Synthetic todorokite produced by microwave heating: An active oxidation catalyst

Microwave heating methods have been applied to the synthesis of a family of layered and tunnel-structured manganese oxide materials. These materials are known to interact strongly with microwave radiation, and thus pronounced effects on the microstructure might be expected. The work presented here is a study of the synthesis, characterization, and catalytic activity of a one-dimensional tunnel-structured manganese oxide catalyst known as OMS-1 (octahedral molecular sieve). The synthetic methods employed in the production of OMS-1 include constant temperature aging, ion exchange, in situ coprecipitation, and hydrothermal treatment. Heating was done using conventional convection methods and microwave radiation to probe the effect of microwave radiation on the material characteristics. The products were examined using X-ray diffraction, elemental analysis, determinations of the average manganese oxidation number, Auger spectroscopy, scanning electron microscopy, thermal stability studies, infrared spectroscopy, and surface area measurements. Catalytic activity was tested in the oxidative dehydrogenation reaction of ethylbenzene to styrene. The materials produced using microwave radiation were shown to have bulk characteristics similar to those prepared using conventional heating. However, the surface properties were shown to be different, resulting in different catalytic results. The differences in the properties and catalytic activity of the materials, as well as the implications of microwave heating as a synthetic tool, are discussed. (C) 1999 Academic Press.