||Indoor air pollution can have significant health effects as people spend more than 90 % of their time in home, office and other indoor environments. The health effects of these indoor air pollutants are complicated, especially of the volatile organic compounds (VOCs). In the past two decades, photocatalyst titanium dioxide (TiO2) has been used to degrade a large variety of volatile organic compounds and kill airborne bacteria at ambient temperature and pressure. Recent years, researchers have focused on the excellent activity for low temperature CO oxidation over the supported gold on titanium dioxide. The motivation of my studies in supported gold catalyst is to find whether there is a way to duplicate this catalyst for other metal-metal oxide system for broader application in indoor air quality control. Nanostructured TiO2 was prepared by a modified sol-gel method. Anatase TiO2 particles of controlled particle size and crystallinity were crystallized from the amorphous TiO2 gel spheres by thermal treatment methods. This procedure enabled us to prepare TiO2 supports of controlled crystal and aggregate sizes, phase structure and crystallinity, as well as surface chemical property. Highly dispersed, nanostructured gold catalysts were deposited onto TiO2 supports. The catalyst was tested for CO oxidation in operando diffuse reflectance Infrared spectroscopy (DRIFTS) reactor system. The activity and surface reaction of the catalyst were affected by the preparation conditions, pre-treatment, crystal sizes and phase structures of TiO2. Carbonate formation on the support material and sintering of nano gold particles resulted in the deactivation of catalysts. Operando-DRIFTS was also used to investigate the catalytic reactions of eight representative VOCs (methanol, ethanol, propanol, iso-propanol, acetone, toluene, ethylbenzene and chlorobenzene) on the gold catalysts.