Catalytic Degradation of a Chemical Warfare Agent Simulant: Reaction Mechanisms on TiO2-Supported Au Nanoparticles

High-vacuum transmission infrared spectroscopy is used to investigate the reaction pathways of the chemical warfare agent simulant dimethyl methylphosphonate (DMMP) on nanoparticulate Au/TiO 2 and pure TiO 2 . The infrared spectral signature of adsorbed CO, a major reaction product, is used to track the oxidation state of Au and Ti during the reaction. We find that small, <5 nm, Au particles on the surface of TiO 2 activate this material toward the oxidative degradation of DMMP, in contrast to pure TiO 2, which is an effective sorbant for DMMP, but little decomposition of this molecule occurs. The direct comparison of the chemistry on the samples reveals that two mechanisms may be responsible for the catalytic activity of the TiO 2 -supported Au nanoparticles. One mechanism occurs under anaerobic conditions, where vapor-phase DMMP reacts upon adsorption to form a variety of organic products and adsorbed CO. The active species in this initial oxidation channel is the lattice oxygen that most likely exists around the periphery of the Au particles. The second mechanism involves charge transfer from the Au particles to gas-phase oxygen, which subsequently reacts with DMMP that is physisorbed on the TiO 2 regions of the material. This chemistry leads to full oxidation of DMMP to release CO 2 from the surface of the particles. The results support recent theoretical studies that predict the chemical potential of oxygen and reductive reagents govern the oxidation state(s) of Au in nanoparticulate Au oxide-supported catalysts.