. Graphical Abstract CO oxidation mechanism on small Pd clusters