A Fe₃O₄(111) surface with both Lewis acid and base sites is formed by reducing α-Fe₂O₃(0001). The dual Lewis sites are composed of O adatoms and Fe_tet1 atoms. Combining scanning tunneling microscopy (STM) and density functional theory (DFT), the atomic structure of the Fe₃O₄(111) surface was identified using the fingerprint of electronic structure of O_ad and uncovered Fe_tet1. Dimethyl methylphosphonate (DMMP) dissociates to yield methoxy and methyl methyl phosphonate, (CH₃O)P(O)₂(CH₃), on the Fe₃O₄(111) surface at room temperature. At higher temperatures, dimethyl ether forms via intramolecular reaction, followed by formation of formaldehyde and methanol from adsorbed methoxy decomposition during temperature programmed reaction. Ultimately, stochiometric combustion at 870 K to produce CO, H₂C=O, CO₂ 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 bandgap, 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.

A pathway of DMMP decomposition on the surface of Fe<sub>3</sub>O<sub>4</sub>(111) films.

A pathway of DMMP decomposition on the surface of Fe₃O₄(111) films.

Fang Xu

Assistant Professor, University of Texas at San Antonio

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