Density Functional Theory (DFT) Study To Unravel the Catalytic Properties of M-Exchanged MFI, (M = Be, Co, Cu, Mg, Mn, Zn) for the Conversion of Methane and Carbon Dioxide to Acetic Acid

Abstract

The conversion of greenhouse gases, such as CO2 and CH4, to value chemicals is a major challenge, because of the high stability of both molecules. In this study, density functional theory (DFT) calculations with long-range corrections and ONIOM were used to analyze the reaction mechanism for the conversion of CO2 and CH4 to acetic acid with MFI zeolite exchanged with Be, Co, Cu, Mg, Mn, and Zn cations. Our results demonstrate that (a) the highest reaction barrier on the reaction mechanism is CH4 dissociation, and the transition state energy in that step is directly related to the energy of the lowest unoccupied molecular orbital and the electronegativity of the metal exchanged zeolites; (b) a charge transfer between CH4 and the metal cation occurs simultaneously to CH4 dissociation; (c) CO2 insertion has a low energy barrier, and the protonation of the acetate species is spontaneous; (d) dispersion interactions are the main contributions to CH4 adsorption energies, whereas, in the rest of the steps of the reaction mechanism, the contribution of dispersion to the energies of reaction is almost negligible; (e) desorption of acetic acid could be promoted by the coadsorption of water; and (f) CH4 dissociation on Cu-MFI has an apparent activation energy of 11.5 kcal/mol, and a forward rate constant of 1.1 s–1 at 398 K.

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

“…This finding further support the proposal that the radical oxygen is a key factor determining the catalytic activity of the active site for C−H bond activation ,, , . Calculations on a broad range of metal‐exchanged zeolites by Curet‐Arana and co‐workers showed that the barrier for C−H bond cleavage is directly related to the energy of the lowest unoccupied molecular orbital (LUMO) and the electronegativity of active site in the metal exchanged zeolites . A periodic hybrid DFT study by Solans‐Monfort et al on the interaction of model adsorbents with Cu and Fe‐exchanged zeolites highlighted the importance of the local environment of EF sites for their adsorption properties and reactivity …”

“…[108,116b, 117, 125] Calculations on a broad range of metal-exchanged zeolites by Curet-Arana and co-workers showed that the barrier for CÀ H bond cleavage is directly related to the energy of the lowest unoccupied molecular orbital (LUMO) and the electronegativity of active site in the metal exchanged zeolites. [126] A periodic hybrid DFT study by Solans-Monfort et al on the interaction of model adsorbents with Cu and Fe-exchanged zeolites highlighted the importance of the local environment of EF sites for their adsorption properties and reactivity. [127] Nørskov and co-workers have computationally screened the activity of wide variety of oxide-and zeolite-based catalysts for the activation of CÀ H bonds in methane.…”

In-Situ FT-IR Spectroscopy Investigation of CH4 and CO2 Reaction

“…Unfortunately, the reaction is thermodynamically unfavorable under moderate conditions ( G 298K = 71.2 kJ/mol). Many works are devoted to selectively break the C-H bond in CH 4 and simultaneously utilize the inertness of CO 2 to realize C-C coupling for the synthesis of high-value chemicals [3][4][5][6][7]. Most of these works are based on theoretical calculation and experiments which always require additional energy supply (such as plasma), few in-situ characterizations studies have been conducted.…”

Análisis DFT de zeolita MFI sustituida con magnesio para la activación de metano.

“…Sustituciones de la zeolita MFI con otros metales como cobre (Cu) y hierro (Fe) también se han estudiado para la activación de CH4 [5]- [7]. La sustitución de Cu se puede dar de dos maneras: Mediante la formación de "oxoclusters" [Cu-O-Cu] 2+ o mediante la sustitución sencilla de Cu +2 en los anillos de MFI (Cu-MFI) [8], [9]. La barrera energética obtenida para la disociación de metano en [Cu-O-Cu] 2+ (82 kJ/mol) es menor que la obtenida en Cu-MFI (129 kJ/mol).…”