Understanding Dimethyl Methylphosphonate Adsorption and Decomposition on Mesoporous CeO₂

The increased risk of chemical warfare agent usage around the world has intensified the search for high-surface-area materials that can strongly adsorb and actively decompose chemical warfare agents. Dimethyl methylphosphonate (DMMP) is a widely used simulant molecule in laboratory studies for the investigation of the adsorption and decomposition behavior of sarin (GB) gas. In this paper, we explore how DMMP interacts with the as-synthesized mesoporous CeO₂. Our mass spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements indicate that DMMP can dissociate on mesoporous CeO₂ at room temperature. Two DMMP dissociation pathways are observed. Based on our characterization of the as-synthesized material, we built the pristine and hydroxylated (110) and (111) CeO₂ surfaces and simulated the DMMP interaction on these surfaces with density functional theory modeling. Our calculations reveal an extremely low activation energy barrier for DMMP dissociation on the (111) pristine CeO₂ surface, which very likely leads to the high activity of mesoporous CeO₂ for DMMP decomposition at room temperature. The two reaction pathways are possibly due to the DMMP dissociation on the pristine and hydroxylated CeO₂ surfaces. The significantly higher activation energy barrier for DMMP to decompose on the hydroxylated CeO₂ surface implies that such a reaction on the hydroxylated CeO₂ surface may occur at higher temperatures or proceed after the pristine CeO₂ surfaces are saturated.