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

TL;DR

This study uses advanced quantum simulations to investigate how alumina surfaces decompose a nerve agent simulant at high temperatures, revealing rapid adsorption and a specific decomposition pathway that could aid neutralization efforts.

Contribution

First-principles BOMD and metadynamics simulations elucidate the mechanism and energetics of DIMP decomposition on alumina surfaces, providing new insights into CWA neutralization processes.

Findings

Alumina quickly adsorbs DIMP at all tested temperatures.

Decomposition proceeds via propene elimination.

Activation barrier decreases with increasing temperature.

Abstract

The enhanced degradation of organophosphorous-based chemical warfare agents (CWAs) on metal-oxide surfaces holds immense promise for neutralization efforts; however, the underlying mechanisms in this process remain poorly understood. We utilize large-scale quantum calculations for the first time to probe the high-temperature degradation of diisopropyl methylphosphonate (DIMP), a nerve agent simulant. Our Born-Oppenheimer molecular dynamics (BOMD) calculations show that the $\gamma$-Al$_2$O$_3$ surface shows immense promise for quickly adsorbing and destroying CWAs. We find that the alumina surface quickly adsorbs DIMP at all temperatures, and subsequent decomposition of DIMP proceeds via a propene elimination. Our BOMD calculations are complemented with metadynamics simulations to produce free energy paths, which show that the activation barrier decreases with temperature and DIMP readily decomposes on $\gamma$-Al$_2$O$_3$. Our first-principle BOMD and metadynamics simulations provide crucial diagnostics for sarin decomposition models and mechanistic information for examining CWA decomposition reactions on other candidate metal oxide surfaces.