Abstract
In numerous studies, the application of the molecular dynamics scheme based on the reactive force field (ReaxFF) method has been proven effective in modeling the catalytic behavior of metal–organic compounds. Recently, this method has been successfully applied for MxOy (M = Cu, Fe, Mn, Ni) transition-metal oxides. Yet, bimetallic metal oxides of the type MnMOx (M = Cu, Fe, Ni) were also present in the experimental system but could not be modeled since not all of the force field parameters were available at the time. To bridge this gap, the force field for modeling bimetallic metal oxides had to be developed. Here, we establish the needed force field parameter sets (namely, Cu/Mn/O, Fe/Mn/O, and Ni/Mn/O) and apply them to the problem of toluene adsorption on bimetallic oxide catalyst surfaces to verify their validity. Each training set consisted of at least 10 crystal structures containing at least Cu–Mn–O, Fe–Mn–O, or Ni–Mn–O atoms in contact obtained from the available structure databases. The parameter training has been done using the in-home-compiled version of the ReaxFF code. After training the force fields for geometry reproduction, the parameters were refined using the optimization by atom charges, comparing the ReaxFF values to those obtained for the respective structures using periodic crystal density functional theory (DFT) codes. The as-developed force fields were then applied to the process of toluene adsorption/degradation on MnMOx catalysts. Results obtained show agreement with previous experimental expectations, although some remarks are given since the initially presumed crystal structure of bimetallic oxide Mn1–xMxOy crystallites may still have an impact on theoretical predictions. The presented are, to the best of the authors’ knowledge, the first applications of the ReaxFF approach to the Mn–(Cu|Fe|Ni)–O–C–H interaction.
Highlights
To design the process for removing volatile organic compounds (VOCs) from the environment, we study reactions to degrade complex organic compounds present in wastewater to CO2 and H2O
Calculations were done for specific crystals of interest: MnFeO3, NiMnO3, and CuMnO4. These calculations were followed by the crystal volume variations, which were compared to the density functional theory (DFT) energy calculations for the validation of force fields
Parameters for the application of the ReaxFF molecular dynamics (MD) method for the theoretical investigation of bimetallic Mn−Cu, Mn−Fe, and Mn−Ni oxides were developed by training them to DFT and crystallographic data, with special emphasis for reproducing structure and charge distribution
Summary
To design the process for removing volatile organic compounds (VOCs) from the environment, we study reactions to degrade complex organic compounds present in wastewater to CO2 and H2O. The step further in the production-degradation economy is to take into account the availability and the price of the catalyst production process. The motivation is to replace noble-metal-based catalysts (such as Pt or Au) with much more available transition-metal oxide catalysts (such as these based on Cu, Fe, Ni, and Mn) as the latter are shown to have similar activity for reactions of interest. This basic approach is explained further below with specific reference to the problem at hand
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