Abstract Silica-based photocatalysts for several selective reactions around room temperature have been developed in recent years. In most cases, the photoactive sites for selective reactions are highly dispersed (isolated) metal oxide species of quantum size at atomic level located on the silica surface. Some of them exhibit photoluminescence spectra with fine structure due to the vibration energy levels of the photoactive sites, which clarifies that the photoexcitation state is localized to a bond in the photoactive species. In addition, even on pure silica materials, a kind of surface quantum defect can function as a photoactive site. Heteroatom and defects on silica surface seem to function as `quantum photocatalysts' for several selective reactions.