Generation of non-thermal plasma combined with catalysts and their application in environmental technology

Non-thermal plasma (NTP) promotes formation and reaction of radicals at low temperature condition. In order to use NTP, selectivity and energy efficiency should be improved. For this purpose combination of NTP and catalysts has been proposed for several industrial applications. Several systems are at first introduced in this review, and then generation of NTP suitable for combination with catalysts will be introduced. The first generation of NTP combined with catalysts was a pulsed streamer corona with a TiO2 solid catalyst. This combination has been commercialized successfully as an indoor air cleaner attached to an air conditioner. However, this system cannot use honeycomb catalysts. A packed bed has therefore been used for testing the combination of NTP and pellet type catalysts. Packed bed uses a layer of ferroelectric pellets of a few mm in diameter. The pellet layer is sandwiched by the electrode energized with AC or pulsed voltages. Each contacting point of the pellets is ionized. The packed bed can be an important candidate for plasma-assisted combustion. An existing application for the packed bed is the volatile organic compounds (VOCs) decomposition. Recently, discharges in honeycomb catalysts have been developed. One end of a honeycomb catalyst is attached with a packed bed or a surface dielectric barrier discharge to generate NTP. This electrode serves as a plasma electrode. When a DC electric field is applied, ionization proceeds along the surface of fine channels of ceramic honeycomb. This honeycomb discharge could be used for various processes to combine NTP and catalysts. It could also be used for surface treatment of honeycomb catalysts by NTP.