A comparison of in- and post-plasma catalysis for toluene abatement through continuous and sequential processes in dielectric barrier discharge reactors

Abstract

In the non-thermal plasma catalysis system, VOCs degradation was significantly affected by the position of the catalyst, as well as operation mode. Hence, it is of great significance to evaluate the performance of In Plasma Catalysis (IPC) and Post Plasma Catalysis (PPC) systems for VOCs abatement using both continuous and sequential processes. Four packed-bed dielectric barrier discharge (DBD) systems were used to degrade toluene with different catalysts under diverse voltages in this study. Results showed that the IPC mineralization rates were higher as compared to PPC, regardless of whether the continuous or sequential processes was used, and irrespective of the applied voltage and type of packed catalyst (e.g. 77.00% and 96.06% in SPPC and SIPC at 20 kV with Ag/ZSM-5 packed). However, PPC was superior to IPC in O3 and N2O reduction. As the applied voltage was raised, the mineralization rate in different reactors increased significantly, yet CO2 selectivity was insusceptible to voltage variation. NTP alone exhibited a mineralization rate and CO2 selectivity of 9.67%–22.62% and 53.85%–58.26%, respectively. While the mineralization rate and CO2 selectivity were remarkably improved with the presence of Ag/ZSM-5 (19.08%–41.59% and 93.99%–95.91% in CIPC). With respect to different catalysts investigated in this study, at 20 kV, Ag/ZSM-5 exhibited the highest mineralization rate - 96.06% in SIPC, and CO2 selectivity - 98.43% in SPPC; while the lowest concentrations of O3 (198 ppm) and N2O (8.01 ppm) were obtained in the Mn/ZSM-5 packed bed reactor. Possible reaction mechanisms were also proposed by analyzing the organic intermediates that were produced during continuous and sequential treatments, and remained in the adsorbents of IPC and PPC reactors.