The effect of defects on TiO2 (110) on the decomposition of DCOOD was investigated by temperature-programmed reaction spectroscopy (TPRS). Different concentrations of anion vacancy defects were created on the TiO2 (110) surface by electron beam irradiation in order to minimize structural damage to the surface. For comparison, defects were also created by argon bombardment. The oxidation state produced by the defects and their concentrations were characterized by X-ray photoelectron spectroscopy (XPS). The selectivity of the reaction for the production of carbon monoxide, formaldehyde, and D-2 was increased significantly by the defects. An appreciable decrease in the temperature for CO and D2CO formation on the defective surfaces produced by electron beam irradiation was observed, compared to the stoichiometric surface, suggestive of changes in the kinetics of the decomposition. The presence of isotopic exchange in the products provides evidence for the formation of formyl intermediates during DCOOD decomposition.