Kinetic Monte Carlo Simulation for NO Oxidation Over (√5x√5)R27° Pdo(101)

Under realistic operating conditions, in heterogeneous oxidation catalysts, the active surface for catalysis may actually be surface oxide instead of pristine, metal surface. We used Density Functional theory to investigate the stability of Pd(100) and Pd(111) surfaces under NO oxidation conditions, for various oxygen and NO pressures at 600K. Results, which represent first approximation because only thermodynamics analysis was included, were presented [Phys. Rev. B 79, 125410 (2009)]. Under conditions of interest (PO2 =1 bar and PNO =1mbar) according to thermodynamic phase diagram, Pd should be oxidized completely to be bulk palladium oxide. However, kinetic limitations may exist such that its formation is slow compared to the cycling of the NSR system. In addition the presence of reductants during the rich phase of the NSR cycle may return the surface to the pristine metal.

The idea of first principles kinetic Monte Carlo (kMC) simulations for heterogeneous catalysis is to combine an accurate description of the elementary processes (use DFT theory to obtain the kinetic parameters of the individual processes) and to take into account their statistical interplay over an extended time scale in order to properly evaluate the surface chemical kinetics. KMC simulations are performed in order to check the stability of the PdO(101) surface oxide over Pd(100) under relevant NO oxidation conditions.