Active sites on silica-supported zirconium oxide for photoinduced direct methane conversion and photoluminescence

Photoactivity of silica-supported zirconium oxide (ZrO2/SiO2) of low loading below 1 mol% for photoinduced direct methane conversion at room temperature was examined. Very low loading samples below 0.1 mol% exhibited high activity for methane coupling upon photoirradiation. The highly dispersed Zr oxide species on the silica surface had different electronic and local structure from ZrO2 particles, and exhibited fine structural phosphorescence spectra. From the fine structure, it was revealed that the highly dispersed zirconium oxide species have photoactive Zr–O–Si linkage whose vibration energy was estimated to be 955 cm−1. From the decay curve analysis and quenching experiment, it is proposed that the Zr species have around 28±5 ms of excitation lifetime at 77 K and they are responsible for the photoinduced direct methane coupling at room temperature.