Photoluminescence study of silica–alumina catalyst

On a silica–alumina catalyst, which was reported to be active for photoinduced non-oxidative coupling of methane, two kinds of phosphorescent emission sites were confirmed by the analysis of phosphorescence spectra and their decay curves. The first type of emission sites, which are mainly observed after evacuation at 673 K, exhibit a broad band at around 455 nm and longer emission lifetime such as 7×102 ms at 77 K. Other sites, which are generated by evacuation at higher temperature such as 1073 K, exhibit a fine structural spectrum and shorter emission lifetime such as 33 ms at 77 K. From the change in the spectrum with pretreatment temperature and with the amount of adsorbed probe molecules (H2O, NH3), the former sites are assigned to hydroxy groups on the surface and the latter to the surface sites which are generated through the desorption of isolated hydroxy groups.