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

非热等离子体处理被认为是处理有害气体最有效的方法之一。然而，需要解决的问题是提高能源效率和控制不良副产品。为了提高能源效率，研究了催化剂/吸附剂在等离子体中的应用。微波放电在这方面很有吸引力，因为与传统的非热等离子体相比，微波放电具有不同的等离子体特性，并且能够加热诸如催化剂之类的材料。本文研制了微波等离子体反应器，并将其用于有害气体的分解。反应器由一根垂直插入波导的石英玻璃管组成。为了在大气压下维持等离子体，一根由氧化铝管覆盖的细碳棒同轴地置于石英玻璃管内，作为电子源。重点研究了等离子体与光催化剂的结合。实验气体选择NO和甲苯（C_6H_5CH_3）。结果表明，微波等离子体可以在低微波功率（<10W）的常压下稳定产生。结果表明，微波等离子体法可以有效地分解NO和甲苯。等离子体与光催化剂（TiO_2）的结合是在低功耗下提高效率的有效方法。NO和甲苯的分解速率随比能密度的增加而增加，而能量效率随比能密度的增加而降低。然而，分解效率非单调地依赖于气体流速。所获得的能量效率与传统的非热等离子体过程（如直流电晕和介质阻挡放电诱导等离子体过程）相同。

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.