| The emission of volatile organic compounds (VOCs) by various industrial processes is increasing year after year and they do great harm to the environment and human. Non-thermal plasma (NTP) technology has been widely investigated for the removal of dilute VOCs due to its unique properties, such as quick response at ambient temperature, high-energy electrons with short residence times, and wide application. However. NTP alone has many disadvantages, such as high energy consumption, low CO2selectivity and undesired byproduct formation. In this study, efficient catalysts are combined in the post-plasma to develop a cost-efficient plasma/catalyst system for VOCs emission abatement in air.Ag/Co3O4and Mn-based catalysts are prepared by co-precipitation method and characterized by BET, XRD. XPS techniques. Catalytic activities of the materials are evaluated for the oxidation of toluene on home-made plasma-catalysis system. Influencing factors such as loading of active component, GHSV. original concentration, humidity and reaction temperature are taken into consideration. The main research results and conclusions are as follows:(1) Both of toluene decomposition and ozone generation rise with increasing the specific energy density ε and they are linearly dependent on each other. The FTIR spectra show that toluene is only partially oxidized and several hazardous by-products such as formic acid (HCOOH), N2O, CO and ozone (O3) are detected.(2) It is shown that the catalytic activity gradually enhances with an increase of Ag loading on Co3O4and the sample which calcined at673K exhibites the best activity. XRD and XPS results show that highly dispersed valent Ag exhibit superior catalytic activity for toluene oxidation. However, when Ag/Co3O4catalyst combine with plasma, toluene removal efficiency is not good. Toluene removal efficiency is only40%at SIE of28.8J/L(3) Toluene removal efficiency is10%by only plasma. When combine with Mn-based oxides, toluene removal efficiency is99%with ozone residual72ppm at SIE of49.2J/L, specifically in the order:NTP+Ce-Mn> NTP+Co-Mn> NTP+Ni-Mn. When combine with alumina-supported Mn-based oxides, toluene removal efficiency is100%with no ozone residual at a specific energy density of28.8J/L, specifically in the order:NTP+Mn-Co/Al> NTP+Mn-Ce/Al> NTP+Mn-Ni/Al> NTP. For NTP-Co-Mn/Al system, in addition to a small amount of N2O and CO, main product is CO2And the absorption signals of CO2increase with SIE increasing.(4) The cobalt can not only improve Mn’s activity but also maintain its activity. Toluene removal efficiency is the best at Co/Mn ratio of1:1. Both Co3Mn3O4and lattice oxygen species play a critical role in the catalyst reactivity. Toluene decomposition on catalyst firstly increases with ozone concentration increasing to350ppm, and then slightly decreases with ozone concentration further increasing. Considering both toluene decomposition and ozone utilization, optimal plasma catalysis can only be realized at room temperature. With regard to ozone slip control, however, a catalyst bed temperature of up to350K is preferred to improve its decomposition efficiency.(5) Toluene removal efficiency increases with Mn-Co loading amounts at SIE of19.2J/L. When SIE>28J/L, toluene can be almost removed irrespective of the Mn-Co loading amounts. Toluene removal efficiency decreases with initial concentration and GHSV increasing. There is an optimum water vapor content (RH=28%) for the highest toluene removal and ozone removal. Compared to the single and in parallel plasma catalysis processing, in-series processing is always better in reducing the total plasma energy consumption under certain conditions. |
PDF Full Text Request