Development of a Microwave-induced Plasma Reactor Combined with Catalyst for Harmful Gas Treatment

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Non-thermal plasma processing has been considered as one of the most effective methods for harmful gas treatment. However, the issues to be solved are the improvement of the energy efficiency and the control of undesirable by-products. To improve the energy efficiency, utilization of catalyst/adsorbent into plasmas was investigated. Microwave discharges are attractive for this purpose due to their property to have different plasma compared to the conventional non-thermal plasmas and due to their ability to heat a material such as a catalyst. In this study, a microwave induced plasma reactor was developed and used for decomposition of harmful gas. The reactor consists of a quartz glass tube which inserts in the waveguide vertically. To sustain the plasma at atmospheric pressure, a fine carbon rod covered by an alumina tube is set inside the quartz glass tube coaxially to act as a source of electrons. Especially, the combination of plasma with photocatalyst was studed. NO and toluene (C_6H_5CH_3) were chosen as test gases. As a results, the microwave plasma could be generated stably at atmospheric pressure with low microwave power (<10W). It was found that efficient decomposition of NO and toluene was possible using the microwave plasma process. The combination of the plasma and photocatalyst (TiO_2) was effective for improving efficiency at lower power consumption. The NO and toluene decomposition rates increase with increasing the specific energy density, while the energy efficiency decreases with increasing the specific energy density. However, decomposition efficiency nonmonotonically depends on the gas flow rate. The energy efficiency obtained was the same order with conventional non-thermal plasma processes such as dc corona and dielectric barrier discharges induced plasma processes.