The technologically useful properties of a solid often depend upon the types and concentrations of the defects it contains. Defects affect the effectiveness of catalysts including photocatalysts, the performance of photo-active devices, the sensitivity of solid-state electrolyte sensors, and the efficiency of devices for converting sunlight to electrical power. A model describing the reaction and diffusion of the various point defects and vacancy clusters in TiO2 was developed and implemented using the continuum simulator FLOOPS. The model comprises Fickian diffusion, electric drift motion, cluster formation, and dissociation as well as the exchange between defects and the lattice, with the governing activation energies obtained from literature. The possibilities for demonstrating surface and optical phenomena in TiO2 were demonstrated. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake, UT 11/4-9/2007).