O2 activation by AuAg clusters on a defective (100)MgO surface

In the present work, we discuss the electronic properties of supported dispersed bimetallic clusters with respect to their size, geometry, and Au_n/Ag_m (n + m = 6) composition. We have studied with supercell-density functional theory calculations the role of the charge transfer from the MgO defective support toward the cluster in the activation of O₂ by Au_nAg_m clusters. We first considered gas-phase clusters with different atomic compositions; then, we deposited all of them on a pristine (100)MgO surface and finally on a more realistic (100)MgO F-center. We performed a global and unrestricted search of the (cluster + surface) geometry. The Mexican enhanced genetic algorithm has been used to exhaustively explore the potential energy surface. Our results show that O₂ activation depends on the Au_n/Ag_m ratio. It has been found that both metals involved play different and important roles toward (a) the actual O₂ dissociation and (b) weakening of the oxygen-cluster bond, which, in turn, may promote the possibility of a catalytic process to take place, such as the oxidation process of CO and NO_x among others.

Theoretical investigation of oxidation of NO (NO + ½ O2 → NO2) on surfaces of nickel-doped nanocages (Ni-C60 and Ni-B30N30)

In present study, the NO oxidation on Ni-carbon nanocage and Ni-boron nitride nanocage surfaces was investigated. The Ni-C₆₀ and Ni-B₃₀N₃₀ catalysts can oxidize the NO molecule by Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. In this study, the NO molecule was joined to Ni atom of the Ni-surface-O₂* and Ni-surface-O* to generate the intermediates with low barrier energies. It can be concluded that the cis-Ni-surface-ONOO* complex in the ER pathway is more stable than four-elements-ring complex in LH pathway ca 0.06 and 0.08 eV, respectively. In the LH pathway, the studied catalysts were deactivated by irreversible absorption of NO₂ molecules in Ni atoms of Ni-C₆₀ and Ni-B₃₀N₃₀. In contrast, in the ER pathway two NO₂ molecules were released in the normal temperature. In this study, the abilities of the Ni-C₆₀ and Ni-B₃₀N₃₀ to oxidation of NO molecule was demonstrated. Finally, the systematic scheme to design of metal-doped nano-catalysts to oxidation of toxic gases was proposed.

Promotion mechanism of CeO2addition on the low temperature SCR reaction over MnOx/TiO2: a new insight from the kinetic study

A new insight into CeO₂addition on the SCR reaction over MnO_x/TiO₂was drawn according to steady-state kinetic analysis.