Synthesis and catalytic properties of magnesia fine powders prepared by microwave cold plasma heating
A fine powder of magnesia was prepared using microwave cold plasma as the heat source, and its crystal structure and catalytic properties were examined. Magnesium hydroxide was used as the raw material, and magnesia samples were prepared with variable parameters of microwave output and treatment time. After the start of heating, the temperature of the plasma immediately rose to 1100 °C. Magnesia fine powders were formed by heating the hydroxide for 1–2 min. The samples obtained had a large specific surface area (e.g. 350 m2 g–1>). The morphology of the samples was observed by scanning electron microscopy, and they were seen to be net-like with micropores of a few hundred nanometres in diameter as opposed to the flat morphology obtained in general electric furnace heating. Solid basicity measurements revealed that the magnesia powders had strong surface basic sites of 27.0 ⩽H–<33.0. When the catalytic properties were examined using the condensation of benzaldehyde and the oxidative coupling of methane, which are typical base-catalytic reactions, the magnesia prepared by plasma heating exhibited high activity in both reactions.