Using Fourier transform infrared spectroscopy (FTIR) we studied the overall reaction pathways and ultimate fate of dimethyl methylphosphonate (DMMP), a chemical warfare agent simulant, on a commercial nanoparticulate (similar to 20 nm) titania material. Our data show that the initial uptake occurs through both molecular and reactive adsorption. Molecular adsorption is driven by hydrogen-bond formation to isolated hydroxyl groups. The reactive chemisorption appears to occur through interaction with both Lewis acid sites and active oxygen species present on the TiO2 surface. The reactive sites are found to be poisoned quickly by oxidation products that include a strongly bound, nonvolatile phosphorus compound. Thermal reactivation of the TiO2 in oxygen restores the physisorption capacity of the particles toward the DMMP, but the reactive adsorption pathway is nearly completely eliminated.