A novel adsorption model for molecular oxygen on reduced TiO2 (110) was presented, based on extensive first principles density functional calculations of the structure, bonding, and energetics of adsorbed oxygen species by changing the number of adsorbed O2 molecules per vacancy. Calculations predicted formation of tetraoxygen anchored at the vacancy site, allowing adsorption of three O2 molecules per vacancy in saturation coverage. The O4 complex was substantially more stable than two separately adsorbed O2 molecules. Thermally-activated O2 desorption would take place via two channels that require overcoming barriers of 0.41 and 1.25 eV, respectively. A strong O2 coverage dependence of the activation energy for CO oxidation on TiO2(110) was discussed. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake, UT 11/4-9/2007).