Facile Decomposition of Organophosphonates by Dual Lewis Sites on a Fe₃O₄(111) Film

Abstract

Dimethyl methylphosphonate (DMMP) is used as a simulant for toxic nerve agents and pesticides, rendering the understanding of surface chemistry requisite to design effective materials for organophosphonate (catalytic) decomposition at room temperature. In this work, DMMP surface chemistry is studied on an iron oxide surface in a very well-defined environment using temperature-programmed reaction, isotopic labeling, scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory. DMMP, (CH 3 O) 2 P(O)(CH 3 ), dissociates to yield methoxy and methyl methylphosphonate, (CH 3 O)-P(O) 2 (CH 3 ), on the surface at room temperature. At higher temperatures, dimethyl ether is formed via intramolecular reaction, followed by the formation of formaldehyde and methanol from adsorbed methoxy decomposition during temperature-programmed reaction. Ultimately, stochiometric combustion at 870 K produces CO, H 2 CO, and CO 2 via reaction with lattice oxygen, with PO x remaining on the surface. Excess oxygen from the bulk is required to drive these higher temperature pathways. Neither hydrolysis nor a photoreaction is observed, when exposing the adsorbed DMMP to water or light above the band gap, respectively. No evolution of P-containing species is detected, indicating efficient trapping of this contaminant. The activity for DMMP decomposition at room temperature is reduced by the accumulation of PO x . However, a significant amount of reaction persists after multiple temperature-programmed reaction experiments.

Understanding Dimethyl Methylphosphonate Adsorption and Decomposition on Mesoporous CeO2

“…Adsorption of DMMP on CeO 2 (110) and (111) surfaces is a straightforward process. Similar to other metal oxides, ,,,− DMMP is adsorbed on the Ce atom via its phosphoryl oxygen, as depicted in Figure a,b. The calculated energy of DMMP adsorption on the CeO 2 (110) surface (−164.8 kJ mol –1 ) is considerably higher than that on the (111) surface (−116.9 kJ mol –1 ), which is, most likely, explained by a stronger electrostatic repulsion between the phosphoryl oxygen of DMMP and a surface oxygen atom on the CeO 2 (111) surface.…”

Adsorption and Decomposition of Dimethyl Methylphosphonate on Size-Selected Zirconium Oxide Trimer Clusters

“…In the case of our experiment, it is possible that dimethyl ether formation occurs via the interaction of either methanol resulting from DMMP decomposition or a surface methoxy with a P–OCH 3 species on a cluster-bound phosphonate. In a recent rigorous study involving the decomposition of DMMP on a well-defined Fe 3 O 4 (111) surface in UHV, it was convincingly demonstrated via isotopic labeling and accompanying DFT calculations that dimethyl ether formation at around 600 K during TPD/R experiments was solely due to intramolecular reaction of surface-bound MMP species, complicating this picture even further . That work also demonstrated that oxygen adatoms on the surface, that is, undercoordinated oxygen atoms, are key to the observed DMMP decomposition pathways.…”

High-Temperature Decomposition of Diisopropyl Methylphosphonate (DIMP) on Alumina: Mechanistic Predictions from Ab Initio Molecular Dynamics

“…1 Recent studies have shown that metal oxides can effectively destroy CWAs due to their high surface area, a large number of highly reactive edges, corner defect sites, unusual lattice planes, and high surface-to-volume ratios. In particular, metal oxides, such as CaO, 3,4 MgO, 5,6 ZnO, [7][8][9] TiO 2 , 10-16 Al 2 O 3 , [17][18][19][20] Fe 3 O 4 , 21 and CuO 22 are candidates as adsorbents for enhancing the decomposition of CWAs. In γ-Al 2 O 3 , Al atoms in the bulk exhibit either a tetrahedral or octahedral coordination.…”