First-principles kinetic Monte Carlo simulations for heterogeneous catalysis: Application to the CO oxidation atRuO2(110)

Abstract

We describe a first-principles statistical mechanics approach enabling us to simulate the steady-state situation of heterogeneous catalysis. In a first step, density-functional theory together with transition-state theory is employed to obtain the energetics of the relevant elementary processes. Subsequently the statistical mechanics problem is solved by the kinetic Monte Carlo method, which accounts for the correlations, fluctuations, and spatial distributions of the chemicals at the surface of the catalyst under steady-state conditions. Applying this approach to the catalytic oxidation of CO at RuO 2 ͑110͒, we determine the surface atomic structure and composition in reactive environments ranging from ultra-high vacuum ͑UHV͒ to technologically relevant conditions, i.e., up to pressures of several atmospheres and elevated temperatures. We also compute the CO 2 formation rates ͑turnover frequencies͒. The results are in quantitative agreement with all existing experimental data. We find that the high catalytic activity of this system is intimately connected with a disordered, dynamic surface "phase" with significant compositional fluctuations. In this active state the catalytic function results from a self-regulating interplay of several elementary processes.

Insight into a Pressure and Materials Gap: CO Oxidation at "Ruthenium" Catalysts

“…The O br /− termination is routinely observed experimentally after high temperature anneals in UHV, whereas the O br /O cus termination can be stabilized by oxygen post-exposure [10,[22][23][24]. Extensive theoretical work over the last years has shown that O and CO adsorption at other sites of the surface is energetically significantly less favorable than adsorption at bridge and cus sites [10,[23][24][25][26], which is consistent with all presently available experimental data [6,10,[27][28][29][30][31][32].…”

“…First-principles calculations revealed only minor lateral interactions between the reactants when adsorbed at this rather open oxide surface [26]. This allows one to quickly summarize the relevant features of the surface binding energetics as follows [26,33]: oxygen atoms bind only with moderate strength to the cus sites (∼0.9 eV/atom), whereas they bind quite strongly to the bridge sites (∼2.3 eV/atom).…”

Resolved-Pore Simulation of CO Oxidation on Rh/Al2O3 in a Catalyst Layer

“…In the second model r 1 ' = 0.5 µm and r 2 ' = 1.5 µm with mixing ratio of n 1 '/n 2 ' = 32 and fractional sintering level of 0.15 were used. The third model was developed for the resolved-pore simulations in this work; it consists of 200 particles with r p = [4,5,6,7,8] µm and probability distribution of [0.32, 0.26, 0.23, 0.13, 0.06]. This model was made to make sure that the majority of macro-pores are larger than 1 µm to avoid the Knudsen flow conditions in any pore in which the flow is explicitly modeled.…”

“…The authors then used first-principles kinetics Monte Carlo (1p-kMC) to show the dominance of the oxide layer on the surface under the relevant pressure conditions [6]. Reuter and co-workers have investigated the CO oxidation on RuO 2 in several different studies [7][8][9]. In one of their most important studies Matera and Reuter show how heat and mass transfer can actually mask intrinsic reactivity of the catalyst for normal modern in situ experiments under typical gas phase conditions [10].…”

kmos: A lattice kinetic Monte Carlo framework

“…Specifically, the CO oxidation at RuO 2 (110) model includes two different active sites per surface unit cell, and a total of 26 inequivalent elementary processes (unimolecular CO adsorption and desorption, dissociative adsorption and associative desorption of O 2 , CO and O diffusion, as well as CO oxidation and CO 2 decomposition). [3,33] The PdO(101) model includes the same types of elementary reactions and also two different active sites per unit cell. In addition, it accounts for nearest-neighbor lateral interactions that modify the rate constants of all diffusion, desorption and reaction steps.…”