Photoactive sites on pure silica materials for nonoxidative direct methane coupling

Some pure silica materials, such as amorphous silica and mesoporous silica (MCM-41, FSM-16), were examined as photocatalysts for nonoxidative direct methane coupling around room temperature. It was confirmed that these materials exhibited photoactivity for the reaction around room temperature to produce mainly ethane and hydrogen, and that mesoporous silica, FSM-16, exhibited the highest activity among them. The photoactive sites on these pure silica materials were formed through dehydroxylation of the surface hydroxyl groups at high temperature (e.g., 1073 K) before the photoreaction. The linear relationship was obtained between the area intensity of the nonbridging oxygen hole center (NBOHC) band in diffuse–reflectance UV–visible spectra and the photoactivities in the nonoxidative direct methane coupling, showing that the NBOHCs, which would be generated together with the E′E′ center, were the photoactive sites for this reaction.