Highly dispersed magnesium oxide species on silica as photoactive sites for photoinduced direct methane coupling and photoluminescence

Abstract

Photoinduced direct methane coupling proceeded around room temperature over highly dispersed magnesium oxide species on silica, which exhibited fine structure in photoluminescence emission spectra. It was found that increasing the emission intensity tends to give an increase in the photoactivity for this reaction. The emission sites in the silica-supported magnesia have vibrational energy around 950 cm⁻¹ and lifetime of excited state around 38 ms, which were similar properties to the previously reported other silica-based photoactive systems for this reaction, such as silica–alumina and silica-supported zirconia. These photoluminescence spectra could be similarly quenched by methane molecules. Thus, it is commonly suggested that in the systems of highly dispersed metal oxide species (MO_x) on silica, the surface Si–O–M bonds are deeply related to the dominant photoactive sites for both the fine structural photoluminescence spectra and photoinduced direct methane coupling.