First-Principles-Based Kinetic Monte Carlo Simulation of Nitric Oxide Reduction over Platinum Nanoparticles under Lean-Burn Conditions

Abstract

The kinetics for NO reduction over supported platinum under lean condition were investigated by firstprinciples-based kinetic Monte Carlo simulation over three-dimensional Pt nanoparticles. Model platinum nanoparticles with diameters ranging from 2.3 to 4.6 nm were constructed using a truncated octahedral cluster consisting of a two (100) facets and eight (111) facets. First-principles density functional theory (DFT) calculations were used to calculate the intrinsic kinetic parameters including the binding energies for all of the surface intermediates as well as the activation barriers and reaction energies that comprise the reaction mechanism over the (100) and (111) facets, as well as the (111)/(100) edge sites on the three-dimensional nanoparticle. Both intra-and inter-facet diffusion of adsorbates were included to model surface diffusion effects over the particle surface. The simulation results show that under lean conditions where there is excess oxygen, NO reduction to N 2 occurs solely on the (100) facets. The oxidation of NO to NO 2 , while much more favored on the (111) facets, can occur on both (100) and (111) facets. Only small amounts of N 2 O form over the (100) facets. The simulated apparent activation energies for N 2 and NO 2 formation over the entire particle are 45 and 42 kJ/mol, respectively. The latter is in agreement with experimentally measured value of 39 kJ/mol [Mulla, S. S., et al., Catal. Lett. 2005, 100, 267]. The effects of particle size on the activities of NO reduction to N 2 and NO oxidation to NO 2 depend upon the ratios of exposed surface sites. For the threedimensional model Pt nanoparticles examined here, the fractions of the (100) terrace sites are similar while the fraction of the (111) terrace sites increases with increasing particle size. As a result, the activity for NO reduction is somewhat insensitive to the particle size which symmetrically increases the numbers of (111) and (100) facets as the size increases. NO reduction, however, increases much more dramatically when the number of the (100) sites increases over the (111) sites. NO oxidation activity, on the other hand, appears to increase with increasing particle size regardless of the symmetry or shape of the particle as the reaction occurs predominantly over the (111) sites but can also take place on the (100) terrace sites. The structure insensitivity for NO oxidation is consistent with experimental results.

Atomistic computer simulations of water interactions and dissolution of inorganic glasses

“…KMC evolves the system from state to state based on reaction rates and can enable simulations of infrequent events and process longer time scales compared to MD simulations. 76,77 Aertsens and coworkers pioneered KMC simulations of glass dissolution of alkali silicate glasses, 75,78,79 where the glass structures were approximated by diamond lattices due to the topological similarity between the lattice and the network structures in silica. Two types of lattice sites, one easily dissolving and one slowly dissolving component represented by silicon and sodium, respectively, were randomly distributed on the lattice sites.…”

Parallel kinetic Monte Carlo simulation framework incorporating accurate models of adsorbate lateral interactions

“…to enable the coupling with ab initio calculations for a first-principles based simulation of chemistries on catalytic surfaces [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] (for reviews, see Refs. [32][33][34].…”

Kinetic modelling of heterogeneous catalytic systems

“…In particular, Mei et al [219] studied NO oxidation and reduction on Pt(1 0 0) and Pt(1 1 1), both planes exposed by cuboctahedral nanoparticles. Spillover of adsorbates was explicitly taken into account in the KMC simulations, and the edge and corner sites were treated as (1 1 1) sites for simplicity.…”