Study On Degradation Of VOCs By Dielectric Barrier Discharge Plasma Assisted Manganese Catalyst

The emissions of VOCs can not only cause environmental pollution,but also harm human health.Compared with the degradation of VOCs in plasma alone system,the plasma catalysis system has higher degradation efficiency,CO_x selectivity and can decrease the generation of by-products.Enhancing the activity of catalyst can significantly improve the VOCs removal rate.The manganese oxides have been widely used for VOCs removal due to its high redox property,good low temperature activity and stability.In this study,the manganese oxide octahedral molecular sieve（OMS-2）was used as a catalyst and its catalytic activity was tuned by doping K and Sn.Moreover,the researches on OMS-2 catalyst for toluene and TCE removal were also investigated,respectively.Finally,in order to analyze the degradation process,the degradation intermediates of toluene and TCE were detected by GC-MS and FTIR.Meanwhile,the synergistic catalytic degradation mechanism was also discussed.（1）Firstly,the influence factors of toluene degradation in plasma alone system were investigated.The results showed that increase the carrier gas flow rate and initial toluene concentration were not conducive to the toluene removal,but favored to improve energy efficiency.The toluene degradation efficiency and CO_x selectivity tend to increase first and then decrease with increasing the carrier gas relative humidity.When the relative humidity was30%,the toluene degradation efficiency was the largest.Compared with the plasma alone system,the plasma catalysis system had higher toluene degradation and mineralization efficiency and inhibited the formation of O₃.The catalytic activity of OMS-2 could be enhanced by doping K.When the initial K/Mn molar ratio was 2,the catalyst reached the highest catalytic activity.The catalyst characterization results showed that doping K could improve the specific surface area,pore volume,oxygen vacancy content,and redox property of OMS-2 catalyst,resulting in the increase of catalytic activity.（2）The incorporation of Sn into K（2）-OMS-2（K/Mn=2）could improve the TCE degradation performance of K（2）-OMS-2 catalyst.When the Sn/Mn molar ratio was 0.1,the Sn（0.1）-K（2）-OMS-2 catalyst exhibited the highest activity with TCE degradation efficiency and CO_x selectivity were 93.4%and 75.5%,respectively.The FTIR result of products showed that DCAC was the main intermediate and the CHCl₃ and CCl₄ were also detected.The catalyst characterization results showed that the introduction of Sn into the K（2）-OMS-2 catalyst can lead to the formation of Sn-Mn-O solid solution and weak Mn-O,which could promote the generation of active oxygen species and facilitate the degradation of TCE.（3）The toluene degradation pathway analysis showed that the active radicals generated by discharge played a crucial role in the degradation of toluene.Furthermore,the benzylalcohol,benzaldehyde and formic acid were the key intermediates in the toluene degradation process.The synergistic mechanism was studied by comparing the toluene degradation efficiency,CO_x selectivity and O₃ concentration evolution in the plasma catalysis system and plasma alone system.The results showed that the plasma catalysis system could generate more active oxygen species than plasma alone system,promoting the degradation and mineralization of toluene and intermediates.TCE degradation products generation mechanism analysis showed that DCAC was a key organic intermediate,which could be generated either by direct reaction of TCE and ClO·,or by addition reaction of TCE and O*and·OH.In addition,the broken C-C bond of DCAC could react with Cl·adsorbed by catalyst to generate CHCl₃ and CCl₄.